Interannual variability of Aureococcus anophagefferens in Quantuck Bay, Long Island: natural test of the DON hypothesis

Abstract

This study examined benthic and pelagic rate processes from the perspective of benthic dissolved organic matter (DOM) and its possible role in Aureococcus anophagefferens population dynamics. Sampling was conducted in Quantuck Bay, Long Island, New York, at three times in the summer of 2000 and two times in the summer of 2001. A. anophagefferens exhibited a large bloom between the May and July 2000 sample periods, but a smaller bloom was captured in the September 2000 sampling. Densities throughout 2001 were significantly lower than during 2000. There were few differences in most parameters measured between years, but the largest difference was the seasonal increase in both particulate (POM) and dissolved organic matter (DOM) during 2000 that was not observed during 2001. In particular, DOP accumulated the most, followed by DON and DOC, which resulted in significant seasonal decreases in the C:N:P ratios of the DOM pools. On the contrary, changes in elemental ratios of POM were not observed. The seasonal accumulation of DON appeared to be driven largely (∼50%) by the flux of DON from the benthos in 2000, but during 2001, all measured DON fluxes were into the sediment from the water column. This is consistent with the lack of accumulation during this year. There was little evidence for changes in microzooplankton grazing pressure between 2000 and 2001, and therefore the accumulation of DON and DOP during 2000 could have provided a competitive advantage to A. anophagefferens over other picoalgal species (e.g., Synechococcus) resulting in the significant blooms observed in 2000.