AbstractSwimming propagules (embryos and larvae) are a critical component of the life histories of benthic marine animals. Larvae that feed (planktotrophic) have been assumed to swim faster, disperse farther and have more complex behavioural patterns than non-feeding (lecithotrophic) larvae. However, a number of recent studies challenge these early assumptions, suggesting a need to revisit them more formally. The current review presents a quantitative analysis of swimming speed and body size in planktotrophic and lecithotrophic propagules across five major marine phyla (Porifera, Cnidaria, Annelida, Mollusca and Echinodermata). Results of the comparative study showed that swimming speed differences among ciliated propagules can be driven by taxonomy, adult mobility (motile vs sessile) and/or larval nutritional mode. On a phylogenetic level, distinct patterns emerge across phyla and life stages, whereby planktotrophic propagules swim faster in some of them, and lecithotrophic propagules swim faster in others. Interestingly, adults with sessile and sedentary lifestyles produce propagules that swam faster than the propagules produced by motile adults. Understanding similarities and differences among marine propagules associated with different reproductive strategies and adult lifestyles are significant from ecological, evolutionary and applied perspectives. Patterns of swimming can directly impact the dispersal/recruitment potential with incidence on the design of larval rearing methods and marine protected areas.

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Literature records of large actiniid sea anemones along the Atlantic coast of Canada currently include three Urticina species: U. felina, U. fecunda and U. crassicornis. The findings of the present morphological and molecular study conducted in eastern Newfoundland suggest that U. felina is often misidentified, and that this region may only harbor two similar-looking species: U. crassicornis and Cribrinopsis similis. The latter were identified using genetic analysis and comparison of key characters with the same species collected from other regions of the North Atlantic (Barents Sea), whereas no specimen corresponding to U. felina was found. Mitochondrial gene sequences of U. crassicornis, U. felina and C. similis were identical except for a different haplotype found in several specimens of U. crassicornis (with one nucleotide substitution), in contrast to five nucleotide insertions in 16S rRNA fragments of U. fecunda. Phylogenetic analysis based on three mitochondrial and two nuclear gene fragments revealed that the most closely related species among the above-mentioned were U. crassicornis and U. felina, nevertheless U. fecunda groups in the same clade as the Urticina species.

Velvet shell, Velutina velutina (Müller, 1776), is a specialist predator of ascidians, like other members of the gastropod family Velutinidae. Globally, invasive ascidians have become problematic, ecologically and economically, yet ecological knowledge of velutinids remains limited. This study outlines the life history and feeding ecology of V. velutina in eastern Canada based on laboratory work complemented by field observations. The life history of V. velutina is closely linked with ascidians, which serve as prey and protection for their egg capsules. Egg capsules were embedded within tunics of Aplidium glabrum (Verrill, 1871) and Ascidia callosa Stimpson, 1852, with a preference for the latter. Seasonal behavioural shifts were consistent annually and corresponded with seawater temperature cycles. Feeding dominated during the coldest months (January–May), growth occurred as water temperature increased to the annual maximum (June and July), transitioning to mating during the warmest period (July–August), and egg capsule deposition dominated as water temperature declined (November–January). Larvae hatched between January and July after 2–4 months of development. Velutina velutina preyed on all ascidian species presented during this study, including golden star tunicate, Botryllus schlosseri (Pallas, 1766), and vase tunicate, Ciona intestinalis (Linnaeus, 1767), two non-indigenous species, although solitary species were preferred.

