Predation risk, foraging and reproduction of an insectivore fish species associated with two estuarine habitats

Predation risk, foraging and reproduction of an insectivore fish species associated with two estuarine habitats | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Predation risk, foraging and reproduction of an insectivore fish species associated with two estuarine habitats Éden Guedes, Juan Pereira, Gitá Brito, Andre Pessanha, Alexandre Júnior This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-2943801/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Pneumatophore fringes and mudflats are extremely valuable habitats and provide structures on which many fish species benefit in terms of food and reduced predation risk. We analysed the spatiotemporal patterns in feeding habits, reproductive aspects and effects of predatory fish presence to assess the ecological drivers of the common halfbeak, Hyporhamphus unifasciatus , in a Brazilian estuary. Sampling was conducted in the rainy (January to July 2016) and dry (August to December 2016) periods. Fish were collected in the two estuarine habitats using a beach seine. In summary, the results demonstrated that the number of predatory fishes was a strong predictor of population abundance and biomass, followed by pneumatophore complexity. The abundance and biomass values tended to increase with increasing habitat structural complexity towards the upper estuary. There was evidence that fish exhibited movement during the rainy season related to spawning events and subsequent juvenile recruitment in this area. Hymnoptera was the item most frequently ingested and made the greatest contributions to the volume of diet in habitat types throughout the year. There was an increase in the condition factor in the rainy season and thus was associated with energy reserves, reproduction and growth (fitness). We concluded that predation is an important ecological process that operates at local spatial scales and that together with the density of pneumatophores, predation is considered an important attractiveness that could affect the abundance of common halfbeak populations associated with estuarine habitats. Diet composition Habitat use Halfbeak Predatory Fishes Structural complexity Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 1. Introduction Estuarine fishes are closely associated with multiple habitat types in tropical estuaries, comprising vegetated (e.g. mangrove, seagrass meadows, and saltmarsh) and unvegetated habitats (e.g mudflat and sandflat) (Honda et al 2013 ; Pessanha et al 2021 ). This habitat heterogeneity exerts a major influence on the species in estuarine regions increasing diversity and species (Marley et al 2020 ). Habitat features, including substratum composition, water conditions (Neves et al 2013 ) and presence and type of vegetation (Wange et al 2009), influence the distribution and abundance of fish species. Each habitat feature influences the way in which fish exploit resources for food, and for spawning sites and/or refuge (James et al 2019 ; Lefcheck et al 2019 ). Previous studies have also highlighted how heterogeneous environments offer more habitat types and niches, thereby allowing more species to coexist in ecosystems (Hamm and Drossel 2017 ; Ochoa-Gómez et al 2018 ). Associations of fishes have been studied extensively in mangrove root systems (Ley et al 2009; Silva et al 2018 ) and seagrass meadows (Jaxion-Harm et al 2012 ; Ho et al 2018 ), showing these habitats to contain abundant food resources and possess characteristics that could reduce the interaction rate between predator and prey (Vaslet et al 2012 ; James et al 2019 ). Additionally, the foraging efficiency and reproductive success of most fishes change with growth. These differences vary from species to species and, in many cases, are often associated with changes in habitats (Sheaves et al 2015 ). In addition, habitat selection for feeding or refuge by fish species has implications for maximizing energy intake and enhancing growth, size distributions and survival rates. Sheaves et al. ( 2015 ), amongst other, have indicated that the habitat requirements for the estuary-dependent juvenile phase may be quite different when compared to the adult stage of the fish life cycle. The pneumatophore fringes of mangroves and mudflats are important habitats that extend into the intertidal and subtidal zones, and are regularly flooded with seawater. In particular, pneumatophores attract to juvenile fish due to structural complexity, the lowest predation risk, and high food availability of epiphytic algae and associated invertebrates on their surface area (MacDonald et al 2008 ; Muzaki et al 2019 ). As such, these shallow habitats function as important nursery grounds for fishes in tropical estuaries (Beck et al 2001 ; Sheaves et al 2015 ). Habitats may also provide potential refuge from predators for small fishes by reducing prey visibility and limiting the movements of large predators (Nanjo et al 2014 ; Muzaki et al 2017 ). Fishes of the family Hemiramphidae, commonly known as halfbeaks, are epipelagic and inhabit shallow, estuarine and freshwater environments (Hughes and Stewart 2006 ). The common halfbeak Hyporhamphus unifasciatus , one the most abundant fish species (Favero et al 2019 ; Passos et al 2013 ), is a small marine fish (length, TL = 300 mm; Froese and Pauly 2011 ), characterized by a lower jaw that is much longer than the upper jaw (Meisner 2001 ), and distributed along the Western Atlantic, from Florida southward through the Caribbean to Uruguay (Banford and Collette 2001 ). This species is restricted to coastal habitats such as seagrass beds, tidal creeks and beaches (Banford 2010 ), where they feed as generalist to more specialized guilds (e.g., herbivorous and insectivores) (Passos et al 2013 ; Silva et al 2018 ). The common halfbeak is an important resource in many fishing communities due to its abundance and economic value (Mourão and Nordi 2003 ; Medeiros et al 2018 ). This species is mostly captured in gillnets and beach seines by artisanal fishers, and today is considered overexploited along the Brazilian coastline (Verba et al 2020 ). To compare how two shallow-water habitat types may affect distribution and abundance for the common halfbeak, changes in diet in juveniles and adults on a temporal scale were first investigated. Next, we tested whether common halfbeaks preferentially inhabit close pneumatophore fringes, such that they are suitable areas for growth because they maximize the condition factor (proxy of energy reserves in the fish body), and that predators would affect abundance. We predicted that density and distribution of fish populations are strongly related to areas with the presence of pneumatophores (used as a proxy for complexity) due to abundant food resources and predation. 2. Material and Methods 2.1 Study area and sampling This study was conducted on the Mamanguape estuary (6º43'02'' S 35º67'46'' W) situated at the Brazilian northeastern coast. This estuary is fringed by a dense mangrove forest of c. 6,000 ha (Rocha et al 2008 ). Prop roots, pneumatophores and mudflats are usually found at the outer edges of a fringe or bordering tidal creeks and channels (Mourão and Nordi 2003 ; Nascimento et al 2011 ). In this region, Köppen classifies climate as As-type (hot and humid) (Alvares et al 2013). Annual rainfall ranges from 1,750 to 2,000 mm, and the average temperatures hover around 26°C (Macedo et al 2010 ). The tide occurs in semi-diurnal tidal regimes, with the mean tidal amplitude varies from 0.2 m (low water) to 2.7 m (high water) (Souza and Furrier 2015 ). Two habitats of the estuary were considered in this study: 1) the intertidal adjacent Avicennia-Laguncularia pneumatophores fringe that can extend away from the mangrove forest, and 2) unvegetated mudflat extending 50 m seaward of the pneumatophore fringe. Monthly sampling was conducted in the estuary in 2016: January to July – rainy season; August to December – dry season (except in September due to inclement weather. Fish were collected with three fike nets, set and retrieved approximately 2 to 3 h before and after mean high water, positioned parallel to mangrove fringe so that the opening (and wings) faced landward in each site. Additionally, beach seine (10m x 1.5m; 8mm mesh size) was hauled parallel to an extension of approximately 30 m and to a maximum depth of 1.5 m, during the low tide. The sampling unit was standardized with three replicates in an effort to capture individuals that use the area. In the laboratory, the fish caught were measured, total size (mm) and weighed (g). In order to better characterize the habitat structure of pneumatophores, sampling was performed at different sites along of estuary whenever possible. Three random quadrats of 25 x 25 cm were set on each site along a mangrove forest. In the quadrats we quantified the density of pneumatophores. 2.2 Abundance and spatial distribution of common halfbeak Abundance and biomass of common halfbeak were analysed separately using a univariate statistics (PERMANOVA) (with 9999 permutations) to test for spatial and temporal changes, and applied on two factors: habitat (two fixed levels: pneumatophore fringes and mudflats), and season (two fixed levels: rainy and dry). A resemblance matrix of data was calculated using Euclidean distance. The variables were log transformed. The log transformation reduced or removed the skewness of original data. Significant factors were further analyzed using a PERMANOVA pair-wise comparison. The analyses were performed using PRIMER v6 + PERMANOVA (Clarke and Gorley 2006 ; Anderson et al 2008 ). 2.3 Reproductive data and condition factor (K) Gonads were macroscopically examined and reproductive stage was described according to Vazzoler ( 1982 ). The gonads of each individual were removed when possible and weighed (in g). The gonodo-somatic index (GSI) is a good indicator of reproductive activity, and was calculated for individuals using the formula: GSI = Weight of gonad/Weight of fish x 100 (Vazzoler 1996 ). Common halfbeak were categorized into size classes: juveniles ( 145 mm) (Favero et al 2019 ). To assess the variation in condition factor of the common halfbeak from both estuarine habitats, we used a Fulton’s condition factor K. Individual values of the condition factor were obtained through the formula K = 100 Wt / Lt 3 where Wt is total wet weight (mg) and Lt total length (mm) (Froese 2006 ). To investigate the distribution of the length frequency, common halfbeak individuals were grouped into 10 mm TL size classes by months, and estimate their recruitment pattern. 2.4 Gut content and diet analysis The gut contents of each individual were removed and examined under a stereomicroscope and each dietary item was identified. To analyze the diet, frequency of occurrence (O%) and volumetric (V%) percentages were calculated to characterise the diet (Hyslop 1980 ), and were then used to calculated the Alimentary Index (IAi) (Kawakami and Vazzoler 1980 ), presented in percentages. The volume of each item was calculated and analyzed by displacement methods (Bemvenuti 1990 ). The method consist of the estimation of volumetric proportion of each item, and then calculated based on the total volume of food eaten per consumer. Empty stomachs were excluded from the analyses. A permutational multivariate analysis of variance (PERMANOVA) (with 9999 permutations) was used to examined variations in volumetric contributions of prey items, and applied on three factors: habitat types (two fixed levels: pneumatophore fringes and mudflats), season (two fixed levels: rainy and dry), and size (two fixed levels: juvenile and adult). A resemblance matrix of data was calculated using Bray-Curtis coefficients. The variables were square-root transformed. Where a significant difference (p < 0.05) was detected for the factor habitat, post hoc tests were conducted. All analyses were performed using the statistical package PRIMER v6 + PERMANOVA (Clarke and Gorley 2006 ; Anderson et al 2008 ). 