A study of dendrochirotid sea cucumbers with a focus on Cucumaria frondosa and its potential use in integrated multi-trophic aquaculture

Sun, Jiamin (2019) A study of dendrochirotid sea cucumbers with a focus on Cucumaria frondosa and its potential use in integrated multi-trophic aquaculture. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

Sea cucumbers play fundamental roles in marine ecosystems, and they have long been commercially harvested for seafood. In light of stock declines worldwide, research on cold-water suspension-feeding species is expanding. This thesis explores two species from the North Atlantic. The first chapter validates an aging technique in Psolus fabricii, based on the growth rings found in its large calcareous dermal plates. Imaging of plates obtained from juveniles of known age confirmed the annual addition of a layer that extends the plate both vertically and horizontally, generating a pair of dark and light rings that can be used for aging. Wild individuals from shallow inshore areas were aged to a maximum of 28 years and their main morphometrics compared with age. The three other experimental chapters focus on Cucumaria frondosa, which has been commercially harvested for decades in North America and was identified as a potential candidate for aquaculture, especially as a biofilter in integrated multi-tropic aquaculture (IMTA). The locomotor and feeding behaviours, and microhabitat selection (spatial distribution) of C. frondosa in response to various environmental factors were investigated in the laboratory. Sea cucumbers moved away from static conditions and fled the strongest flows, and their tentacle deployment and insertion rates (i.e. feeding rate) increased with flow. The flow regime favoured by C. frondosa was 21-40 cm s⁻¹. Individuals were overall more mobile during the night, whereas no feeding differences were detected between diurnal and nocturnal phases. Gradients in phytoplankton concentration modulated the deployment of feeding tentacles but did not trigger any displacement toward the food source. C. frondosa exhibited a clear preference for substrates composed of bare rocks and rocks with coralline algae and displayed a slight preference for darker substrate backgrounds. Finally, C. frondosa held in effluent water from salmon culture was determined to assimilate the waste, which modulated its biochemical composition; however, its health condition declined, suggesting that it cannot find appropriate or sufficient nutrients for growth and reproduction in these wastes. The findings presented here aim to improve our understanding of the biology and ecology of cold-water suspension-feeding sea cucumbers to guide and assist fisheries management and aquaculture development.

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