Frequent fissiparous asexual reproduction in Kolga hyalina (Holothuroidea:Elpidiidae) in the abyssal central Arctic.

Frequent fissiparous asexual reproduction in Kolga hyalina (Holothuroidea:Elpidiidae) in the abyssal central Arctic. | Authorea try { document.documentElement.classList.add('js'); } catch (e) { } var _gaq = _gaq || []; _gaq.push(['_setAccount', 'G-8VDV14Y67G']); _gaq.push(['_trackPageview']); (function() { var ga = document.createElement('script'); ga.type = 'text/javascript'; ga.async = true; ga.src = ('https:' == document.location.protocol ? 'https://ssl' : 'http://www') + '.google-analytics.com/ga.js'; var s = document.getElementsByTagName('script')[0]; s.parentNode.insertBefore(ga, s); })(); Skip to main content Preprints Collections Wiley Open Research IET Open Research Ecological Society of Japan All Collections About About Authorea FAQs Contact Us Quick Search anywhere Search for preprint articles, keywords, etc. Search Search ADVANCED SEARCH SCROLL This is a preprint and has not been peer reviewed. Data may be preliminary. 12 September 2025 V1 Latest version Share on Frequent fissiparous asexual reproduction in Kolga hyalina (Holothuroidea:Elpidiidae) in the abyssal central Arctic. Authors : Autun Purser 0000-0001-5427-0151 [email protected] , Lilian Boehringer , Carolin Uhlir , and Antje Boetius Authors Info & Affiliations https://doi.org/10.22541/au.175767225.57471748/v1 258 views 144 downloads Contents Abstract Supplementary Material Information & Authors Metrics & Citations View Options References Figures Tables Media Share Abstract In the deep sea, holothurians often dominate the megafauna biomass of abyssal plains. Their role as deposit feeders is significant, in organic matter recycling as well as in deep-sea food webs. As with their shallow water relatives, abyssal sea cucumbers show substantial temporal and spatial dynamism in abundance; however, rarely reaching such massive accumulations due to much lower energy supplies. With a sexual reproduction dependent on extracorporeal fertilization, the generally low population densities observed in the abyss have long presented an enigma to deep-sea biology. Two expeditions with the research icebreaker RV Polarstern to the Central Arctic Ocean have collected images of the abyssal Arctic seafloor indicating that fissiparous, asexual reproduction in adults of the deposit feeding holothurian Kolga hyalina species was occurring in the summer months of both 2012 and 2023 at depths in excess of 4000 m. A substantial proportion of holothurians were observed to develop transverse incisions in their middle sections, in a manner reminiscent of fissiparous holothurians previously observed in some tropical and shallow reef environments. In the summer of 2012, 12.3% (SD=8.28) of K. hyalina individuals observed were in the process of splitting, whereas in 2023, 7.9% (SD=4.79) of observed individuals were undergoing fissiparity. These expeditions surveyed contrasting regions of arctic seafloor, differing in food supply, including areas with fresh food falls of the ice algae Melosira arctica, and areas without such food falls. Though K. hyalina individuals were found to be clearly attracted to algal food falls and fed from them, the presence or absence of this material apparently did not impact on the ratio of holothurian individuals exhibiting asexual reproductive behaviour. Interestingly, many individuals observed in the process of splitting were also developing gonadal cells, indicative of active sexual reproduction. Possibly the capacity to employ both reproductive strategies is an advantage in a region where benthic food availability has become very dynamic. These observations are the first evidence of fissiparity occurring in abyssal holothurians globally, and within polar holothurians at any depth. The ability to carry out both sexual and asexual reproduction in the changeable Central Arctic environment is a trait which may explain the dominance of Kolga hyalina in the Central Arctic abyss. Frequent fissiparous asexual reproduction in Kolga hyalina (Holothuroidea:Elpidiidae) in the abyssal central Arctic. Authors Autun Purser 1* , Lilian Boehringer 1* , Carolin Uhlir 3 , Antje Boetius 1,2 # Affiliations 1 Alfred Wegener Institute, Helmholtz Center for Polar and Marine Research, Bremerhaven, Germany 2 MARUM Center for Marine Environmental Sciences, University Bremen, Germany 3 German Centre for Marine Biodiversity Research (DZMB), Senckenberg am Meer, Hamburg, Germany *Denotes equal contribution #present address: Monterey Bay Aquarium Research Institute, Moss Landing, CA 95039 USA Abstract In the deep sea, holothurians often dominate the megafauna biomass of abyssal plains. Their role as deposit feeders is significant, in organic matter recycling as well as in deep-sea food webs. As with their shallow water relatives, abyssal sea cucumbers show substantial temporal and spatial dynamism in abundance; however, rarely reaching such massive accumulations due to much lower energy supplies. With a sexual reproduction dependent on extracorporeal fertilization, the generally low population densities observed in the abyss have long presented an enigma to deep-sea biology. Two expeditions with the research icebreaker RV Polarstern to the Central Arctic Ocean have collected images of the abyssal Arctic seafloor indicating that fissiparous, asexual reproduction in adults of the deposit feeding holothurian Kolga hyalina species was occurring in the summer months of both 2012 and 2023 at depths in excess of 4000 m. A substantial proportion of holothurians were observed to develop transverse incisions in their middle sections, in a manner reminiscent of fissiparous