2.5 Predatory fishes In order to clarify the abundance of common halfbeak, the predatory fish abundance was estimate in both habitats. Predatory fish species in habitat types were chosen on two criteria: 1) carnivorous with tendency to piscivory, and 2) predator fishes which live in water column or close to water surface. The classification of fish species as piscivores was based upon published dietary data from a preliminary study conducted at the estuary (Campos et al 2015 ; Silva et al 2018 ; Pessanha et al 2021 ). Fourteen species were recorded: jacks (Carangidae: Caranx latus and C. hippos ), snooks (Centropomidae: Centropomus paralellus, C. undecimales, C. ensiferus , and C. pectinatus ), snappers (Lutjanidae: Lutjanus alexandrei, L. analis, L. apodus , and L. jocu ), randalls soap (Serranidae: Rypticus randalli ), barracuda (Sphyraenidae: Sphyrena barracuda ) and needle fishes (Belonidae: Strongylura timucu and S. marina ). Additionally, to analyze the influence of predatory fishes on abundance of common halfbeak. Abundance of predators were expressed by pooling and combining the number of individuals into family groups in each habitat and seasons. We used the t-test also to examine the hypothesis of no difference in number of predatory fish species between habitats during in each season. A multiple regression analysis with number of predatory fishes and habitat structure of pneumatophores as predictors and abundance and biomass of H. unifascitus as response variables was performed (Palomares and Pauli 1989). These data were checked for multicolinearity, normality and homogeneity of variance and were log-transformed, log 10 (x + 1), to meet the assumptions of multiple regression. We performed hierarchical linear regression analysis: in step 1, the number of predatory fishes as the predictor variable was used because it was assumed to explain a statistically significant amount of variance in fish distribution. In step 2, structure of pneumatophores was added. The analysis were performed using the statistical package SPSS. 3. Results 3.1 Abundance and spatial distribution A total of 534 common halfbeak were caught, totaling 1466.66 grams. The pneumatophore fringes showed the highest number of individuals and biomass compared to the mudflat (Fig. 1 ). Seasonally, higher values for the number of individuals and biomass were recorded during the rainy period. Statistically, the spatial effect was overall not significant on the number of individuals (pseudo-F 2, 82 = 0.75; P > 0.001) and biomass (pseudo-F 2, 82 = 0.04; P > 0.001). Significant differences were found between seasons for both the number of individuals and biomass. However, the interaction effects were not significant between habitat types and seasonal factors (number of individuals: pseudo-F 2, 82 = 0.20 and biomass: pseudo-F 2, 82 = 0.26; P > 0.001). The monthly length frequency distribution of common halfbeak ranging from 15 to 180 mm TL. Monthly observations showed that the percentages of this species tended to increase during the rainy season (from April to July), principally large-size individuals (Fig. 2 ). The percentages of small-size classes (< 100 mm TL) showed the reverse trend, occurring in higher abundance in the dry season (from October to December) (Fig. 2 ). 3.2 Reproductive data and Condition factor (K) In the estuary, two periods of reproductive activity were observed in our study (Fig. 3 ). The first period matched the beginning of the rainy season, but a peak of mature females was registered in July, suggesting that individuals spawn in this season. The second period was few apparent, starting in the dry season in approximately October, and the peak of mature females occurred in January (see Pneumatophore fringe). The changes in the gonodosomatic index (GSI) of the males showed the same pattern for both habitats, and the values tended to be relatively lower than those of the females (Fig. 3 ). The condition factor (K) for all fish samples was determined by month and did not reveal similar patterns when compared to habitats), showing the highest values in mudflat (Fig. 4 ). However, there was some indication that the condition factor values for common halfbeak slight decreased during the dry season in both habitat types 3.3 Diet For the diet study, 311 stomachs with prey were analysed from common halfbeak, of which 41 stomachs were empty (13.2%). In general, common halfbeak fed on prey items fell onto the water surface (Table 1 ). In this case, the diet was comprised mainly of insects, which accounted for more than 97% of the overall IAi in juveniles and adults in both habitat types. Although plant material, copepods and other insects were frequently consumed, they were only present in small volumes. Table 1 Alimentary Index (IAi%) of food items consumed by juvenile and adults of Hyporhamphus unifasciatus among habitats (Mudflat and Pneumatophore zones) in Mamanguape estuary (O%= Frequency of occurrence, and V%= volume percentage) Mudflat Pneumatophore fringes Juvenile (n = 39) Adult (n = 33) Juvenile (n = 96) Adult (n = 143) Food items O% V% IAi% O% V% IAi% O% V% IAi% O% V% IAi% Foraminifera 1.20 0.02 0.01 Diatoms 1.20 0.02 0.01 0.83 3.20 0.06 Trematoda 5.6 0.2 0.01 6.67 0.12 0.03 8.43 0.22 0.03 7.44 0.30 0.05 Sipuncula 6.02 0.37 0.04 4.13 0.22 0.02 Errantia Polychaeta 1.20 0.43 0.01 7.44 3.32 0.55 Sedentary Polychaeta 0.83 0.29 0.01 Copepods 8.3 0.4 0.05 16.67 0.61 0.42 9.64 0.47 0.08 6.61 0.13 0.02 Gammaridae 1.65 0.11 Cyprid larvae 1.20 0.02 0.01 0.83 0.01 Brachyura larvae 6.67 0.20 0.06 1.20 1.87 0.04 0.83 0.01 Brachyura 3.33 0.98 0.14 0.83 0.10 Tanaidacea 1.20 0.02 0.01 Hymenoptera 88.9 70.5 99.8 56.67 41.89 98.08 84.34 67.17 97.74 77.69 56.13 97.33 Coleoptera 2.8 0.3 0.01 1.20 0.02 0.01 1.65 0.12 0.01 Diptera 13.33 0.16 0.09 2.41 0.95 0.04 4.96 1.01 0.11 Hemiptera 6.02 1.34 0.14 2.48 0.16 0.01 Plant material 13.9 0.5 0.10 20.00 1.39 1.15 19.28 5.65 1.88 9.92 8.28 1.83 No significant differences in the dietary compositions of common halfbeak were found between habitat types (PERMANOVA: pseudo-F 1,245 = 1.87, P > 0.05) and seasons (PERMANOVA: pseudo-F 1,245 = 1.13, P > 0.05), which was attributed to the consumption of Hymenoptera throughout the year in the estuary. Significant differences in diet were found among size classes (PERMANOVA: pseudo-F 1,245 = 3.13, P < 0.001). The interaction effects were significant between size and seasonal factors (PERMANOVA: pseudo- F 1,245 = 3.52; P < 0.001). 3.4 Effect of presence of predatory fish species Predatory fishes were present during the whole study period, with jacks and snooks the main species in estuarine habitats, accounting for more than 70% of the species sampled (Fig. 5 ). Jacks and snooks were best represented in terms of abundance in the rainy and dry seasons, respectively. Snappers were abundant (range 7–15%) in mudflats during the dry season and pneumatophore fringes during the rainy season. Randall soap fish, needle fish and barracuda occurred in low numbers in both habitats during the study (Fig. 5 ). The analysis showed that the abundance of predatory fishes was not significantly different between habitats (t = 9.085; P > 0.01). Unlike spatial abundance, however, there was a significant difference in the abundance of predatory fishes within each habitat during the seasons (Lower: t = 12.184; P < 0.01; Upper: t = 29.685; P < 0.01). The hierarchical multiple regression model results showed that the abundance of predatory fishes and habitat types were significant predictors of variations in the abundance and biomass of common halfbeak, as evidenced by the consistent increase in R 2 in each step (Table 2 ). The number of predatory fishes was significantly negatively related to abundance (β= -0.554; P < 0.01) and biomass (β= -0.462; P < 0.01) and explained 30.7% and 21.4% of the variance in the model, respectively. Then, pneumatophore fringes were significantly related to abundance (β = 0.180; P < 0.01) and biomass (β = 0.223; P < 0.01) and explained 4.7% and 6.1% of the variance in the model, respectively (Table 2 ). Table 2 Results of the hierarchical multiple regression models computed on both number of individuals and biomass the Hyporhamphus unifasciatus of two groups of predictor variables. Significance: ** p value < 0.01 Number of individuals Biomass Predictor variables Model 1(β) Model 2(β) Model 1(β) Model 2(β) Predatory fishes (abundance) − 0.554 ** − 0.526 ** − 0.462 ** - 0.423** Pneumatophore complexity Density 0.228 ** 0.287** R 2 0.307 0.347 0.214 0.275 4. Discussion Our results demonstrated that the increased habitat structure, provided by pneumatophore fringes, had the strongest association with habitat selection for common halfbeak. This habitat constitutes important sites for this species to complete its life cycle, as spawning and foraging habitats, because both juvenile and adult life stages are caught in this kind of habitat. Apparently, there is some evidence that fishes move to pneumatophore fringes during the rainy season to spawn and are subsequently recruited in this area. The results also indicated that common halfbeaks altered their habitat use on a seasonal basis during the rainy season. H. unifascitus showed higher abundance in pneumatophore fringes during this period, which could be a consequence of biotic interactions (predation) and spawning periods. Therefore, the structure of the pneumatophores supported the high biomass of common halfbeak that uses these areas for reproduction, growth and development in this tropical estuary. Notably, the differences in the distribution and abundance of common halfbeak were determined by complex responses to habitat characteristics and biotic interactions and offer insights into how habitat use can influence fitness. In terms of the number of individuals and biomass, the multiple regression model revealed a positive correlation related to pneumatophore presence. In this case, the pneumatophore fringes attracted halfbeak because suspended habitats in the water column increased foraging and shelter opportunities and consequently increased the survival of individuals. In this study, support for the predator refuge hypothesis exists because there are a greater number of refuges for fishes in pneumatophore fringes than in adjacent habitats, such as subtidal deeper areas or nonvegetated mudflats (Silva et al 2018 ). In fact, these results were consistent with the results of previous studies that highlight that pneumatophore density can affect the abundance of fishes (Green et al 2012 ; Vaslet et al 2012 ). For example, MacKenzie and Cormier ( 2012 ) reported that the vertical structure and arrangement provided by pneumatophore height that emerge from sediment often produce a dense structure impenetrable by larger organisms. According to Rönnbäck et al ( 1999 ), because the structure is more complex, small fish such as halfbeak might also show higher manoeuvrability and motility to the exploitation of this habitat during high tides for feeding. Some studies have indicated that the arrangement of pneumatophores is also responsible for creating shade for fish species to hide between structures (Cocheret de la Morinière et al 2004; Verweij et al 2006 ). From another perspective, the pneumatophore arrangement supports trapping of sediment and organic matter and directly influences prey availability (Kamal et al 2014 ). Together, these factors are considered important contributors to the increased attraction of fish to mangroves (Ochoa-Gómez et al 2018 ). The populations of common halfbeak found in each estuarine habitat also responded differently to the seasonal conditions in different ways, and these shifts may be in response to predation risk: in pneumatophore fringes, the higher abundance and biomass of predatory fishes were registered during the rainy season, while in mudflats, they were registered during the dry season. The number of predatory fishes was a strong predictor of population abundance and was confirmed by the multiple regression model. From this work, there was a vast difference in abundance of Jack and Snook species among habitat types, and this appeared indirectly affected abundance of common halfbeak around pneumatophore fringes. Clearly, these temporal pattern differences among habitats reflect natural variability in baseline habitat quality, where the structure of pneumatophores likely provided additional resources that allowed for greater abundance. Rilov et al ( 2007 ) suggested that the quality of a habitat was linked to predation risk. These results are consistent with those of MacKenzier and Cormier (2012), who describe the same pattern for fish species in reefs and seagrass beds, respectively. This was not surprising at first because species move presumably to sites in response to foraging efficiency and capture rate (Ho et al 2019). In particular, it is also important to recognize here that during the rainy season, when there was an increase in predatory fishes and prey fishes in pneumatophore fringes, the main predators in this area (jacks and snappers) were small in size or juveniles. In many instances, however, the potential predation risk might be affected by the apparent presence of juvenile predatory fishes and thus induce changes in prey behaviour leading to adjustments in refuge use and spatial distribution (Ori et al 2010). It is possible that the intensity of predation will be influenced by opportunistic attacks of the interspecific schooling of piscivorous juveniles when fish are concentrated in the pneumatophore fringes. This conclusion was well supported by detailed studies of observations relative to the aggregation effect in foraging behaviour of juvenile predatory fishes (Lukas and Benkert 1983; Juanes and Conover 1994 ). Sancho ( 2000 ) examined another aspect of predation by juveniles. The author found a “midwater” hunting behaviour consisting of midwater high-speed attacks on spawning fishes in reefs and therefore may be considered an important behaviour in carangid species. Findings in diet composition in our study showed some differences compared to the results of previous studies. Common halfbeak is commonly regarded as an herbivorous fish, and plant material forms a very significant part of its diet (Vasconcelos Filho et al 2003 ; Paiva et al 2008 ). The small amount of animal prey found in gut contents may be partly considered to be