The discovery of nursery sites of the sea cucumber Cucumaria frondosa in the Canadian Arctic offers opportunities to gather knowledge on the ecology of juveniles. Here, their size and spatial distributions were examined and inter-individual and inter-specific relations were assessed. Out of 893 juveniles collected between 1 and 3 m depths in the fall, 95% were early recruits (<1-year-old). They chiefly occurred on rubbles (similar to 80%) representing the main substratum (similar to 44%) in the nursery. The length of early recruits across all depths was similar to 1520 mu m, with the smallest found at 3 m (similar to 1407 mu m). Fewer recruits were identified in the following spring (51.5%), allowing the calculation of a growth rate (similar to 114 & micro;m mo(-1)). Their density was consistently similar to 7400 ind m & sup2; across depths. Juveniles were mostly found aggregated on flat surfaces (62.7%) or in shallow depressions (18.4%) on the underside of the stones, but also occurred on seaweed holdfasts (2.7%). The average nearest neighbour distance was similar to 0.37 cm, with some juveniles touching each other. More individuals were observed with their body oriented in the same direction (45%) than in opposite directions (25%). Four sympatric species were identified on the same substratum; the polychaete Spirorbis spirorbis (49.7%), encrusting bryozoans in order Cheilostomatida (40.5%), the limpet Testudinalia testudinalis (6.9%), and calcareous encrusting algae (2.9%). Data on newly settled sea cucumbers in the wild are rare. The present findings provide essential information on the population dynamics and carrying capacity of C. frondosa in support of local subsistence harvests and emerging small-scale commercial fisheries led by the Inuit community.

A new holothuroid, Psolus comanchei sp. nov., is described from methane seeps on the Koryak slope and non-vent (background) communities of the Piip Volcano in the bathyal western Bering Sea. The new species differs by lacking ossicles in the sole skin and presenting mushroom-cap-shaped ossicles on the test, tentacles and tube feet. Molecular analyses (COI, 16S) confirm P. comanchei sp. nov. is distinct from congeners but closely related to North Pacific, Arctic, and Atlantic species (P. eximius, P. chitonoides, P. fabricii, P. peronii and P. phantapus) and an unidentified Psolus sp. from the Emperor Seamount Chain. COI data also confirm its presence in the East Pacific. Our phylogeny challenges the monophyly of Psolus, revealing at least two polyphyletic lineages. The close relationships among North Pacific, amphiboreal, and boreal-Arctic species suggest a North Pacific origin for this clade. Although common near seeps, P. comanchei sp. nov. is not obligate to reducing environments.

Crystal cells in echinoderms have been described in the literature as a type of coelomocyte (immune cell) containing a crystalline structure. Their putative function has been widely ascribed to osmoregulation but this assertion was never robustly tested. In the present paper, a review of crystal cells and crystalline structures provides evidence supporting a different identity and function. First, the same microcrystals can be found either free or encapsulated by a cell membrane (with or without a structure resembling a nucleus). Specifically, they are typically non-encapsulated when found inside tissues of internal organs and encapsulated when free floating in the hydrovascular or perivisceral fluids. Although usually individually packaged, microcrystals were also observed encapsulated in groups of up to four, with or without other particles. Their morphological features, coupled with their chemical and optical properties, match that of microcrystals of uric acid, described in other phyla, including chordates. Two pathways of excretion of these crystallised by-products were evidenced: rejected with sea water out of the respiratory tree and expelled via transrectal coelomoducts among coelomocyte aggregates. Overall, the present synthesis strongly supports that ‘crystal cells’ historically described as a distinct type of coelomocyte in holothuroids are phagocytes that have engulfed uric acid microcrystals generated as waste by metabolic activities.

Senescence and immortality are central biological paradigms. While regenerative capabilities in Deuterostomia are known, the fate of lost and discarded tissues has been presumed terminal. Here, we demonstrate that explanted epidermal, connective, neural, and muscle tissue from the sea cucumber Psolus fabricii (Holothuroidea: Echinodermata) healed and continued to grow in natural, nonaxenic seawater without supplementation for more than 3 years. In experimental trials, these explants, termed LiPfe (living immortal P. fabricii explants) displayed immune activity, cell cycling, tissue reorganization, and absorption of dissolved amino acids, underscoring their active living state. Comparative experiments conducted on explanted tissues from related species demonstrated no equivalent tissue survival, highlighting the unique properties of P. fabricii, which do not have parallels in the current literature. Our findings challenge conventional perceptions of tissue immortality and present a new class of experimental model, free from ethical concerns, with substantial implications for regenerative biology, biomedical research, and tissue engineering.

