Biological control of fouling in suspended scallop cultivation

Abstract

Fouling of scallop shells and cultivation nets by living organisms is costly to remove and can reduce scallop growth. Here we investigate biological control of fouling in suspended scallop ( Pecten maximus) cultivation. In preliminary trials in the Irish Sea, off the Isle of Man, sea urchins ( Echinus esculentus and Psammechinus miliaris) and hermit crabs ( Pagurus spp.) removed fouling from nets more efficiently than did a range of other invertebrates. Sea urchins and hermit crabs were subsequently deployed from August 2000 to January 2001 at various densities (hermit crabs and E. esculentus at 1, 2, or 3 per net and P. miliaris at 3, 5 or 7 per net) in pearl nets containing scallops. After 6 months, the survival of biological control organisms and their effect on scallop growth and mortality, and fouling of nets and scallop shells, were assessed. Only P. miliaris was associated with increased scallop shell growth, but no biological control organism reduced scallop growth or survival. All three biological control organisms significantly reduced the weight of fouling on nets (often by as much as 50%) and fouling of scallop shells; results were largely independent of biological control organism density. Sea urchins were most effective, removing hydroids and solitary tunicates efficiently; they could thus be commercially exploited alongside scallops in a form of polyculture. These results suggest that biological control could be an efficient and environmentally sound method of addressing the problem of fouling in scallop cultivation.