Phytoplankton response to waste-water nutrient enrichment in continuous culture

Abstract

Three marine phytoplankton, Dunaliella tertiolecta Butcher, Phaeodactylum tricornutum Bohlin, and Thalassiosira pseudonana (3H) Hasle & Heindal, were grown on waste water-sea water mixtures in continuous-flow monocultures. P. tricornutum increased in biomass with increasing waste-water additions until a mixture of about 40 % waste water-60 % sea water was reached. The other species did not increase in biomass beyond a 20 % waste water-80 % sea water mixture and even showed some inhibition at higher waste water additions. The carbon/nitrogen ( C N ) ratio of the algae was consistently below 6 when nitrogen was not limiting growth, but increased with decreasing dilution rate under nitrogen-limiting conditions, depending on whether NH 4 +-N or NO 3 −-N was the main nitrogen source. Species dominance in enriched cultures is controlled by a complex interaction of environmental factors. By altering the chemical composition ( C N ratio) of dominant phytoplankton such as P. tricornutum in mass culture through control of nitrogen source and concentration, it may be possible to increase the nutritional value of these organisms so that they represent a balanced diet for the growth of herbivorous shellfish.