Discovery of nursery habitats of the sea cucumber Cucumaria frondosa in Qikiqtait (Canadian Arctic) allows the first study of ontogenetic development in wild individuals. Here, podia count, dermal ossicle density, and body wall melanization were examined along with sexual changes across size classes. Age corresponding to major steps of the life cycle was estimated. Individuals developed a gonad at ∼5 mm in length (∼8–12 months old) and reached sexual maturity at ∼80 mm (∼4–5 y old), followed by a period of allometric gonad development until functional maturity was attained at ∼116 mm (∼6–7 y old). Juveniles were uniformly orange while subadults acquired the brown pigmentation after developing their first gonad tissues. The number of podia increased by ∼68-fold before first sexual maturity and thereafter doubled. The smallest juveniles displayed a dense layer of ossicles on the body wall; subsequently, the ossicles thinned out. This study provides the most detailed outline of sexual maturation in wild sea cucumbers, including a clearer picture of age-related phenotypic development, supporting local sustainable harvesting and management practices.

Finfish aquaculture production in marine habitats can alter benthic communities through the sedimentation of fish feces and excess feed. The direct impacts of aquaculture wastes on habitat-forming species such as cold-water corals, and other benthic megafauna, are not well understood. Here, the soft coral Gersemia rubiformis and the sea anemone Aulactinia stella were exposed twice daily to low (5 g C m-2 d-1) or high (10 g C m-2 d-1) concentrations of salmon feed/feces, inorganic sediment (0 g C m-2 d-1), or no sedimentation over 28 days. Behaviour was recorded using timelapse videos and direct observations, and biochemical analyses were conducted post-trial. When exposed to wastes, G. rubiformis spent more time in an expanded state, which may assist with sediment and/or bacterial removal. Similarly, individuals of A. stella exposed to wastes spent more time with their tentacles extended and showed increased eversion of their pharynx, potentially as feeding mechanisms. Though no change in lipid composition was detected because of aquaculture waste exposure in either species after 28 days, a shift in the overall fatty acid composition was identified for G. rubiformis. As well, tracer fatty acids associated with salmon waste (18:2ω6 and 18:1ω9) were elevated in the biochemical profiles of both species following the low and high-waste treatments, suggesting selective assimilation of salmon feed. This study showed behavioural and biochemical effects in both G. rubiformis and A. stella over a short period of exposure to aquaculture wastes, raising important questions regarding the effects of long-term exposure to wastes.

Nearshore areas around Qikiqtait in the Canadian Arctic have been identified as nursery habitats for the sea cucumber Cucumaria frondosa, which is locally consumed and being explored for small-scale commercial fisheries. This study characterized this species' demographics along a depth gradient (similar to 0.5-11.5 m) at three sites inside and adjacent to nursery grounds using a mini-class remotely operated vehicle (ROV). A novel technique involving the superimposition of virtual quadrats was developed to minimize perspective biases for the analysis of images captured obliquely relative to the seafloor. Overall densities at Katak and Kataaluk were a magnitude lower than at Sanikiluaq, suggesting spatial variability in environmental conditions. Smaller individuals (similar to 5 cm) occurred mostly on rubble between 1 and 3 m at Sanikiluaq, larger ones (similar to 10 cm) on gravel at 2-7 m at Kataaluk, and a mix of both size classes occupied gravel, rubble, boulders, and bedrock between 3 and 11 m at Katak. Globally, body sizes tended to increase with depth, evoking cohorts of sea cucumbers undergoing stepwise downward migrations as they grew. This study provides foundational data on C. frondosa around its nursery habitats. It also enhances the usefulness of mini-class ROVs to investigate benthic assemblages in ice-covered areas through community-led initiatives.

