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Sea anemones are often presented as a major component of benthic communities and described as ecologically important in benthic food webs. However, studies on the trophic ecology of deep-sea species are rare. Here, the feeding habits and dietary sources of three species of bathyal sea anemones (Actinostola callosa, Actinauge cristata, Urticina sp.) from the Northwest Atlantic were studied in a multi-faceted approach including stable isotopes, gastrovascular contents, lipid and fatty acids analysis and observations in a mesocosm. Stable isotope analysis showed that A. callosa sits at a slightly lower trophic level than A. cristata and Urticina sp. and that the two latter species rely on different carbon sources at roughly the same trophic level. The gastrovascular cavity contents and mesocosm study revealed that all three species ingest a variety of food items, from inorganic materials to a diversity of metazoans, including whole large prey. Total lipid content varied across species and was highest in Urticina sp. Phospholipids constituted the main lipid class in all three species, with consistently high levels of wax ester storage lipids. All sea anemones were also characterized by high proportions of mono and polyunsaturated fatty acids (MUFA and PUFA) as well as ω3 and ω9 FAs, and strikingly low proportions of 20:4ω6 (ARA). High values of 20:5ω3 (EPA), 20:1ω9 and 22:1ω11(13) evoke a diet centered on zooplankton, with notable particularities. For instance, Urticina sp. had the highest PUFA to saturated FAs ratio, indicative of carnivory. Overall, results suggest that the three sea anemone species occupy different niches in the spectrum of opportunistic polyphagous predation/feeding, with Urticina sp. relying chiefly on more energetic and larger prey and A. cristata targeting smaller zooplankton, foraminifera and particulate food, highlighting that large actinians play diverse roles in benthic food webs.

Among arthropods, pycnogonids are generally considered of minor ecological significance in marine ecosystems. However, the fact that they can host a wide diversity and high abundance of epibiotic organisms suggests that their role in benthic communities may be underestimated. The present study characterized the diversity, dynamics and role of the epibiotic community associated with deep-sea pycnogonids (Nymphon hirtipes). Despite their small size, they hosted a mean of 62 macro-organisms belonging to at least 26 species from 11 different phyla. Foraminifera was the dominant phylum while other phyla, such as Bryozoa, Cnidaria (Hydrozoa), Porifera and Brachiopoda were common. The macro-epibiont burden varied from 1 to 235 organisms per pycnogonid; it was consistent across depths and locations but fluctuated as a function of sex and of the reproductive state in males. Specifically, most colonized individuals were females, which are larger and thus offer more surface for epibionts. Among males, burdens peaked in those carrying larvae. Maximum epibiont burden and coverage was correlated with the cessation of grooming at the beginning of the breeding period. Micro-epibionts consisted of bacterial mats covering most body parts. Several epibionts were estimated to have negative effects on their host (e.g. increasing drag, preventing mating, decreasing limb mobility and impeding feeding). However, because this species dies after reproducing, epibiosis may be considered as a positive trade-off since it may provide food to the mobile juveniles living on the male for several months. Furthermore, epibionts could be used as camouflage during this period. N. hirtipes has been identified as a common component of the benthofauna in the deep sea of the North Atlantic and Arctic Oceans, and the present study indicates that it displays the greatest diversity and burden of associates ever reported among pycnogonids.

In shallow benthic communities, sponges are widely recognized for their ability to contribute to food webs by cycling nutrients and mediating carbon fluxes through filter feeding. In comparison, little is known about filter feeding in deep-sea species and how it may be modulated by environmental conditions. Here, a rare opportunity to maintain live healthy deep-sea sponges for an extended period led to a preliminary experimental study of their feeding metrics. This work focused on demosponges collected from the continental slope of eastern Canada at ~ 1000 m depth. Filtration rates (as clearance of phytoplankton cells) at holding temperature (6 °C) were positively correlated with food particle concentration, ranging on average from 18.8 to 160.6 cells ml −1 h −1 at nominal concentrations of 10,000–40,000 cells ml −1 . Cell clearance was not significantly affected by decreasing seawater temperature, from 6 °C to 3 °C or 0 °C, although two of the sponges showed decreased filtration rates. Low pH (~ 7.5) and the presence of a predatory sea star markedly depressed or inhibited feeding activity in all sponges tested. While performed under laboratory conditions on a limited number of specimens, this work highlights the possible sensitivity of deep-sea demosponges to various types and levels of biotic and abiotic factors, inferring a consequent vulnerability to natural and anthropogenic disturbances.

