Distribution, Habitats and Behavior of the Non-Indigenous Brachyuran Percnon gibbesi (Percnidae) of Southwestern Mediterranean (Algeria)

Distribution, Habitats and Behavior of the Non-Indigenous Brachyuran Percnon gibbesi (Percnidae) of Southwestern Mediterranean (Algeria) | 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 Distribution, Habitats and Behavior of the Non-Indigenous Brachyuran Percnon gibbesi (Percnidae) of Southwestern Mediterranean (Algeria) Neila Bada, Farid Derbal, Sabah Nouacer, Mounira Rachedi This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4125895/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 Some ecological aspects of the alien crab Percnon gibbesi (H. Milne Edwards, 1853) have been approached by visual surveys in the southwestern Mediterranean waters (East, Algeria). This sampling method, applied on a coastal line of 16.2 km and between 0 and − 3 m depth, allowed us to collect information on abundances and densities by size category, nature of the habitat and behavior of this species. Overall 22 diurnal dives (3 observations/dive) were carried out in 2 different adjacent costal sectors, the Bay of Annaba (Sector 1: Lever de l’Aurore-Amphore), located at the east, and Cap de Garde (Sector 2: Cap de Garde - Djenen El Bey beach), located at the west of the Bay. We recorded an average total of 5325 individuals (± 15.62) with numerical dominance in sector 2 (4472 ± 9 ind.). Medium-sized individuals dominated numerically in sector 1 (412 ± 10 ind.), while large individuals were better represented in sector 2 (1980 ± 12.77 ind.). Average densities in two sectors varied to according on measurement unit (surface, dive time). Whatever the sector, the rock cracks sheltered the greatest number of individuals. No individual was observed on homogeneous bottoms. Overall, crabs are indifferent in the presence of an observer. Ecology Alien crab Percnon gibbesi Algeria Mediterranean Visual survey Figures Figure 1 Figure 2 Figure 3 Figure 4 Introduction One of the major threats to the environment and conservation of marine biodiversity around the world is biological invasions (Katsanevakis et al. 2013 ). Invasive species belonging to native habitats with different characteristics can cause potential risks for the native biota invaded, and thus, lead to socio-economic impacts (Occhipinti-Ambrogi 2007 ). The Mediterranean Sea, which is recognized as a hotspot for biodiversity, was not spared from this intrusion of non-native species (Zenetos et al. 2012 ). The highest rate of non indigenous species in the Mediterranean was recorded in 2018 (Katsanevakis et al. 2020 ). Nevertheless, the dispersal capacity of alien species can be affected by the distance from the source area (Occhipinti-Ambrogi 2007 ). Around seven hundred marine exotic species have been found in the Mediterranean (Galil et al. 2014 ). For crustacean decapods, 78 species were reported in the Mediterranean and among them 20 species are invasive (Zenetos et al. 2010). On the Algerian coast, 4 non-native decapods have been recently described (Grimes et al. 2018 ) including the flat crab Percnon gibbesi (Menail et al. 2019 ; Hussein et al. 2020 ). The invasive flat crab P. gibbesi (H. Milne-Edwards, 1853) is native to the American Pacific and both of African and American inter-tropical Atlantic and African and American inter-tropical coasts and the Pacific American coasts (Relini et al. 2000 ). It is usually present from Madeira to the Gulf of Guinea, from Florida to Brazil and from California to Chile (Manning and Holthuis, 1981). Percnon gibbesi crab was mostly found on sloping rocks, with different sizes of loose rocks and a large number of small holes (Pipitone et al. 2001 ). This brachyuran frequents the rocky shore substrates of the subtidal zone, 0–4 m deep (Deudero et al. 2005 ). Moreover, this species has spread to all Mediterranean coasts and it has become the most widespread non-native crab in Mediterranean waters (Katsanevakis et al. 2011 ). Since 1999, many observations from different localities in the Mediterranean have been reported: the first time at Linosa Italy (Relini et al. 2000 ), then on Mallorca and Menorca Islands (Garcia and Reviriego 2000 ), in Ibiza (Muller 2001), in Sardinia, the Tyrrhenian Sea, Sicily and Malta (Pipitone et al. 2001 ; Sciberras and Schembri 2007 ) on Turkish waters (Yokes and Galil 2006 ), in Greece (Cannicci et al. 2008 ), and in other riparian countries of the Mediterranean Sea such as Albania, Cyprus, Israel and Lebanon (Katsanevakis et al. 2011 ). In North Africa, P. gibbesi was already reported in Libya (Elkrwe et al. 2008), Tunisia (Sghaier et al. 2011 ), Egypt (Azzurro et al. 2011) and Algeria at 5 different localities (Collo, RaisHamidou, Sidi Fredj, Gulf of Annaba and Oran Bay) (Katsanevakis et al. 2011 ; Lamouti and Bachari 2011; Menail et al. 2019 ; Hussein et al. 2020 ). Despite the expansion of P. gibbesi along the Algerian coasts, the biology and ecology of this species are very little known (Bada and Derbal 2018 ). The new information (abundance, densities, habitat frequented, behavior) that we provide at the present study are complementary to the ecological database of the Mediterranean invasions. This information will provide a better understanding of the success of its establishment in this new environment. Materials and Methods Study Area and Methodology By way of comparison, the study area was delimited into two different sectors; the first one covered the Annaba Gulf (Sector 1) while the second on is located outside of it (Sector 2). The sector 1, is more subject to human activities (activities of Annaba port, balnear station, discharges of domestic water, urbanization and establishment of tourist complexes, artisanal and recreational fishing) it it stretches from Lever de l’Aurore beach (36°54'44.68"N -7°46'18.75"E) to the Cap de Garde (36°58'04.66"N − 07°47'28.01"E) (Table 1 ). A part from the beaches (Lever de l’Aurore, Gassiot, Saint Cloud, Rizi Amor, La Caroube, Toche, Belvedere, Ain Achir, Les Amphores) which are generally made up of course and fine sands with some rugged linear transects (rocks and seagrass), the rest of the area is rocky with a sparse to dense seagrass between 0 and − 12 m. The sector 2, removed from human activities, is located between Cap de Garde and Djenen El Bey Beach (36°57'22.1"N − 07'43'19.5"E) (Table 2 ). Being a very rugged area (rocks and Posidonia meadows), this sector is considered a remote area and very difficult to access by road. It has recently been proposed by the Ministry of the Environment and Renewable Energy (GENBI programme: Environmental Governance and Biodiversity) for the creation of a marine protected area (Lamouti 2019 ), hence the choice to compare two distinct area. Table 1 Coordinates and distance of sampling transect stations (Sector 1: Gulf of Annaba) Station Departure position Arrival position Distance (m) Station 1 36°54'36.91"N7°46'18.07"E 6°54'44.91"N7°46'18.95"E 259 Station 2 36°54'44.91"N7°46'18.95"E 36°54'57.83"N7°46'13.57"E 500 Station 3 36°55'0.64"N 7°46'5.86"E 36°55'2.34"N7°46'3.93"E 173 Station 4 36°55'18.14"N7°45'49.15"E 36°55'31.71"N7°45'44.56"E 482 Station 5 36°55'47.09"N7°45'39.49"E 36°55'57.88"N7°45'45.79"E 416 Station 6 36°56'2.90"N7°45'56.60"E 36°56'30.28"N7°46'3.84"E 1431 Station 7 36°56'48.47"N7°46'18.22"E 36°56'58.33"N7°46'41.78"E 953 Station 8 36°56'58.33"N7°46'41.78"E 6°57'21.25"N7°46'50.84"E 1325 Station 9 36°57'29.93"N7°46'50.29"E 36°57'39.37"N7°47'1.41"E 547 Station 10 36°57'39.37"N 7°47'1.41"E 36°57'47.30"N7°47'13.79"E 612 Station 11 36°57'57.46"N °47'32.58"E 36°58'3.49"N7°47'26.74"E 600 Table 2 Coordinates and distance of sampling transect stations (Sector 2: located between Cap de Garde and Djenen El Bey Beach) Station Starting position Arrival position Distance (m) Station A 36°58'5.20"N7°47'4.42"E 36°58'2.28"N7°46'34.29"E 1839 Station B 36°58'2.28"N7°46'34.29"E 6°57'48.27"N7°46'33.10"E 607 Station C 6°57'48.27"N7°46'33.10"E 6°57'43.28"N7°46'26.80"E 232 Station D 6°57'43.28"N7°46'26.80"E 6°57'40.18"N7°46'21.32"E 353 Station E 6°57'40.18"N7°46'21.32"E 36°57'33.83"N7°46'8.04"E 526 Station F 36°57'33.83"N7°46'8.04"E 36°57'32.04"N7°45'45.38"E 884 Station G 6°57'32.04"N7°45'45.38"E 6°57'29.71"N7°45'24.51"E 819 Station H 6°57'29.71"N7°45'24.51"E 36°57'26.30"N7°45'9.89"E 745 Station I 36°57'26.30"N7°45'9.89"E 36°57'23.68"N7°44'40.22"E 1076 Station J 36°57'24.49"N7°44'36.65"E 36°57'23.41"N 7°44'6.43"E 1005 Station K 36°57'22.91"N7°44'2.39"E 36°57'22.75"N7°43'44.16"E 844 This study covered an approximate coastal linear of 16.2 km (sector 1: 7.298 km, sector 2: 8.93 km). We divided each sector into 11 stations (Fig. 1 ) with different linear transects going from 173 m (minimum) to 1839 m (maximum) (Table 1 , 2 ). Spatio-temporal monitoring was carried out in the summer period of 2017 and 2018, between 11 a.m. and 4 pm GTM (Greenwich mean time). On the linear transect, the visual surveys were repeated three times according to the three predetermined size categories (Small: 25 mm) in free diving on linear transects (width: 2 m, depth: 0–3 m). The habitat frequented (sand, rocks, seagrass) and behavior of the crabs (slow escape, fast escape, indifferent or neutral) was studied in 2 sectors according to three size categories. Statistical analysis To study the distribution of P. gibbesi according to the size of individuals and the two prospected sectors, the mean crabs' densities (number of individuals / 50 m 2 ) were compared by the two-way ANOVA test (both fixed factors). The variable sector was considered as a factor P having two levels (sector 1 and sector 2) and the size of individuals as factor I with three levels (S: small, M: medium and L: large). The interaction effects between these two factors were also investigated. Variations density of P. gibbesi among the stations were compared by one-way ANOVA in each sector. Stations were considered as the independent variable and density was used as the dependent variable. The normality of the data and the homoscedasticity of the variances were verified before the application of each test. In that case the normality of the data was tested by the Shapiro-Wilk tests while the homoscedasticity of the variances was verified by the Cochran C test (Sokal and Rohlf 