Utilization of Gracilaria chilensis (Rhodophyta: Gracilariaceae) as a Biofilter in the Depuration of Effluents from Tank Cultures of Fish, Oysters, and Sea Urchins

Abstract

An evaluation was made on a seasonal basis of the effect of the marinemacroalga culture Gracilaria chilensis on concentrations of some solubleand particulate wastes emitted during tank cultures of a fish Isaciaconteptionis, an oyster Crassostrea gigas, and a sea urchin Loxechinusalbus species. The animals were each cultured in separate tanks, andeffluent from each was directed through separate tanks, which containeddense cultures of the Gracilaria chilensis. Inflow-outflow monitoringwas conducted for the presence of nitrate, nitrite, ammonium, andphosphate. Also evaluated were particulate nitrogen and phosphate. Themost significant wastes were ammonium from the fish culture and nitratefrom the oyster culture. These were completely removed from the water,with minor exceptions, by the alga during all seasons of the year.Lesser amounts of soluble phosphate and nitrite, arising from the fishcultures, were also removed. Of the particulate matter, only nitrogenwas in evidence from the fish cultures in the summer. It was concludedthat Gracilaria chilensis culture was highly efficient at biofiltrationof the soluble nutrients tested but had little effect on particulateemissions. The best growth of Gracilaria chilensis occurred in theammonium-rich effluent from the fish culture.