incidentally ingested during herbivory, as suggested by MacKenzie and Cormier ( 2012 ). The present study, however, found that both juveniles and adults preyed primarily on Hymnoptera, which were widely abundant in fish occupying both habitats. Campos et al ( 2015 ) also found that common halfbeak fed mainly on Hymnoptera prey and suggested that this species was characterized as an insectivore in the Mamanguape estuary. Studies of other Hemiramphidae species also described insects as main food resources, especially for the diet of larger individuals, which tended to be dominated by terrestrial insects (Kanai et al 2017 ; Abidin et al 2019 ). Indeed, clearly, common halfbeak utilized allochthonous food items (terrestrial insects), which is very useful information for assessing its potential interactions with local food webs (Sheaves et al 2015 ). No clear trend in the quantitative and qualitative dietary constituents could be observed between habitats and seasons. In fact, Hymnoptera species were found in very high abundance in gut contents. Most likely, they constitute a very abundant food resource that may be easily collected provided that fish display adequate behaviour to access the item. The prey encounter rate is dependent on the abundance of that prey in the environment (Pinnegar et al 2003 ). Hymnoptera have been widely documented and are often regarded as the most abundant insect group in mangroves (Delabie et al 2006; Nielsen 2010 ). Additionally, these prey also fall from the mangrove forest in the surface layers of the water and are sequentially detected and captured by common halfbeak. The pronounced foraging tactic of common halfbeak to target prey (Hymnoptera) is similar the registered by Delabie et al (2006), and is thus presumed to be related to the presence of insects on the seawater surface. This behaviour has been registered by other Hemiramphidae across different habitats (Tabassum et al 2017 ; Abidin et al 2019 ), where insects were ingested in proximity to floating objects or sucked from the water surface (Kanai et al 2017 ). The combination of both a lower number of individuals and non-spawning females in the mudflats during the rainy season might suggest that the adults migrate to spawning grounds located in pneumatophore fringes. According to Fowler et al ( 2008 ), these spawning-related in the Hyporhamphu s genus constitute an important part of the life history of these schooling species. The use of structured habitats, for example seagrass and mangroves, is closely associated with habitat specifics for spawning, possibly because they represent substrates for egg attachment and increased reproductive success in the case of Hemiramphidae (Hughes and Stewart 2006 ). Large eggs with adhesive filaments are characteristics shared among many of the other members of this family (Oya et al 2002 ; Nuttall et al 2012 ). Therefore, fish may utilize habitats such as resting areas to conserve energy before spawning and between spawning events (van der Meulen et al 2014 ). We suggested that the peak of the spawning period during the rainy season, confirmed by the GSI data of females, is driven by three explanations proposed: seasonal changes in predatory fishes, low turbidity linked to rainfall and the presence of young halfbeak caught in the early dry season (see October for young-of-the-year records). The hypothesized lower predation pressure in pneumatophore fringes during these seasons potentially reduces the risk of large nutritious eggs in the halfbeak (Fowler et al 2008 ; Nuttall et al 2012 ), while the spawning strategy registered during the period of more turbid waters in the Mamanguape Estuary can minimize visual predation on eggs and increase survival. This spawning strategy has also been registered for Hyporhampuhus melanochir and other hemiramphids in Australia (Hughes and Steward 2006), and other studies have reported larvae and small juveniles using areas upstream of estuaries related to the lowest salinity in this area (Döring et al 2017 ). Therefore, spawning during the rainy season maximizes the potential for eggs to be transported because of the high flow of rivers (Islam et al 2006 ). In the current study, a second short spawning period was registered during the dry season, related to higher GSI data in mudflats and recruits that occurred from January to February. Here, water temperature may also have been an important factor in the spawning season because of influences on the metabolic demands of fishes. Water temperature has been identified as a fundamental factor that can influence fish reproduction and growth in tropical estuaries (Mareea et al 2000 ; Pankhurst and Munday 2011 ). The condition factor (K) showed that the two habitat types were not equally valuable for common halfbeak, especially when comparing their seasonal patterns. Our results demonstrated significant influences of habitat use on the condition factor in the rainy season, and this was important for predicting that energy storage was allocated to growth and survival (Mogensen and Post 2012 ). Therefore, the condition factor may act to predict the fitness of fishes. Furthermore, pneumatophore fringes provided the best environment because they exhibited favourable conditions for rapidly growing juvenile fish and maximized reproductive fitness. Our results were in accordance with this hypothesis. In this study, the relation between the K-factor and gonadal development had greater importance in influencing this index. Similar results were reported for Atherinella brasiliensis in this estuary, indicating that habitats that differ in food resources can offer the opportunity to maximize the fitness (Júnior et al 2020). In conclusion, this study clearly demonstrates that configuration of habitat was considered an important determinant of abundance patterns in space and time of common halfbeak populations associated with estuarine areas. The structure of these habitats represented by pneumatophores may contribute to these patterns due to the greater habitat complexity providing shelter from predation, increased microhabitat availability and abundant food. This is consistent with the attractiveness hypothesis for fishes in mangrove areas, which suggests that fishes select habitats because of increased food supply, and increased living space or shelter (Nagelkerken et al 2008 ). Several conclusions from this study may prove to be generally applicable in other systems, principally related to predation risk and utilization of food resources in shallow coastal ecosystems. Further investigations based on an ecosystem perspective are needed to understand how the availability of allochthonous food items can supply energy and materials to estuarine food chains and coastal marine ecosystems. Declarations Acknowledgments We thank students of the Laboratory of Fish Ecology (UEPB) for helping in both the laboratory and the field. Financial support was provided by the National Counsel of Technological and Scientific Development (CNPq; Grant# 308340/2018-3). 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3","display":"","copyAsset":false,"role":"figure","size":23591,"visible":true,"origin":"","legend":"\u003cp\u003eMonthly values of the gonodo-somatic index (mean GSI± standard error) with female and males \u003cem\u003eHyporhamphus unifasciatus\u003c/em\u003e caught in\u003cem\u003e \u003c/em\u003emudflat and pneumatophore fringes of the Mamanguape Estuary between January and December 2016.\u003c/p\u003e","description":"","filename":"FIG3Eden.png","url":"https://assets-eu.researchsquare.com/files/rs-2943801/v1/acb2016227fced927468562b.png"},{"id":37332524,"identity":"1860f600-9b3e-48d0-9b9a-6d5986371170","added_by":"auto","created_at":"2023-05-22 15:16:35","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":36275,"visible":true,"origin":"","legend":"\u003cp\u003eBoxplot of monthly values of the condition factors of \u003cem\u003eHyporhamphus unifasciatus\u003c/em\u003e in mudflat (A) and pneumatophore fringes (B) of the Mamanguape Estuary between January and December 2016. Bold lines indicate medians, hinges indicate the 25th and 75th percentiles.\u003c/p\u003e","description":"","filename":"Fig4Eden.png","url":"https://assets-eu.researchsquare.com/files/rs-2943801/v1/d606742889204e74b1c6e60a.png"},{"id":37331198,"identity":"645c9a3d-9a03-4970-bfaf-acb81cad4ab7","added_by":"auto","created_at":"2023-05-22 15:08:35","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":23903,"visible":true,"origin":"","legend":"\u003cp\u003eRelative abundance and abundance (mean number of individuals ± standard error) of predatory fishes caught in\u003cem\u003e \u003c/em\u003emudflat (A) and pneumatophore fringes (B) of the Mamanguape Estuary between January and December 2016.\u003c/p\u003e","description":"","filename":"FIG5Eden.png","url":"https://assets-eu.researchsquare.com/files/rs-2943801/v1/b89c82decd8ef393b8ccf41e.png"},{"id":37622583,"identity":"c5caf7a0-b933-4b7e-bf7a-751234d8d38d","added_by":"auto","created_at":"2023-05-29 21:19:57","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":622192,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-2943801/v1/ca6fc3e1-c26a-4958-aa6b-1ec5c567601b.pdf"}],"financialInterests":"","formattedTitle":"Predation risk, foraging and reproduction of an insectivore fish species associated with two estuarine habitats","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eEstuarine fishes are closely associated with multiple habitat types in tropical estuaries, comprising vegetated (e.g. mangrove, seagrass meadows, and saltmarsh) and unvegetated habitats (e.g mudflat and sandflat) (Honda et al \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2013\u003c/span\u003e; Pessanha et al \u003cspan citationid=\"CR58\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). This habitat heterogeneity exerts a major influence on the species in estuarine regions increasing diversity and species (Marley et al \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). Habitat features, including substratum composition, water conditions (Neves et al \u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e2013\u003c/span\u003e) and presence and type of vegetation (Wange et al 2009), influence the distribution and abundance of fish species. Each habitat feature influences the way in which fish exploit resources for food, and for spawning sites and/or refuge (James et al \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Lefcheck et al \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). Previous studies have also highlighted how heterogeneous environments offer more habitat types and niches, thereby allowing more species to coexist in ecosystems (Hamm and Drossel \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2017\u003c/span\u003e; Ochoa-G\u0026oacute;mez et al \u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e2018\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eAssociations of fishes have been studied extensively in mangrove root systems (Ley et al 2009; Silva et al \u003cspan citationid=\"CR65\" class=\"CitationRef\"\u003e2018\u003c/span\u003e) and seagrass meadows (Jaxion-Harm et al \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2012\u003c/span\u003e; Ho et al \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2018\u003c/span\u003e), showing these habitats to contain abundant food resources and possess characteristics that could reduce the interaction rate between predator and prey (Vaslet et al \u003cspan citationid=\"CR70\" class=\"CitationRef\"\u003e2012\u003c/span\u003e; James et al \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). Additionally, the foraging efficiency and reproductive success of most fishes change with growth. These differences vary from species to species and, in many cases, are often associated with changes in habitats (Sheaves et al \u003cspan citationid=\"CR64\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). In addition, habitat selection for feeding or refuge by fish species has implications for maximizing energy intake and enhancing growth, size distributions and survival rates. Sheaves et al. (\u003cspan citationid=\"CR64\" class=\"CitationRef\"\u003e2015\u003c/span\u003e), amongst other, have indicated that the habitat requirements for the estuary-dependent juvenile phase may be quite different when compared to the adult stage of the fish life cycle.