holothurians previously observed in some tropical and shallow reef environments. In the summer of 2012, 12.3% (SD=8.28) of K. hyalina individuals observed were in the process of splitting, whereas in 2023, 7.9% (SD=4.79) of observed individuals were undergoing fissiparity. These expeditions surveyed contrasting regions of arctic seafloor, differing in food supply, including areas with fresh food falls of the ice algae Melosira arctica, and areas without such food falls. Though K. hyalina individuals were found to be clearly attracted to algal food falls and fed from them, the presence or absence of this material apparently did not impact on the ratio of holothurian individuals exhibiting asexual reproductive behaviour. Interestingly, many individuals observed in the process of splitting were also developing gonadal cells, indicative of active sexual reproduction. Possibly the capacity to employ both reproductive strategies is an advantage in a region where benthic food availability has become very dynamic. These observations are the first evidence of fissiparity occurring in abyssal holothurians globally, and within polar holothurians at any depth. The ability to carry out both sexual and asexual reproduction in the changeable Central Arctic environment is a trait which may explain the dominance of Kolga hyalina in the Central Arctic abyss. Keywords Kolga hyalina, Central Arctic, abyssal, fissiparity in holothurians, asexual production INTRODUCTION In Arctic waters, holothurians are represented solely by elasipodid species from the family Elpidiidae 1 . Species of the genus Elpidia are known to be eurybathic ( E. glacialis THÉEL, 1876) or endemic to bathy-abyssal Arctic waters ( E. belyaevi ROGACHEVA, 2007 , E. heckeri BARANOVA, 1989), while the species Kolga hyalina DANIELSSEN & KOREN, 1879 is known only from deep Arctic waters 1,2 . Elpidia heckeri and Kolga hyalina 3 are particularly abundant and widespread in the Central Arctic Ocean (CAO) 4 . Photographic surveys from the seafloor of Fram Strait, the main deep water pathway to the CAO, have shown both species to inhabit depths of Arctic waters in excess of ca. 1500 m 5 and into the trenches of the north west Pacific 1 . K. hyalina is also reported from the deep North Atlantic 6 . As mobile surface deposit feeders, these species have been observed to respond rapidly to changing food availability conditions, with greatly differing densities throughout the year 7,8 and interannually 6 . K. hyalina have been shown to feed on occasional sea ice algal food falls in the CAO when such events occur, such as the Melosira arctica DICKIE, 1852 foodfalls observed in the CAO in 2012 9 . Based on previous work conducted on the reproduction of either E. heckeri or K. hyalina, both species have been assumed to reproduce sexually, and likely seasonally, in response to particle flux, following periods of elevated sea surface or under ice production, influencing the timing of reproduction, particularly tightly so with K. hyalina 10 . In 2023, the RV Polarstern 11 PS138 “ArcWatch-1” expedition surveyed with the Ocean Floor Observation and Bathymetry System (OFOBS) towed camera sled at numerous sites across the CAO basins, with the aim to compute benthic fauna densities and to compare these results with those observed across the same CAO region during the 2012 RV Polarstern ARK-XXVII/3 PS80 “IceArc” expedition, conducted with the same vessel and similar towed camera equipment 12 . During the 2023 expedition, epibenthic physical sampling was also conducted at the survey sites to attain physical samples of imaged fauna 13 . During these camera surveys, numerous tortuously shaped K. hyalina individuals were observed across the central Arctic basins, showing transversal constrictions in the mid sections. Further examination of these images led to the conclusion that the individuals were in the process of fissiparous reproduction – splitting as adults into pairs of individuals. In this study we present an analysis of the size, abundance, distribution and fissiparous state of K. hyalina holothurians from across the CAO basins, as observed during both the 2012 (ARK-XXVII/3, PS80) and 2023 (PS138) expeditions with the research vessel RV Polarstern. Specifically, we investigated the hypothesis that the number of K. hyalina individuals exhibiting lateral constrictions was higher with more food abundance and that the Kolga splitting were larger than those not splitting. Additionally, we reevaluated benthic images from a series of adjacent published studies and unpublished image data sets conducted across the HAUSGARTEN observatory, a time series ocean observatory array assessing environmental and fauna change across the Fram strait, gateway from the Atlantic Ocean to the CAO – a region abundant in K. hyalina and E. heckeri 5,7,8,14 . Our results are discussed in light of the recent and ongoing environmental and ice drift changes within the Arctic Ocean ecosystem and with regard to what is known on factors inducing fissiparity in holothurians. METHODS The ARK27-3 PS80 (IceArc) and PS138 (ArcWatch) expeditions During the summer of 2012 the ARK27-3 ‘IceArc’ 12 RV Polarstern expedition surveyed the ice, water column and seafloor of the central Arctic basins from 82° N to 89° N. A range of instruments were used to link surface processes to seafloor benthic fauna activities, with a highlight being the discovery that large under ice algae blooms of M. arctica could reach the seafloor as large food falls following death, supporting a diverse and abundant benthic biomass 9 . During the summer of 2023, the PS138 ‘ArcWatch-1’ 13 expedition revisited and resurveyed some of the same stations visited in 2012 