Phytoplankton form the basis of the aquatic food chain in many estuaries.  The growth of these 'plants' is dependent on external physical (light, temperature, salinity and circulation) and chemical (nutrients) factors as well as grazing pressure.  Changes in these factors can cause changes in overall phytoplankton abundance (measured as chlorophyll a) and species composition.

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Community Composition

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Isle of Wight Characterization

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Community Composition

Starting in Feb. 2001, phyto plankton community data have been collected monthly from fourteen stations in the Coastal Bays by the Maryland DNR.  Data collection at the six sites in the St. Martin River and Newport Bay systems began in 1998 (samples were collected monthly from June through September). View phytoplankton status map.

Phytoplankton are not always easily identifiable to the species level, although some species level information exists.  Phytoplankton are typically identified to the genus level with an associated size range, although some could only be identified to the group level with an associated size range. The level of classification limits diversity comparisons to the defined groups. For a comprehensive analysis of phytoplankton occurrence in the Coastal Bays, visit the 2004 Coastal Bays Ecosystem Health Assessment website.

Brown Tide

Brown tide sites are monitored every other week from May to July for the organism, Aureococcus anophagefferens.  Due to it's extremely small size a special analysis is needed to identify it's abundance.  Brown tide monitoring began in 1999.  Brown tide abundance results are available for all years. For a full report of brown tide occurrence, visit the 2004 Coastal Bays Ecosystem Health Assessment.

Isle of Wight Characterization

Nine groups of algae have been identified in the coastal bays including diatoms,     dinoflagellates, blue-greens, greens, euglenoids, chrysophytes, cryptophytes, prasinophytes and unidentified flagellates. 

Blue green algae (an indicator of nutrient enriched waters) typically dominate the upper St. Martin River sites in August.  Dinoflagellates may dominate the community during most of the sampling period due to their mobility to optimize their local position in the water column with respect to light and nutrients. Diatoms tend to be non-motile and will sink from the water column in deeper estuaries. Diatoms were a consistently strong proportion of phytoplankton carbon stocks among the St. Martin River sites. In shallow estuaries, diatoms may benefit from windy periods that resuspend cells and hinder their incorporation into the sediments, keeping these species as consistent members of the algal community. The September dominance of euglenoids may be a function of a competitive advantage by the group during reduced plankton abundance in the area at a time when nutrients are low. 

Dominance according to algal carbon contribution to phytoplankton stock contrasts with the picture for cell counts. The difference in abundance and carbon evaluations of the ecosystem are most striking in August when bluegreens dominate the water column by numbers at all sites but carbon measures are dominated by the contribution from dinoflagellates. Diatoms and dinoflagellates tend to be larger cells than the bluegreens and will contribute more carbon per cell to the carbon standing stock. However, the smaller bluegreen cells often contribute more to productivity by having a smaller surface area and typically higher turnover rates.  Carbon standing stocks have declined in the system by August but productivity is often at a peak at this time of year for estuaries (Day et al. 1989) and may be suggested in this system by the shift to dominance by smaller celled algae in midsummer.

FROM:  Isle of Wight Watershed Characterization Report, Part of the Watershed Restoration Action Strategy.  A technical report:  Algae Including Phytoplankton, Harmful Algae Blooms and Macroalgae.

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