Swimming behaviours and sensory abilities of early pelagic stages play a prominent role in the life history and ecology of sessile/sedentary benthic species, with implications for settlement, recruitment and dispersal. Light is a particularly important driver of navigational behaviour in the ocean, as a signal of key habitat characteristics (e.g., depth, shelter). Work to date on phototaxis has largely focused on planktotrophic larvae that feed during development, and much less on the larger lecithotrophic larvae that rely on maternal provisions (yolk). It remains unclear how responses to light might differ among ciliated propagules of different sizes and nutritional modes. The present study explored if/how phototactic responses are modulated by ontogeny (from embryo to larva), nutritional mode and light colour (wavelength) in ciliated propagules using four co-occurring species of echinoderms: the sea stars Asterias rubens and Crossaster papposus, the sea urchin Strongylocentrotus droebachiensis and the sea cucumber Cucumaria frondosa. Two types of behavioural responses to stimuli (white, red, and blue light) were examined: 1) taxis when the light stimulus was placed at one end of the chamber (net movement towards or away from the light stimulus) and 2) activity level, using a suite of swimming metrics, under uniform illumination. All four species consistently displayed some level of photosensitivity to white light and responses varied intra- and interspecifically. When the stimulus was red or blue light, planktotrophs modified their phototactic responses in a species- and stage-specific manner, while lecithotrophs generally displayed responses without a clear net direction. Swimming speeds displayed stage and species-specific variation under constant red or blue light, but swimming trajectories were consistently straighter under red light, resulting in greater displacement. Taken together, the results suggest that propagules of species with different life-history strategies respond to light stimuli in distinctive stage-wise manners. Interestingly, ontogenetic patterns were not conserved within nutritional modes or taxa. Further investigations of species-specific responses to light might help clarify its roles, in combination with factors such as buoyancy and gravity, in the ecology of propagules of benthic invertebrates.

Sexual dimorphism has been reported in all extant echinoderm classes except crinoids, but has never been examined from a phylogenetic, biogeographical, or life-history perspective. This review provides a literature survey of sexual dimorphism in holothuroids and uses this dataset to analyze putative drivers. Sexually dimorphic genital papillae were found in Persiculida and Dendrochirotida but not in other holothuroid taxa. No planktotrophic species (feeding larvae) had known genital dimorphism, though many lecithotrophs (non-feeding larvae) displayed clear morphological differences between male and female papillae. Males with genital dimorphism had digitate or extensible papillae while females had unbranched papillae. Extensible papillae were common among males in brooding species, suggesting an adaptive advantage for certain reproductive strategies such as sperm transfer or pseudo-copulation. Digitate papillae bearing many gonopore openings were common among free-spawning, lecithotrophic males (similar to 80% of species) and may serve to disperse sperm into the water column. Finally, we found that external dimorphism of the genital papillae in a case study of the dendrochirotid Cucumaria frondosa (Gunnerus, 1767) provided a reliable method of sex determination. These results suggest that genital dimorphism among dendrochirotid sea cucumbers is widespread and may facilitate determination of sex in the field where sacrificing animals is not practical.

While developmental strategies can modulate the dispersal and recruitment of marine benthic species, the significance and drivers of propagule motility throughout ontogeny remain incompletely understood. Species with lecithotrophic (non-feeding) development are rarely studied, despite their predominance in some taxa, including echinoderms. Quantification of the swimming capacity (i.e. speed and trajectory) of early life history stages and its variability with environmental factors is required to improve the ability to predict population connectivity and assess trade-offs associated with complex life histories. In general, lecithotrophic larvae of echinoderms are ascribed weak swimming abilities relative to planktotrophic larvae, although explicit measures are scarce. Here, we explored selected metrics of swimming capacity in four co-occurring species of North Atlantic echinoderms displaying different types of pelagic development: planktotrophs represented by the sea star Asterias rubens and the sea urchin Strongylocentrotus droebachiensis, and lecithotrophs represented by the sea star Crossaster papposus and the sea cucumber Cucumaria frondosa. Swimming was characterized in still water based on the horizontal speed and path straightness of early life-history stages, from late blastula (hatched embryo) to late-stage larva. We tested the hypotheses that swimming capacity of propagules increases with progression through developmental stages and with increasing seawater temperature. Swimming speed increased with ontogeny in two of the four species (A. rubens and C. papposus) and with temperature in all species, although the effects of temperature were not uniform across life stages. The fastest swimming speeds across all species and temperatures were recorded in lecithotrophic propagules (i.e. max speed 1.2 mm s− 1 in the brachiolaria of C. papposus), whereas propagules of species with planktotrophic development displayed faster relative speeds (body lengths s− 1). Relative speeds increased with temperature in all tested species except C. papposus. Swimming paths typically increased in straightness from early to later developmental stages, and also became straighter with increased temperature in most species, except in C. papposus where they became more circular and complex. In general, planktotrophic and lecithotrophic propagules had similar swimming capacities when tested at the same level of increased temperature, though several stage-specific differences were detected; propagules of species with planktotrophic development had greater relative speeds at the gastrula stage and greater path-corrected speeds at the larval stage. Swimming paths and swimming speeds were similar between propagules of species with planktotrophic development and lecithotrophic development, suggesting that phylogenetically conserved, ontogenetic patterns of swimming capacity (seen here between two sea stars) may supersede the contribution of larval nutritional mode.