during IceArc, as well as investigating both the Lomonosov and Gakkel Ridges ( Figure 1 ). A key aim of the PS138 expedition was to observe whether the benthic community had remained stable across the central Arctic basins between 2012 and 2023. To achieve this, extensive towed camera surveys were conducted in 2023, repeating transects conducted in 2012 wherever possible – given ice conditions and diplomatic permissions excluding the Russian EEZ in 2023. In 2012 the Ocean Floor Observation System (OFOS) was used to automatically image the seafloor every approximately 30 seconds from a height of 1.5 m 15 across nine seafloor stations, recording several hundred images from each location, each covering approximately 4m 2 of seafloor 12,15 . The 2023 expedition employed the same sampling strategy with the Ocean Floor Observation and Bathymetry System (OFOBS), an improved towed sled system incorporating the same cameras as those used in 2012, whilst adding a sidescan sonar, an improved Inertial Navigation System (INS) and Dynamic Velocity Logger (DVL) to structurally map the seafloor and improve the geolocation of collected image data 16 . During the 2023 expedition, 16 OFOBS deployments were made. During both expeditions survey stations were selected to best assess the spatial distribution of benthic fauna across the central Arctic ocean basins, cut by the Lomonosov and Gakkel ridges, covering as representative a range of depths and ice coverages as were feasible within the expedition timeframes. The image data was supported with physically sampled K. hyalina by epibenthic sledge (EBS 17 ) with two nets of 500 µm mesh size and 300 µm in the codends 13 . Specimens were either fixed in pre-cooled 96% denatured ethanol for genetics or fixed in 4% formaldehyde solution, frozen in -20°C for microplastic analyses or dissected directly on board for gut content analyses ( Supplementary Table 1 ). Fixed specimens are currently stored at the German Center for Marine Biodiversity Research (DZMB), Senckenberg am Meer in Hamburg, Germany. Image analysis Every image collected from each station surveyed with the OFOS and OFOBS systems during 2012 and 2023 were inspected using the PAPARA(ZZ)I software application, v3.0 18 . All images were scaled using the laser pointers present in each image. K. hyalina observations were counted for each image, the widths and lengths on each individual measured and the fissiparous state (splitting / non-splitting) logged. This data was then used to determine the average abundances of both splitting and non-splitting K. hyalina across each station. Whether or not K. hyalina individuals were within one body length of visible algal detritus was also logged for each observed individual. All splitting K. hyalina were further characterized by the location of the split, to assess whether or not a particular point marked the region of the split. Splits were characterized as occurring between head and first pair of legs (Post-head split), between first and second leg pair (First leg split), between second and third leg pair (Second leg split), between third and fourth leg pair (Third leg split) and between fourth and fifth leg pair (Fourth leg split). If a split appeared to fall exactly on a leg pair, then the split was characterized as occurring on the lower section, e.g. if a split was occurring at the second pair of legs, it was assigned as a ‘Second leg split’. Figure 2 shows examples of the various stages of fissiparity in K. hyalina observed during the PS80 and PS138 expeditions. Also, we compared images of previous missions to the Fram strait 7,8 obtained with OFOS/OFOBS. Images from the deep Pacific were not available to this study. RESULTS Kolga hyalina distribution in the central Arctic During the 2012 “IceArc” and 2023 “ArcWatch-1” expeditions ( Figure 1 ), a total of 2403 K. hyalina individuals were observed during 12 of the 25 survey dives ( Table 1 ) across a depth range of 1962 to 4373 m water depth. 10117 images were inspected overall covering a total area of almost 40000 m 2 of seafloor. K. hyalina were not found on rocky or particularly steep areas of CAO seafloor, such as the steeper regions of the Gakkel Ridge or Lomonosov Ridge (red points on Figure 1 ). Where present, abundances varied from 0.011 individuals m -2 (SD=0.06) at station PS80/369 in 2012, near the North Pole at 88° 55’ N to 5.031 individuals m -2 (SD=0.93) at station PS80/340 at 85° 03’ N in 2023 ( Table 2 ). Out of eight EBS stations, K. hyalina was sampled at four stations in the Amundsen Basin (PS138-74, PS138-100, PS138-147 and PS138-194) and one station (PS138-71) on the Gakkel Ridge ( Supplementary Table 1 ). It was not sampled at stations in the Nansen Basin. Generally, the densities of K. hyalina increased with increasing latitude during both years surveyed, though the lowest observed densities were north of the Lomonosov ridge at PS80/369 in 2012. No K. hyalina were observed at the North Pole station in 2023 13 , despite a comparable depth and seafloor sediment structure to the PS138/053 and PS80/340 stations south of the Lomonosov ridge flank in the Amundsen Basin. There were very little visible algal detritus aggregates observed in the 2023 PS138 data – a marked contrast from the 2012 PS80 data. We did not detect a link between the occurrence of algal patches and fissiparity. Fissiparity in Kolga hyalina in the central Arctic Fissiparity was observed in 202 individual holothurians observed within images collected from across survey dives conducted in both 2012 and 2023 ( Figure 1 , Table 1 ). Figure 2 shows a selection of K. hyalina individuals in various states of fissiparity, from not exhibiting signs of splitting, to