1981). However, when main effects ANOVA tests were significant, Post-hoc comparisons were conducted using Turkey's honest significant difference HSD test (Zar 1984) to identify the sources of variation. To determine the substrate preference of P. gibbesi , the mean abundances of the two types of rocky substrate were compared by computing a two-sample t statistic. All statistical analyzes were performed by the software Statistica v.7. Results In the two sampled sectors and over the 16.2 km prospected by free diving, we recorded a total mean abundance of 5325 ± 15.62 individuals of P. gibbesi . The population generally evolved at very shallow depths in the infralittoral stage (-10 cm). The distribution of individuals was unevenly distributed between the 2 sampled sectors with higher mean abundance in sector 2 (4472 ± 9 ind.) compared to the sector 1 (853 ± 8.54 ind.). Also, the total mean density was 4 times higher in the sector 2 (25 ± 0.05 ind./50 m²) than in sector 1 (6 ± 0.06 ind./50 m²). The two way- ANOVA test highlights this large difference (F = 65461.4 P < 0.001). (Table 3 ). Table 3 Anova of Percnon gibbesi according to the size of individuals and to the two prospected sectors. df degrees of freedom, MS mean square, F Statistic significance level, p level of probability, Cochran’s test C = 0.302626, P = 0.885834 Source of variation df MS F p < 0.001 Sectors Sizes Sectors x Sizes Residual 1 184.2264 65461.4 *** 2 32.7353 11631.9 *** 2 8.5699 3045.2 *** 12 0.0028 *: significant correlation (P ≤ 0.05), **: highly significant correlation (P ≤ 0.01), ***: very highly significant (P ≤ 0.001) The P. gibbesi population in sector 1 was numerically structured as follows: Small (79 ± 6.56 ind.), Medium (412 ± 10 ind.) and Large (362 ± 7.51 ind.) (Fig. 2A). In the sector 2, the population was organized as follows: Small (786 ± 5.51 individuals), Medium (1706 ± 6.81 ind.) and Large (1980 ± 12.77 ind.) (Fig. 2B). The distribution of this invasive crab by size was variable as well as between stations and sectors (Fig. 2C). Percnon gibbesi was totally absent in 3 stations (stat. 3, 9 and 10) among the 11 stations prospected of the sector 1 while in the sector 2, the species was present overall the stations except in station D where it was totally absent. The mean densities by distance vary considerably across the different sampled stations and sectors (Fig. 3 ). The highest mean density of P. gibbesi in the sector 1 was observed in station 1 (41 ind. ± 0.71/50 m²) where the lowest one was recorded in station 8 (1 ind. ± 0.08/50 m²) (Fig. 3 A). Differences between pairs stations were confirmed by Tukey’s post comparison test: no significant difference in mean density were saved at both of station 8 and 4 (Table 4 ). In the sector 2 the highest mean density was recorded in station C (145 ind. ± 0.33/50 m²) and lowest density in station A (9 ind. ± 0.17/50 m²) (Fig. 3 B). Very highly significant differences in density were demonstrated by the analysis of variance one-way test (F = 68568.9; P < 0.001). In the sector 2, the Tukey HSD test reveals similar densities in the stations: H and I with values respectively equal to 26.2 and 26.73 individual/50 m 2 (Table 5 ). Table 4 Tukey HSD test; variable DV_1 Homogenous Groups, alpha = 0.05 Error: Within MS = 0 .15139, df = 14.000 Stations Mean DV_1 1 2 3 4 5 6 7 Station 8 1 **** Station 4 1 **** Station 5 3 **** Station 6 5 **** Station 11 8 **** Station 7 9 **** Station 2 14 **** Station 1 41 **** Table 5 Tukey HSD test; variable DV_1Homogenous Groups, alpha = 0.05 Error: Within MS = 0 .06906, df = 20.000 Sector 2 Mean DV_1 1 2 3 4 5 6 7 8 9 Station A 9 **** Station B 11 **** Station F 18 **** Station E 22 **** Station J 24 **** Station H 26.2 **** Station I 26.7 **** Station G 36 **** Station K 45 **** Station C 145 **** The two-way ANOVA test has been revealed significant differences between the two study sectors for the factors considered (size categories, sectors) and for the interaction between these 2 factors (Table 3 ). The P. gibbesi crab was absent in Posidonia oceanica seagrass as well as over sandy bottoms, its presence was limited exclusively to rocky substrates, namely in cracks (Fig. 4 ). Posidonia oceanica seagrass and sandy bottoms were not occupied by this alien crab. The one-way ANOVA revealed significant differences between the types of rocky substrate (F = 443709.78; P ≤ 0.001). Indeed, the t statistic test (t = 177.4037; P < 0.001) revealed significant differences between the crab's densities in the 2 types of rocky substrate in the sector 1 as well as in the sector 2 where the student t-test is equal to 966.2234 (P < 0.001). A mean abundance of 802 (± 7.02 SE) individuals was counted in cracks vs 51.33 (± 2.08 SE) individuals in crevices in the anthropogenic sector. In the sector 2 the mean abundance of P. gibbesi was 4279 (± 2.08 SE) individuals in cracks vs 192 (± 2.08 SE) individuals in crevices. The distribution of P. gibbesi was mostly limited to cracks (95%) vs (5%) in crevices whatever the sector prospected. Regardless of the sector and size class, crabs are indifferent to the observer. Discussion After several records of P. gibbesi on different regions of the Algerian coasts: Skikda (Katsanevakis et al. 2011 ), Algiers (Lamouti and Bachari 2011), Jijel (Noël and Prouzet 2017), Oran (Hussein et al. 2020 ) and also in the western region of the Annaba Gulf (Menail et al. 2019 ), our observations by visual surveys carried out on a total linear transect of 16.2 km for two successive years (summer 2017 and 2018) confirm not only the establishment of this alien species in the Gulf of Annaba, but also its expansion along the Eastern Algerian coasts, both inside and outside of the Gulf. The presence of this subtropical crab on the Algerian coasts from East to West is an obvious and logical extension of its distribution area along the countries of North Africa (Azzuro et al 2011 ; Sghaier et al. 2011 ; Grimes et al. 2018 ) and throughout the Mediterranean Sea (Katsanevakis et al. 2011 ). Recently, another alien crab has appeared on Algerian coast, the American blue crab: Callinectes sapidus , is know present from the Eastern (Benabdi et al. 2019 ; Hamida and Kara 2021 ) to the Western coasts of Algeria (Ragkousis et al. 2020 ). In the Mellah lagoon (East, Algeria), the invasion of this non-native species, were recorded in mass (Kara and Chaoui 2021 ). In the Gulf of Annaba, this species has been recently observed invading the extreme East of Sidi-Salem beach, near the mouth of a freshwater stream (B.N., personal observation). The recent presence of this species has even been reported in Lake Tonga (Wilaya El-Tarf), a freshwater lake classified as a Ramsar site since 1982 (Tahri and Boutabia 2022 ). The main driver of the P. gibbesi intrusion at the Eastern Algerian coasts would probably result from the migration of adult individuals from the bordering Tunisian coast or by accidental transport through shipping. The Western current of the Mediterranean, which runs along the North African coasts (Moroccan, Algerian and Tunisian), then rises towards Sicily, runs along the north-eastern Italian coast, then along the French coast, and drops down along the Spanish coast, could facilitate and play a role on the transport of planktonic larvae along the Algerian coast from west to east. The relatively long larval phase of P. gibbesi (Paula and Hartnoll 1989 ) would facilitate the subsequent colonization of post-larvae and megalops (Hartnoll 1992 ) along east Algerian coasts. It is very likely that there is a time lake between the apparition of this species along the eastern coasts of Algeria and its records, since the population observed in free diving seemed well established. Monitoring exotic fauna, in particular by visual surveys, is often a delicate task, hence the importance of developing medium and long-term programs between the different countries of the Mediterranean coast to collect information on these changes in biodiversity. At the present time, it is difficult to determine exactly the ways arrival of P. gibbesi in the eastern Algerian waters. This massive proliferation on shallow rocky bottoms (< 10 cm), especially in sector 2, was probably favored by the ideal physico-chemical conditions of the area (especially edaphic) and by the rarefaction of predators on this prey. Indeed, the studies carried out on the feeding habits of many coastal teleost in the study area, as is the case of Sparidae (Benchalel et al. 2010 ), Scorpaenidae (Omri et al. 2019 ), Labridae (Boughamou et al. 2016 ), Mullidae (Broudraa et al. 2018) and Serranidae (Zaidi et al. 2017 ; Rachedi et al. 2018 ) did not record the presence of this prey in the stomach contents of ichthyologic predators cited previously. The absence of P. gibbesi in the stomacal content of teleosts fish could be explained by the non-identification of the species in view of the highly digestible state of the prey in which they are generally found. Indeed, it is known that the P. gibbesi crab is strictly subtidal and limited to the uppermost reaches of infralittoral zone characterized by rocky shores (Pipitone et al. 2001 ; Deudero et al. 2005 ; Thessalou-Legaki et al. 2006 ) and occasionally the wide bare rock ledges or in crevices on vertical rock walls with a moderate algal cover (Deudero et al. 2005 ; Sciberras and Schembri 2008 ). The absence of this species on sandy or homogeneous rocky bottoms or in P. oceanica seagrass at both sectors has also been observed in other regions of the Mediterranean (Sciberras and Schembri 2008 ; Félix-Hackradt et al. 2018 ). We suppose that the density of P. gibbesi is closely linked to the availability of algae and adequate rocky structure. Pipitone et al. ( 2001 ), revealed that the strong affinity of P. gibbesi for rocky bottoms result probably of the security hidden protection of predation and that availability of food resources. The present comparative study revealed a very high significant differences in the abundance of P. gibbesi in two different sectors, one exposed to anthropogenic actions (sector 1) and the other far from any source of human pressure (sector 2). We can suppose that this numerical disparity in abundance P. gibbesi is due principally to the distance between the studied sectors and