\u003c/p\u003e \u003cp\u003eThe pneumatophore fringes of mangroves and mudflats are important habitats that extend into the intertidal and subtidal zones, and are regularly flooded with seawater. In particular, pneumatophores attract to juvenile fish due to structural complexity, the lowest predation risk, and high food availability of epiphytic algae and associated invertebrates on their surface area (MacDonald et al \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2008\u003c/span\u003e; Muzaki et al \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). As such, these shallow habitats function as important nursery grounds for fishes in tropical estuaries (Beck et al \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2001\u003c/span\u003e; Sheaves et al \u003cspan citationid=\"CR64\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). Habitats may also provide potential refuge from predators for small fishes by reducing prey visibility and limiting the movements of large predators (Nanjo et al \u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e2014\u003c/span\u003e; Muzaki et al \u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e2017\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eFishes of the family Hemiramphidae, commonly known as halfbeaks, are epipelagic and inhabit shallow, estuarine and freshwater environments (Hughes and Stewart \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2006\u003c/span\u003e). The common halfbeak \u003cem\u003eHyporhamphus unifasciatus\u003c/em\u003e, one the most abundant fish species (Favero et al \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Passos et al \u003cspan citationid=\"CR57\" class=\"CitationRef\"\u003e2013\u003c/span\u003e), is a small marine fish (length, TL\u0026thinsp;=\u0026thinsp;300 mm; Froese and Pauly \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2011\u003c/span\u003e), characterized by a lower jaw that is much longer than the upper jaw (Meisner \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e2001\u003c/span\u003e), and distributed along the Western Atlantic, from Florida southward through the Caribbean to Uruguay (Banford and Collette \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2001\u003c/span\u003e). This species is restricted to coastal habitats such as seagrass beds, tidal creeks and beaches (Banford \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2010\u003c/span\u003e), where they feed as generalist to more specialized guilds (e.g., herbivorous and insectivores) (Passos et al \u003cspan citationid=\"CR57\" class=\"CitationRef\"\u003e2013\u003c/span\u003e; Silva et al \u003cspan citationid=\"CR65\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). The common halfbeak is an important resource in many fishing communities due to its abundance and economic value (Mour\u0026atilde;o and Nordi \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e2003\u003c/span\u003e; Medeiros et al \u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). This species is mostly captured in gillnets and beach seines by artisanal fishers, and today is considered overexploited along the Brazilian coastline (Verba et al \u003cspan citationid=\"CR73\" class=\"CitationRef\"\u003e2020\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eTo compare how two shallow-water habitat types may affect distribution and abundance for the common halfbeak, changes in diet in juveniles and adults on a temporal scale were first investigated. Next, we tested whether common halfbeaks preferentially inhabit close pneumatophore fringes, such that they are suitable areas for growth because they maximize the condition factor (proxy of energy reserves in the fish body), and that predators would affect abundance. We predicted that density and distribution of fish populations are strongly related to areas with the presence of pneumatophores (used as a proxy for complexity) due to abundant food resources and predation.\u003c/p\u003e"},{"header":"2. Material and Methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1 Study area and sampling\u003c/h2\u003e \u003cp\u003eThis study was conducted on the Mamanguape estuary (6\u0026ordm;43'02'' S 35\u0026ordm;67'46'' W) situated at the Brazilian northeastern coast. This estuary is fringed by a dense mangrove forest of c. 6,000 ha (Rocha et al \u003cspan citationid=\"CR61\" class=\"CitationRef\"\u003e2008\u003c/span\u003e). Prop roots, pneumatophores and mudflats are usually found at the outer edges of a fringe or bordering tidal creeks and channels (Mour\u0026atilde;o and Nordi \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e2003\u003c/span\u003e; Nascimento et al \u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e2011\u003c/span\u003e). In this region, K\u0026ouml;ppen classifies climate as As-type (hot and humid) (Alvares et al 2013). Annual rainfall ranges from 1,750 to 2,000 mm, and the average temperatures hover around 26\u0026deg;C (Macedo et al \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2010\u003c/span\u003e). The tide occurs in semi-diurnal tidal regimes, with the mean tidal amplitude varies from 0.2 m (low water) to 2.7 m (high water) (Souza and Furrier \u003cspan citationid=\"CR66\" class=\"CitationRef\"\u003e2015\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eTwo habitats of the estuary were considered in this study: 1) the intertidal adjacent \u003cem\u003eAvicennia-Laguncularia\u003c/em\u003e pneumatophores fringe that can extend away from the mangrove forest, and 2) unvegetated mudflat extending 50 m seaward of the pneumatophore fringe. Monthly sampling was conducted in the estuary in 2016: January to July \u0026ndash; rainy season; August to December \u0026ndash; dry season (except in September due to inclement weather. Fish were collected with three fike nets, set and retrieved approximately 2 to 3 h before and after mean high water, positioned parallel to mangrove fringe so that the opening (and wings) faced landward in each site. Additionally, beach seine (10m x 1.5m; 8mm mesh size) was hauled parallel to an extension of approximately 30 m and to a maximum depth of 1.5 m, during the low tide. The sampling unit was standardized with three replicates in an effort to capture individuals that use the area. In the laboratory, the fish caught were measured, total size (mm) and weighed (g). In order to better characterize the habitat structure of pneumatophores, sampling was performed at different sites along of estuary whenever possible. Three random quadrats of 25 x 25 cm were set on each site along a mangrove forest. In the quadrats we quantified the density of pneumatophores.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2 Abundance and spatial distribution of common halfbeak\u003c/h2\u003e \u003cp\u003eAbundance and biomass of common halfbeak were analysed separately using a univariate statistics (PERMANOVA) (with 9999 permutations) to test for spatial and temporal changes, and applied on two factors: habitat (two fixed levels: pneumatophore fringes and mudflats), and season (two fixed levels: rainy and dry). A resemblance matrix of data was calculated using Euclidean distance. The variables were log transformed. The log transformation reduced or removed the skewness of original data. Significant factors were further analyzed using a PERMANOVA pair-wise comparison. The analyses were performed using PRIMER v6\u0026thinsp;+\u0026thinsp;PERMANOVA (Clarke and Gorley \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2006\u003c/span\u003e; Anderson et al \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2008\u003c/span\u003e).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e2.3 Reproductive data and condition factor (K)\u003c/h2\u003e \u003cp\u003eGonads were macroscopically examined and reproductive stage was described according to Vazzoler (\u003cspan citationid=\"CR71\" class=\"CitationRef\"\u003e1982\u003c/span\u003e). The gonads of each individual were removed when possible and weighed (in g). The gonodo-somatic index (GSI) is a good indicator of reproductive activity, and was calculated for individuals using the formula: GSI\u0026thinsp;=\u0026thinsp;Weight of gonad/Weight of fish x 100 (Vazzoler \u003cspan citationid=\"CR72\" class=\"CitationRef\"\u003e1996\u003c/span\u003e). Common halfbeak were categorized into size classes: juveniles (\u0026lt;\u0026thinsp;144 mm) and adults (\u0026gt;\u0026thinsp;145 mm) (Favero et al \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2019\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eTo assess the variation in condition factor of the common halfbeak from both estuarine habitats, we used a Fulton\u0026rsquo;s condition factor K. Individual values of the condition factor were obtained through the formula K\u0026thinsp;=\u0026thinsp;100 Wt / Lt\u003csup\u003e3\u003c/sup\u003e where Wt is total wet weight (mg) and Lt total length (mm) (Froese \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2006\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eTo investigate the distribution of the length frequency, common halfbeak individuals were grouped into 10 mm TL size classes by months, and estimate their recruitment pattern.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003e2.4 Gut content and diet analysis\u003c/h2\u003e \u003cp\u003eThe gut contents of each individual were removed and examined under a stereomicroscope and each dietary item was identified. To analyze the diet, frequency of occurrence (O%) and volumetric (V%) percentages were calculated to characterise the diet (Hyslop \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e1980\u003c/span\u003e), and were then used to calculated the Alimentary Index (IAi) (Kawakami and Vazzoler \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e1980\u003c/span\u003e), presented in percentages. The volume of each item was calculated and analyzed by displacement methods (Bemvenuti \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e1990\u003c/span\u003e). The method consist of the estimation of volumetric proportion of each item, and then calculated based on the total volume of food eaten per consumer. Empty stomachs were excluded from the analyses.\u003c/p\u003e \u003cp\u003eA permutational multivariate analysis of variance (PERMANOVA) (with 9999 permutations) was used to examined variations in volumetric contributions of prey items, and applied on three factors: habitat types (two fixed levels: pneumatophore fringes and mudflats), season (two fixed levels: rainy and dry), and size (two fixed levels: juvenile and adult). A resemblance matrix of data was calculated using Bray-Curtis coefficients. The variables were square-root transformed. Where a significant difference (p\u0026thinsp;\u0026lt;\u0026thinsp;0.05) was detected for the factor habitat, post hoc tests were conducted. All analyses were performed using the statistical package PRIMER v6\u0026thinsp;+\u0026thinsp;PERMANOVA (Clarke and Gorley \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2006\u003c/span\u003e; Anderson et al \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2008\u003c/span\u003e).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003e2.5 Predatory fishes\u003c/h2\u003e \u003cp\u003eIn order to clarify the abundance of common halfbeak, the predatory fish abundance was estimate in both habitats. Predatory fish species in habitat types were chosen on two criteria: 1) carnivorous with tendency to piscivory, and 2) predator fishes which live in water column or close to water surface. The classification of fish species as piscivores was based upon published dietary data from a preliminary study conducted at the estuary (Campos et al \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2015\u003c/span\u003e; Silva et al \u003cspan citationid=\"CR65\" class=\"CitationRef\"\u003e2018\u003c/span\u003e; Pessanha et al \u003cspan citationid=\"CR58\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Fourteen species were recorded: jacks (Carangidae: \u003cem\u003eCaranx latus\u003c/em\u003e and \u003cem\u003eC. hippos\u003c/em\u003e), snooks (Centropomidae: \u003cem\u003eCentropomus paralellus, C. undecimales, C. ensiferus\u003c/em\u003e, and \u003cem\u003eC. pectinatus\u003c/em\u003e), snappers (Lutjanidae: \u003cem\u003eLutjanus alexandrei, L. analis, L. apodus\u003c/em\u003e, and \u003cem\u003eL. jocu\u003c/em\u003e), randalls soap (Serranidae: \u003cem\u003eRypticus randalli\u003c/em\u003e), barracuda (Sphyraenidae: \u003cem\u003eSphyrena barracuda\u003c/em\u003e) and needle fishes (Belonidae: \u003cem\u003eStrongylura timucu\u003c/em\u003e and \u003cem\u003eS. marina\u003c/em\u003e). Additionally, to analyze the influence of predatory fishes on abundance of common halfbeak. Abundance of predators were expressed by pooling and combining the number of individuals into family groups in each habitat and seasons. We used the t-test also to examine the hypothesis of no difference in number of predatory fish species between habitats during in each season.\u003c/p\u003e \u003cp\u003eA multiple regression analysis with number of predatory fishes and habitat structure of pneumatophores as predictors and abundance and biomass of \u003cem\u003eH. unifascitus\u003c/em\u003e as response variables was performed (Palomares and Pauli 1989). These data were checked for multicolinearity, normality and homogeneity of variance and were log-transformed, log\u003csub\u003e10\u003c/sub\u003e(x\u0026thinsp;+\u0026thinsp;1), to meet the assumptions of multiple regression. We performed hierarchical linear regression analysis: in step 1, the number of predatory fishes as the predictor variable was used because it was assumed to explain a statistically significant amount of variance in fish distribution. In step 2, structure of pneumatophores was added. The analysis were performed using the statistical package SPSS.