potential post-split individuals and those potentially regrowing. Numerous observed individuals showed signs of gonad development typical for the species, as reported from samples collected during “IceArc” 12 and RV Akademik Mstislav Keldysh expedition 72 10 ( Figure 2b, 2g, 2e and 2f ). Figures 2e and 2f shows individuals in the process of splitting, with gonadal cells particularly clearly visible on both sides of the transverse incision. The abundances of K. hyalina individuals undergoing fissiparity varied across survey dives, but did not increase or decrease as a percentage of K. hyalina individuals observed with latitude ( Figure 3 ). Lengths and widths of K. hyalina did not differ significantly by latitude nor year of observation. Length and width ratios between splitting and non-splitting individuals was minimal, though size ranges of observed individuals did cluster by survey dive ( Figure 4 ). With the exception of K. hyalina individuals observed at the northerly PS138_127 station on the Lomonosov Ridge flank (length and width ranges of 2 – 5 and 0.4 – 1.4 cm respectively), individuals across the survey dives were of 5 – 15 cm length and 1 – 3 cm width. Though the variance ranges in length and width were roughly on the order of 3 cm and 1 cm at each station, there were considerable overlaps between stations. The location of the transverse incision on K. hyalina individuals was quite varied, with examples of incisions immediately behind the head ( Figure 2b ), at or after the first pair of legs ( Figure 2c ), second pair of legs ( Figure 2c ), third pair of legs ( Figure 2d ) or fourth pair of legs ( Figure 2e ) were all observed during most surveys, though approximately 50% of incisions were observed to occur after the first or second pair of legs ( Figure 5 ). On rare occasions, what appeared to be highly deformed K. hyalina individuals were observed, perhaps exhibiting regrowth following splitting ( Figure 2g and Figure 2h ), or as small ‘nubbins’ with reduced width ( Figure 2i and Figure 2j ). Individuals in these states were very limited in abundance, with less than 10 observed across the full dataset. Overall, size of the individual was not a relevant factor in occurrence of fissiparity. Out of 178 physically collected specimens by EBS, six specimens showed fissiparity at two stations (PS138_71; PS138_147 13 ) and were fixed in 96% ethanol for future analyses ( Figure 2k ). The comparison with previously published data from the HAUSGARTEN study site in Fram Strait showed that the K. hyalina present between 1997 and 2015 15 showed no signs of fissiparity. Annual HAUSGARTEN transect images conducted from 2015 – 2024 were also examined, and again, no signs of fissiparity were observed. DISCUSSION Kolga hyalina as indicator species for carbon flux dynamics in the deep Arctic Ocean A recent review of benthic biodiversity of the deep Arctic Ocean points to the substantial undersampling of all size classes and to fundamental gaps in knowledge on distribution patterns in their highly diverse habitats only recently discovered with the availability of camera surveys 19 . Echinoderms are among the more species-rich and abundant groups of the Arctic benthic deep-sea epifauna. Especially the elpidiid sea cucumber Kolga hyalina was found to be common to the deep slope and abyssal plains with a depth range of 2500-4400 m, comprising roughly 50% of the central Arctic Ocean area . K. hyalina is a benthopelagic species, able to change its buoyancy and to swim in the near-bottom water layer 15,20 . This trait may help the species respond rapidly to seasonal accumulations of organic matter at the seafloor. K. hyalina is known as opportunistic detritus feeder associated with events of high detrital fluxes 8,9,20 . Where K. hyalina is dominant, its relative E. heckeri is often present in low in numbers, and vice versa 7,8,15 . Connected to recent food falls, K. hyalina was found to make up for 3-4 g wet weight per m -2 seafloor at maximum observed densities on the abyssal plain of the Arctic Ocean, whereas the much smaller E. heckeri concentrations peaked at 3-4 g wet weight per m -2 seafloor. Substantial sampling effort of K. hyalina individuals in 2012 and 2018 was used to assess reproduction strategies, with samples suggesting a spawning period for K. hyalina in August/September at the time of the sea ice minimum in the CAO 21 . A previous study 22 found that K. hyalina’s close relative Kolga nana THEEL, 1879 produces gametes already at sizes as small as a few mm; though its average size is a few cm in length. This early reproductive maturity was also suggested to be an adaptation to resource-scarcity in the Arctic deep-sea environment. Food availability at the seafloor in the central Arctic Despite being primarily ice covered and thus exhibiting rather low primary production rates 19 , substantial algal biomass can accumulate in the CAO, pelagically in the under ice upper waters 23 , within sea ice 24 and melt water ponds 25 , and in sessile concentrations of filamentous under ice algae, such as M. arctica 9 . On algae death, or ice melting, these algae can sink rapidly to the deep Arctic seafloor 26 . Larger food falls of diatom chains can clearly be seen directly influencing the behaviour of benthic megafauna, with impacts on local biogeochemistry and food webs 9 . The regions of seafloor exposed to such pulses of material are likely determined by surface ice flow transport pathways 27 , as well as ice thicknesses, rates, periodicity and rates of ice melting, parameters expected to change in forthcoming years within a warming Arctic –28 . Increasing distance from the marginal ice zone into the more continually