Use of long-term data and multivariate ordination techniques to identify environmental factors governing estuarine phytoplankton species dynamics. From Rothenberger et al. (2009).
Phytoplankton assemblages were strongly related to temperature and total nitrogen : total phosphorus (TN:TP) ratios, with expected seasonal changes in species composition. Inter-annual changes in river discharge influenced whether phytoplankton assemblages were dominated by diatoms and phototrophic flagellates, or by mixotrophic and heterotrophic dinoflagellates. From this analysis, increasing NH4 + concentrations also emerged as an important influence on the phytoplankton assemblages. Raphidophytes (including potentially toxic Heterosigma akashiwo
), haptophytes, chlorophytes, and the bloom-forming dinoflagellate Heterocapsa rotundata
increased in more recent years (2000- 2006), concomitant with increasing NH4 + concentrations (e.g., 105 cells of H. rotundata mL-1 at NH4 + > 14 μM). Abundance of the toxigenic dinoflagellate Prorocentrum minimum
was positively related to dissolved organic nitrogen (DON), whereas the highest abundance of the grouping Pfiesteria
-like’ dinoflagellates, and Karlodinium veneficum
occurred during summer and fall and was related to high TP concentrations, temperature, and salinity. The data suggested an increasingly important role of NH4 + in controlling phytoplankton assemblage structure, including increased abundance of some harmful species, in this eutrophic estuary. The field study was supported by other field research and by laboratory experiments (e.g., NH4 + supports more rapid growth of H. akashiwo than nitrate or urea).
The CAAE has also characterized blooms in the Neuse Estuary that have been dominated or co-dominated by Prorocentrum minimum (e.g. see Springer et al. 2005, Harmful Algae 4: 533-551). The developing bloom was first detected from a web-based alert provided by the Center’s real-time remote monitoring (RTRM) platforms, indicating elevated dissolved oxygen (DO) and pH levels in the upper estuary. These data were used to augment shipboard sampling in characterizing bloom initiation, development, movement, and dissipation over a 7-month period (October 2001-April 2002).