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

In estuarine waters, phytoplankton are exposed to rapidly changing conditions that may affect community structure and function. In this study we determined the effects of mixing, turbidity, and limiting nutrient (N) additions on natural phytoplankton growth rates and algal group-specific biomass changes. Mesocosm bioassays were used to quantify the short-term (2–3 day) responses of phytoplankton from the Neuse river estuary, NC. Growth rates were higher under static conditions in N-amended tanks, while biomass of most algal groups was higher under mixed, turbid conditions with N additions. Shifts in community composition did not follow any consistent pattern but each factor influenced phytoplankton growth, biomass, and community composition. 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 waters. The combination of biomarker quantifications and the radiolabeling method is a useful tool for assessing phytoplankton responses and offers insights into the mechanisms driving blooms and bloom species in estuarine waters.