Nekton community change along estuarine salinity gradients: Can salinity zones be defined? |
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| Authors: | Marin F D Greenwood |
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| Institution: | 1.Florida Fish and Wildlife Conservation Commission,Fish and Wildlife Research Institute,St. Petersburg,Florida |
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| Abstract: | Organisms tend to inhabit predictable portions of estuaries along salinity gradients between the ocean inlets (salinity >
35 psu) and the freshwater tributaries (salinity = 0). Previous studies have suggested that the continuous change in biological
community structure along this gradient is relatively rapid at certain salinities. This is the basis for estuarine salinity
zonation schemes similar to the classic Venice System (i.e., 0–0.5, 0.5–5, 5–18, 18–30, 30–40, > 40). An extensive database
(n > 16,000 samples) of frequency of occurrence of nekton was used to assess evidence for estuarine salinity zones in two
southwest Florida estuaries: Tampa Bay and Charlotte Harbor. Rapid change in nekton community structure occurred at each end
of the estuarine salinity gradient, with comparatively slow (but steady) change in between. There was little strong evidence
for estuarine salinity zones at anything other than low salinities (0.1–1). As previously suggested by other authors, estuaries
may be regarded as ecoclines, because they form areas of relatively slow but progressive ecological change. The ends of the
estuarine salinity gradient appear to be ecotones (areas of rapid change) at the interfaces with adjacent freshwater and marine
habitats. This study highlights the rapid change that occurs in nekton community structure at low salinities, which is of
relevance to those managing freshwater inflow to estuaries. |
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