Studying morphological abnormalities provides valuable insights into the developmental processes, species adaptability, gene expression, and the potential effect of environmental pressures. Dysmorphic features are well known within several taxa like arthropods but has much less been investigated in others like echinoderms, and specially sea cucumbers (Holothuroidea). The dendrochirotid Cucumaria frondosa (Gunnerus, 1767), which is the most studied and economically important holothuroid species in the North Atlantic, is known to present different colour morphotypes but anatomical variations have rarely been reported. This study tallied dysmorphic features across a sample of more than 900 individuals of C. frondosa examined over five years. About 1.3% and 15.9% of individuals presented non-standard external or internal anatomical characteristics, respectively. Individuals with unusual body plans, including two posterior ends and two cloaca/anuses, or an abnormal number of tentacles, were discovered. Others exhibited supernumerary organs, or organs of unusual shape and size, e.g., ramified/split ambulacra and longitudinal muscle bands, ramified or supernumerary Polian vesicles, hypertrophied madreporites, inter-vesicle protrusions, and hypertrophied circular haemal vessels. These features are described here for the first time in C. frondosa and have not been reported before in holothuroids. The severity of the morphological changes along with their possible drivers and impacts is discussed.

Studies correlating behavior and health are common for vertebrates but are comparatively limited for invertebrates, particularly within the phylum Echinodermata. Behavioral studies in echinoderms are scarce, chiefly focusing on covering and righting behaviors. Given the lack of consensus on the meaning and potential use of the righting time in echinoderms, measured as the time necessary to return to a natural position after being overturned, the present work aimed to establish links between this behavior and reliable but invasive health indicators. Through an experimental infection with the yeast Saccharomyces cerevisiae, we assessed whether the righting time of the sea urchin Echinometra lucunter mirrored a distruption in cellular and humoral immune markers. Our hypothesis posited that for righting time to serve as a reliable health indicator, infected sea urchins should exhibit extended righting times to match any altered immunological responses, analyzed through cellular and humoral immune parameters. The results demonstrated clear alterations in the latter, including elevated total coelomocyte counts and increased proportions of phagocytes, alongside a decreased proportion of vibratile cells and reduced coelomocyte viability. Furthermore, all analyzed biochemical parameters-specifically total protein and echinochrome concentrations, and alkaline phosphatase activity-increased in yeast-infested animals. However, while the righting time of yeast-infected animals showed a tendency to be elevated compared to that of control animals, it did not significantly differ. Consequently, our findings indicate that righting time does not seem to be a sensitive proxy of the health status of E. lucunter, and its application as a stress marker or predictor of sublethal changes in health condition should be approached with caution in this and other echinoderms.

A case of extreme parental care in a sea star was documented using two distinct events during which brooding females of Henricia sanguinolenta prevented a predator (Leptasterias polaris) from eating most of their under-body brood for several days. Clear signs of detrimental effects on the brooding mother included mucous secretion and superficial epidermal damage on the aboral surface of the body. This is to our knowledge one of the rare records of an echinoderm parent placing their physical integrity directly at risk to protect/defend their brood against active predation.

Hard substrata of allochthonous origin, such as ice-rafted dropstones, can provide essential habitat for benthic communities in the polar and subpolar deep sea, acting as "islands" in otherwise finer-grained sedimentary environments. The present study explored the diversity and distribution patterns of morphospecies (msp/mspp) present on dropstones collected at depths of similar to 200-500 m in the Labrador Sea (LAB) and similar to 700-1300 m in Baffin Bay (BAF), respectively spanning subarctic and Arctic regions of eastern Canada. Specifically, the zonation, intraand interspecific interactions, and succession of all colonizers were examined. Based on in-situ images, drop- stones exhibited similar to 94% greater epibenthic megafaunal richness than similar surfaces of the substratum immediately surrounding them. Analysis of three dropstones collected from each of six sites documented a total of 101 sessile and motile taxa spanning 10 phyla. Across sites, bryozoans dominated at all depths and locations (27 mspp, plus 3 dead) followed by poriferans (27 mspp), 19 cnidarians, eight arthropods, eight annelids, five chordates (tunicates), three echinoderms, three molluscs, and one foraminifer. There were 19 mspp that spanned both LAB and BAF, with greater overall richness in the subarctic region (62 vs 26 mspp). A total of 64 sessile mspp occurred above the stone-sediment interface (e.g., cnidarians and poriferans), whereas 22 mspp (mostly bryozoans) occurred at the stone-sediment interface; one morphospecies of polychaete occurred below. The most abundant morphospecies was an arborescent bryozoan, while two encrusting bryozoans covered the most surface area. Eight morphospecies occurred as just one individual or colony per stone, and 35 mspp appeared to maintain an exclusion zone between conspecifics (e.g., tube-dwelling annelids, hydrozoans, and anthozoans). Conversely, in 51 mspp conspecifics occurred abutting one another (e.g., bryozoans and poriferans). Allospecific exclusion zones appeared to occur in 27 mspp (e.g., bryozoans and annelids), whereas 59 allospecifics (e.g., poriferans, cnidarians, and chordates) occurred within touching distance. Secondary colonization (including cases of epibiosis) was observed in 83 mspp, documenting 204 unique pairings of hosts and colonizers. The number and diversity of morphospecies colonizing dropstones in the deep sea of the eastern Canadian Arctic and subarctic support the role of dropstones as oases that facilitate connectivity in an otherwise poorly diversified epibenthic environment.