\u003c/p\u003e \u003c/div\u003e"},{"header":"3. Results","content":"\u003cdiv id=\"Sec9\" class=\"Section2\"\u003e\n \u003ch2\u003e3.1 Abundance and spatial distribution\u003c/h2\u003e\n \u003cdiv class=\"BlockQuote\"\u003e\n \u003cp\u003eA total of 534 common halfbeak were caught, totaling 1466.66 grams. The pneumatophore fringes showed the highest number of individuals and biomass compared to the mudflat (Fig. \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e). Seasonally, higher values for the number of individuals and biomass were recorded during the rainy period. Statistically, the spatial effect was overall not significant on the number of individuals (pseudo-F\u003csub\u003e2, 82\u003c/sub\u003e= 0.75; \u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026gt;\u0026thinsp;0.001) and biomass (pseudo-F\u003csub\u003e2, 82\u003c/sub\u003e= 0.04; \u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026gt;\u0026thinsp;0.001). Significant differences were found between seasons for both the number of individuals and biomass. However, the interaction effects were not significant between habitat types and seasonal factors (number of individuals: pseudo-F\u003csub\u003e2, 82\u003c/sub\u003e= 0.20 and biomass: pseudo-F\u003csub\u003e2, 82\u003c/sub\u003e= 0.26; \u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026gt;\u0026thinsp;0.001).\u003c/p\u003e\n \u003c/div\u003e\n \u003cp\u003eThe monthly length frequency distribution of common halfbeak ranging from 15 to 180 mm TL. Monthly observations showed that the percentages of this species tended to increase during the rainy season (from April to July), principally large-size individuals (Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e). The percentages of small-size classes (\u0026lt;\u0026thinsp;100 mm TL) showed the reverse trend, occurring in higher abundance in the dry season (from October to December) (Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e).\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec10\" class=\"Section2\"\u003e\n \u003ch2\u003e3.2 Reproductive data and Condition factor (K)\u003c/h2\u003e\n \u003cp\u003eIn the estuary, two periods of reproductive activity were observed in our study (Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e). The first period matched the beginning of the rainy season, but a peak of mature females was registered in July, suggesting that individuals spawn in this season. The second period was few apparent, starting in the dry season in approximately October, and the peak of mature females occurred in January (see Pneumatophore fringe). The changes in the gonodosomatic index (GSI) of the males showed the same pattern for both habitats, and the values tended to be relatively lower than those of the females (Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e).\u003c/p\u003e\n \u003cp\u003eThe condition factor (K) for all fish samples was determined by month and did not reveal similar patterns when compared to habitats), showing the highest values in mudflat (Fig. \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e). However, there was some indication that the condition factor values for common halfbeak slight decreased during the dry season in both habitat types\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec11\" class=\"Section2\"\u003e\n \u003ch2\u003e3.3 Diet\u003c/h2\u003e\n \u003cp\u003eFor the diet study, 311 stomachs with prey were analysed from common halfbeak, of which 41 stomachs were empty (13.2%). In general, common halfbeak fed on prey items fell onto the water surface (Table \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e). In this case, the diet was comprised mainly of insects, which accounted for more than 97% of the overall IAi in juveniles and adults in both habitat types. Although plant material, copepods and other insects were frequently consumed, they were only present in small volumes.\u0026nbsp;\u003c/p\u003e\u0026nbsp;\u003ctable id=\"Tab1\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eAlimentary Index (IAi%) of food items consumed by juvenile and adults of \u003cem\u003eHyporhamphus unifasciatus\u003c/em\u003e among habitats (Mudflat and Pneumatophore zones) in Mamanguape estuary (O%= Frequency of occurrence, and V%= volume percentage)\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\" style=\"width: 17.1849%;\"\u003e\u0026nbsp;\u003c/th\u003e\n \u003cth align=\"left\" colspan=\"6\" style=\"width: 27.7237%;\"\u003e\n \u003cp\u003eMudflat\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\" colspan=\"6\" style=\"width: 33.4204%;\"\u003e\n \u003cp\u003ePneumatophore fringes\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\" style=\"width: 17.1849%;\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\" colspan=\"3\" style=\"width: 13.8619%;\"\u003e\n \u003cp\u003e\u003cstrong\u003eJuvenile (n\u0026thinsp;=\u0026thinsp;39)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colspan=\"3\" style=\"width: 13.8619%;\"\u003e\n \u003cp\u003e\u003cstrong\u003eAdult (n\u0026thinsp;=\u0026thinsp;33)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colspan=\"3\" style=\"width: 18.3242%;\"\u003e\n \u003cp\u003e\u003cstrong\u003eJuvenile (n\u0026thinsp;=\u0026thinsp;96)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" colspan=\"3\" style=\"width: 15.1911%;\"\u003e\n \u003cp\u003e\u003cstrong\u003eAdult (n\u0026thinsp;=\u0026thinsp;143)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\" style=\"width: 17.1849%;\"\u003e\n \u003cp\u003eFood items\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.3674%;\"\u003e\n \u003cp\u003eO%\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.3674%;\"\u003e\n \u003cp\u003eV%\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 5.2219%;\"\u003e\n \u003cp\u003eIAi%\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.6523%;\"\u003e\n \u003cp\u003eO%\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.6523%;\"\u003e\n \u003cp\u003eV%\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.6523%;\"\u003e\n \u003cp\u003eIAi%\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 7.5955%;\"\u003e\n \u003cp\u003eO%\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.6523%;\"\u003e\n \u003cp\u003eV%\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 6.0764%;\"\u003e\n \u003cp\u003eIAi%\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 5.8865%;\"\u003e\n \u003cp\u003eO%\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.6523%;\"\u003e\n \u003cp\u003eV%\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.6523%;\"\u003e\n \u003cp\u003eIAi%\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\" style=\"width: 17.1849%;\"\u003e\n \u003cp\u003eForaminifera\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.3674%;\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.3674%;\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 5.2219%;\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.6523%;\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.6523%;\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.6523%;\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 7.5955%;\"\u003e\n \u003cp\u003e1.20\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.6523%;\"\u003e\n \u003cp\u003e0.02\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 6.0764%;\"\u003e\n \u003cp\u003e0.01\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 5.8865%;\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.6523%;\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.6523%;\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\" style=\"width: 17.1849%;\"\u003e\n \u003cp\u003eDiatoms\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.3674%;\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.3674%;\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 5.2219%;\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.6523%;\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.6523%;\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.6523%;\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 7.5955%;\"\u003e\n \u003cp\u003e1.20\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.6523%;\"\u003e\n \u003cp\u003e0.02\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 6.0764%;\"\u003e\n \u003cp\u003e0.01\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 5.8865%;\"\u003e\n \u003cp\u003e0.83\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.6523%;\"\u003e\n \u003cp\u003e3.20\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.6523%;\"\u003e\n \u003cp\u003e0.06\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\" style=\"width: 17.1849%;\"\u003e\n \u003cp\u003eTrematoda\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.3674%;\"\u003e\n \u003cp\u003e5.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.3674%;\"\u003e\n \u003cp\u003e0.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 5.2219%;\"\u003e\n \u003cp\u003e0.01\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.6523%;\"\u003e\n \u003cp\u003e6.67\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.6523%;\"\u003e\n \u003cp\u003e0.12\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.6523%;\"\u003e\n \u003cp\u003e0.03\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 7.5955%;\"\u003e\n \u003cp\u003e8.43\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.6523%;\"\u003e\n \u003cp\u003e0.22\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 6.0764%;\"\u003e\n \u003cp\u003e0.03\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 5.8865%;\"\u003e\n \u003cp\u003e7.44\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.6523%;\"\u003e\n \u003cp\u003e0.30\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.6523%;\"\u003e\n \u003cp\u003e0.05\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\" style=\"width: 17.1849%;\"\u003e\n \u003cp\u003eSipuncula\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.3674%;\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.3674%;\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 5.2219%;\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.6523%;\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.6523%;\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.6523%;\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 7.5955%;\"\u003e\n \u003cp\u003e6.02\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.6523%;\"\u003e\n \u003cp\u003e0.37\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 6.0764%;\"\u003e\n \u003cp\u003e0.04\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 5.8865%;\"\u003e\n \u003cp\u003e4.13\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.6523%;\"\u003e\n \u003cp\u003e0.22\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.6523%;\"\u003e\n \u003cp\u003e0.02\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\" style=\"width: 17.1849%;\"\u003e\n \u003cp\u003eErrantia Polychaeta\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.3674%;\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.3674%;\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 5.2219%;\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.6523%;\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.6523%;\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.6523%;\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 7.5955%;\"\u003e\n \u003cp\u003e1.20\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.6523%;\"\u003e\n \u003cp\u003e0.43\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 6.0764%;\"\u003e\n \u003cp\u003e0.01\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 5.8865%;\"\u003e\n \u003cp\u003e7.44\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.6523%;\"\u003e\n \u003cp\u003e3.32\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.6523%;\"\u003e\n \u003cp\u003e0.55\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\" style=\"width: 17.1849%;\"\u003e\n \u003cp\u003eSedentary Polychaeta\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.3674%;\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.3674%;\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 5.2219%;\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.6523%;\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.6523%;\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.6523%;\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 7.5955%;\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.6523%;\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 6.0764%;\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 5.8865%;\"\u003e\n \u003cp\u003e0.83\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.6523%;\"\u003e\n \u003cp\u003e0.29\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.6523%;\"\u003e\n \u003cp\u003e0.01\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\" style=\"width: 17.1849%;\"\u003e\n \u003cp\u003eCopepods\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.3674%;\"\u003e\n \u003cp\u003e8.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.3674%;\"\u003e\n \u003cp\u003e0.