Egg pigmentation is proposed to serve numerous ecological, physiological, and adaptive functions in egg-laying animals. Despite the predominance and taxonomic diversity of egg layers, syntheses reviewing the putative functions and drivers of egg pigmentation have been relatively narrow in scope, centring almost exclusively on birds. Nonvertebrate and aquatic species are essentially overlooked, yet many of them produce maternally provisioned eggs in strikingly varied colours, from pale yellow to bright red or green. We explore the ways in which these colour patterns correlate with behavioural, morphological, geographic and phylogenetic variables in extant classes of Echinodermata, a phylum that has close phylogenetic ties with chordates and representatives in nearly all marine environments. Results of multivariate analyses show that intensely pigmented eggs are characteristic of pelagic or external development whereas pale eggs are commonly brooded internally. Of the five egg colours catalogued, orange and yellow are the most common. Yellow eggs are a primitive character, associated with all types of development (predominant in internal brooders), whereas green eggs are always pelagic, occur in the most derived orders of each class and are restricted to the Indo-Pacific Ocean. Orange eggs are geographically ubiquitous and may represent a 'universal' egg pigment that functions well under a diversity of environmental conditions. Finally, green occurs chiefly in the classes Holothuroidea and Ophiuroidea, orange in Asteroidea, yellow in Echinoidea, and brown in Holothuroidea. By examining an unprecedented combination of egg colours/intensities and reproductive strategies, this phylum-wide study sheds new light on the role and drivers of egg pigmentation, drawing parallels with theories developed from the study of more derived vertebrate taxa. The primary use of pigments (of any colour) to protect externally developing eggs from oxidative damage and predation is supported by the comparatively pale colour of equally large, internally brooded eggs. Secondarily, geographic location drives the evolution of egg colour diversity, presumably through the selection of better-adapted, more costly pigments in response to ecological pressure.

Sea cucumber fisheries have existed for centuries, driven primarily by the Chinese markets. In recent decades, overfishing has severely depleted commercial sea cucumber populations worldwide. Consequently, a growing number of countries are becoming interested in developing aquaculture programs. Every year billions of larvae and millions of juveniles are successfully grown in aquaculture facilities and new initiatives are booming. Here we introduce briefly the main species that have so far been successfully cultivated: Apostichopus japonicus, Holothuria scabra and Isostichopus fuscus. We describe common techniques for the culture of larvae and juveniles and outline some of the main challenges of this industry.