ice-covered central Arctic regions correlates with a decrease in the measured seafloor concentrations of organic carbon, pigments, bacterial cell abundance and nutrients, though not necessarily with the abundance of seafloor megafauna, such as the deposit feeding holothurians E. heckeri and K. hyalina 15 . During the current study, the 2012 expedition towed camera surveys imaged a patchy distribution of M. arctica algal aggregates on the seafloor, with E. heckeri and K. hyalina clearly seen to be actively feeding on these aggregates 9 . Densities of these fauna in areas with less or no visible algal detritus were however not significantly different, showing a potentially opportunistic feeding behaviour. By comparing the 2012 K. hyalina abundances presented herein with those from the PS138 results in 2023, a year where algal aggregates at the seafloor were mostly absent from the majority of seafloor surveys, we conclude that abundances in K. hyalina were not influenced by algal megafauna presence / absence. Reported fissiparity in marine invertebrates Fissiparity, or clonal reproduction in adult invertebrates, is a known reproductive strategy in echinoderms, reported widely for brittle stars 32 , sea stars 33 and shallow water, tropical holothurians 34 in particular. At least 18 species of sea cucumbers are known to be able to reproduce by fissiparity. In some species of shallow water sea cucumbers, individuals have been observed split into an anterior and posterior parts, with each thereafter regenerating the missing half through tissue remodeling and growth, over a period of days to weeks. The biological process of fission is not well understood; first transcriptomic studies show upregulation of genes involved in the disintegration of connective tissue, in total metabolism, and in regulation of omni potency of cells 35 . Furthermore, the advantages and triggers governing asexual or sexual reproductive behaviour in animals capable of both reproductive strategies is obtuse and poorly understood for the majority of species, though the capability to do so has remained with some species since the Cretaceous 36,37 . The hypotheses as to the diversity of potential drivers determining which reproductive strategy an individual will employ, include the commonly held assumption that asexual reproduction is a successful approach for local colonization and population maintenance of a region, whereas sexual reproduction allows for a greater dispersal 38 . Furthermore, it is believed in some species that fissiparity is linked to high food availability, because it requires the rapid build-up of biomass and biomolecules before fission. Particularly well studied cnidarians such as reef forming and solitary corals 39–41 utilize both reproductive strategies extensively. Other corals, such as the branched species Montastraea annularis (Ellis & Solander, 1786) appear to utilize the asexual fissiparous reproductive pathway as a means to keep a presence in high energy, frequently disturbed environments 42 . Similarly, in Coscinasterias calamaria (Gray, 1840) , a seastar occupying the shallow intertidal and subtidal seafloor around Rottnest Island and the adjacent mainland of Western Australia, fission was more evident in individuals sampled in the higher energy intertidal environments than the subtidal 43 , a pattern also observed in the sea cucumber Holothuria atra JAEGAR, 1833, in regions of the Great Barrier Reef of varying exposure severity 44 . In H. atra and other fissiparous sea cucumbers, asexual reproduction results in two individuals with greatly different internal anatomies at time of splitting; the anterior containing the buccal complex and generally, the gonads, with the posterior keeping the cloaca and respiratory trees. Despite this, post-split survivorship has been observed to be equal for both posterior and anterior halves of recently split H. atra individuals – with each rapidly developing the missing organs 45 . In an asteroid species, temperature stress associated with the intertidal region has been associated with elevated fissiparity in C. calamaria 46 . In sea stars, such as Nepanthia belcheri PERRIER, 1875, colonisation of highly temporally changeable environments, with variable food and temperature regimes has been identified as a trigger for fissiparous asexual reproduction over sexual 47 . In New Zealand intertidal populations of the seastar Coscinasterias muricata VERRILL, 1867, temperature was found to be unrelated to the percentage of individuals exhibiting fissiparous behaviour, but volume and flux duration of food supply a more significant factor; elevated concentrations and extended durations of food supply resulted in rapid growth of individuals, and in the species asexual reproduction is more common in smaller individuals, which switch to sexual reproduction on reaching a particular size. In the same study, populations occupying sheltered subtidal fjord environments exhibited no asexual reproduction, given a stable food supply and environmental setting. Occupation of microhabitats within a locale, such as the front and back faces of the Belize Barrier Reef by species and individuals exhibiting or limited to asexual or sexual reproduction has been observed to be largely determined by the physical energy and stability of the microhabitat; fissiparous individuals and species of brittle stars favoring fissiparity were observed to be far more abundant on within the high energy exposed Front Reef Zone, with the more stable Back Reef Zone microhabitat being populated by non-fissiparous species and individuals 32 . In areas of the deep sea with sparce habitat features required for colonization by a particular