Integrating green sea urchins (Strongylocentrotus droebachiensis) with Atlantic sea scallops (Placopecten magellanicus) is feasible, but biofouling grazing control requires further optimization

The Atlantic sea scallop ( Placopecten magellanicus ) aquaculture industry regularly cleans gear and shellfish to control biofouling, forming a major part of operational costs. An emerging solution is to integrate sea urchins with shellfish using their grazing activity to feed on and control biofouling. This study aimed to determine whether the co-culture of scallops with green sea urchins ( Strongylocentrotus droebachiensis ) was possible in a Gulf of Maine (USA) farm. A combination of differing sizes of scallops (Four large (96.89 mm length) or 30 small (44.53 mm) per lantern net tier), and differing sizes and stocking densities of sea urchins (small or large: 11.64 and 24.92 mm test diameter respectively; 2, 4 or 8 individuals per tier), with a control for each shellfish size treatment without sea urchins was trialed. Results showed that these species can be successfully co-cultured with high survival, strong growth and marketable characteristics presenting a potential pathway to optimize space and gear. In this specific experimental design the sea urchins did not reduce biofouling on shell surfaces, most likely due to scallop escape responses. Biofouling on lantern net surfaces was not notably reduced by the sea urchins, most likely due to insufficient sea urchin size, too low densities, and/or too small gear mesh size. Sea urchin gonad index doubled and color improved indicating that biofouling was utilized as a food source, highlighting the potential for further optimization work with larger gear mesh sizes and higher sea urchin biomass to determine whether these can improve biofouling reduction.