The study of larval transport and recruitment in the deep sea is crucial to the understanding of species distributions, community assembly, and the potential effects of anthropogenic activity and climate change on the maintenance of biodiversity. This study sought to better understand the role of substratum features in deep-sea larval recruitment at high latitudes. Four settlement frames composed of blocks of different substrata (mesh, plastic, stone, and wood) were deployed for 9 to 13 months at bathyal depths in the Labrador Sea (northeastern Canada). Colonial hydrozoans dominated as recruits, with one taxon (family Campanulariidae) colonizing all substratum types across all geographic sites. Other taxa, including arthropods, octocorals, and other anthozoans recruited only onto specific substrata and consistent microhabitats within them. Overall, higher morphospecies and phylum richness characterized the three-dimensional mesh substratum relative to other substratum types, whereas the complex surface area offered by projections in the plastic substratum had higher densities of individuals or colonies for all morphospecies combined. Wood, offered as a single elongated panel, was the most heavily colonized, whereas both mesh and stone hosted morphospecies not found on any other substratum type. Factors such as geographic location, depth, altitude above the sea floor, and orientation/obstruction of the frame, may have modulated recruitment patterns. These results provide foundational knowledge on larval recruitment patterns and early colonization by opportunistic hard-bottom benthic taxa in a poorly-studied region of the Eastern Canadian deep sea.

As oil and gas exploration expands in deep-sea environments, understanding the impacts of wastes produced by this industry is urgent. One of the main wastes of offshore drilling is the discharge of drill muds, commonly including barite and bentonite clay. Here, we investigated the effects of these two byproducts on the expansion behaviour, mucus secretion and cnidocyte density of the solitary cup coral Flabellum (Ulocyathus) alabastrum. A total of 96 live corals were exposed over 10 days to one of three treatments (barite, bentonite, or barite and bentonite combined) or assigned as an untreated control. Daily waste additions aimed to reach a total sedimentation depth of 6.3 mm (common 'probable no-effects threshold'). Photography was used to monitor behavioural changes and mucus production, and histology was used to assess changes in tentacle cnidocytes. Overall, responses of F. alabastrum in the form of excessive polyp expansion (swelling) and mucus production were more severe under the barite and bentonite combined treatment, followed by barite alone, bentonite alone and lowest/absent in the control. Moreover, elevated nematocyte densities were measured under exposure to the mix of barite and bentonite. However, F. alabastrum returned to baseline metrics during a 10-day recovery period. The results suggest that sedimentation of common drill mud ingredients to <6.3 mm depth can cause observable and non-lethal responses in F. alabastrum, but remain conservative relative to what may be experienced in situ. As the most adverse effects were observed under the barite and bentonite combination treatment (tested together for the first time here), potential synergistic effects of the two should be considered in future research. Understanding long-term consequences, as well as impacts of more abrasive drilling waste (drill cuttings) on F. alabastrum requires further study.

Sea cucumbers paradoxically suffer from being both highly prized and commonly disregarded. As an Asian medicine and delicacy, they command fabulous prices and are thus overfished, poached, and trafficked. As noncharismatic animals, many are understudied and inadequately protected. Despite presenting a rich diversity of life histories, members of this broad taxonomic group (class Holothuroidea) are often managed simply as “sea cucumbers” in fisheries worldwide. One cannot imagine fishes (class Pisces) being given the same universal treatment. Yet this may happen for species of sea cucumber that differ on the same fundamental level as tilapia and tuna. As more sea cucumbers reach an endangered status and wild populations become depleted to the point of collapse, critical questions arise about the relevance of established conservation and governance strategies. This article reviews the main threats faced by exploited sea cucumbers, outlines conservation and governance effectiveness, identifies gaps in knowledge, and explores management and research perspectives in the context of climate change and booming fisheries crime. We stress the perilous state of harvested sea cucumbers globally and the urgent need for action.