species, such as the exclusively epizoic Ophiacantha cosmica LYMAN, 1878 , found on the stalked polymetallic nodule sponges of the deep Pacific (4000 m and deeper) , fissiparity seems key to maintaining populations on these widely distributed and occasional habitat features, whilst sexual reproduction utilising the transport pathways offered by overlying waters may allow the occasional successful colonisation of distant stalks 48 . In some marine species seem capable of both simultaneous asexual and sexual reproduction, asexual reproduction may offer a more secure approach for occupation and continual colonisation of a region in species with a low fecundity, such as the ophiocomid brittle star Ophiocomella ophiactoides CLARK, 1900 . Though, in this species, which undergoes continual gonad development, this additional sexual reproductive facility is indicative of the use of planktotrophic ophioplutei capable of colonizing more distant regions of seafloor, as with O. cosmica , covering the potential eventuality that the currently occupied habitat becomes less attractive following degradation or overcrowding 49 . Aside from fissiparity in sea stars, brittle stars and holothurians as a mode of continual occupation of primarily variable environments, asexual reproduction into two viable individuals can be a response to parasitism, as a means to reduce the costs associated with parasitism. In the case of the polychaete Pygospio elegans CLAPARÈDE, 1863 annelid, an experimental study in which individuals exposed to the trematode Lepocreadium setiferoides MARTIN, 1938 entered a fissiparous state earlier than unexposed individuals, forming smaller individuals post-splitting than was observed in individuals unexposed to the termatodes 50 . Interestingly, even exposure to the parasite (not infection) triggered the onset of early fissiparity. In the seastar Coscinasterias acutispina (STIMPSON, 1862), endoparasitism by Dendrogaster okadai (YOSII, 1931)also triggers fissiparity 33 . The majority of fissiparous fauna described to date have been reported from the tidal and subtidal regions of the world ocean, with data on fissiparous species and behaviour at greater depths less abundant, potentially as a result of disparate sampling effort rather than ecological favoring the strategy at shallow depths. Some reports of active fissiparous behaviour have been made in polar regions however, though few at depth. Fissiparous brittle stars 51,52 and sea stars 53 from a range of species have been found in numerous contrasting Arctic seafloor habitats. Though a number of tropical holothurian species exhibit fissiparity naturally in shallow waters, or artificially in aquaculture, there have to date been no reports of fissiparity in sea cucumbers within the Arctic, prior to the current study. The limited work conducted to date with E. heckeri and K. hyalina 10 from within the central Arctic also did not report any indications of fissiparity in either of the two species; but found evidence for gonad development and sexual reproduction in different members of the family Elpidiidae 1 . Curiously, extended annual photo surveys conducted with the same camera sled employed in the current study have not observed individuals from either species in the process of splitting outside of the CAO, i.e. across the Fram Strait 5,7,8 . Kolga hyalina fissiparity in the central Arctic The abundance of K. hyalina individuals observed in a fissiparous state during the ARK-XXVII/3 PS80 “IceArc” and RV Polarstern PS138 “ArcWatch-1” was a surprise, as K. hyalina have been observed in abundance in the marginal ice zone of the Fram Strait at various stations of the HAUSGARTEN LTER 14 for more than two decades, though never in a fissiparous state 7,8 . The observations reported herein are the first we are aware of fissiparous deep-sea holothurians anywhere globally, with the great majority of asexual reproduction in holothurians reported in the shallow tropics 54 . Potentially, the timing of the HAUSGARTEN observations has not coincided with fissiparous reproduction, but given that expeditions to the region have taken place in various months between April and October over the last 25 years, it seems unlikely that should such reproduction be occurring, that it was missed temporally during all annual expeditions. The new generation of cost-effective time lapse cameras being introduced currently to the LTER 55 have not in the initial few years of deployment (operating on a daily frequency throughout full years at various observatory stations) have not yet recorded images of any holothurians exhibiting fissiparity 56,57 . As new data is annually collected it is hoped that a definitive answer on whether or not fissiparity in K. hyalina is limited to the CAO or also occurring in other arctic regions. The selection of asexual fissiparous reproduction over sexual reproduction does not seem to inhibit or prevent gonadal development in K. hyalina. Inspection of the collected image data show numerous examples of gonadal cells clearly visible in both halves of splitting individuals 58 ( Figure 2 ). It would seem also that size of an individual is not a driving factor in determining fissiparity (or indeed sexual reproduction) as being the selected mode of reproduction, with no significant differences in individual sizes indicated between splitting or non-splitting individuals across any surveyed Arctic station in the current study ( Figures 3 and 4 ). Latitude does not seem a factor either, and given that latitude correlates roughly with distance from the more productive marginal ice zone, general surface productivity therefore also does not seem a determining factor. Depth may play a role in influencing fissiparous activity. The 2023 station, PS138/127, was the only station at a depth of approx. 