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 elements 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 samples analyzed for foraminifera in this survey of finfish and mollusk farms, 48 contained no living specimens, Thirty-three of the 48 barren samples were collected during summer/autumn when anthropogenic and natural OM fluxes are highest, and bottom-water oxygen concentrations can become severely depressed, At the four sites in Atlantic Canada, OM concentrations in the 0-2 cm layer of bottom sediment ranged from 4 to 26%, and there was a general inverse association, more pronounced during the summer months, between species per sample and mean OM, Some abundant calcareous species (e.g., Buccella frigida, Haynesina orbiculare and Elphidium excavatum) show seasonal variation in addition to their apparent response to OM contamination, Seasonal variation is also evident among prominent arenaceous taxa (e.g., Hemisphaerammina bradyi). These temporal variations are superimposed on distinctive spatial changes in assemblage character that occur in passing from control environments to heavily OM-contaminated areas located directly below fish cages and mussel lines, Species diversity usually increases at sites where average sediment OM levels are less than about 15%. The five most abundant polychaetes in a 14-sample set show a wide range of sensitivity to both direct (food source) and indirect (low oxygen concentration) effects of OM loading. Nephtys neotena shows a weak direct relationship 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 minuta during the reduced-stress winter/spring interval, Other taxa are restricted solely to proximal, OM-enriched aquaculture settings, a feature that they share with some of the opportunistic foraminiferal species, Nepthys neotena and Cossura longicirrata are part of this apparently OM-tolerant assemblage.