Specimens of the neogastropod Buccinum scalariforme (60–70 mm shell height) collected between 700 and 1450 m depth along the continental slope of eastern Canada were kept for 4 years in mesocosm settings. Their mating, spawning and development were assessed, thereby generating the first complete life cycle account of a deep-sea gastropod. Egg laying occurred in March and September, with a total of 9 egg masses laid in 2013 and 2015, coinciding with periods of maximum deposition of particulate organic matter (phytodetritus). Oviposition lasted 2–3 days and the female protected the egg mass for ~3 more days until it had hardened. Typically, egg masses contained 50–75 egg capsules, each measuring 5–8 mm in diameter. A capsule contained between 100 and 150 spherical eggs (300–500 µm) of which ≤50 developed into embryos. Potential fecundity calculated from the entire egg mass at spawning was between 1500 and 2250 propagules; it drastically decreased over ~4–5 months of development to an effective fecundity of 30–50 juveniles emerging from the mass (0–2 juveniles per capsule). Development went through early embryonic stages in ~15 days and reached the trocophore in 15–21 days, followed by intracapsular veliger larva (480 µm) and intracapsular pediveliger (~1000 µm) after ~90 days. Completion of development relied on oophagy and adelphophagy. The juveniles hatched at a shell height of 1–2 mm and consumed the capsule membrane. Over 2.5 years, they reached a maximum size of ~8–10 mm shell height at an average of 9.8 µm day −1 . Estimations indicate that B. scalariforme could require between 20 and 50 years to reach maximum adult size. Large gastropods like B. scalariforme are among the most abundant motile benthic invertebrates of the bathyal zone of eastern Canada. Knowledge of their reproductive biology constitutes a first step in assessing their vulnerability and resilience to ever growing anthropogenic pressures, including fisheries, and oil/gas exploration and exploitation.

While reproduction in deep-sea corals remains incompletely understood, there is a particularly crucial shortage of information related to corals living in deep waters of the Arctic Ocean. In the present study, colonies of the deep-sea pennatulacean coral Umbellula encrinus were collected in Baffin Bay (High Canadian Arctic) at bathyal depths between 2006 and 2010. From examination of gamete sizes, maturity levels and densities at several time points, U. encrinus was determined to be a gonochoric species with an equal sex ratio and a broadcast-spawning strategy. Fully mature oocytes measured between 800-950 μm in diameter, consistent with lecithotrophic larval development. Potential fecundity was ∼4200 mature oocytes colony−1 and ∼5300 mature spermatocysts colony−1. Gametogenesis was synchronous between sexes; a single main cohort of oocytes and spermatocysts was seen to increase in size throughout the year. Gametogenetically mature colonies were detected in late June during the earliest possible spring samplings. Spent colonies were detected in July and August. Early stages of gametogenesis appeared in early September shortly after the spawning months and more advanced growth stages occurred in late September and early November, after which time sampling was prevented by ice cover. The spawning season in U. encrinus appears to occur once a year, closely following the disappearance of the ice cover in early spring, when chlorophyll-a in Baffin Bay increases. The initiation of gametogenesis coincides with a period of sustained phytoplankton production and continues until the entire bay freezes over in fall. Since mature gametes were found in both male and female colonies just after the spring melt, gamete maturation likely continues under the ice. Both depth and latitude were shown to impact gamete development and fecundity in U. encrinus, with more advanced and fertile colonies occurring in deeper water and at higher latitudes.

Pycnogonids (sea spiders) are commonly collected at bathyal and abyssal depths all around the world; however, little is known about species from deep-water habitats. The present study explores the life history of Nymphon hirtipes collected in northeastern Newfoundland between 700 and 1450 m depth and monitored in mesocosms for over 2 years. The pycnogonids were found in association with octocorals, hydrozoans and sea anemones. Adult females developed mature oocytes between June and August. Paired mating followed by oviposition occurred between early July and mid-October. Up to three egg masses were brooded by each male. It took a maximum of 4 months for the propagules to hatch from the egg mass. Offspring developed from walking leg-bearing larvae to early juveniles over the next ~5 months before leaving the male’s protection. Mating and oviposition coincided with the highest water temperatures of the annual cycle and dispersal of juveniles occurred in spring, when phytodetritus deposition was high and as ocean temperature rose markedly. All the females died after oviposition and the males ~9 months later, after juvenile dispersal. The sex ratio of mature individuals (~55–60 mm leg span) was 2 males for 3 females. Fecundity was estimated to be 184–288 eggs per adult female. Adults of N. hirtipes were seen feeding on hydrozoan polyps, small sea anemones (Stephanauge nexilis) and nudibranchs. Larvae and early juveniles did not feed while brooded by the male. Upon dispersal, their feeding apparatus became functional and they began feeding on hydrozoan polyps. After 13 months of growth post hatching, the juveniles reached ~21 mm leg span. Curve fitting estimated that ~7 years are required to reach the adult size of 55 mm leg span.