their proximity to the Annaba City and thus, the increasing of anthropogenic activities, represented particularly by the impact of balnear tourism, coastal urbanization and industrialization which are often accompanied by domestic and industrial pollution problems. Indeed, a total of 7 beaches (Lever de l’Aurore, Saint Cloud, Chapuis, La Caroube, Toche, Belvedere, Ain Achir), several hotels and balnear and water sports resorts are located along sector 1, which could explain the low abundance of P. gibbesi observed in all the sampled stations. The homogeneous topographical nature of the substrate in sector 1, such as the presence of large sandy areas, scattered P. oceanica seagrass and flat boulders, certainly constitute unfavorable habitats for the establishment of this species in this sector. In the two sampled sectors, the three size categories (S, M and L) are significantly represented but always with numerical proportions in favor of individuals of medium and large size. While free diving, small crabs could escape the observer when counting, hence their number is underestimated within established populations. Around Balearic Islands, Cannicci et al. ( 1999 ) revealed that the medium individual’s size category of P. gibbesi predominated the distribution of the population. They have also reported that the small individuals were less abundant and they have supposed that was related to the sampling period and recruitment. The highest mean densities never exceed 3 ind/m², a maximum value observed in station C in sector 2. Overall, the mean density is always less than 1 ind./m². Within "Capo Gallo-Isola delle Femmine" MPA, in the north-west of Sicily, the mean density (ind./100 m² ± se) of the whole area was estimated to 42 ± 6.67 individuals, i.e. less than 1 ind./m² with an almost similar population size class frequency distribution (S: 37%, M: 35%, L: 28%) (Agnetta et al. 2012). Around Dragonera Islands (Spain), the highest densities are recorded on pebble substrates, reaching up to 3 ind./m² (Deudero et al. 2005 ). However, the rapid expansion of this crab in Mediterranean waters with its ability to occupy disturbed areas (Cannicci et al. 2006) and its resistance to temperature changes (Calado 2006) have shown that their densities can be very high, reaching up to 11.9 ind./m² (Sciberras and Schembri 2007 ). On the basis of our freediving visual surveys, we found that this invasive species has a preference for rocky and isolated environments where its chances of establishment and survival would be higher compared to homogeneous habitats and areas of high anthropic pressure. Concerning the behaviour of P. gibbesi we observed that when there is a hydrodynamic tension, this flat crab becomes more active it will be able to makes jumps between cracks to collect suspended algal particles. The behaviour of young individuals observed is slightly different compared to the other larger individuals, the small individuals seem to be more sensitive to the presence of observer, they are perfectly concealed in the cracks and crevasses and their presence are always accompanied by larger individuals. Other interesting aspects in this study deserve to be clarified on this invasive species such as the (i) nocturnal incursions observed out of the water, probably in search of food (ii) the bacterial attacks that we observed at abdominal level and (iii) unexplained mortality in adult individuals during the summer at very shallow depths. The collection of all this information could allow the scientific community to better understand the movements and the establishment of this species on the Algerian east coasts and along the Mediterranean in general. Declarations Acknowledgements The authors are most grateful to the Editor and an anonymous reviewer for their helpful comments and suggestions. This scientific work received no financial support. Authors contributions: Authors 1 contributed equally to the design of the experimental protocol and the writing of the final manuscript. Co-authors 2 statistically processed the raw data and approved the final version of the article. Author Contribution The authors state that all the authors have contributed equally to designing the experimental protocol, writing and proof editing the paper in its final edition and approved it for submission. Funding The present experiment is part of a PhD thesis of Bada Neila and did not benefit from any particular financial support. Data Availability The raw data used to generate the submitted results is available and can be provided, if necessary, to the journal or the designated experts. Ethical Approval and Consent of Participation The study has not been submitted, partially or totally to any other journal, and does not present any conflict of interest. Human and Animal Ethics The biological material used in this study is a non-native marine product and of no interest for consumption and doesn’t require animal ethics. However, the experimental protocol was validated by the scientific council of the Badji-Mokhtar University, Annaba, Algeria. 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Milne Edwards, 1853) (Crustacea: Decapoda: Percnidae) in Oran Bay (Northwestern Algeria). Acta Aquat Turc 16(3):396–399 Kara MH, Chaoui L (2021) Strong invasion of Mellah lagoon (South-Western Mediterranean) by the American blue crab Callinectes sapidus Rathbun, 1896. Mar Pollut Bull 164 112089.s Katsanevakis S, Stelzenmüller V, South A, Sørensen TK, Jones PJ, Kerr S et al (2011) Ecosystem-based marine spatial management: review of concepts, policies, tools, and critical issues. Ocean Coast Manag 54(11):807–820 Katsanevakis S, Zenetos A, Belchior C, Cardoso AC (2013) Invading European Seas: assessing pathways of introduction of marine aliens. Ocean Coast Manag 76:64–74 Katsanevakis S, Poursanidis D, Hoffman R, Rizgalla J, Rothman SBS, Levitt-Barmats YA et al (2020) Unpublished Mediterranean records of marine alien and cryptogenic species. BioInvasions Rec 9(2):165–182 Lamouti S, Rebzani C, Bachari NEI (2011) Répartition de deux espèces introduites à caractère invasif dans la région centre de la côte algéroise: Caulerpa racemosa et Oculina patagonica . In: Actes de la Conférence Méditerranéenne Côtière et Maritime, Edition 2, Maroc : 361–366 Lamouti S (2019) Etude de classement de la partie marine des monts de l’Edough en Aire Marine Protégée. Rapport MEER/GIZ, 78p Noël P, Prouzet A (2017) Doris, 17/12/2017: Percnon gibbesi (H. Milne Edwards, 1853), https://doris.ffessm.fr/ref/specie/2848 . Données d’observations pour la reconnaissance et l’identification de la faune et la flore subaquatiques. Lastassessed 26/09/2019 Menail AA, Rachedi M, Derbal F (2019) New locality records and morphological characterization of the invasive crab population Percnon gibbesi (Decapoda: Grapsoidea) in the extreme west of the gulf of Annaba (Algeria). Vie et Milieu 69(2–3):169–175 Occhipinti-Ambrogi A (2007) Global change and marine communities: alien species and climate change. Mar Poll Bull 55(7–9):342–352 Omri N, Derbal F, Kara MH (2019) Diet of the black scorpionfish Scorpaena porcus (Scorpaenidae) of the gulf of Annaba, Algeria. Cybium 43(2):179–186 Paula J, Hartnoll RG (1989) The larval and post-larval development of Percnon gibbesi (Crustacea, Brachyura, Grapsidae) and the identity of the larval genus Pluteocaris . J Zool Lond 218:17–37 Pipitone C, Badalamenti F, Sparrow A (2001) Contribution to the knowledge of Percnon gibbesi (Decapoda, Grapsidae), an exotic species spreading rapidly in Sicilian waters. Crustaceana 1009–1017 Rachedi M, Derbal F, Kara MH (2018) Feeding habits of the comber Serranus cabrilla (Linnaeus, 1758) (Teleostei, Serranidae) from the gulf of Annaba (Eastern coast of Algeria). Cah Biol Mar 59:149–158 Ragkousis M, Abdelali N, Azzurro E, Badreddine A, Bariche M, Bitar G et al (2020) New Alien Mediterranean Biodiversity Records (October 2020). Mediterr Mar Sci 21(3):631–652 Relini M, Orsi L, Puccio V, Azzurro E (2000) The exotic crab Percnon gibbesi (H. Milne Edwards, 1853) (Decapoda, Grapsidae) in the Central Mediterranean. Sci Mar 64(3):337–340 Sciberras M, Schembri PJ (2007) A critical review of records of alien marine species from the Maltese Islands and surrounding waters (Central Mediterranean). Mediterr Mar Sci 8(1):41–66 Sciberras M, Schembri PJ (2008) Biology and interspecific interactions of the alien crab Percnon gibbesi in the Maltese Islands. Mar Biol Res 4(5):321–332 Sghaier YR, Zakhama-Sraieb R, Benamer I, Charfi-Cheikhrouha F (2011) Occurrence of the seagrass Halophila stipulacea (Hydrocharitaceae) in the southern Mediterranean Sea. Bot Mar 54(6):575–582 Tahri M, Boutabia L (2022) First appearance of the American blue crab Callinectes sapidus Rathbun, 1896 (Crustacea: Decapoda: Brachyura) in freshwater of Western Mediterranean, Algeria. Afr J Ecol 60:1293–1296 Thessalou-Legaki M, Zenetos A, Kambouroglou V, Corsini-Foka M, Kouraklis P, Dounas C, Nicolaidou A (2006) The establishment of the invasive crab Percnon gibbesi (H. Milne Edwards, 1853) (Crustacea: Decapoda: Grapsidae) in Greek waters. Aquat Invasions 1(3):133–136 Yokes B, Galil BS (2006) New records of alien decapods (Crustacea) from the Mediterranean coast of Turkey, with a description of a new palaemonid species. Zoosystema-Paris 28(3):747–755 Zaidi R, Derbal F, Kara MH (2017) Temporal and ontogenic variations of diet of the goldblotch grouper Epinephelus costae (Serranidae) in the eastern coast of Algeria. J Mar Biol Assoc 97(2):259–267 Zenetos A (2010) Trend in aliens species in the Mediterranean. An answer to Galil, 2009 «Taking stock: inventory of alien species in the Mediterranean Sea». Biol Invasions 12(9):3379–3381 Zenetos Α, Gofas S, Morri C, Rosso A, Violanti D, Garcia Raso JE, Cinar ME, Almoglabin A, Ates AS et al (2012) Alien species in the Mediterranean Sea by 2012. A contribution to the application of European Union’s Marine Strategy Framework Directive (MSFD). Part 2. Introduction trends and pathways. Mediterr Mar Sci 13(2):328–352 Additional Declarations No competing interests reported. Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-4125895","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":281463237,"identity":"a6395659-25b9-4467-8bf2-2a0617b5cb05","order_by":0,"name":"Neila Bada","email":"","orcid":"","institution":"Badji Mokhtar University","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Neila","middleName":"","lastName":"Bada","suffix":""},{"id":281463238,"identity":"facba7c7-8e07-46ca-b47a-eee84d0b6d2b","order_by":1,"name":"Farid Derbal","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAABFklEQVRIie3PMUvDQBTA8SeBc0nq2hDJfQLhHQd20fotnBMKydJCxowZpC66B6L4FVoEcbxwYJZ8gIKD7dJJIaNDQXOZk1g3wftPx/F+3D0Ane4vJoAARC6AASiq+MxtLtc/EuSKsDwtA95censRAC6tK+kn6thHBsXtdv2JSEfXxkJaiRE+XMpN/crYPUnaiV0WI3aDyO4kifL7ZzJbvgZYkwk/Fe0EVwEZmrg7SA0TxUdpzpaZp4jwn7rI25bYO8SLhljzYciysOonK0IcE9FXJLfm6FFn2v+KXQaH/Bhxkhr1LmnpsYUzjYSH3bsMiheyeY/xPD2Sj1UVf1GaheowdrtIy1ebSdx3XEWT30zrdDrdf+gbt+1l6rEwYTQAAAAASUVORK5CYII=","orcid":"","institution":"Badji Mokhtar University","correspondingAuthor":true,"submittingAuthor":false,"prefix":"","firstName":"Farid","middleName":"","lastName":"Derbal","suffix":""},{"id":281463239,"identity":"b1144573-5723-4e87-ac4d-4d9f41a8d0d3","order_by":2,"name":"Sabah Nouacer","email":"","orcid":"","institution":"Badji Mokhtar University","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Sabah","middleName":"","lastName":"Nouacer","suffix":""},{"id":281463240,"identity":"3974887c-38bd-4750-ad85-069da3d06c90","order_by":3,"name":"Mounira Rachedi","email":"","orcid":"","institution":"Chadli Benjedid University","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Mounira","middleName":"","lastName":"Rachedi","suffix":""}],"badges":[],"createdAt":"2024-03-18 21:28:18","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-4125895/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4125895/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":53200492,"identity":"bff9a15a-58d8-4b36-b349-09649eb39445","added_by":"auto","created_at":"2024-03-21 19:27:34","extension":"jpg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":52485,"visible":true,"origin":"","legend":"\u003cp\u003eStudy area and sampling locations at the 2 sectors (sector 1: station 1 to 11, sector 2: station A to K)\u003c/p\u003e","description":"","filename":"Picture1.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4125895/v1/f38e5c6a773274adf8155a0e.jpg"},{"id":53200493,"identity":"86a64fad-a250-4dfc-b88b-06e6f09d9363","added_by":"auto","created_at":"2024-03-21 19:27:34","extension":"jpg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":72627,"visible":true,"origin":"","legend":"\u003cp\u003eMean abundance of the \u003cem\u003ePercnon gibbesi\u003c/em\u003e population by size categories in the 2 prospected sectors of the Annaba Gulf (A: Sector 1; B: Sector 2; C: sectors 1+2). The different letters in graph C indicate significant differences between sampling point\u003c/p\u003e","description":"","filename":"Picture2.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4125895/v1/b3529732d0e1eac967c408ab.jpg"},{"id":53201272,"identity":"6cbb95d0-1ce4-4b84-95e6-db9a4e3ea096","added_by":"auto","created_at":"2024-03-21 19:35:38","extension":"jpg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":64928,"visible":true,"origin":"","legend":"\u003cp\u003eMean densities/50 m\u003csup\u003e2\u003c/sup\u003e of the population of \u003cem\u003ePercnon gibbesi\u003c/em\u003e in each station of the 2 sampled sectors in the bay of Annaba (A: sector 1, B: sector 2)\u003c/p\u003e","description":"","filename":"Picture3.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4125895/v1/ab5dc57c50919107fa3ff313.jpg"},{"id":53200490,"identity":"9dd5a18e-344c-46d9-85de-3cdc545a6da7","added_by":"auto","created_at":"2024-03-21 19:27:34","extension":"jpg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":36331,"visible":true,"origin":"","legend":"\u003cp\u003eMean abundances of the \u003cem\u003ePercnon gibbesi \u003c/em\u003eon the different rocky substrate (FL = fault, CR = crevices) by sector and the 2 sectors combined. The different letters indicate significant differences between sampling point\u003c/p\u003e","description":"","filename":"Picture4.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4125895/v1/6ea6be4796a5be5311222b6f.jpg"},{"id":55264696,"identity":"cd10899b-534f-4046-9055-78760e98dc51","added_by":"auto","created_at":"2024-04-25 01:46:57","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":747360,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4125895/v1/e4bf25e5-6f75-49ea-9259-4fa6b3c93c37.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Distribution, Habitats and Behavior of the Non-Indigenous Brachyuran Percnon gibbesi (Percnidae) of Southwestern Mediterranean (Algeria)","fulltext":[{"header":"Introduction","content":"\u003cp\u003eOne of the major threats to the environment and conservation of marine biodiversity around the world is biological invasions (Katsanevakis et al. \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2013\u003c/span\u003e). Invasive species belonging to native habitats with different characteristics can cause potential risks for the native biota invaded, and thus, lead to socio-economic impacts (Occhipinti-Ambrogi \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2007\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe Mediterranean Sea, which is recognized as a hotspot for biodiversity, was not spared from this intrusion of non-native species (Zenetos et al. \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e2012\u003c/span\u003e). The highest rate of non indigenous species in the Mediterranean was recorded in 2018 (Katsanevakis et al. \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). Nevertheless, the dispersal capacity of alien species can be affected by the distance from the source area (Occhipinti-Ambrogi \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2007\u003c/span\u003e). Around seven hundred marine exotic species have been found in the Mediterranean (Galil et al. \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). For crustacean decapods, 78 species were reported in the Mediterranean and among them 20 species are invasive (Zenetos et al. 2010). On the Algerian coast, 4 non-native decapods have been recently described (Grimes et al. \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2018\u003c/span\u003e) including the flat crab \u003cem\u003ePercnon gibbesi\u003c/em\u003e (Menail et al. \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Hussein et al. \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). The invasive flat crab \u003cem\u003eP. gibbesi\u003c/em\u003e (H. Milne-Edwards, 1853) is native to the American Pacific and both of African and American inter-tropical Atlantic and African and American inter-tropical coasts and the Pacific American coasts (Relini et al. \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2000\u003c/span\u003e). It is usually present from Madeira to the Gulf of Guinea, from Florida to Brazil and from California to Chile (Manning and Holthuis, 1981). \u003cem\u003ePercnon gibbesi\u003c/em\u003e crab was mostly found on sloping rocks, with different sizes of loose rocks and a large number of small holes (Pipitone et al. \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2001\u003c/span\u003e). This brachyuran frequents the rocky shore substrates of the subtidal zone, 0\u0026ndash;4 m deep (Deudero et al. \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2005\u003c/span\u003e). Moreover, this species has spread to all Mediterranean coasts and it has become the most widespread non-native crab in Mediterranean waters (Katsanevakis et al. \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2011\u003c/span\u003e). Since 1999, many observations from different localities in the Mediterranean have been reported: the first time at Linosa Italy (Relini et al. \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2000\u003c/span\u003e), then on Mallorca and Menorca Islands (Garcia and Reviriego \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2000\u003c/span\u003e), in Ibiza (Muller 2001), in Sardinia, the Tyrrhenian Sea, Sicily and Malta (Pipitone et al. \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2001\u003c/span\u003e; Sciberras and Schembri \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e2007\u003c/span\u003e) on Turkish waters (Yokes and Galil \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e2006\u003c/span\u003e), in Greece (Cannicci et al. \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2008\u003c/span\u003e), and in other riparian countries of the Mediterranean Sea such as Albania, Cyprus, Israel and Lebanon (Katsanevakis et al. \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2011\u003c/span\u003e). In North Africa, \u003cem\u003eP. gibbesi\u003c/em\u003e was already reported in Libya (Elkrwe et al. 2008), Tunisia (Sghaier et al. \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2011\u003c/span\u003e), Egypt (Azzurro et al. 2011) and Algeria at 5 different localities (Collo, RaisHamidou, Sidi Fredj, Gulf of Annaba and Oran Bay) (Katsanevakis et al. \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2011\u003c/span\u003e; Lamouti and Bachari 2011; Menail et al. \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Hussein et al. \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2020\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eDespite the expansion of \u003cem\u003eP. gibbesi\u003c/em\u003e along the Algerian coasts, the biology and ecology of this species are very little known (Bada and Derbal \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). The new information (abundance, densities, habitat frequented, behavior) that we provide at the present study are complementary to the ecological database of the Mediterranean invasions. This information will provide a better understanding of the success of its establishment in this new environment.