Seasonal variability in estuarine planktonic and benthic algal populations

Background/Question/Methods

Microalgal populations are trophically important to a variety of micro- and macroheterotrophs in marine and estuarine systems. In Chesapeake Bay, microalgae facilitate the survival and development of ecologically and economically relevant fauna that include regional shellfish and finfish populations. Studies of microalgal communities in Chesapeake Bay have traditionally focused on phytoplankton, while benthic microalgae (microphytobenthos) have largely been ignored. This project aims to develop a broad-scale picture of microphytobenthic community structure and dynamics within intertidal wetlands of lower Chesapeake Bay in relation to phytoplankton communities. Whole water samples and sediment cores were collected over a two-year period at eight sites throughout lower Chesapeake Bay for quantification of phytoplankton and microphytobenthic community composition and analysis of seasonal trends within and between both microalgal communities.  

Results/Conclusions

In the benthos, 104 taxa were identified over the 2-year period, with diatoms being the most prolific (60 species). The microphytobenthic community composition was dominated by diatoms in the winter and early spring months, with a gradual shift to cyanobacteria during the late spring into the summer, and a return to diatom dominance early to mid-fall. This seasonal pattern was observed in both years of the study. Total cell abundances and biomass followed similar trends, increasing in spring, reaching their maximum during the summer, before decreasing during the fall and into the winter. Species richness and diversity was much more variable, with values fluctuating erratically throughout the sampling period.  In the water column, 137 taxa were identified. Similar to the benthos, diatoms were the most diverse group (72 species). Diatoms also remained dominant in both abundance and biomass throughout the sampling period, with peak species richness from the fall to early spring months, and diversity peaking in the fall and spring/early summer seasons.  These results provide evidence for the microphytobenthos as a diverse community that is similar to, but significantly different than the neighboring planktonic populations.