Loss of seasonal variability in nekton community structure in a tidal river: evidence for homogenization in a flow-altered system
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Modifications to riverine systems that alter freshwater inflow to downstream estuarine habitats have resulted in altered patterns of nekton distribution and abundance. To examine how nekton assemblages respond to variable hydrologic patterns, we used trawl and seine survey data to compare the seasonal trends (dry vs. wet season) expected of a natural system to those of a river with regulated flow discharges that often magnify high flow events. Nekton assemblages differed between seasons in a representative natural system, similar to other estuaries of the region. For example, assemblage differences were characterized by significantly higher abundance and richness in trawl surveys, and significantly higher richness in seine surveys in the wet relative to the dry season. These seasonal trends were dampened in the altered system. Species important in defining seasonal dissimilarities in both systems were characterized as estuarine resident species, including Anchoa mitchilli, Menidia spp., Cynoscion arenarius, and Trinectes maculatus, yet were observed largely to have opposing seasonal trends in abundance between the two rivers. Our comparison provides evidence that flow modifications result in a loss of natural seasonal variability in estuarine nekton assemblages, but additional investigations of flow-altered systems are needed to confirm these findings.
KeywordsCaloosahatchee River Density Disturbance Estuarine High flow Myakka River
The authors thank the staff of the Florida Fish & Wildlife Conservation Commission’s Charlotte Harbor Field Laboratory for sample collection and logistics. Comments from two anonymous reviewers improved the quality of this manuscript. Field sampling was supported by the South Florida Water Management District (CP040063), the Florida Department of Environmental Protection Coastal Management Program (CZ906), funds collected from the state of Florida saltwater fishing license sales, and the Department of the Interior, US Fish & Wildlife Service Federal Aid for Sport Fish Restoration Grant Number F-43. Additional support was provided through University of Windsor scholarships to J.A. Olin and Natural Sciences & Engineering Research Council (NSERC) of Canada Discovery grant funds to A.T. Fisk.
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