\u003c/p\u003e"},{"header":"Materials and Methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eStudy Area and Methodology\u003c/h2\u003e \u003cp\u003eBy way of comparison, the study area was delimited into two different sectors; the first one covered the Annaba Gulf (Sector 1) while the second on is located outside of it (Sector 2). The sector 1, is more subject to human activities (activities of Annaba port, balnear station, discharges of domestic water, urbanization and establishment of tourist complexes, artisanal and recreational fishing) it it stretches from Lever de l\u0026rsquo;Aurore beach (36\u0026deg;54'44.68\"N -7\u0026deg;46'18.75\"E) to the Cap de Garde (36\u0026deg;58'04.66\"N \u0026minus;\u0026thinsp;07\u0026deg;47'28.01\"E) (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). A part from the beaches (Lever de l\u0026rsquo;Aurore, Gassiot, Saint Cloud, Rizi Amor, La Caroube, Toche, Belvedere, Ain Achir, Les Amphores) which are generally made up of course and fine sands with some rugged linear transects (rocks and seagrass), the rest of the area is rocky with a sparse to dense seagrass between 0 and \u0026minus;\u0026thinsp;12 m. The sector 2, removed from human activities, is located between Cap de Garde and Djenen El Bey Beach (36\u0026deg;57'22.1\"N \u0026minus;\u0026thinsp;07'43'19.5\"E) (Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). Being a very rugged area (rocks and \u003cem\u003ePosidonia\u003c/em\u003e meadows), this sector is considered a remote area and very difficult to access by road. It has recently been proposed by the Ministry of the Environment and Renewable Energy (GENBI programme: Environmental Governance and Biodiversity) for the creation of a marine protected area (Lamouti \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2019\u003c/span\u003e), hence the choice to compare two distinct area.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eCoordinates and distance of sampling transect stations (Sector 1: Gulf of Annaba)\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"4\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eStation\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eDeparture position\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eArrival position\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eDistance (m)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eStation 1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e36\u0026deg;54'36.91\"N7\u0026deg;46'18.07\"E\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e6\u0026deg;54'44.91\"N7\u0026deg;46'18.95\"E\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e259\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eStation 2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e36\u0026deg;54'44.91\"N7\u0026deg;46'18.95\"E\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e36\u0026deg;54'57.83\"N7\u0026deg;46'13.57\"E\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e500\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eStation 3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e36\u0026deg;55'0.64\"N 7\u0026deg;46'5.86\"E\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e36\u0026deg;55'2.34\"N7\u0026deg;46'3.93\"E\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e173\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eStation 4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e36\u0026deg;55'18.14\"N7\u0026deg;45'49.15\"E\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e36\u0026deg;55'31.71\"N7\u0026deg;45'44.56\"E\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e482\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eStation 5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e36\u0026deg;55'47.09\"N7\u0026deg;45'39.49\"E\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e36\u0026deg;55'57.88\"N7\u0026deg;45'45.79\"E\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e416\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eStation 6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e36\u0026deg;56'2.90\"N7\u0026deg;45'56.60\"E\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e36\u0026deg;56'30.28\"N7\u0026deg;46'3.84\"E\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e1431\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eStation 7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e36\u0026deg;56'48.47\"N7\u0026deg;46'18.22\"E\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e36\u0026deg;56'58.33\"N7\u0026deg;46'41.78\"E\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e953\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eStation 8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e36\u0026deg;56'58.33\"N7\u0026deg;46'41.78\"E\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e6\u0026deg;57'21.25\"N7\u0026deg;46'50.84\"E\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e1325\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eStation 9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e36\u0026deg;57'29.93\"N7\u0026deg;46'50.29\"E\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e36\u0026deg;57'39.37\"N7\u0026deg;47'1.41\"E\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e547\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eStation 10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e36\u0026deg;57'39.37\"N 7\u0026deg;47'1.41\"E\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e36\u0026deg;57'47.30\"N7\u0026deg;47'13.79\"E\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e612\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eStation 11\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e36\u0026deg;57'57.46\"N \u0026deg;47'32.58\"E\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e36\u0026deg;58'3.49\"N7\u0026deg;47'26.74\"E\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e600\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eCoordinates and distance of sampling transect stations (Sector 2: located between Cap de Garde and Djenen El Bey Beach)\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"4\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eStation\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eStarting position\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eArrival position\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eDistance (m)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eStation A\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e36\u0026deg;58'5.20\"N7\u0026deg;47'4.42\"E\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e36\u0026deg;58'2.28\"N7\u0026deg;46'34.29\"E\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e1839\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eStation B\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e36\u0026deg;58'2.28\"N7\u0026deg;46'34.29\"E\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e6\u0026deg;57'48.27\"N7\u0026deg;46'33.10\"E\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e607\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eStation C\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e6\u0026deg;57'48.27\"N7\u0026deg;46'33.10\"E\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e6\u0026deg;57'43.28\"N7\u0026deg;46'26.80\"E\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e232\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eStation D\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e6\u0026deg;57'43.28\"N7\u0026deg;46'26.80\"E\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e6\u0026deg;57'40.18\"N7\u0026deg;46'21.32\"E\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e353\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eStation E\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e6\u0026deg;57'40.18\"N7\u0026deg;46'21.32\"E\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e36\u0026deg;57'33.83\"N7\u0026deg;46'8.04\"E\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e526\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eStation F\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e36\u0026deg;57'33.83\"N7\u0026deg;46'8.04\"E\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e36\u0026deg;57'32.04\"N7\u0026deg;45'45.38\"E\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e884\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eStation G\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e6\u0026deg;57'32.04\"N7\u0026deg;45'45.38\"E\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e6\u0026deg;57'29.71\"N7\u0026deg;45'24.51\"E\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e819\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eStation H\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e6\u0026deg;57'29.71\"N7\u0026deg;45'24.51\"E\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e36\u0026deg;57'26.30\"N7\u0026deg;45'9.89\"E\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e745\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eStation I\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e36\u0026deg;57'26.30\"N7\u0026deg;45'9.89\"E\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e36\u0026deg;57'23.68\"N7\u0026deg;44'40.22\"E\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e1076\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eStation J\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e36\u0026deg;57'24.49\"N7\u0026deg;44'36.65\"E\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e36\u0026deg;57'23.41\"N 7\u0026deg;44'6.43\"E\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e1005\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eStation K\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e36\u0026deg;57'22.91\"N7\u0026deg;44'2.39\"E\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e36\u0026deg;57'22.75\"N7\u0026deg;43'44.16\"E\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e844\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eThis study covered an approximate coastal linear of 16.2 km (sector 1: 7.298 km, sector 2: 8.93 km). We divided each sector into 11 stations (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e) with different linear transects going from 173 m (minimum) to 1839 m (maximum) (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e, \u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). Spatio-temporal monitoring was carried out in the summer period of 2017 and 2018, between 11 a.m. and 4 pm GTM (Greenwich mean time). On the linear transect, the visual surveys were repeated three times according to the three predetermined size categories (Small: \u0026lt; 15 mm, Medium: 15\u0026ndash;25 mm, Large: \u0026gt; 25 mm) in free diving on linear transects (width: 2 m, depth: 0\u0026ndash;3 m). The habitat frequented (sand, rocks, seagrass) and behavior of the crabs (slow escape, fast escape, indifferent or neutral) was studied in 2 sectors according to three size categories.