Ecological roles of exploited sea cucumbers

Sea cucumbers (Echinodermata: Holothuroidea) are large and abundant members of marine benthic communities. Overexploitation worldwide has raised concern because they have important functions within ecosystems. The ecological roles of commercially exploited sea cucumbers (Aspidochirotida and Dendrochirotida) are reviewed here, focusing on recent literature. Of the more than 70 species commercially exploited, at least 12 regularly bury into sand and mud, playing major roles in bioturbation. Most aspidochirotids are deposit-feeders, reducing the organic load and redistributing surface sediments, making them bioremediators for coastal mariculture. Sea cucumbers excrete inorganic nitrogen and phosphorus, enhancing the productivity of benthic biota. This form of nutrient recycling is crucial in ecosystems in oligotrophic waters such as coral reefs. Feeding and excretion by sea cucumbers also act to increase seawater alkalinity which contributes to local buffering of ocean acidification. Sea cucumbers host more than 200 species of parasitic and commensal symbionts from seven phyla, thereby enhancing ecosystem biodiversity. They are preyed on by many taxa, thereby transferring animal tissue and nutrients (derived from detritus and microalgae) to higher trophic levels. Overexploitation of sea cucumbers is likely to decrease sediment health, reduce nutrient recycling and potential benefits of deposit-feeding to seawater chemistry, diminish biodiversity of associated symbionts, and reduce the transfer of organic matter from detritus to higher trophic levels. Ecosystem-based fisheries management needs to consider the importance of sea cucumbers in marine ecosystems and implement regulatory measures to safeguard their ecological roles.