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 5.2219%;\"\u003e\n \u003cp\u003e0.05\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.6523%;\"\u003e\n \u003cp\u003e16.67\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.6523%;\"\u003e\n \u003cp\u003e0.61\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.6523%;\"\u003e\n \u003cp\u003e0.42\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 7.5955%;\"\u003e\n \u003cp\u003e9.64\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.6523%;\"\u003e\n \u003cp\u003e0.47\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 6.0764%;\"\u003e\n \u003cp\u003e0.08\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 5.8865%;\"\u003e\n \u003cp\u003e6.61\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.6523%;\"\u003e\n \u003cp\u003e0.13\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.6523%;\"\u003e\n \u003cp\u003e0.02\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\" style=\"width: 17.1849%;\"\u003e\n \u003cp\u003eGammaridae\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.3674%;\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.3674%;\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 5.2219%;\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.6523%;\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.6523%;\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.6523%;\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 7.5955%;\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.6523%;\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 6.0764%;\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 5.8865%;\"\u003e\n \u003cp\u003e1.65\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.6523%;\"\u003e\n \u003cp\u003e0.11\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.6523%;\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\" style=\"width: 17.1849%;\"\u003e\n \u003cp\u003eCyprid larvae\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.3674%;\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.3674%;\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 5.2219%;\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.6523%;\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.6523%;\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.6523%;\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 7.5955%;\"\u003e\n \u003cp\u003e1.20\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.6523%;\"\u003e\n \u003cp\u003e0.02\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 6.0764%;\"\u003e\n \u003cp\u003e0.01\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 5.8865%;\"\u003e\n \u003cp\u003e0.83\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.6523%;\"\u003e\n \u003cp\u003e0.01\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.6523%;\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\" style=\"width: 17.1849%;\"\u003e\n \u003cp\u003eBrachyura larvae\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.3674%;\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.3674%;\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 5.2219%;\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.6523%;\"\u003e\n \u003cp\u003e6.67\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.6523%;\"\u003e\n \u003cp\u003e0.20\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.6523%;\"\u003e\n \u003cp\u003e0.06\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 7.5955%;\"\u003e\n \u003cp\u003e1.20\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.6523%;\"\u003e\n \u003cp\u003e1.87\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 6.0764%;\"\u003e\n \u003cp\u003e0.04\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 5.8865%;\"\u003e\n \u003cp\u003e0.83\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.6523%;\"\u003e\n \u003cp\u003e0.01\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.6523%;\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\" style=\"width: 17.1849%;\"\u003e\n \u003cp\u003eBrachyura\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.3674%;\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.3674%;\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 5.2219%;\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.6523%;\"\u003e\n \u003cp\u003e3.33\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.6523%;\"\u003e\n \u003cp\u003e0.98\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.6523%;\"\u003e\n \u003cp\u003e0.14\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 7.5955%;\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.6523%;\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 6.0764%;\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 5.8865%;\"\u003e\n \u003cp\u003e0.83\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.6523%;\"\u003e\n \u003cp\u003e0.10\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.6523%;\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\" style=\"width: 17.1849%;\"\u003e\n \u003cp\u003eTanaidacea\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.3674%;\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.3674%;\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 5.2219%;\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.6523%;\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.6523%;\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.6523%;\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 7.5955%;\"\u003e\n \u003cp\u003e1.20\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.6523%;\"\u003e\n \u003cp\u003e0.02\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 6.0764%;\"\u003e\n \u003cp\u003e0.01\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 5.8865%;\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.6523%;\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.6523%;\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\" style=\"width: 17.1849%;\"\u003e\n \u003cp\u003eHymenoptera\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.3674%;\"\u003e\n \u003cp\u003e\u003cstrong\u003e88.9\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.3674%;\"\u003e\n \u003cp\u003e\u003cstrong\u003e70.5\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 5.2219%;\"\u003e\n \u003cp\u003e\u003cstrong\u003e99.8\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.6523%;\"\u003e\n \u003cp\u003e\u003cstrong\u003e56.67\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.6523%;\"\u003e\n \u003cp\u003e\u003cstrong\u003e41.89\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.6523%;\"\u003e\n \u003cp\u003e\u003cstrong\u003e98.08\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 7.5955%;\"\u003e\n \u003cp\u003e\u003cstrong\u003e84.34\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.6523%;\"\u003e\n \u003cp\u003e\u003cstrong\u003e67.17\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 6.0764%;\"\u003e\n \u003cp\u003e\u003cstrong\u003e97.74\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 5.8865%;\"\u003e\n \u003cp\u003e\u003cstrong\u003e77.69\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.6523%;\"\u003e\n \u003cp\u003e\u003cstrong\u003e56.13\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.6523%;\"\u003e\n \u003cp\u003e\u003cstrong\u003e97.33\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\" style=\"width: 17.1849%;\"\u003e\n \u003cp\u003eColeoptera\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.3674%;\"\u003e\n \u003cp\u003e2.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.3674%;\"\u003e\n \u003cp\u003e0.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 5.2219%;\"\u003e\n \u003cp\u003e0.01\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.6523%;\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.6523%;\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.6523%;\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 7.5955%;\"\u003e\n \u003cp\u003e1.20\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.6523%;\"\u003e\n \u003cp\u003e0.02\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 6.0764%;\"\u003e\n \u003cp\u003e0.01\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 5.8865%;\"\u003e\n \u003cp\u003e1.65\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.6523%;\"\u003e\n \u003cp\u003e0.12\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.6523%;\"\u003e\n \u003cp\u003e0.01\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\" style=\"width: 17.1849%;\"\u003e\n \u003cp\u003eDiptera\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.3674%;\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.3674%;\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 5.2219%;\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.6523%;\"\u003e\n \u003cp\u003e13.33\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.6523%;\"\u003e\n \u003cp\u003e0.16\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.6523%;\"\u003e\n \u003cp\u003e0.09\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 7.5955%;\"\u003e\n \u003cp\u003e2.41\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.6523%;\"\u003e\n \u003cp\u003e0.95\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 6.0764%;\"\u003e\n \u003cp\u003e0.04\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 5.8865%;\"\u003e\n \u003cp\u003e4.96\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.6523%;\"\u003e\n \u003cp\u003e1.01\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.6523%;\"\u003e\n \u003cp\u003e0.11\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\" style=\"width: 17.1849%;\"\u003e\n \u003cp\u003eHemiptera\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.3674%;\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.3674%;\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 5.2219%;\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.6523%;\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.6523%;\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.6523%;\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 7.5955%;\"\u003e\n \u003cp\u003e6.02\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.6523%;\"\u003e\n \u003cp\u003e1.34\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 6.0764%;\"\u003e\n \u003cp\u003e0.14\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 5.8865%;\"\u003e\n \u003cp\u003e2.48\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.6523%;\"\u003e\n \u003cp\u003e0.16\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.6523%;\"\u003e\n \u003cp\u003e0.01\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\" style=\"width: 17.1849%;\"\u003e\n \u003cp\u003ePlant material\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.3674%;\"\u003e\n \u003cp\u003e13.9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.3674%;\"\u003e\n \u003cp\u003e0.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 5.2219%;\"\u003e\n \u003cp\u003e0.10\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.6523%;\"\u003e\n \u003cp\u003e20.00\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.6523%;\"\u003e\n \u003cp\u003e1.39\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.6523%;\"\u003e\n \u003cp\u003e1.15\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 7.5955%;\"\u003e\n \u003cp\u003e19.28\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.6523%;\"\u003e\n \u003cp\u003e5.65\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 6.0764%;\"\u003e\n \u003cp\u003e1.88\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 5.8865%;\"\u003e\n \u003cp\u003e9.92\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.6523%;\"\u003e\n \u003cp\u003e8.28\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 4.6523%;\"\u003e\n \u003cp\u003e1.83\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n \u003cp\u003e\u003c/p\u003e\n \u003cp\u003e\u003cbr\u003e\u003c/p\u003e\n \u003cp\u003eNo significant differences in the dietary compositions of common halfbeak were found between habitat types (PERMANOVA: pseudo-F\u003csub\u003e1,245\u003c/sub\u003e= 1.87, P\u0026thinsp;\u0026gt;\u0026thinsp;0.05) and seasons (PERMANOVA: pseudo-F\u003csub\u003e1,245\u003c/sub\u003e= 1.13, P\u0026thinsp;\u0026gt;\u0026thinsp;0.05), which was attributed to the consumption of Hymenoptera throughout the year in the estuary. Significant differences in diet were found among size classes (PERMANOVA: pseudo-F\u003csub\u003e1,245\u003c/sub\u003e= 3.13, P\u0026thinsp;\u0026lt;\u0026thinsp;0.001). The interaction effects were significant between size and seasonal factors (PERMANOVA: pseudo- F\u003csub\u003e1,245\u003c/sub\u003e= 3.52; \u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.001).\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec12\" class=\"Section2\"\u003e\n \u003ch2\u003e3.4 Effect of presence of predatory fish species\u003c/h2\u003e\n \u003cp\u003ePredatory fishes were present during the whole study period, with jacks and snooks the main species in estuarine habitats, accounting for more than 70% of the species sampled (Fig. \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003e). Jacks and snooks were best represented in terms of abundance in the rainy and dry seasons, respectively. Snappers were abundant (range 7\u0026ndash;15%) in mudflats during the dry season and pneumatophore fringes during the rainy season. Randall soap fish, needle fish and barracuda occurred in low numbers in both habitats during the study (Fig. \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003e).\u003c/p\u003e\n \u003cp\u003eThe analysis showed that the abundance of predatory fishes was not significantly different between habitats (t\u0026thinsp;=\u0026thinsp;9.085; P\u0026thinsp;\u0026gt;\u0026thinsp;0.01). Unlike spatial abundance, however, there was a significant difference in the abundance of predatory fishes within each habitat during the seasons (Lower: t\u0026thinsp;=\u0026thinsp;12.184; P\u0026thinsp;\u0026lt;\u0026thinsp;0.01; Upper: t\u0026thinsp;=\u0026thinsp;29.685; P\u0026thinsp;\u0026lt;\u0026thinsp;0.01).