When assessing oyster-reef habitat in estuaries it is important to
understand the influence of salinity on the spatial and temporal variability
of associated organisms. How comparable is community structure among
stations located at different points along the salinity gradients of
estuaries or among tidal tributaries that experience different levels of
freshwater inflow? Do assemblages vary seasonally in response to changing
salinity and freshwater inflow? To address these questions, multivariate
techniques were employed to analyze decapod crustacean and fish abundance
data. Organisms were collected at three reefs along the salinity gradient of
three estuaries: the Caloosahatchee River and estuary, Estero River and Bay,
and Faka Union Canal and Bay. Additional collections were made from reefs
located near the mouths of Estero Bay's five tidal tributaries. Samples were
dominated by the decapods Eurypanopeus depressus and Petrolisthes armatus. Commonly occurring species included the
decapods Panopeus obesus, Alpheus heterochaelis and Rhithropanopeus harrisii and the fishes Gobiosoma robustum, Lophogobius cyprinoides and Gobiesox strumosus. Analysis of similarities suggested
differences among stations located along the salinity gradients of all three
estuaries. Community structure also varied among stations located near the
mouths of the tidal tributaries of Estero Bay. Multidimensional scaling
identified community structure present at upper stations as distinct from
that downstream and at high-flow tributaries as distinct from that near
low-flow tributaries. Upper stations and stations near high-flow tributaries
were typified by E. depressus and gobiid fishes. Downstream stations and stations near
low-flow tributaries were typified by E. depressus and P. armatus. Percent dissimilarity was
greatest when upper and lower stations were compared along the salinity
gradient or when low salinity and high-salinity sites were compared among
tributaries. Within-station sample variability tended to be higher upstream
or in association with high-flow tributaries.