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003eStatistical analysis\u003c/h2\u003e \u003cp\u003eTo study the distribution of \u003cem\u003eP. gibbesi\u003c/em\u003e according to the size of individuals and the two prospected sectors, the mean crabs' densities (number of individuals / 50 m\u003csup\u003e2\u003c/sup\u003e) were compared by the two-way ANOVA test (both fixed factors). The variable sector was considered as a factor P having two levels (sector 1 and sector 2) and the size of individuals as factor I with three levels (S: small, M: medium and L: large). The interaction effects between these two factors were also investigated.\u003c/p\u003e \u003cp\u003eVariations density of \u003cem\u003eP. gibbesi\u003c/em\u003e among the stations were compared by one-way ANOVA in each sector. Stations were considered as the independent variable and density was used as the dependent variable. The normality of the data and the homoscedasticity of the variances were verified before the application of each test. In that case the normality of the data was tested by the Shapiro-Wilk tests while the homoscedasticity of the variances was verified by the Cochran C test (Sokal and Rohlf 1981).\u003c/p\u003e \u003cp\u003eHowever, when main effects ANOVA tests were significant, Post-hoc comparisons were conducted using Turkey's honest significant difference HSD test (Zar 1984) to identify the sources of variation. To determine the substrate preference of \u003cem\u003eP. gibbesi\u003c/em\u003e, the mean abundances of the two types of rocky substrate were compared by computing a two-sample t statistic. All statistical analyzes were performed by the software Statistica v.7.\u003c/p\u003e \u003c/div\u003e"},{"header":"Results","content":"\u003cp\u003eIn the two sampled sectors and over the 16.2 km prospected by free diving, we recorded a total mean abundance of 5325\u0026thinsp;\u0026plusmn;\u0026thinsp;15.62 individuals of \u003cem\u003eP. gibbesi\u003c/em\u003e. The population generally evolved at very shallow depths in the infralittoral stage (-10 cm). The distribution of individuals was unevenly distributed between the 2 sampled sectors with higher mean abundance in sector 2 (4472\u0026thinsp;\u0026plusmn;\u0026thinsp;9 ind.) compared to the sector 1 (853\u0026thinsp;\u0026plusmn;\u0026thinsp;8.54 ind.). Also, the total mean density was 4 times higher in the sector 2 (25\u0026thinsp;\u0026plusmn;\u0026thinsp;0.05 ind./50 m\u0026sup2;) than in sector 1 (6\u0026thinsp;\u0026plusmn;\u0026thinsp;0.06 ind./50 m\u0026sup2;). The two way- ANOVA test highlights this large difference (F\u0026thinsp;=\u0026thinsp;65461.4 P\u0026thinsp;\u0026lt;\u0026thinsp;0.001). (Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eAnova of \u003cem\u003ePercnon gibbesi\u003c/em\u003e according to the size of individuals and to the two prospected sectors. df degrees of freedom, MS mean square, F Statistic significance level, p level of probability, Cochran\u0026rsquo;s test C\u0026thinsp;=\u0026thinsp;0.302626, P\u0026thinsp;=\u0026thinsp;0.885834\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"2\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSource of variation\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003edf MS F p\u0026thinsp;\u0026lt;\u0026thinsp;0.001\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSectors\u003c/p\u003e \u003cp\u003eSizes\u003c/p\u003e \u003cp\u003eSectors x Sizes\u003c/p\u003e \u003cp\u003eResidual\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1 184.2264 65461.4 ***\u003c/p\u003e \u003cp\u003e2 32.7353 11631.9 ***\u003c/p\u003e \u003cp\u003e2 8.5699 3045.2 ***\u003c/p\u003e \u003cp\u003e12 0.0028\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003ctfoot\u003e \u003ctr\u003e\u003ctd colspan=\"2\"\u003e*: significant correlation (P\u0026thinsp;\u0026le;\u0026thinsp;0.05), **: highly significant correlation (P\u0026thinsp;\u0026le;\u0026thinsp;0.01), ***: very highly significant (P\u0026thinsp;\u0026le;\u0026thinsp;0.001)\u003c/td\u003e\u003c/tr\u003e \u003c/tfoot\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eThe \u003cem\u003eP. gibbesi\u003c/em\u003e population in sector 1 was numerically structured as follows: Small (79\u0026thinsp;\u0026plusmn;\u0026thinsp;6.56 ind.), Medium (412\u0026thinsp;\u0026plusmn;\u0026thinsp;10 ind.) and Large (362\u0026thinsp;\u0026plusmn;\u0026thinsp;7.51 ind.) (Fig.\u0026nbsp;2A). In the sector 2, the population was organized as follows: Small (786\u0026thinsp;\u0026plusmn;\u0026thinsp;5.51 individuals), Medium (1706\u0026thinsp;\u0026plusmn;\u0026thinsp;6.81 ind.) and Large (1980\u0026thinsp;\u0026plusmn;\u0026thinsp;12.77 ind.) (Fig.\u0026nbsp;2B). The distribution of this invasive crab by size was variable as well as between stations and sectors (Fig.\u0026nbsp;2C).\u003c/p\u003e \u003cp\u003e \u003cem\u003ePercnon gibbesi\u003c/em\u003e was totally absent in 3 stations (stat. 3, 9 and 10) among the 11 stations prospected of the sector 1 while in the sector 2, the species was present overall the stations except in station D where it was totally absent. The mean densities by distance vary considerably across the different sampled stations and sectors (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e3\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe highest mean density of \u003cem\u003eP. gibbesi\u003c/em\u003e in the sector 1 was observed in station 1 (41 ind. \u0026plusmn; 0.71/50 m\u0026sup2;) where the lowest one was recorded in station 8 (1 ind. \u0026plusmn; 0.08/50 m\u0026sup2;) (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e3\u003c/span\u003eA). Differences between pairs stations were confirmed by Tukey\u0026rsquo;s post comparison test: no significant difference in mean density were saved at both of station 8 and 4 (Table\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e). In the sector 2 the highest mean density was recorded in station C (145 ind. \u0026plusmn; 0.33/50 m\u0026sup2;) and lowest density in station A (9 ind. \u0026plusmn; 0.17/50 m\u0026sup2;) (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e3\u003c/span\u003eB). Very highly significant differences in density were demonstrated by the analysis of variance one-way test (F\u0026thinsp;=\u0026thinsp;68568.9; P\u0026thinsp;\u0026lt;\u0026thinsp;0.001). In the sector 2, the Tukey HSD test reveals similar densities in the stations: H and I with values respectively equal to 26.2 and 26.73 individual/50 m\u003csup\u003e2\u003c/sup\u003e (Table\u0026nbsp;\u003cspan refid=\"Tab5\" class=\"InternalRef\"\u003e5\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab4\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 4\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eTukey HSD test; variable DV_1 Homogenous Groups, alpha\u0026thinsp;=\u0026thinsp;0.05 Error: Within MS\u0026thinsp;=\u0026thinsp;0 .15139, df\u0026thinsp;=\u0026thinsp;14.000\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"9\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c9\" colnum=\"9\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eStations\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eMean DV_1\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c8\"\u003e \u003cp\u003e6\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c9\"\u003e \u003cp\u003e7\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eStation 8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e****\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eStation 4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e****\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eStation 5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e****\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eStation 6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e****\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eStation 11\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e****\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eStation 7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e****\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eStation 2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e14\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e****\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eStation 1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e41\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e****\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab5\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 5\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eTukey HSD test; variable DV_1Homogenous Groups, alpha\u0026thinsp;=\u0026thinsp;0.05 Error: Within MS\u0026thinsp;=\u0026thinsp;0 .06906, df\u0026thinsp;=\u0026thinsp;20.000\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"11\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c9\" colnum=\"9\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c10\" colnum=\"10\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c11\" colnum=\"11\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSector 2\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eMean DV_1\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c8\"\u003e \u003cp\u003e6\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c9\"\u003e \u003cp\u003e7\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c10\"\u003e \u003cp\u003e8\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c11\"\u003e \u003cp\u003e9\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eStation A\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e****\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eStation B\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e11\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e****\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eStation F\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e18\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e****\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eStation E\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e22\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e****\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eStation J\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e24\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e****\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eStation H\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e26.