Various aspects of reproduction were studied in three deep-sea octocorals belonging to the order Alcyonacea that co-occur at bathyal depths on the continental edge and the slope of eastern Canada. The main goals were to expand knowledge of deep-water heterotrophic corals and ascertain whether reproductive strategies could explain the known patterns of occurrence. Anthomastus grandiflorus is a gonochoric species with a female-biased sex ratio that exhibits internal fertilization and brooding of planula larvae. Conversely, Primnoa resedaeformis and Keratoisis ornata rely on broadcast spawning and external fertilization; their sexuality remains undetermined as spermatocysts were not found. In P. resedaeformis , the presence of mixed size classes of oocytes in samples from all months, depths, and locations studied suggests continuous oogenesis or overlapping development of oocyte cohorts, indicative of a gametogenic cycle spanning more than a year. No evidence of periodicity was found in this species, although it could have been masked by the striking bathymetric variation in potential relative fecundity (oocytes polyp −1 ). The two other octocorals displayed a clear annual breeding pattern. Spawning in K. ornata and larval release in A. grandiflorus occurred in late summer and fall, respectively, possibly in response to environmental factors, as supported by shifts in the reproductive peak of A. grandiflorus across latitudes. The three species are presumed to share a nonfeeding larval mode, and data on their reproductive potential do not present any striking disparities. Published data on bycatches and video surveys in Atlantic Canada indicate that the gonochoric brooder A. grandiflorus is more widely distributed than the two free spawners, P. resedaeformis and K. ornata , which is contrary to common dispersal potential paradigms.

P>Biological traits of the sea cucumber Cucumaria frondosa (Gunnerus) relevant to both ecological and management perspectives were investigated in the Newfoundland region. Abundance, size and fitness of adults were maximal on hard substrates. Larvae settled similar to 5 weeks post-spawning and juveniles reached a maximum length of 6 mm after 24 months. Additional size classes of sea cucumbers kept under natural environmental conditions exhibited slow seasonal growth attuned to phytoplankton blooms, indicating that similar to 25 years may be required to reach market size. Juveniles of the predator sea star Solaster endeca (L.) readily fed upon 1.5-2 mm long sea cucumbers. Predation rates on adult C. frondosa by adult S. endeca were modulated by temperature and biased towards injured specimens, suggesting that trawling may exacerbate predation pressure. The combination of slow growth and high predatory pressure enhanced by fishing activities emphasises the need for precautionary management of this emerging fishery in Atlantic Canada.

Growth rate (linear skeleton extension) was determined in live specimens of the deep-sea cup coral Flabellum alabastrum (Anthozoa: Flabellidae) collected between 600 and 1,200 m off insular Newfoundland (eastern Canada) and kept under laboratory conditions for over 2 years. Smaller individuals grew faster (~5 mm year−1) than larger ones (~1 mm year−1). Seasonal variations in extension rates and qualitative appearance of the growth bands were recorded, with maximum extension occurring in late summer and early fall during maxima in seawater temperature, zooplankton levels, and deposition of suspended detritus. Estimates from a growth model indicate that the largest individuals of F. alabastrum (~43 mm calyx height) are at least 45 years old.

The present contribution aims at describing a disease that affects auricularia larvae of the holothuroid Isostichopus fuscus farmed in a land-based system along the coast of Ecuador. During the early stages of the disease, opaque cells become visible around the digestive tract of the larvae, soon followed by the collapse of the intestine and stomach. In worst cases, the digestive tract completely shrivels up and disappears, preventing the larvae from feeding. When it occurs, the infection affects 90-100% of the larvae and is usually fatal. Optic microscopy, SEM and TEM indicate that the agent of the disease is an amoeboid protozoan that enters through the body wall and the digestive tract. The protozoans are presumed to feed on the intestinal contents and/or tissues, typically causing the death of the larvae. A close monitoring and the use of environmental parameters allow the survival of a small proportion of the culture.

Specimens of the pearlfish Carapus mourlani (Carapidae) were observed for the first time in association with the sea cucumber Isostichopus fuscus (Holothuroidea: Echinodermata) along the coast of Ecuador. Out of 4345 sea cucumbers collected from various depths between 5 and 60 m, 12 harbored a pearlfish either in the coelomic cavity, the respiratory tree, or the digestive tract, yielding a prevalence of ca. 0.0028. The presence of C. mourlani appeared to be detrimental to the holothurian host in some cases. Side effects resulting from coelomic cavity infections included less advanced gonad maturity (reduced gonadal tubule diameter and length, lower ratio of mature oocytes) and a significant proportion of necrotic and shriveled gonadal tubules, devoid of gametes. Aside from discussing this evidence, the present paper briefly describes the biology of the pearlfish, its relationship with the host, and its daily activity cycle.