1962 m, with all other K. hyalina occupied stations being at depths of 4000 m or deeper ( Table 1 ). At this station K. hyalina individuals were less than half the length on average (less than 4 cm) than those observed at other stations (7.5 cm or longer on average) whilst also being proportionally thinner ( Figure 4 ). K. hyalina at this shallower station were extremely numerous, at more than 4.5 individuals m -2 , though far fewer were exhibiting fissiparity than was observed at the similarly K. hyalina abundant, though deeper at 4351 m, PS80/340 station. As few physical samples were collected during the expedition ( Figure 2k ) it remains to be determined if the holothurians occupying this shallow station, on the flanks of the Lomonosov ridge, are genetically distinct from other Arctic communities imaged in the current study, or if regional differences in food supply volume, flux or temporality are driving the generally small differences in K. hyalina individuals observed during the current study ( Figure 4 ). Potentially, the smaller size of the holothurians at PS138/127 at time of survey could indicate that splitting had previously occurred recently in the region and the high abundance of small individuals the result of splitting – certainly, the very few images collected within which small holothurians, potentially recently split K. hyalina individuals ( Figure 2i and 2j ), are very few in number, and outliers in K. hyalina size few at each surveyed station ( Figure 4 ). Aside from potentially the smaller individuals observed at station PS138/127, no other indications of smaller, recently split individuals were observed at any station, indicating perhaps a rapid return to ‘full’ ‘size after splitting or a near simultaneous splitting in a population. The differences in size of individuals, though moderate, between sites correlates with conclusions made from physical sampling during ARK-XXVII/3 PS80 “IceArc” in 2012 and sampling made in 2018 (RV Akademik Mstislav Keldysh cruise 72), where gametogenesis was linked to periodic food availability and growth 59 . Altogether, the relatively high frequency with which fissparity occurs in CAO K. hyalina , but not in the populations outside of the Arctic suggests that food availability or nutritional status are not the main trigger. It remains to be investigated if the observed CAO K. hyalina are a species distinct from those observed elsewhere. CONCLUSION The observation of basin-wide transverse fission in the abundant Arctic abyssal sea cucumber K. hyalina is an intriguing example of the potentially important role of asexual reproduction may have in deep-sea ecology. The ARK-XXVII/3 PS80 “IceArc” and RV Polarstern PS138 “ArcWatch-1” collected images of 3216 K. hyalina individuals from the CAO, with just under 10% of these undergoing asexual fissiparous reproduction at depths of in excess of 4000 m. Interestingly, this species is known for rapid responses to algal food falls, and extreme population dynamics in time and space. These are the first observations of fissiparity in K. hyalina , or indeed in any holothurian at such depths. Additionally, these are the first observations of fissiparity in polar holothurians at any depth of which we are aware. Previously this trait was only known from tropical and shallow water sea cucumber species, with species-specific factors and environmental conditions, such as nutritional status being identified to trigger fission in shallow waters. Whether asexual reproduction in K. hyalina of the CAO is changing with the Atlantification of the Arctic, and how this mode of reproduction may impact on distribution and local food and carbon transport webs will need further research to determine, particularly in context with the changing ice drift pathways across the CAO associated with ongoing global warming 60 . Further research is needed to elucidate triggers, long-term impacts on genetic diversity, and for optimization of conservation efforts of the northerly polar deep-sea ecosystem. AUTHOR CONTRIBUTIONS A.P. conceived the study. A.B. and A.P. wrote the manuscript with input from all participants. A.P., L.B. and A.B. collected the data. C.U. collected the physical K. hyalina specimens. A.B. wrote the cruise proposals and was expedition leader for both the PS80 and PS138 expeditions. ACKNOWLEDGEMENTS The captains, crews, meteorologists and onboard scientific parties of the IceArc (ARK27-3, PS80) and ArcWatch (PS138) expeditions are thanked for their enthusiasm and support at sea in the collection of this data. Ulrich Hoge is thanked for running the OFOBS system during PS138, and the ARK27-3 OFOS team for archiving and making publicly available the images from 2012 via the PANGAEA data repository. FUNDING INFORMATION The IceArc expedition data collection was funded by the PACES (Polar Regions and Coasts in a Changing Earth System) program of the Helmholtz Association, with additional funds made available to A.B. by the European Research Council Advanced Investigator grant 294757 (ABYSS) and the Leibniz program of the Deutsche Forschungsgemeinschaft, and to B.R. for the Bundesministerium für Bildung, Wissenschaft, Forschung und Technologie project 03F0605E. The data collected from the PS138 “ArcWatch-1” expedition was funded via AWI Grant No. AWI_PS138_01. L.B. was funded by INSPIRES III of the Alfred Wegener Institute. CONFLICT OF INTEREST STATEMENT The authors declare no conflict of interests. DATA AVAILABILITY STATEMENT All image data collected during the 2012 “IceArc” and 2023 “ArcWatch-1” (https://doi.org/10.1594/PANGAEA.971424) expeditions are publicly available from the PANGAEA archive 58 . Towed sled videos are available from the authors on request. ORCID Lilian Boehringer 0000-0001-7322-5145 Autun Purser 0000-0001-5427-0151 Carolin Uhlir 0000-0002-1373-456X Antje Boetius 0000-0003-2117-4176 REFERENCES 1. Rogacheva, A. V. Revision of the Arctic group of species of the family Elpidiidae (Elasipodida, Holothuroidea). Marine Biology Research 3 , 367–396 (2007).2. Budaeva, N. & Rogacheva, A. V. Colonization of the Arctic Ocean by two cosmopolitan genera of marine invertebrates. Invertebrate Zoology 10 , 127–142 (2013).3. Danielssen, D. C. Fra den norske Nordhavsexpedition . (1884).4. Kremenetskaia, A., Ezhova, O., Drozdov, A. 