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e****\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eStation I\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e26.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e****\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eStation G\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e36\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e****\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eStation K\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e45\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e****\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eStation C\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e145\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e \u003cp\u003e****\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eThe two-way ANOVA test has been revealed significant differences between the two study sectors for the factors considered (size categories, sectors) and for the interaction between these 2 factors (Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). The \u003cem\u003eP. gibbesi\u003c/em\u003e crab was absent in \u003cem\u003ePosidonia oceanica\u003c/em\u003e seagrass as well as over sandy bottoms, its presence was limited exclusively to rocky substrates, namely in cracks (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e4\u003c/span\u003e). \u003cem\u003ePosidonia oceanica\u003c/em\u003e seagrass and sandy bottoms were not occupied by this alien crab. The one-way ANOVA revealed significant differences between the types of rocky substrate (F\u0026thinsp;=\u0026thinsp;443709.78; P\u0026thinsp;\u0026le;\u0026thinsp;0.001). Indeed, the t statistic test (t\u0026thinsp;=\u0026thinsp;177.4037; P\u0026thinsp;\u0026lt;\u0026thinsp;0.001) revealed significant differences between the crab's densities in the 2 types of rocky substrate in the sector 1 as well as in the sector 2 where the student t-test is equal to 966.2234 (P\u0026thinsp;\u0026lt;\u0026thinsp;0.001).\u003c/p\u003e \u003cp\u003eA mean abundance of 802 (\u0026plusmn;\u0026thinsp;7.02 SE) individuals was counted in cracks \u003cem\u003evs\u003c/em\u003e 51.33 (\u0026plusmn;\u0026thinsp;2.08 SE) individuals in crevices in the anthropogenic sector. In the sector 2 the mean abundance of \u003cem\u003eP. gibbesi\u003c/em\u003e was 4279 (\u0026plusmn;\u0026thinsp;2.08 SE) individuals in cracks vs 192 (\u0026plusmn;\u0026thinsp;2.08 SE) individuals in crevices. The distribution of \u003cem\u003eP. gibbesi\u003c/em\u003e was mostly limited to cracks (95%) \u003cem\u003evs\u003c/em\u003e (5%) in crevices whatever the sector prospected.\u003c/p\u003e \u003cp\u003eRegardless of the sector and size class, crabs are indifferent to the observer.\u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003eAfter several records of \u003cem\u003eP. gibbesi\u003c/em\u003e on different regions of the Algerian coasts: Skikda (Katsanevakis et al. \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2011\u003c/span\u003e), Algiers (Lamouti and Bachari 2011), Jijel (No\u0026euml;l and Prouzet 2017), Oran (Hussein et al. \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2020\u003c/span\u003e) and also in the western region of the Annaba Gulf (Menail et al. \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2019\u003c/span\u003e), our observations by visual surveys carried out on a total linear transect of 16.2 km for two successive years (summer 2017 and 2018) confirm not only the establishment of this alien species in the Gulf of Annaba, but also its expansion along the Eastern Algerian coasts, both inside and outside of the Gulf. The presence of this subtropical crab on the Algerian coasts from East to West is an obvious and logical extension of its distribution area along the countries of North Africa (Azzuro et al \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2011\u003c/span\u003e; Sghaier et al. \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2011\u003c/span\u003e; Grimes et al. \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2018\u003c/span\u003e) and throughout the Mediterranean Sea (Katsanevakis et al. \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2011\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eRecently, another alien crab has appeared on Algerian coast, the American blue crab: \u003cem\u003eCallinectes sapidus\u003c/em\u003e, is know present from the Eastern (Benabdi et al. \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Hamida and Kara \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2021\u003c/span\u003e) to the Western coasts of Algeria (Ragkousis et al. \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). In the Mellah lagoon (East, Algeria), the invasion of this non-native species, were recorded in mass (Kara and Chaoui \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). In the Gulf of Annaba, this species has been recently observed invading the extreme East of Sidi-Salem beach, near the mouth of a freshwater stream (B.N., personal observation). The recent presence of this species has even been reported in Lake Tonga (Wilaya El-Tarf), a freshwater lake classified as a Ramsar site since 1982 (Tahri and Boutabia \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e2022\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe main driver of the \u003cem\u003eP. gibbesi\u003c/em\u003e intrusion at the Eastern Algerian coasts would probably result from the migration of adult individuals from the bordering Tunisian coast or by accidental transport through shipping. The Western current of the Mediterranean, which runs along the North African coasts (Moroccan, Algerian and Tunisian), then rises towards Sicily, runs along the north-eastern Italian coast, then along the French coast, and drops down along the Spanish coast, could facilitate and play a role on the transport of planktonic larvae along the Algerian coast from west to east. The relatively long larval phase of \u003cem\u003eP. gibbesi\u003c/em\u003e (Paula and Hartnoll \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e1989\u003c/span\u003e) would facilitate the subsequent colonization of post-larvae and megalops (Hartnoll \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e1992\u003c/span\u003e) along east Algerian coasts. It is very likely that there is a time lake between the apparition of this species along the eastern coasts of Algeria and its records, since the population observed in free diving seemed well established. Monitoring exotic fauna, in particular by visual surveys, is often a delicate task, hence the importance of developing medium and long-term programs between the different countries of the Mediterranean coast to collect information on these changes in biodiversity. At the present time, it is difficult to determine exactly the ways arrival of \u003cem\u003eP. gibbesi\u003c/em\u003e in the eastern Algerian waters. This massive proliferation on shallow rocky bottoms (\u0026lt;\u0026thinsp;10 cm), especially in sector 2, was probably favored by the ideal physico-chemical conditions of the area (especially edaphic) and by the rarefaction of predators on this prey. Indeed, the studies carried out on the feeding habits of many coastal teleost in the study area, as is the case of Sparidae (Benchalel et al. \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2010\u003c/span\u003e), Scorpaenidae (Omri et al. \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2019\u003c/span\u003e), Labridae (Boughamou et al. \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2016\u003c/span\u003e), Mullidae (Broudraa et al. 2018) and Serranidae (Zaidi et al. \u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e2017\u003c/span\u003e; Rachedi et al. \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e2018\u003c/span\u003e) did not record the presence of this prey in the stomach contents of ichthyologic predators cited previously. The absence of \u003cem\u003eP. gibbesi\u003c/em\u003e in the stomacal content of teleosts fish could be explained by the non-identification of the species in view of the highly digestible state of the prey in which they are generally found. Indeed, it is known that the \u003cem\u003eP. gibbesi\u003c/em\u003e crab is strictly subtidal and limited to the uppermost reaches of infralittoral zone characterized by rocky shores (Pipitone et al. \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2001\u003c/span\u003e; Deudero et al. \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2005\u003c/span\u003e; Thessalou-Legaki et al. \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e2006\u003c/span\u003e) and occasionally the wide bare rock ledges or in crevices on vertical rock walls with a moderate algal cover (Deudero et al. \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2005\u003c/span\u003e; Sciberras and Schembri \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2008\u003c/span\u003e). The absence of this species on sandy or homogeneous rocky bottoms or in \u003cem\u003eP. oceanica\u003c/em\u003e seagrass at both sectors has also been observed in other regions of the Mediterranean (Sciberras and Schembri \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2008\u003c/span\u003e; F\u0026eacute;lix-Hackradt et al. \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). We suppose that the density of \u003cem\u003eP. gibbesi\u003c/em\u003e is closely linked to the availability of algae and adequate rocky structure. Pipitone et al. (\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2001\u003c/span\u003e), revealed that the strong affinity of \u003cem\u003eP. gibbesi\u003c/em\u003e for rocky bottoms result probably of the security hidden protection of predation and that availability of food resources.