This paper presents evidence of a commensal association between an opisthobranch (Plakobranchus ocellatus) and a sea cucumber (Holothuria atra). Field observations revealed that occurrences of P. ocellatus specimens and egg filaments were much more frequent on the body wall of H. atra than oil that of two other holothurian species living in the same habitat. Roughly 95% of H. atra were colonized by P. ocellatus during the night, which corresponds to the active period of H. atra and the resting period of P. ocellatus. The proportion decreased to ca. 21% in the daytime when sea Cucumbers are resting and most opisthobranchs are foraging. Laboratory trials confirmed the daily pattern of association and the fact that P. ocellatus lay their eggs oil the body wall of H. atra. Furthermore, multiple-choice experiments showed that ca. 71% of P. ocellatus favoured H. atra, whereas only ca. 9% colonised other species of sea cucumber. Because H. atra is known to exude toxic chemicals that deter several species of invertebrates and fishes, the opisthobranch may use the sea cucumber as a refuge against predators and as a secure spawning ground.

Summary Holothurians are among the most commercially valuable echinoderms for which successful spawning induction under laboratory conditions is still difficult to obtain on a reliable basis. The present study demonstrates that the transfer of perivisceral coelomic fluid (PCF) can be used as a reliable tool to induce spawning in mature individuals. PCF collected from holothurians that had been in the typical spawning posture, without shedding gametes, for ca. 20 min triggered spawning in 71 to 100% of conspecifics. The individuals responded to the injection of a 2–3 ml aliquot by displaying the spawning posture within 30–62 min and by massive gamete broadcast 57–83 min later. The results varied according to the time of PCF collection with respect to the spawning activity of the donor and the amount of PCF injected. The inductive substance was found not to be sex—specific since positive responses were observed in individuals of the same or opposite sex as the donor. The PCF of a spawning donor was also active when added to the surrounding seawater, as it induced the typical posturing in 47–65% of mature individuals and subsequent gamete release in 20–31% of them less than 85 min later. PCF collected from immature or non—spawning individuals did not induce spawning. Although most experiments were performed with Bohadschia argus, similar results were obtained with B. marmorata, Holothuria leucospilota and H. atra. Inter—specific trials were also successful, inferring that the chemical involved is not species—specific. Nonetheless, PCF from spawning asteroids and echinoids did not induce spawning behaviour or gamete release in holothurians. The results showed that holothurian PCF acts as a carrier of inductive substances during spawning. Its efficacy even when diluted in seawater could partly explain the epidemic arid synchronous spawning observed in some holothurian populations.

The tropical holothurians, Holothuria leucospilota, Bohadschia argus and B. marmorata responded to tactile stimulation by expelling Cuvierian tubules in proportion to the intensity of the stimulation. They were able to target the stimulated area with variable success depending on the location of the stimulus, Field surveys showed that 2.3-6.1% of H. leucospilota presented signs of having recently used their Cuvierian tubules and laboratory experiments revealed that they released tubules in response to several natural predators. The tubules did not adhere nor cause any distress to fish, but proved effective in discouraging attacks. Crabs, molluscs and echinoderms were entangled and also efficiently repelled. H. leucospilota without tubules were wounded and even killed by predators that were usually discouraged by tubule discharge. Conversely, after having induced the release of tubules once, 96% of the predators placed in the presence of H. leucospilota three days later remained at a distance. Released tubules that did not adhere to any surface were quickly retracted, while regeneration of a complete set of tubules took 15-18 days. The release of Cuvierian tubules by tropical holothurians therefore appears to be a sensitive defence mechanism. Data on H. leucospilota further suggest that they are readily used against predators in the field.