SURVEY OF LIVING FORAMINIFERA AND POLYCHAETE POPULATIONS AT SOME CANADIAN AQUACULTURE SITES - POTENTIAL FOR IMPACT MAPPING AND MONITORING

Living benthic foraminifera and polychaetes have potential as robust e lements of assemblage models that can be used to monitor the temporal and spatial impact of organic matter (OM) fluxes from various kinds of marine aquaculture operations on local benthic environments, Of 148 s amples analyzed for foraminifera in this survey of finfish and mollusk farms, 48 contained no living specimens, Thirty-three of the 48 barre n samples were collected during summer/autumn when anthropogenic and n atural OM fluxes are highest, and bottom-water oxygen concentrations c an become severely depressed, At the four sites in Atlantic Canada, OM concentrations in the 0-2 cm layer of bottom sediment ranged from 4 t o 26%, and there was a general inverse association, more pronounced du ring the summer months, between species per sample and mean OM, Some a bundant calcareous species (e.g., Buccella frigida, Haynesina orbicula re and Elphidium excavatum) show seasonal variation in addition to the ir apparent response to OM contamination, Seasonal variation is also e vident among prominent arenaceous taxa (e.g., Hemisphaerammina bradyi) . These temporal variations are superimposed on distinctive spatial ch anges in assemblage character that occur in passing from control envir onments to heavily OM-contaminated areas located directly below fish c ages and mussel lines, Species diversity usually increases at sites wh ere average sediment OM levels are less than about 15%. The five most abundant polychaetes in a 14-sample set show a wide range of sensitivi ty to both direct (food source) and indirect (low oxygen concentration ) effects of OM loading. Nephtys neotena shows a weak direct relations hip to OM that is consistent with its ubiquitous spatial and temporal distribution. As benthic conditions become less contaminated by OM at mussel line sites, N. neotena is replaced by forms such as Pholoe minu ta during the reduced-stress winter/spring interval, Other taxa are re stricted solely to proximal, OM-enriched aquaculture settings, a featu re that they share with some of the opportunistic foraminiferal specie s, Nepthys neotena and Cossura longicirrata are part of this apparentl y OM-tolerant assemblage.