\u003c/p\u003e\n \u003cp\u003eThe hierarchical multiple regression model results showed that the abundance of predatory fishes and habitat types were significant predictors of variations in the abundance and biomass of common halfbeak, as evidenced by the consistent increase in R\u003csup\u003e2\u003c/sup\u003e in each step (Table \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e). The number of predatory fishes was significantly negatively related to abundance (\u0026beta;= -0.554; P\u0026thinsp;\u0026lt;\u0026thinsp;0.01) and biomass (\u0026beta;= -0.462; P\u0026thinsp;\u0026lt;\u0026thinsp;0.01) and explained 30.7% and 21.4% of the variance in the model, respectively. Then, pneumatophore fringes were significantly related to abundance (\u0026beta;\u0026thinsp;=\u0026thinsp;0.180; P\u0026thinsp;\u0026lt;\u0026thinsp;0.01) and biomass (\u0026beta;\u0026thinsp;=\u0026thinsp;0.223; P\u0026thinsp;\u0026lt;\u0026thinsp;0.01) and explained 4.7% and 6.1% of the variance in the model, respectively (Table \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e).\u0026nbsp;\u003c/p\u003e\u0026nbsp;\u003ctable id=\"Tab2\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eResults of the hierarchical multiple regression models computed on both number of individuals and biomass the \u003cem\u003eHyporhamphus unifasciatus\u003c/em\u003e of two groups of predictor variables. Significance: ** p value\u0026thinsp;\u0026lt;\u0026thinsp;0.01\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\" style=\"width: 32.6553%;\"\u003e\u0026nbsp;\u003c/th\u003e\n \u003cth align=\"left\" colspan=\"2\" style=\"width: 27.3777%;\"\u003e\n \u003cp\u003eNumber of individuals\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\" colspan=\"2\" style=\"width: 30.3463%;\"\u003e\n \u003cp\u003eBiomass\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003cth align=\"left\" style=\"width: 32.6553%;\"\u003e\n \u003cp\u003ePredictor variables\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\" style=\"width: 13.359%;\"\u003e\n \u003cp\u003eModel 1(\u0026beta;)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\" style=\"width: 14.0187%;\"\u003e\n \u003cp\u003eModel 2(\u0026beta;)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\" style=\"width: 16.9874%;\"\u003e\n \u003cp\u003eModel 1(\u0026beta;)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\" style=\"width: 13.359%;\"\u003e\n \u003cp\u003eModel 2(\u0026beta;)\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\" style=\"width: 32.6553%;\"\u003e\n \u003cp\u003ePredatory fishes (abundance)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\" style=\"width: 13.359%;\"\u003e\n \u003cp\u003e\u0026minus;\u0026thinsp;0.554 **\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\" style=\"width: 14.0187%;\"\u003e\n \u003cp\u003e\u0026minus;\u0026thinsp;0.526 **\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\" style=\"width: 16.9874%;\"\u003e\n \u003cp\u003e\u0026minus;\u0026thinsp;0.462 **\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\" style=\"width: 13.359%;\"\u003e\n \u003cp\u003e- 0.423**\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\" style=\"width: 32.6553%;\"\u003e\n \u003cp\u003ePneumatophore complexity\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 13.359%;\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 14.0187%;\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 16.9874%;\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 13.359%;\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\" style=\"width: 32.6553%;\"\u003e\n \u003cp\u003eDensity\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 13.359%;\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"char\" style=\"width: 14.0187%;\"\u003e\n \u003cp\u003e0.228 **\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 16.9874%;\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"char\" style=\"width: 13.359%;\"\u003e\n \u003cp\u003e0.287**\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\" style=\"width: 32.6553%;\"\u003e\n \u003cp\u003eR\u003csup\u003e2\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\" style=\"width: 13.359%;\"\u003e\n \u003cp\u003e0.307\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\" style=\"width: 14.0187%;\"\u003e\n \u003cp\u003e0.347\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\" style=\"width: 16.9874%;\"\u003e\n \u003cp\u003e0.214\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\" style=\"width: 13.359%;\"\u003e\n \u003cp\u003e0.275\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n\u003c/div\u003e"},{"header":"4. Discussion","content":"\u003cp\u003e Our results demonstrated that the increased habitat structure, provided by pneumatophore fringes, had the strongest association with habitat selection for common halfbeak. This habitat constitutes important sites for this species to complete its life cycle, as spawning and foraging habitats, because both juvenile and adult life stages are caught in this kind of habitat. Apparently, there is some evidence that fishes move to pneumatophore fringes during the rainy season to spawn and are subsequently recruited in this area. The results also indicated that common halfbeaks altered their habitat use on a seasonal basis during the rainy season. \u003cem\u003eH. unifascitus\u003c/em\u003e showed higher abundance in pneumatophore fringes during this period, which could be a consequence of biotic interactions (predation) and spawning periods. Therefore, the structure of the pneumatophores supported the high biomass of common halfbeak that uses these areas for reproduction, growth and development in this tropical estuary. Notably, the differences in the distribution and abundance of common halfbeak were determined by complex responses to habitat characteristics and biotic interactions and offer insights into how habitat use can influence fitness.\u003c/p\u003e \u003cp\u003eIn terms of the number of individuals and biomass, the multiple regression model revealed a positive correlation related to pneumatophore presence. In this case, the pneumatophore fringes attracted halfbeak because suspended habitats in the water column increased foraging and shelter opportunities and consequently increased the survival of individuals. In this study, support for the predator refuge hypothesis exists because there are a greater number of refuges for fishes in pneumatophore fringes than in adjacent habitats, such as subtidal deeper areas or nonvegetated mudflats (Silva et al \u003cspan citationid=\"CR65\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). In fact, these results were consistent with the results of previous studies that highlight that pneumatophore density can affect the abundance of fishes (Green et al \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2012\u003c/span\u003e; Vaslet et al \u003cspan citationid=\"CR70\" class=\"CitationRef\"\u003e2012\u003c/span\u003e). For example, MacKenzie and Cormier (\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e2012\u003c/span\u003e) reported that the vertical structure and arrangement provided by pneumatophore height that emerge from sediment often produce a dense structure impenetrable by larger organisms. According to R\u0026ouml;nnb\u0026auml;ck et al (\u003cspan citationid=\"CR62\" class=\"CitationRef\"\u003e1999\u003c/span\u003e), because the structure is more complex, small fish such as halfbeak might also show higher manoeuvrability and motility to the exploitation of this habitat during high tides for feeding. Some studies have indicated that the arrangement of pneumatophores is also responsible for creating shade for fish species to hide between structures (Cocheret de la Morini\u0026egrave;re et al 2004; Verweij et al \u003cspan citationid=\"CR74\" class=\"CitationRef\"\u003e2006\u003c/span\u003e). From another perspective, the pneumatophore arrangement supports trapping of sediment and organic matter and directly influences prey availability (Kamal et al \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). Together, these factors are considered important contributors to the increased attraction of fish to mangroves (Ochoa-G\u0026oacute;mez et al \u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e2018\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe populations of common halfbeak found in each estuarine habitat also responded differently to the seasonal conditions in different ways, and these shifts may be in response to predation risk: in pneumatophore fringes, the higher abundance and biomass of predatory fishes were registered during the rainy season, while in mudflats, they were registered during the dry season. The number of predatory fishes was a strong predictor of population abundance and was confirmed by the multiple regression model. From this work, there was a vast difference in abundance of Jack and Snook species among habitat types, and this appeared indirectly affected abundance of common halfbeak around pneumatophore fringes. Clearly, these temporal pattern differences among habitats reflect natural variability in baseline habitat quality, where the structure of pneumatophores likely provided additional resources that allowed for greater abundance. Rilov et al (\u003cspan citationid=\"CR60\" class=\"CitationRef\"\u003e2007\u003c/span\u003e) suggested that the quality of a habitat was linked to predation risk. These results are consistent with those of MacKenzier and Cormier (2012), who describe the same pattern for fish species in reefs and seagrass beds, respectively. This was not surprising at first because species move presumably to sites in response to foraging efficiency and capture rate (Ho et al 2019).\u003c/p\u003e \u003cp\u003eIn particular, it is also important to recognize here that during the rainy season, when there was an increase in predatory fishes and prey fishes in pneumatophore fringes, the main predators in this area (jacks and snappers) were small in size or juveniles. In many instances, however, the potential predation risk might be affected by the apparent presence of juvenile predatory fishes and thus induce changes in prey behaviour leading to adjustments in refuge use and spatial distribution (Ori et al 2010). It is possible that the intensity of predation will be influenced by opportunistic attacks of the interspecific schooling of piscivorous juveniles when fish are concentrated in the pneumatophore fringes. This conclusion was well supported by detailed studies of observations relative to the aggregation effect in foraging behaviour of juvenile predatory fishes (Lukas and Benkert 1983; Juanes and Conover \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e1994\u003c/span\u003e). Sancho (\u003cspan citationid=\"CR63\" class=\"CitationRef\"\u003e2000\u003c/span\u003e) examined another aspect of predation by juveniles. The author found a \u0026ldquo;midwater\u0026rdquo; hunting behaviour consisting of midwater high-speed attacks on spawning fishes in reefs and therefore may be considered an important behaviour in carangid species.\u003c/p\u003e \u003cp\u003eFindings in diet composition in our study showed some differences compared to the results of previous studies. Common halfbeak is commonly regarded as an herbivorous fish, and plant material forms a very significant part of its diet (Vasconcelos Filho et al \u003cspan citationid=\"CR69\" class=\"CitationRef\"\u003e2003\u003c/span\u003e; Paiva et al \u003cspan citationid=\"CR54\" class=\"CitationRef\"\u003e2008\u003c/span\u003e). The small amount of animal prey found in gut contents may be partly considered to be incidentally ingested during herbivory, as suggested by MacKenzie and Cormier (\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e2012\u003c/span\u003e). The present study, however, found that both juveniles and adults preyed primarily on Hymnoptera, which were widely abundant in fish occupying both habitats. Campos et al (\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2015\u003c/span\u003e) also found that common halfbeak fed mainly on Hymnoptera prey and suggested that this species was characterized as an insectivore in the Mamanguape estuary. Studies of other Hemiramphidae species also described insects as main food resources, especially for the diet of larger individuals, which tended to be dominated by terrestrial insects (Kanai et al \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2017\u003c/span\u003e; Abidin et al \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). Indeed, clearly, common halfbeak utilized allochthonous food items (terrestrial insects), which is very useful information for assessing its potential interactions with local food webs (Sheaves et al \u003cspan citationid=\"CR64\" class=\"CitationRef\"\u003e2015\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eNo clear trend in the quantitative and qualitative dietary constituents could be observed between habitats and seasons. In fact, Hymnoptera species were found in very high abundance in gut contents. Most likely, they constitute a very abundant food