There has been recent interest in Washington State, USA in the culture of the California sea cucumber (Apostichopus californicus) for both wild-stock enhancement and as an aquaculture resource. The species is a good candidate for Integrated Multi-Trophic Aquaculture (IMTA), where the animals are supported entirely on the excess organic waste from existing floating aquaculture operations (e.g. bivalves or finfish). To determine how A. californicus would perform when held beneath a mussel aquaculture site, a field study was carried out in Totten Inlet, WA. Enclosures with different densities of sea cucumbers were deployed beneath existing M. galloprovincialis aquaculture rafts. The effects of A. californicus density on growth rate was measured, and the effect of cucumber presence on deposition of nitrogen, carbon, and total organic matter (TOM) within enclosures was determined.
During the summer and fall of 2020, sea cucumber were placed at two sites at two different densities in Totten Inlet, WA. At the first site, 12 plastic oyster cages 56 cm (L) × 56 cm (W) × 18 cm (H) were modified to hold treatments of 2 and 4 cucumber/.30 m² (6 and 12/m²). These cages were hung six meters below floating M. galloprovincialis rafts along with an equal number of empty cages. A second “Control” site was placed 250 m away from raft enclosures in a similar configuration. Bi weekly measurements were taken throughout a 3-month period.
At the end of the study there were no significant differences for sea cucumber growth (mass) between different density cages (p < .05). TOM was significantly higher under the raft, but was not predicted by cucumber density (p<.05). Carbon and Nitrogen values significantly decreased after out plant, and were higher under the raft site, but were not affected by sea cucumber density (p<.05) (Table 1, Fig. 1). These results suggest that while C and N values were comparatively higher under mussel aquaculture in late summer, the presence of sea cucumber at low density within cages had no effect on the quantity of C or N in accumulating sediments in Totten Inlet.