Sydney rock oyster, Saccostrea commercialis (Iredale & Roughley), filtration of shrimp farm effluent: the effects on water quality

Shrimp pond effluent water can contain higher concentrations of dissolved n utrients and suspended particulates than the influent water. Consequently, there are concerns about adverse environmental impacts on coastal waters ca used by eutrophication and increased turbidity. One potential method of imp roving effluent water quality prior to discharge or recirculation is to use bivalves to filter the effluent. In this study, we examined the effects of the Sydney rock oyster, Saccostrea commercialis (Iredale & Roughley), on t he water quality of shrimp pond effluent, Effluent from a shrimp farm stock ed with Penaeus japonicus (Bate) was pumped directly into 34-L tanks stocke d with different densities of oysters, Combinations of live and dead oyster s were used to test the effects of three different densities of live oyster s (24, 16 and 8 live oysters per tank). The concentrations of total suspend ed solids, the proportion of organic and inorganic matter, total nitrogen. total phosphorous, chlorophyll a and the total number of bacteria in the po nd effluent water were determined before and after filtration by oysters. T he oysters significantly reduced the concentration of all the parameters ex amined, with the highest oyster density having the greatest effect, Shrimp pond effluent contained a higher proportion of inorganic matter (72%) than organic matter (28%). The organic component appeared to be mainly detritus, with chlorophyll a comprising only a minor proportion. Filtration by the h igh density of oysters reduced the effluent total suspended solids to 49% o f the initial level, the bacterial numbers to 58%, total nitrogen to 80% an d total phosphorous to 67%, The combined effects of settlement and oyster f iltration reduced the concentration of chlorophyll a to 8% of the initial e ffluent value.