Growing sea urchins & scallops together

General description: Shellfish growers are looking for ways to produce more than one product on their farms while making better use of permitted space & reducing the labor involved in removing biofouling – the biological material that builds up on aquaculture gear and shellfish shells.

This study explored whether green sea urchins could be grown alongside Atlantic sea scallops in the same gear. Because sea urchins naturally graze on organisms that contribute to biofouling, we wanted to see whether their grazing could help reduce biofouling and cleaning effort.

The study showed that sea urchins and scallops could be successfully grown together, but biofouling was not reduced enough to demonstrate a clear benefit. The results highlight the need for follow-up research to determine whether increasing grazing pressure could improve biofouling control (hint – our follow up research does improve it!).

This was such a fun project that brought together a hard working graduate & undergraduate student (Southwood, Jenkins, Elba) team to help plan, implement, & collect data for the study. We are grateful for funding and support from USDA Northeast SARE, Northeastern Regional Aquaculture Center (NRAC), & Hatch.

Link: https://www.sciencedirect.com/science/article/pii/S0044848626004230

Abstract: The Atlantic sea scallop (Placopecten magellanicus) aquaculture industry regularly cleans gear & 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 & 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), & differing sizes and stocking densities of sea urchins (small or large: 11.64 & 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 & marketable characteristics presenting a potential pathway to optimize space & 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, &/or too small gear mesh size. Sea urchin gonad index doubled & color improved indicating that biofouling was utilized as a food source, highlighting the potential for further optimization work with larger gear mesh sizes & higher sea urchin biomass to determine whether these can improve biofouling reduction.