Shallow-water annelids of the genus Ophryotrocha have become a popular biological system for exploring ecological, behavioral, developmental, and toxicological questions. Here we report on the successful maintenance in holding tanks, complete life cycle, and reproductive phenology of a first deep-water representative that could be used as a model species. This Ophryotrocha , which has yet to be formally described, is large (12–16 mm long) and exhibits simultaneous hermaphroditism. Specimens collected off northeast Newfoundland (eastern Canada) between 500 and 1500 m depth were monitored under flow-through laboratory conditions for over three years. They consistently exhibited seasonal feeding from April to February, followed by a reproductive season between February and May. Gametogenesis was initiated in early January and completed in early to mid-February, followed by courtship, which mainly involved pairs of individuals attached head to tail for hours to days. Transparent gelatinous masses containing 80–110 eggs were laid from mid-February to late-March. Propagules developed in the mass to the 1-chaetiger stage and, at an ambient temperature of ~1–4 °C, offspring emerged 30–45 days post-laying. Only ~40–45% of the eggs laid developed to the 1-chaetiger stage, with evidence of adelphophagy. After emerging from the gelatinous mass, 1-chaetiger stages remained aggregated and were guarded by adults for a few days before dispersing. All parents died following the dispersal of their offspring. The new generation reached sexual maturity in 8–9 months and was ready to reproduce the following January–February. A few cases of segmenting adult worms were also observed. Three complete generations developed successively to sexual maturity over the course of this study.

Asteroids (sea stars) can be important predators in benthic communities and are often present in ecologically important and vulnerable deep-sea coral and sponge habitats. However, explicit studies on the trophic ecology of deep-sea asteroids are rare. We investigated the diets of seven species of deep-sea asteroid from the bathyal zone of Newfoundland and Labrador, eastern Canada. A multifaceted approach including live animal observations, stomach content analysis, and stable isotope analysis revealed the asteroids to be either top predators of megafauna or secondary consumers (mud ingesters, infaunal predators, and suspension feeders). The stable isotope signatures of Ceramaster granularis, Hippasteria phrygiana, and Mediaster bairdi are characteristic of high-level predators, having δ15N values 4.4‰ (more than one trophic level) above Ctenodiscus crispatus, Leptychaster arcticus, Novodinia americana, and Zoroaster fulgens. We present strong evidence that corals and sponges are common food items for two of the predatory species, C. granularis and H. phrygiana. During laboratory feeding trials, live H. phrygiana fed on several species of soft coral and C. granularis fed on sponges. Stomach content analysis of wild-caught individuals revealed sclerites from sea pens (e.g. Pennatula sp.) in the stomachs of both asteroid species; H. phrygiana also contained sclerites from at least two other species of octocoral and siliceous sponge spicules were present in the stomachs of C. granularis. The stomach contents of the secondary consumers contained a range of invertebrate material. Leptychaster arcticus and Ctenodiscus crispatus feed infaunally on bulk sediment and molluscs, Zoroaster fulgens is a generalist infaunal predator, and the brisingid Novodinia americana is a specialist suspension feeder on benthopelagic crustaceans. This study provides a foundation for understanding the ecological roles of bathyal asteroids, and suggests that some species may have the potential to be important modulators of deep-sea benthic communities.

This study examined the influence of temporal and spatial factors on the determination of reproductive cycles in selected deep-water echinoderms. The prevalence of inter-individual synchrony in the gametogenesis of three ubiquitous species, Phormosoma placenta (Echinoidea), Hippasteria phrygiana (Asteroidea) and Mesothuria lactea (Holothuroidea) collected off the coast of Newfoundland and Labrador (eastern Canada), was determined. Analyses revealed diverse degrees of gametogenic asynchrony at the scales examined (within trawls, between trawls over similar or different periods, as well as among depths and locations over the same period). Taken as a whole, samples did not show any annual or seasonal patterns, whereas some sets of samples, taken over a particular time period in the same area and at the same depth, revealed well synchronized maturing and/or spawning periods in P. placenta and H. phrygiana. This study presents evidence that determination of reproductive cycles in many deep-sea species may be affected by low sampling resolution inherent to most deep-sea studies. More accurate assessments of reproductive patterns and periodicities may require much tighter collection designs as several species are likely to rely on long-term or transient pairing and aggregation to synchronize their breeding activities.