Co-culturing green sea urchins, Strongylocentrotus droebachiensis, with blue mussels, Mytilus edulis, to control biofouling at an integrated multi-trophic aquaculture site




Bartsch, Andrea

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Prevention and removal of biofouling from nets and product is a huge expense in the aquaculture industry. Of the many technologies that slow the accumulation of biofouling, copper-based coatings are used most commonly as they are a relatively inexpensive and effective option. However, they can leach into the marine environment and have potentially harmful impacts on marine life. In previous studies, sea urchins have shown potential as a non-toxic alternative to control fouling. In this field study, five different stocking densities (i.e. 0, 30, 60, 90, 120 urchins net-1 or 0, 2.46, 4.91, 7.37, 9.82 urchins m-2) of green sea urchins, Strongylocentrotus droebachiensis, were randomly placed in 30 mussel predator exclusions nets (with six replicates per density treatment) in order to test the effect of urchin density on biofouling intensity and urchin/mussel growth. Mussel predator exclusion nets were chosen to house the urchins since they are necessary to protect mussels from diving ducks and sea otters on the west coast of Vancouver Island, British Columbia, Canada. The urchins provide a means of controlling biofouling as well an additional marketable crop to offset predator net expenses. After 174 days, the percent net occlusion, mussel growth, and urchin growth were quantified. Nets with urchins were significantly less fouled than those without urchins. Fouling on nets with higher stocking densities of urchins (90 and 120 urchins net-1) was significantly less than that on nets with the lowest stocking density (30 urchins net-1). Fouling was no longer significantly reduced at densities >60 urchins net-1 or 4.91 urchins m-2. While fouling was significantly reduced in the presence of urchins, it was not completely eliminated as they were only able to access the inside surface of the nets. There was no significant difference in mussel growth at the different urchin stocking densities, but urchin somatic growth and gonad growth did decline with increasing urchin stocking density. Mussels and sea urchins can be successfully co-cultured with no food inputs, but there is a trade-off between biofouling control and urchin growth.



Biofouling, Sea urchin, Mussel, Aquaculture