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Invertebrate Reproduction & Development 64 , 33–47 (2020).60. Krumpen, T. et al. Arctic warming interrupts the Transpolar Drift and affects long-range transport of sea ice and ice-rafted matter. Sci Rep 9 , 5459 (2019). FIGURES Figure 1. OFOS and OFOBS deployment transect stations from the 2012 “IceArc” and 2023 “ArcWatch-1” expeditions. Black spots indicate Kolga hyalina observations at 2012 stations, white spots indicate K. hyalina observations in 2023. Red spots indicate stations from 2012 or 2023 where no K. hyalina were observed during transects. Figure 2. Categories of Kolga hyalina fissiparity observed during the PS80 and PS138 expeditions. Fissiparity was characterized as a) not occurring (detail from TIMER_2023_09_03 at 19_53_40 IMG_0528.jpg), b) occurring between head and first pair of legs (Post-head split) (detail from TIMER_2023_08_28 at 15_37_13 IMG_0807.JPG), c) between first and second leg pair (First leg split) (detail from TIMER_2023_08_24 at 19_40_48 IMG_0644.JPG), d) between second and third leg pair (Second leg split) (detail from TIMER_2023_09_03 at 19_08_00 IMG_0387.JPG), e) between third and fourth leg pair (Third leg split) (detail from TIMER_2023_08_19 at 17_20_27 IMG_0549.JPG) or f) between fourth and fifth leg pair (Fourth leg split). g) Occasional individuals seem to exhibit regrowth, rather than splitting, with a smaller, less developed anterior or posterior segment in evidence (detail from 2012_09_08 at 11_57_48 6E0C2185.JPG). h) Occasionally, several splits seem to be in the process of occurring, or splitting in conjunction with regrowth (detail from 2012_09_08 at 19_06_27 6E0C3508.JPG). i) Potentially re-growing fragment (detail from 2012_09_08 at 11_40_56 6E0C2160.JPG). j) A non-splitting K. hyalina individual (left) and a potential regrowing fragment (right) (detail from 2012_09_08 at 12_00_20 6E0C2194.JPG). k) Physical samples of splitting K. hyalina collected during the PS138 expedition. White bars indicates length of 10 cm. Figure 3. Densities of Kolga hyalina observed in fissiparous or non-fissiparous states across survey stations during the PS80 and PS138 expeditions to the central Arctic. Latitude of station, Station name and number of analysed seafloor images are shown on the x-axis. Grey bars indicate densities of non-fissiparous individuals, with orange bars indicating densities of fissiparous individuals. Red bars indicate standard deviations in densities. Where standard deviations exceeded 0.5, the number is given. Figure 4. Scatterplot showing every Kolga hyalina observed during the PS80 and PS138 expeditions, subdivided by survey deployment (colour) and plotted individual width against length. Figure 5. a) Numbers of Kolga hyalina undergoing fissiparity at each station, with subdivided columns indicating at which point on the individuals body fissiparity was occurring (immediately behind the head, at or after the 1 st leg, 2 nd leg, 3 rd leg or 4 th leg). TABLES Table 1. Latitude, Longitude, average depths, number of collected images and areas covered by photo transects conducted during the 2012 “IceArc” and 2023 “ArcWatch-1” expeditions. Table 2. Abundances of Kolga hyalina holothurians observed during the 2012 “IceArc” and 2023 “ArcWatch-1” expeditions. Average densities of holothurians, densities of cucumbers not in proximity to algal concentrations, densities of holothurians near algal concentrations and the numbers of holothurians undergoing fissiparity are presented. SUPPORTING INFORMATION Supplementary Table 1. Specimens of Kolga hyalina physically sampled by epibenthic sledge during PS138 with information on their processing, current storage and fixation for further analyses. Supplementary Material File (table1.docx) Download 17.86 KB File (table2.docx) Download 15.48 KB Information & Authors Information Version history V1 Version 1 12 September 2025 Copyright This work is licensed under a Non Exclusive No Reuse License. Keywords abyssal asexual reproduction central arctic fissiparity in holothurians kolga hyalina Authors Affiliations Autun Purser 0000-0001-5427-0151 [email protected] Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research View all articles by this author Lilian Boehringer Alfred-Wegener-Institut Helmholtz-Zentrum fur Polar- und Meeresforschung View all articles by this author Carolin Uhlir Senckenberg am Meer German Centre for Marine Biodiversity Research View all articles by this author Antje Boetius Alfred-Wegener-Institut Helmholtz-Zentrum fur Polar- und Meeresforschung View all articles by this author Metrics & Citations Metrics Article Usage 258 views 144 downloads .FvxKWukQNSOunydq8rnd { width: 100px; } Citations Download citation Autun Purser, Lilian Boehringer, Carolin Uhlir, et al. Frequent fissiparous asexual reproduction in Kolga hyalina (Holothuroidea:Elpidiidae) in the abyssal central Arctic.. Authorea . 12 September 2025. 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