SEASONAL STUDIES OF SESTON LIPIDS IN RELATION TO MICROPLANKTON SPECIES COMPOSITION AND SCALLOP GROWTH IN SOUTH-BROAD-COVE, NEWFOUNDLAND

The concentration and nutritional quality of suspended particulate mat ter at an experimental scallop aquaculture site on the east coast of N ewfoundland, Canada, was determined at 3 depths over an 8 mo sampling period. Lipid classes and fatty acids were measured chromatographicall y and the seston components were identified and quantified by microsco py. These measurements were correlated and then related to the growth of juvenile scallops Placopecten magellanicus introduced to the site. The low seston concentrations observed throughout the year were punctu ated by 4 large inputs: the spring diatom bloom, a resuspension event, a summer microzooplankton and nanoflagellate bloom, and a fall increa se in zooplankton faecal pellet and heterotrophic dinoflagellate conce ntrations. The largest inputs of lipids were associated with the resus pension event and the summer bloom. The resuspended particles included the benthic pennate diatom Gyrosigma spp, which contained large lipid globules. High concentrations of polyunsaturated triacylglycerols occ urred at this time; more saturated triacylglycerols were prominent in the summer. The acyl lipids contained unusually high proportions of th e long-chain polyunsaturated fatty acid 20:4 omega 5 which was correla ted (p < 0.05) with the proportion of microzooplankton in the seston. The C-16 fatty acid ratio 16:1 omega 7/16:0, used previously as a diat om biomarker, was strongly correlated (p < 0.01) with the proportion o f centric diatoms. Scallop growth appeared to be related less to the m ajor inputs of total lipids to the water column and more to the propor tion of the essential fatty acid 22:6 omega 3 in the acyl Lipids. This fatty acid was associated principally with cryptophytes (p < 0.02).