Marine Biology

Estuarine Plankton

The estuarine plankton is also reduced in number of species. It follows the same trend as the macrofauna and macrovegetation. Diatoms frequently dominate the phytoplankton, but dinflagellates may achieve dominance during the warmer months and may remain dominant in some estuaries during  all times. Dominant diatom genera include Sksletomama, Asteriomella , Chaeroceros , Nitchia , Thalastionema and Melosiva . Abundant dinflagellate genera include Gymnodinium , Gonyaulax , Peridinium and Ceratium . The phytoplankton may also be temporarily enriched by resuspension of characteristic bottom-dwelling forms/diatoms. High turbidity and rapid flushing may restrict phytoplankton numbers and productivity in some estuaries.

Where turbidity is low and flushing time long, diverse populations and relatively high productivity may result. Consequently, depending on prevailing conditions, estuaries may differ considerably in both phytoplankton numbers and productivity.

Zooplankton in estuaries mirror the phytoplankton in being limited in species composition. The species composition also varies, both seasonally and with salinity gradients up the estuary. Few true estuarine zooplankters occur in larger, more stable estuaries, where salinity gradients are less variable. Shallow, rapidly flushed estuaries are inhabited mainly by a typical marine zooplankton assemblage carried in and out with the tide. Characteristic estuarine zooplankters include species of the copepod genera Eurytemora, Acartia, Pseudodiaptomus , and Centropages, certain mysid  genera Neomysis , and Mesopodopsis and certain amphipods, such as speices of Gammarus. The estuarine zooplankton average about 1 ml/m³  displacement volume or somewhat greater than the concentration in adjacent coastal waters.