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Although hydrostatic pressure is one of the most prominent abiotic drivers of faunal bathymetric ranges, it is one of the least understood. To better understand hyperbaric constraints on depth distributions, we explored responses to high pressure of adult echinoderms from eastern Canada. The sea urchin Strongylocentrotus droebachiensis, the sea star Leptasterias polaris and the sea cucumber Cucumaria frondosa were exposed to various pressures within and beyond their known bathymetric distribution (i.e. surface pressure; pressure at the midpoint in bathymetric distribution; pressure at twice the maximum depth in the species bathymetric distribution) for different durations (24 h, 72 h, 9 days). Survival was compromised by exposure to the highest pressure levels, with the sea urchin exhibiting the highest mortality. After 72-h exposure, mortality was observed for sea urchin and sea cucumber individuals while all sea star individuals survived. Following 9-day exposure of sea star individuals to high pressure, 100% mortality occurred. Exposure to pressures typical of natural distributions had little effect on the selected health and motor metrics. Pressures atypical of natural ranges negatively affected the motor functions of all species, irrespective of exposure duration. During and after 24-h exposure, feeding was reduced in sea urchin and sea cucumber individuals, but was unchanged in sea star individuals. Overall, there were no clear signs of acclimation to high pressure following sustained periods of exposure in any species. These results highlight constraints applied by hydrostatic pressure beyond current bathymetric ranges on life-sustaining behaviours in echinoderms. The potential of long-lived echinoderms to survive downward migration to greater depths is species-specific, suggesting there may be winners and losers in the face of near-future climate-driven migration patterns.

Understanding the trophic ecology of deep-sea communities provides valuable insight into deep-water ecosystem functioning, and can help inform fisheries management and conservation initiatives. However, few deep-sea food webs have been studied so far in the Northwest Atlantic. Here, stable isotope, gut content, and morphometric analyses were combined to explore trophic relationships in a deep-water fish assemblage off eastern Canada. While a weak depth effect was found on the isotopic composition of the species analyzed, isotopic and dietary records revealed the existence of two main, strongly coupled trophic pathways. The pelagic pathway either comprised pelagic fishes (e.g., meso- and bathypelagic species), primarily feeding on zooplankton and fish, or benthopelagic predators that showed a more pelagic-oriented diet. Such fishes displayed the lowest values of stable N and C isotope ratios. In contrast, demersal fishes representing the benthic trophic pathway had significantly higher values of δ15N and δ13C, and a taxonomically more benthic-oriented and diverse diet. Furthermore, smaller body sizes, larger mouths, and adaptations (e.g., bioluminescent structures and lures) prevailed in the pelagic species, consistent with living in a relatively food-poor environment. The largest average body sizes were found in the demersal fishes suggesting enhanced food intake and growth investment for the species. Only juvenile individuals of threatened species, such as Coryphaenoides rupestris and Rajella fyllae were caught, providing evidence of the vulnerability of such species to commercial fishing.

The deep-sea pennatulacean coral Anthoptilum grandiflorum exhibits a cosmopolitan distribution and was recently determined to serve as habitat for other invertebrates and fish larvae in the northwest Atlantic. Colonies collected at bathyal depths between 2006 and 2010 in eastern Canada were analysed to determine their fecundity and characterize spatial and temporal trends in their reproductive cycle. Anthoptilum grandiflorum is a gonochoric broadcast spawner with a sex ratio that does not differ significantly from equality (although one hermaphrodite colony was observed). In male colonies, all the spermatocysts synthesized become mature over the annual cycle, while only ~21 % of the initial production of oocytes reaches maturity in female colonies. Female potential fecundity based on mature oocytes just before spawning was on average 13 oocytes polyp−1; male potential fecundity was 48 spermatocysts polyp−1. The spawning period of A. grandiflorum differs between geographic regions, from April (in southern Newfoundland) to July (in Labrador), closely following regional spring phytoplankton blooms after accounting for the deposition of planktic detritus. Release of oocytes by a live colony held in the laboratory was recorded in April 2011, coincident with field data for similar latitudes. Seawater temperatures at the time of spawning were around 3.6–4.8 °C in all regions and in the laboratory. Early stages of gametogenesis were detected in colonies collected shortly after the spawning season, and early and late growth stages occurred successively until December. Mature colonies were observed between April and July (depending on latitude). The diameter of mature oocytes (~1,100 μm maximum diameter) is consistent with lecithotrophic larval development.

This study developed an objective quantitative method for detecting small-scale temporal or spatial differences in gametogenesis in echinoderms. The method was applied to conventional monthly samples of the planktotrophic brittle star, Ophiopholis aculeata, collected at a single site in Newfoundland (eastern Canada) at 10–15 m depth. The samples were analysed to determine gonad index, oocyte size and gonadal stage using histology. The maturity stage index (MSI) was developed to integrate a measure of brittle star size (disc diameter), oocyte size and oocyte density. The MSIs ranged from 0 to 800 and had significantly different means among the four gametogenic stages (early growth, growth, mature and spent). The MSI was more sensitive in revealing significant differences between consecutive stages than any of its individual constituents. The MSI was also applied to gametogenic data from the lecithotrophic holothuroid, Mesothuria lactea, again revealing significant differences between successive oogenic stages. This method is expected to be useful in field and experimental studies of gametogenesis in echinoderms (and possibly other taxa), where it is important to detect not just the timing of annual peaks in reproduction but small differences in reproductive status among individuals or populations (e.g. from different habitats or feeding regimes).

