Labeling patterns of carbon 14 in net plankton during a winter spring bloom

Hitchcock, G. L.

Weekly surface samples were collected in lower Narragansett Bay, Rhode Island [USA], during the 1975 winter-spring bloom and fractionated by nets to nannoplankton (< 20 .mu.m) and total (< 158 .mu.m) size fractions. Each size fraction was assayed for particulate C, N, carbohydrate, protein, chlorophyll a and cell counts. The < 20 .mu.m values were subtracted from the < 158 .mu.m values to estimate the composition of the 20 .mu.m-158 .mu.m fraction (termed net plankton). As nutrients (primarily nitrogen) decreased to undetectable levels with the culmination of the diatom bloom, the ratios of protein/carbohydrate, carbohydrate C, and C/chlorophyll a in the net plankton indicated the diatom population was increasingly nutrient-limited. Each size fraction was also incubated at a saturating light intensity with 14C; following filtration, the cells were extracted with solvents to obtain labelled polysaccharide and protein. The daily rates of polysaccharide and protein synthesis in the net plankton declined as the bloom entered the stationary phase. When the diatom population was at its maximum density the majority of the 14C was found in the ethanol-soluble fraction; this may be due to high light intensities or nutrient effects.