The apodid sea cucumber Chiridota laevis has been a documented member of endobenthic marine communities in northern waters for over a century and the rare studies available on its biology identify it as distinctive species and promising model for research. The present study sought to elucidate fundamental aspects of its life history that remained unresolved. Adults were determined to be protandric, with individuals primarily demonstrating solely male or female gametes from winter (close to spawning) to the spring and summer months before undergoing a sex change in the fall months. Additionally, gametes of both sexes reached maturity synchronously in late winter (February to March). In mesocosms, free spawning occurred in February, as the temperature reached ~2.0 °C. The negatively buoyant eggs were encased in a sticky casing and fell to the sediment where they adhered to each other to form a mat on the muddy substratum. The realized fecundity was ~15,000 offspring. Development was lecithotrophic, demersal, and abbreviated, characterized by the absence of a pelagic larval stage. Embryos reached the gastrula stage after about 7 days post fertilization; the calcareous ring appeared at 6 weeks, and juveniles hatched from the sticky casing at 7 weeks, immediately becoming endobenthic. The size of late embryos and juveniles remained similar (~350 μm) until they began actively feeding at about 10 weeks of age. Feeding juveniles more than doubled in size in the first week (740 μm), reached 3.5 mm by year one, and measured up to 11 mm by year two. This growth rate suggests that it may take this species up to 7 years to reach adult size at ~24 mm contracted length.

Biomineralization research in echinoderms has been focused on skeletal structures, which provide strength and protection. Other minerals, specifically extracellular microcrystals, are described here for the first time in echinoderms. Six morphotypes were isolated from a holothuroid and classified into three chemical compounds. Uric acid crystals were associated with fluids from the hydrovascular system, perivisceral coelom and respiratory tree, while calcium carbonate crystals were detected in the epithelium of the respiratory tree and calcium oxalate dihydrate crystals were found in tissues of the cloaca, integument, Polian vesicle and tentacle. Uric acid crystals were mostly non-encapsulated in tissues, whereas, in fluids, they were often encapsulated by phagocytes, alone or in groups, suggesting that they are waste products. Calcium carbonate crystals in the respiratory tree and calcium oxalate dihydrate crystals in the cloaca suggest that they are being expelled from the body. Insofar as calcium oxalate dihydrate crystals could be involved in calcium regulation, we speculate that they might be crystallized and retained in ossicle-associated integumentary tissues and tentacles, which are susceptible to damage and could use them as a calcium reserve to synthesize and repair ossicles. Observations of microcrystals in different holothuroid species examined suggest their ubiquity in the class Holothuroidea and more generally, deuterostomes.

Cucumaria frondosa (Gunnerus, 1767) is the most harvested sea cucumber in the world, with small-scale fisheries being contemplated in the Canadian Arctic. This study assessed regional fluctuations in appearance and nutritional profile of C. frondosa by sampling individuals at three locations in Nunavut (Canada) and subsampling different body compartments. Protein and lipid varied across sites, as did phospholipid and triacylglycerol, the main lipid classes. Mono-unsaturated and poly-unsaturated fatty acids (MUFA and PUFA) dominated over saturated fatty acids (SFA) at each site. Seven essential and eight non-essential amino acids were detected in concentrations varying up to fivefold between sites. Results showed higher lipid content, MUFA, glyceryl ether, and acetone-mobile polar lipid in gonad, triacylglycerol in stomach, PUFA in muscles and stomach, amino acids and phospholipids in muscles, and astaxanthin in muscles and gonad. Ovaries had higher lipid content, glyceryl ether, sterols, and astaxanthin, whereas testes had higher SFA, MUFA, and levels of triacylglycerol, acetone-mobile polar lipids, and free fatty acids. This study suggests harvesting site and traded product itself (different organs), could be tailored to target pharmaceutical, nutraceutical, or food markets. The findings will help design small-scale commercial initiatives by Inuit in support of local consumption (food security) and eventual exports (novel income).