resource that may be easily collected provided that fish display adequate behaviour to access the item. The prey encounter rate is dependent on the abundance of that prey in the environment (Pinnegar et al \u003cspan citationid=\"CR59\" class=\"CitationRef\"\u003e2003\u003c/span\u003e). Hymnoptera have been widely documented and are often regarded as the most abundant insect group in mangroves (Delabie et al 2006; Nielsen \u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e2010\u003c/span\u003e). Additionally, these prey also fall from the mangrove forest in the surface layers of the water and are sequentially detected and captured by common halfbeak. The pronounced foraging tactic of common halfbeak to target prey (Hymnoptera) is similar the registered by Delabie et al (2006), and is thus presumed to be related to the presence of insects on the seawater surface. This behaviour has been registered by other Hemiramphidae across different habitats (Tabassum et al \u003cspan citationid=\"CR67\" class=\"CitationRef\"\u003e2017\u003c/span\u003e; Abidin et al \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2019\u003c/span\u003e), where insects were ingested in proximity to floating objects or sucked from the water surface (Kanai et al \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2017\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe combination of both a lower number of individuals and non-spawning females in the mudflats during the rainy season might suggest that the adults migrate to spawning grounds located in pneumatophore fringes. According to Fowler et al (\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2008\u003c/span\u003e), these spawning-related in the \u003cem\u003eHyporhamphu\u003c/em\u003es genus constitute an important part of the life history of these schooling species. The use of structured habitats, for example seagrass and mangroves, is closely associated with habitat specifics for spawning, possibly because they represent substrates for egg attachment and increased reproductive success in the case of Hemiramphidae (Hughes and Stewart \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2006\u003c/span\u003e). Large eggs with adhesive filaments are characteristics shared among many of the other members of this family (Oya et al \u003cspan citationid=\"CR53\" class=\"CitationRef\"\u003e2002\u003c/span\u003e; Nuttall et al \u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e2012\u003c/span\u003e). Therefore, fish may utilize habitats such as resting areas to conserve energy before spawning and between spawning events (van der Meulen et al \u003cspan citationid=\"CR68\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). We suggested that the peak of the spawning period during the rainy season, confirmed by the GSI data of females, is driven by three explanations proposed: seasonal changes in predatory fishes, low turbidity linked to rainfall and the presence of young halfbeak caught in the early dry season (see October for young-of-the-year records). The hypothesized lower predation pressure in pneumatophore fringes during these seasons potentially reduces the risk of large nutritious eggs in the halfbeak (Fowler et al \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2008\u003c/span\u003e; Nuttall et al \u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e2012\u003c/span\u003e), while the spawning strategy registered during the period of more turbid waters in the Mamanguape Estuary can minimize visual predation on eggs and increase survival. This spawning strategy has also been registered for \u003cem\u003eHyporhampuhus melanochir\u003c/em\u003e and other hemiramphids in Australia (Hughes and Steward 2006), and other studies have reported larvae and small juveniles using areas upstream of estuaries related to the lowest salinity in this area (D\u0026ouml;ring et al \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). Therefore, spawning during the rainy season maximizes the potential for eggs to be transported because of the high flow of rivers (Islam et al \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2006\u003c/span\u003e). In the current study, a second short spawning period was registered during the dry season, related to higher GSI data in mudflats and recruits that occurred from January to February. Here, water temperature may also have been an important factor in the spawning season because of influences on the metabolic demands of fishes. Water temperature has been identified as a fundamental factor that can influence fish reproduction and growth in tropical estuaries (Mareea et al \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e2000\u003c/span\u003e; Pankhurst and Munday \u003cspan citationid=\"CR56\" class=\"CitationRef\"\u003e2011\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe condition factor (K) showed that the two habitat types were not equally valuable for common halfbeak, especially when comparing their seasonal patterns. Our results demonstrated significant influences of habitat use on the condition factor in the rainy season, and this was important for predicting that energy storage was allocated to growth and survival (Mogensen and Post \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e2012\u003c/span\u003e). Therefore, the condition factor may act to predict the fitness of fishes. Furthermore, pneumatophore fringes provided the best environment because they exhibited favourable conditions for rapidly growing juvenile fish and maximized reproductive fitness. Our results were in accordance with this hypothesis. In this study, the relation between the K-factor and gonadal development had greater importance in influencing this index. Similar results were reported for \u003cem\u003eAtherinella brasiliensis\u003c/em\u003e in this estuary, indicating that habitats that differ in food resources can offer the opportunity to maximize the fitness (J\u0026uacute;nior et al 2020).\u003c/p\u003e \u003cp\u003eIn conclusion, this study clearly demonstrates that configuration of habitat was considered an important determinant of abundance patterns in space and time of common halfbeak populations associated with estuarine areas. The structure of these habitats represented by pneumatophores may contribute to these patterns due to the greater habitat complexity providing shelter from predation, increased microhabitat availability and abundant food. This is consistent with the attractiveness hypothesis for fishes in mangrove areas, which suggests that fishes select habitats because of increased food supply, and increased living space or shelter (Nagelkerken et al \u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e2008\u003c/span\u003e). Several conclusions from this study may prove to be generally applicable in other systems, principally related to predation risk and utilization of food resources in shallow coastal ecosystems. Further investigations based on an ecosystem perspective are needed to understand how the availability of allochthonous food items can supply energy and materials to estuarine food chains and coastal marine ecosystems.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgments\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eWe thank students of the Laboratory of Fish Ecology (UEPB) for helping in both the laboratory and the field. Financial support was provided by the National Counsel of Technological and Scientific Development (CNPq; Grant# 308340/2018-3). This study was conducted under SISBIO Collection of Species Permit number 24557-27/10/2010 issued by ICMBio, Brazilian Environmental Agency, and follows the ethics rules which regulates the scientific use of animals in Brazil (Federal Law 11.794 of October 08, 2008).\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eAbidin, D.A.Z., S.K. Das, and M.A. Ghaffar. 2019. Length-weight relationship, condition factors and trophic level of Buffon\u0026apos;s river-garfish \u003cem\u003eZenarchopterus buffonis\u003c/em\u003e from the coastal waters of Malaysia. \u003cem\u003eSongklanakarin Journal of Science and Technology \u003c/em\u003e41(5): 1162-1170\u003c/li\u003e\n\u003cli\u003eAlvares, C.A., C.A. Alvares, J.L. Stape, P.C. Sentelhas, J.D.M. Gon\u0026ccedil;alves, and G. Sparovek. 2014. K\u0026ouml;ppen\u0026rsquo;s climate classification map for Brazil. \u003cem\u003eMeteorologische Zeitschrift\u003c/em\u003e\u003cem\u003e \u003c/em\u003e22(6): 711-728. \u003c/li\u003e\n\u003cli\u003eAnderson, MJ., R.N. Gorley, and K.R. Clarke. 2008.\u003cem\u003ePERMANOVA + for PRIMER: guide to software and statistical methods\u003c/em\u003e.PRIMER\u0026ndash;E Ltd., Plymouth, United Kingdom.\u003c/li\u003e\n\u003cli\u003eBanford, H.M. 2010. \u003cem\u003eHyporhamphus collettei\u003c/em\u003e, a new species of inshore halfbeak (Hemiramphidae) endemic to Bermuda, with comments on the biogeography of the \u003cem\u003eHyporhamphus unifasciatus\u003c/em\u003e species group. \u003cem\u003eProceedings of the Biological Society of Washington, \u003c/em\u003e123(4): 345\u0026ndash;358. \u003c/li\u003e\n\u003cli\u003eBanford, H.M., and B. Collette. 2001. A new species of halfbeak, \u003cem\u003eHyporhamphus naos\u003c/em\u003e (Beloniformes: Hemiramphidae), from the tropical eastern Pacific. \u003cem\u003eRevista de Biologia Tropical\u003c/em\u003e\u003cem\u003e \u003c/em\u003e49 Suppl 1(1): 39-49.\u003c/li\u003e\n\u003cli\u003eBeck, M.W., K. L. Heck, K.W. Able, D.L. Childers, D.B. Eggleston, B.M. Gillanders, B. Halpern, C.G. Hays, K. Hoshino, T.J. Minello, R.J. Orth, P.F. Sheridan, and M.P. Weinstein. 2001. The identification, conservation, and management of estuarine and marine nurseries for fish and invertebrates: a better understanding of the habitats that serve as nurseries for marine species and the factors that create site-specific variability in nursery quality will improve conservation and management of these areas. \u003cem\u003eBioscience \u003c/em\u003e51: 633\u0026ndash;641.\u003c/li\u003e\n\u003cli\u003eBemvenuti, M.A. 1990. H\u0026aacute;bitos alimentares de peixes-rei (Atherinidae) na regi\u0026atilde;o estuarina da Lagoa dos Patos, Brasil. \u003cem\u003eAtl\u0026acirc;ntica \u003c/em\u003e12 (1): 79-102.\u003c/li\u003e\n\u003cli\u003eCampos, D.M.A.R., A.F. Silva, N.S. Sales, R.E.M.C.C. Oliveira, and A.L.M. Pessanha. 2015. 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The case of Don- gzhaigang Bay, Hainan Island, China. \u003cem\u003eEstuarine, Coastal and Shelf Science\u003c/em\u003e 85(2): 208-216.\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Diet composition, Habitat use, Halfbeak, Predatory Fishes, Structural complexity","lastPublishedDoi":"10.21203/rs.3.rs-2943801/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-2943801/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003ePneumatophore fringes and mudflats are extremely valuable habitats and provide structures on which many fish species benefit in terms of food and reduced predation risk. We analysed the spatiotemporal patterns in feeding habits, reproductive aspects and effects of predatory fish presence to assess the ecological drivers of the common halfbeak, \u003cem\u003eHyporhamphus unifasciatus\u003c/em\u003e, in a Brazilian estuary. Sampling was conducted in the rainy (January to July 2016) and dry (August to December 2016) periods. Fish were collected in the two estuarine habitats using a beach seine. In summary, the results demonstrated that the number of predatory fishes was a strong predictor of population abundance and biomass, followed by pneumatophore complexity. The abundance and biomass values tended to increase with increasing habitat structural complexity towards the upper estuary. There was evidence that fish exhibited movement during the rainy season related to spawning events and subsequent juvenile recruitment in this area. Hymnoptera was the item most frequently ingested and made the greatest contributions to the volume of diet in habitat types throughout the year. There was an increase in the condition factor in the rainy season and thus was associated with energy reserves, reproduction and growth (fitness). We concluded that predation is an important ecological process that operates at local spatial scales and that together with the density of pneumatophores, predation is considered an important attractiveness that could affect the abundance of common halfbeak populations associated with estuarine habitats.\u003c/p\u003e","manuscriptTitle":"Predation risk, foraging and reproduction of an insectivore fish species associated with two estuarine habitats","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2023-05-22 15:08:31","doi":"10.21203/rs.3.rs-2943801/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"3722574d-70bb-4ae5-ada1-7ecec00250d0","owner":[],"postedDate":"May 22nd, 2023","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2023-05-29T21:19:44+00:00","versionOfRecord":[],"versionCreatedAt":"2023-05-22 15:08:31","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-2943801","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-2943801","identity":"rs-2943801","version":["v1"]},"buildId":"_2-kVJe1T_tPrBINL-cwx","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}