LAUSR

AbstractBiodeposits from farmed mussels severely influencethe biogeochemistry of sediments by increasing thelevels of organic matter (OM). Mitigation of suchnegative impacts is important for the developmentof sustainable aquaculture operations. As a steptowards developing methods for remediation ofcoastal sediments affected by mussel farming, theeffects of the polychaete, Hediste diversicolor wasevaluated experimentally. In a series of field- andlaboratory experiments we tested hypotheses aboutthe effects of polychaetes on sediment oxygen con-sumption, nutrient fluxes and sulphide pools underdifferent polychaete densities and sedimentationregimes. The experimental results support the ideathat polychaetes can mitigate negative effects onthe benthic environment beneath mussel farms.H. diversicolor oxidized the sediment and generallyenhanced the oxygen consumption, and thus thedecomposition of OM. The accumulation of porewater sulphides were reduced and fluxes of nutri-ents across the sediment-water interface increased.Additional calculations suggest that the effects ofpolychaetes were mainly indirect and driven byincreased microbial activity due to the borrowingactivity of the polychaetes. Trends of increasingdecomposition with increasing polychaete densitysuggest that the decomposition could be furtherenhanced by higher densities. Overall, we con-cluded that H. diversicolor is a potentially strongcandidate for remediation of mussel farm sedi-ments. The results show that sediments inhabitedby H. diversicolor have high assimilative capacityof OM and oxygen conditions are significantlyimproved following the addition of polychaetes atnaturally occurring densities. However, technologi-cal developments are needed in order to allow theapproach to be used in practice.Keywords: sediment remediation, oxygenconsumption, biogeochemistry, Hediste diversi-color, mussel faecesIntroductionAquaculture is well known to cause environmen-tal impacts due to increased sedimentation andaltered nutrient cycling (Holmer, Duarte, Heilskov,Olesen & Terrados 2003; Giles, Pilditch & Bell2006; Nizzoli, Welsh, Fano & Viaroli 2006;Richard, Archambault, Thouzeau, McKindsey D Robert, McKindsey, Chaillou A Callier, Richard, McKindsey, Archam-bault & Desrosiers 2009; Carlsson, Glud P Robert et al. 2013), which stimu-late O