Co-culturing green sea urchins (Strongylocentrotus droebachiensis) with mussels (Mytilus spp.) to control biofouling at an integrated multi-trophic aquaculture site

Abstract

In a field study, five different stocking densities (i.e. 0, 30, 60, 90, 120ind.net−1 or 0, 2.46, 4.91, 7.37, 9.82ind.m−2) of adult green sea urchins (Strongylocentrotus droebachiensis) were randomly assigned to 30 predator-exclusion nets (i.e. n=6) around cultured mussels (Mytilus spp.) to test the effect of urchin density on biofouling intensity (percent net occlusion) and urchin/mussel growth. After 174days of culture, nets in all treatments containing sea urchins were significantly less fouled than those in the control treatment without urchins. Fouling intensities on nets with the two highest stocking densities of urchins (90 and 120ind.net−1) were approximately 40% less than that on nets with urchins held at the lowest stocking density (30ind.net−1) and 45% less than that on nets without urchins. The differences in fouling intensity among nets with 60, 90, and 120ind.net−1 were not statistically significant. While fouling was significantly reduced in the presence of urchins compared to the control treatment with no urchins, it was not completely eliminated since they were only able to access the inside surface of the nets. Sea urchin somatic and gonad growth declined with increasing stocking density, but there was no significant difference in mussel growth at the different urchin stocking densities. Mussels and sea urchins can be successfully co-cultured with no food input, but there may be a trade-off between the effectiveness of biofouling control and sea urchin growth. Statement of relevanceThis paper examined the use of sea urchins (Strongylocentrotus droebachiensis) to mitigate biofouling in mussel (Mytilus spp.) aquaculture and the effect of sea urchin density on biofouling coverage and mussel growth. Treatments containing sea urchins showed significantly less fouling than a control treatment without urchins. Urchin density had no significant effect on mussel growth.