Print PageEstuaries along the south shore of Long Island, NY (USA) have been experiencing intense and disruptive ‘brown tides’, blooms of the pelagophyte Aureococcus anophagefferens, for over two decades. A. anophagefferens is a poor food source for many planktonic and benthic grazers, and brown tides are blamed for losses of hard clams, seagrass, and bay scallops. It is thought that A. anophagefferens dominates the phytoplankton by being a superior competitor for the low levels of inorganic and organic nitrogen (such as urea) available once a bloom begins, but neither the conditions that lead to a bloom nor the effects of a bloom on the whole plankton community are well understood. We have used terminal restriction fragment length polymorphism (TRFLP) analysis of 18S rRNA, 16S rRNA, and urease genes ordinated by nonmetric multidimensional scaling (NMS) to examine the planktonic microbial community in years and locations with and without brown tide.
Results/Conclusions
The planktonic communities in Great South Bay (GSB) and Quantuck Bay (QB) tend to change in a predictable manner seasonally, though large changes in the community can occur in less than a week. Significant differences were seen in the plankton community between seasons using perMANOVA analysis, and interannual variability was also important, especially in urease community profiles. There was a good correlation between the abundance of A. anophagefferens determined microscopically and the contribution of A. anophagefferens–specific (nuclear and plastid, respectively) terminal restriction fragments (TRFs) to the total 18S and 16S TRFs. When A. anophagefferens was not abundant, diatoms and dinoflagellates dominated in the spring and picocyanobacteria in the summer, consistent with previous studies done by microscopy. In QB, where brown tides occurred every sampling year, temperature was strongly related to community structure. In 2008, when GSB experienced a dense and widespread brown tide, both 18S and 16S communities were separated according to the abundance of A. anophagefferens along an axis that was related to wind speed. In contrast, wind was not an important factor in structuring the GSB community during the non-brown-tide year 2009. In both GSB and QB, BIOENV analysis indicated that urea concentrations and total chlorophyll were important factors influencing community structure from the perspective of 18S, 16S and urease genes. Our results suggest that mixing may be an important physical factor for brown tides that has not been previously considered, while biological and chemical factors are more important in structuring plankton communities during non-brown-tide years.
