WWW.WAS.ORG • WORLD AQUACULTURE • JUNE 2023 47 industry worldwide with average prices ranging from US$ 30-3500/ kg (Purcell et al. 2018). Putting this in perspective, the average price of Atlantic salmon in March 2023 was ~ US$ 10/kg while bluefin tuna was ~ US$ 36/kg (FAO 2023). Thus, inclusion of sea cucumbers into an IMTA system provides a secondary revenue stream of product that does not require an external food source as the fed fish species do. Second, sea cucumbers are a delicacy food item in many Asian cultures. They contain valuable bioactive compounds used for cosmetic and pharmaceutical applications (Purcell et al. 2012). They are also an important food source for many coastal indigenous peoples worldwide. Third, their potential as an organic-detrital extractive organism is somewhat legendary, especially in large tropical species that can bioturbate tens of thousands of kilograms of sediment per km2 area per year (H. scabra, Lee et al. 2018). Species such as A. californicus also may offer another benefit to IMTA systems, such as a reduction in net/cage biofouling at finfish sites1 (Ahlgren 1989, Fig. 2), a problem that usually requires time-consuming and expensive cleaning procedures to tackle. Fourth, sea cucumbers do not appear to negatively interact with other IMTA partner species and very rarely experience disease issues, making them ideal for inclusion in most aquatic farm environments. Given these benefits, many studies are actively exploring IMTA systems with sea cucumber species native to Canada, China, Italy, Japan, Kenya, Malta, Scotland, South Korea and USA, among others. (CONTINUED ON PAGE 48) Sea cucumbers are softbodied, sea-bottom-dwelling marine invertebrates closely related to sea urchins, brittle stars and sea stars, all of which are echinoderms. Many are benthic deposit feeders, creeping along the ocean floor, grazing on organic material (Figs. 1A and 1B). Others are suspension feeders that capture microscopic algae and organic detritus floating in the ocean (Fig. 1C). Compared to well-known and tasty marine finfish and shellfish that are presently cultured—including salmon, oysters, mussels, clams and scallops—sea cucumbers may not seem that impressive, but these unassuming animals have the potential to transform how we farm food in the ocean. Sea Cucumbers and IMTA Integrated multi-trophic aquaculture (IMTA) is a sustainable approach to growing food in water that mimics natural trophic partnerships among organisms to improve productivity and reduce environmental impacts. In a typical marine IMTA system, cultured fish are fed commercial feed. Waste food, faeces and dissolved inorganic nutrients, including ammonia, nitrate, nitrite and phosphate, from the fish are then consumed or absorbed by extractive species, such as shellfish and macroalgae, thus reducing the environmental footprint of the farm. Such an approach can be applied to the culture of freshwater, brackish and marine aquaculture species in open or closed systems, on land or at sea, making IMTA a very practical and cost-effective technique. Deposit-feeding sea cucumbers fit nicely into the IMTA approach for several reasons. First, sea cucumbers are a billion-dollar The Secret Powers of Sea Cucumbers Emaline M. Montgomery and Christopher M. Pearce FIGURE 1. Three commercial species of sea cucumbers with different feeding modes. A – giant red sea cucumber Apostichopus californicus, deposit feeding, Northeast Pacific Ocean. B – sandfish Holothuria scabra, deposit feeding, Southwest Pacific Ocean (Photo: Jean-Francois Hamel, SEVE). C – orange-footed sea cucumber Cucumaria frondosa, suspension feeding, North Atlantic Ocean.