Holothuria scabra, the sandfish, is more than a high-value aquaculture product. It is one of the animals that keep tropical seagrass beds working. CORE Zones are built on that fact.
Sandfish are among the main large deposit feeders on tropical seagrass beds. They feed on organic matter in the surface sediment, turning it over as they go, releasing nutrients that seagrass takes up, and changing sediment chemistry in ways that research links to healthier seagrass and coral. Heavy harvesting has removed them from much of their range in the Indo-Pacific.
Feeding reworks the surface sediment, airing it, helping prevent the oxygen-poor conditions that harm seagrass roots, and releasing nutrients held in the sediment.
Sea cucumbers excrete nitrogen and phosphorus in forms seagrass can use directly, an important nutrient route in nutrient-poor tropical coastal waters.
Sea cucumber digestion dissolves carbonate sand and raises alkalinity locally, which can help buffer acidification around reefs.
In a field experiment, removing sea cucumbers from around corals led to more coral disease and higher coral mortality.
Seagrass detritus makes up much of the diet of H. scabra in tropical seagrass meadows. The animal and the habitat depend on each other.
Sea cucumbers host a wide range of commensal species and link detritus to the animals that feed higher up the food chain.
"Overexploitation of sea cucumbers is likely to decrease sediment health, reduce nutrient recycling, diminish biodiversity of associated symbionts, and reduce the transfer of organic matter from detritus to higher trophic levels."Purcell, Conand, Uthicke & Byrne, Oceanography & Marine Biology Annual Review, 2016 · Full evidence base →
Dried sandfish, sold as bêche-de-mer, is one of the most valued sea cucumber products, with long-standing demand in Chinese, Japanese and Southeast Asian markets. That demand has outrun what wild populations can sustainably supply, and wild stocks are overfished across the Western Indian Ocean.
Sandfish eat the organic matter that settles naturally on the seagrass beds where they live. The seabed is the feed supply, so costs are mostly juveniles, labour, patrol, processing and logistics.
Sandfish feed on the waste of a healthy, full ecosystem. The better the protected area recovers, the better the stocked animals grow, so conservation and production pull in the same direction.
Ranching in protected seagrass avoids the feed and land limits of most high-value aquaculture. What limits production is the area of healthy, protected habitat, and every new CORE Zone adds to it.
The animal that helps regenerate the seabed also earns the income that pays for its protection. That is why the model is built to pay its own way.