Application of photopigment biomarkers for quantifying microalgal community composition and in situ growth rates

In estuarine waters, phytoplankton are exposed to rapidly changing conditio ns that may affect community structure acid function. In this study we dete rmined the effects of mixing, turbidity, and limiting nutrient (N) addition s on natural phytoplankton growth rates and algal group-specific biomass ch anges. Mesocosm bioassays were used to quantify the short-term (2-3 day) re sponses of phytoplankton from the Neuse river estuary, NC. Growth rates wer e higher under static conditions in N-amended tanks, while biomass of most algal groups was higher under mixed, turbid conditions with N additions. Sh ifts in community composition did not Follow any consistent pattern but eac h factor influenced phytoplankton growth, biomass, and community compositio n. Differing growth responses to nutrient additions, mixing, and turbidity resulted in taxonomically-distinct communities. These results highlight the complexity of phytoplankton community structuring processes in estuarine w aters. The combination of biomarker quantifications and the radiolabeling m ethod is a useful tool for assessing phytoplankton responses and offers ins ights into the mechanisms driving blooms and bloom species in estuarine wat ers. (C) 2001 Elsevier Science Ltd. All rights reserved.