The patterns of genetic diversity and connectivity were investigated in Cucumaria frondosa, the most abundant sea cucumber in the North Atlantic, to assist in the management and conservation of this ecologically important marine invertebrate, which is the target of an emerging fishery. Mitochondrial DNA COI sequences of 334 C. frondosa were obtained and analyzed, mainly from its western North Atlantic range, where the commercial fishery is being developed, with complementary sampling in the mid- and eastern North Atlantic. Analysis of molecular variance showed no significant (P > 0.05) differences among subpopulations in the western region suggesting that it constitutes one panmictic population. The same analysis showed low, but significant differences between eastern and western Atlantic populations. Coalescent analyses using isolation with migration models and a Bayesian skyline plot indicated historical divergence and a general increase in population size prior to the last glacial maximum and highly asymmetric gene flow (nearly 100 times lower from west to east) between sea cucumbers from North America and Norway. Results suggest that subpopulations of C. frondosa within the western North Atlantic have been highly connected. We propose that aided by the high-connectivity local subpopulations can recover rapidly from natural (i.e., ice ages) or anthropogenic (i.e., overfishing) population declines through recruitment from deep refugia.

Increasing threats to deep-sea corals highlight the need to expand knowledge of these taxa so that conservation measures can be developed. The present study focused on the reproductive patterns of the deep-sea solitary coral Flabellum angulare. A series of samples (n = 398) collected in 2006–2008 in the northwest Atlantic at depths of 925–1,430 m revealed that gametogenesis was synchronous among males and females and fluctuated seasonally. Initiation of gamete synthesis was estimated to be in August–September and spawning in June. Further analysis and daily monitoring of 30–60 individuals maintained in a flow-through mesocosm showed that gamete release occurred in March–June with a peak in May. Release of oocytes coincided with rising seawater temperatures and high deposition rates indicative of elevated water column productivity. Oocytes (900–1,200 μm diameter) were released through the oral cavity, generally in bundles of 3–5 surrounded by mesenterial filaments and attached to a thread (30–50 mm long). As oocytes became free in the water column, ovulation occurred followed by fertilization. Eggs/embryos initially remained on the tentacles of the spawner before either falling onto the substratum or floating to the surface. The embryos developed into planula larvae measuring 2–3 mm in length within about 24 h. Together, these findings shed new light on the strategies used by deep-sea corals to maximize their reproductive success.

The present study examined the mode and timing of reproduction of poorly understood deep-water octocorals and the environmental factors that may influence their reproductive patterns. Data on reproductive characteristics of the octocoral Drifa glomerata (Alcyonacea: Nephtheidae) collected between 2004 and 2007 at ca. 100–330 m depth off Newfoundland and Labrador (eastern Canada) were compared among years, months and depth ranges. No male gonad was ever observed during the study. The ratio of fertile colonies possessing large pinkish polyps with oocytes/planulae was >50% throughout the year. The number of brooded planula larvae within a single fertile polyp varied between 1 and 10 for a total of approximately 40–3,000 in a whole colony. The size of oocytes and/or planulae was consistently greater in the polyps than in the branchlets, indicating that the development pathway of oocytes to planulae is from the branchlets to the polyps. Although larval production seemed to persist year round, the onset of major planulation events occurred in December–January of two consecutive years, when large mature planulae were released in correlation with the first increase of photoperiod and maximum temperature at 150 m. A second peak in planulation between April and early June followed the phytoplankton bloom. Seasonal trends were more apparent in colonies from

Combining field and laboratory work, this study investigated the reproductive cycle, aggregative behavior, spawning periodicity, development and early growth of the sea star Henricia lisa living at bathyal depths off eastern Canada. Marked differences were found between individuals from ~1,300 and ~600 m deep. The former had a male biased sex ratio and an aperiodic reproductive cycle, whereas the latter displayed an equal sex ratio and a biannual breeding pattern. Furthermore, the maximum size was larger and female fecundity roughly five times higher in shallower compared to deeper populations. In the tanks, aggregative behavior was recorded twice a year during the summer and winter breeding periods. The onset of aggregations and spawning coincided with a temperature of 3–4°C. Males spawned first and females typically responded inside 30–60 min. Between 12 and 20 eggs were retained to be brooded under the arched arms of the female, whereas the remainder were broadcasted and developed without parental care. The fertilized eggs underwent a first cleavage after 12 h, reached the brachiolaria stage in 1 month, became juveniles within 3–4 months and reached ~ 4 mm in diameter after 14–17 months of growth. The embryos and juveniles developed at the same rate whether brooded or not, and development of winter cohorts was typically slower due to lower prevailing temperatures. This study of H. lisa provides the first evidence of lecithotrophy in a seasonally breeding deep-sea echinoderm and of brooding in a deep-sea asteroid.

Samples of Echinarachnius parma (Lamarck), collected during summer 1988 from three sites along the eastern coast of Canada (the northern Gulf of St. Lawrence, Chaleur Bay and the Bay of Fundy), showed sexual dimorphism in the shape of the oral surface in addition to marked changes in the camber of the aboral surface related to the strength of wave and current activity. The oral surface is more concave in males than in females. The dimorphism develops as individuals become sexually mature and is pronounced for individuals measuring >4 cm in diameter. Associated with this shape difference, the volume of females is greater than for males, and this corresponds to the larger size attained by the ovaries compared to the testis. Shape differences between males and females are rare in echinoderms, and E. parma is the first species for which the sexes can be separated with a high degree of accuracy (>80%) on the basis of shape.