\u003c/p\u003e \u003cp\u003eThe present comparative study revealed a very high significant differences in the abundance of \u003cem\u003eP. gibbesi\u003c/em\u003e in two different sectors, one exposed to anthropogenic actions (sector 1) and the other far from any source of human pressure (sector 2). We can suppose that this numerical disparity in abundance \u003cem\u003eP. gibbesi\u003c/em\u003e is due principally to the distance between the studied sectors and their proximity to the Annaba City and thus, the increasing of anthropogenic activities, represented particularly by the impact of balnear tourism, coastal urbanization and industrialization which are often accompanied by domestic and industrial pollution problems. Indeed, a total of 7 beaches (Lever de l\u0026rsquo;Aurore, Saint Cloud, Chapuis, La Caroube, Toche, Belvedere, Ain Achir), several hotels and balnear and water sports resorts are located along sector 1, which could explain the low abundance of \u003cem\u003eP. gibbesi\u003c/em\u003e observed in all the sampled stations. The homogeneous topographical nature of the substrate in sector 1, such as the presence of large sandy areas, scattered \u003cem\u003eP. oceanica\u003c/em\u003e seagrass and flat boulders, certainly constitute unfavorable habitats for the establishment of this species in this sector.\u003c/p\u003e \u003cp\u003eIn the two sampled sectors, the three size categories (S, M and L) are significantly represented but always with numerical proportions in favor of individuals of medium and large size. While free diving, small crabs could escape the observer when counting, hence their number is underestimated within established populations. Around Balearic Islands, Cannicci et al. (\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e1999\u003c/span\u003e) revealed that the medium individual\u0026rsquo;s size category of \u003cem\u003eP. gibbesi\u003c/em\u003e predominated the distribution of the population. They have also reported that the small individuals were less abundant and they have supposed that was related to the sampling period and recruitment.\u003c/p\u003e \u003cp\u003eThe highest mean densities never exceed 3 ind/m\u0026sup2;, a maximum value observed in station C in sector 2. Overall, the mean density is always less than 1 ind./m\u0026sup2;. Within \"Capo Gallo-Isola delle Femmine\" MPA, in the north-west of Sicily, the mean density (ind./100 m\u0026sup2; \u0026plusmn; se) of the whole area was estimated to 42\u0026thinsp;\u0026plusmn;\u0026thinsp;6.67 individuals, i.e. less than 1 ind./m\u0026sup2; with an almost similar population size class frequency distribution (S: 37%, M: 35%, L: 28%) (Agnetta et al. 2012). Around Dragonera Islands (Spain), the highest densities are recorded on pebble substrates, reaching up to 3 ind./m\u0026sup2; (Deudero et al. \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2005\u003c/span\u003e). However, the rapid expansion of this crab in Mediterranean waters with its ability to occupy disturbed areas (Cannicci et al. 2006) and its resistance to temperature changes (Calado 2006) have shown that their densities can be very high, reaching up to 11.9 ind./m\u0026sup2; (Sciberras and Schembri \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e2007\u003c/span\u003e). On the basis of our freediving visual surveys, we found that this invasive species has a preference for rocky and isolated environments where its chances of establishment and survival would be higher compared to homogeneous habitats and areas of high anthropic pressure.\u003c/p\u003e \u003cp\u003eConcerning the behaviour of \u003cem\u003eP. gibbesi\u003c/em\u003e we observed that when there is a hydrodynamic tension, this flat crab becomes more active it will be able to makes jumps between cracks to collect suspended algal particles. The behaviour of young individuals observed is slightly different compared to the other larger individuals, the small individuals seem to be more sensitive to the presence of observer, they are perfectly concealed in the cracks and crevasses and their presence are always accompanied by larger individuals.\u003c/p\u003e \u003cp\u003eOther interesting aspects in this study deserve to be clarified on this invasive species such as the (i) nocturnal incursions observed out of the water, probably in search of food (ii) the bacterial attacks that we observed at abdominal level and (iii) unexplained mortality in adult individuals during the summer at very shallow depths. The collection of all this information could allow the scientific community to better understand the movements and the establishment of this species on the Algerian east coasts and along the Mediterranean in general.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgements\u003c/strong\u003e The authors are most grateful to the Editor and an anonymous reviewer for their helpful comments and suggestions. This scientific work received no financial support.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthors contributions:\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAuthors 1 contributed equally to the design of the experimental protocol and the writing of the final manuscript. Co-authors 2 statistically processed the raw data and approved the final version of the article.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor Contribution\u003c/strong\u003e The authors state that all the authors have contributed equally to designing the experimental protocol, writing and proof editing the paper in its final edition and approved it for submission.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e The present experiment is part of a PhD thesis of Bada Neila and did not benefit from any particular financial support.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData Availability\u003c/strong\u003e The raw data used to generate the submitted results is available and can be provided, if necessary, to the journal or the designated experts.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEthical Approval and Consent of Participation\u003c/strong\u003e The study has not been submitted, partially or totally to any other journal, and does not present any conflict of interest.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eHuman and Animal Ethics\u003c/strong\u003e The biological material used in this study is a non-native marine product and of no interest for consumption and doesn\u0026rsquo;t require animal ethics. However, the experimental protocol was validated by the scientific council of the Badji-Mokhtar University, Annaba, Algeria.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent to Publication\u003c/strong\u003e All the authors approve the submission of paper in its present form.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eAgnetta D, Baccarella A, Gianguzza P, Badalamenti F, Pipitone C (2013) First estimates od density and distribution of the alien crab \u003cem\u003ePercnon gibbesi\u003c/em\u003e (Decapoda, Percnidae) in the Capo Gallo-Isola delle Fermmine MPA/Prime stime di densit\u0026agrave; e distribuzione del granchio alieno \u003cem\u003ePercnon gibbesi\u003c/em\u003e (Decapoda, Percnidae) Nell Capo Gallo-Isola delle Fermmine. 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J Mar Biol Assoc 97(2):259\u0026ndash;267\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eZenetos A (2010) Trend in aliens species in the Mediterranean. An answer to Galil, 2009 \u0026laquo;Taking stock: inventory of alien species in the Mediterranean Sea\u0026raquo;. Biol Invasions 12(9):3379\u0026ndash;3381\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eZenetos Α, Gofas S, Morri C, Rosso A, Violanti D, Garcia Raso JE, Cinar ME, Almoglabin A, Ates AS et al (2012) Alien species in the Mediterranean Sea by 2012. A contribution to the application of European Union\u0026rsquo;s Marine Strategy Framework Directive (MSFD). Part 2. Introduction trends and pathways. Mediterr Mar Sci 13(2):328\u0026ndash;352\u003c/span\u003e\u003c/li\u003e\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":"Ecology, Alien crab, Percnon gibbesi, Algeria, Mediterranean, Visual survey","lastPublishedDoi":"10.21203/rs.3.rs-4125895/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4125895/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eSome ecological aspects of the alien crab \u003cem\u003ePercnon gibbesi\u003c/em\u003e (H. Milne Edwards, 1853) have been approached by visual surveys in the southwestern Mediterranean waters (East, Algeria). This sampling method, applied on a coastal line of 16.2 km and between 0 and \u0026minus;\u0026thinsp;3 m depth, allowed us to collect information on abundances and densities by size category, nature of the habitat and behavior of this species. Overall 22 diurnal dives (3 observations/dive) were carried out in 2 different adjacent costal sectors, the Bay of Annaba (Sector 1: Lever de l\u0026rsquo;Aurore-Amphore), located at the east, and Cap de Garde (Sector 2: Cap de Garde - Djenen El Bey beach), located at the west of the Bay. We recorded an average total of 5325 individuals (\u0026plusmn;\u0026thinsp;15.62) with numerical dominance in sector 2 (4472\u0026thinsp;\u0026plusmn;\u0026thinsp;9 ind.). Medium-sized individuals dominated numerically in sector 1 (412\u0026thinsp;\u0026plusmn;\u0026thinsp;10 ind.), while large individuals were better represented in sector 2 (1980\u0026thinsp;\u0026plusmn;\u0026thinsp;12.77 ind.). Average densities in two sectors varied to according on measurement unit (surface, dive time). Whatever the sector, the rock cracks sheltered the greatest number of individuals. No individual was observed on homogeneous bottoms. Overall, crabs are indifferent in the presence of an observer.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e","manuscriptTitle":"Distribution, Habitats and Behavior of the Non-Indigenous Brachyuran Percnon gibbesi (Percnidae) of Southwestern Mediterranean (Algeria)","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-03-21 19:27:30","doi":"10.21203/rs.3.rs-4125895/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":"b5cbfb7c-8036-4d30-8ef2-74d4a6ba26d9","owner":[],"postedDate":"March 21st, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2024-04-22T16:55:03+00:00","versionOfRecord":[],"versionCreatedAt":"2024-03-21 19:27:30","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-4125895","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4125895","identity":"rs-4125895","version":["v1"]},"buildId":"7rjqhiLT3MXkJMwkYKINL","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}