# The effects of ammonium and phosphate enrichments on clorophyll a, pigment ratio and species composition of phytoplankton of Vineyard Sound

Research paper by S. Vince, I. Valiela

Indexed on: 01 Mar '73Published on: 01 Mar '73Published in: Marine Biology

#### Abstract

Seawater containing natural phytoplankton populations from Vineyard Sound, USA was enriched in the laboratory with three levels each of ammonium and phosphate and with a combination of ammonium and phosphate which provided three different N:P ratios. The addition of ammonium produced more cells and chlorophyll a than the control or the phosphate enrichments. However, enrichment with ammonium and phosphate, regardless of the N:P ratio, yielded the most cells and chlorophyll a. Thus, nitrogen seems to be the primary limiting nutrient, with phosphate showing secondary limiting effects. The ratios of photosynthetic pigments $$\frac{{ - D430 - }}{{ - D663 - }}$$ decreased with the increased chlorophyll a production in the enriched cultures. There were no significant changes in the species composition within the cultures, so that the observed changes in pigment ratio and chlorophyll a content were due to physiological responses.