Estuaries and Coasts

, Volume 35, Issue 6, pp 1443–1452 | Cite as

Comparison of Estuarine Salinity Gradients and Associated Nekton Community Change in the Lower St. Johns River Estuary

  • Cameron B. GuentherEmail author
  • Timothy C. MacDonald


Salinity is an important determinant of estuarine faunal composition; previous studies, however, have indicated conflicting accounts of continuous vs. relatively rapid change in community structure at certain salinities from geographically distinct estuaries. This study uses a large fisheries monitoring database (n > 5,000 samples) to explore evidence for estuarine salinity zonation by nekton in the lower St. Johns River estuary (LSJR). There was little evidence to support the presence of estuarine salinity zones except at the extremes of the salinity gradient (i.e., 0.1–1.0 and 34–39). The LSJR estuarine nekton community exhibits progressively slow ecological change throughout most of the salinity gradient with rapid change at the interfaces with fresh and marine waters—an ecoline bounded by ecotones. This study affirms the rapid change that occurs at the extremes of the salinity spectrum in certain estuaries and is relevant to efforts to manage surface water resources and estuarine ecosystems. Given the disparity in the results of the studies examining biological salinity zones in estuaries, it would be wise to have, at minimum, a regional understanding of how communities are structured along the gradient from freshwater to marine.


Estuary Fish Nekton Oligohaline Salinity zones 



We thank the field crews of the Florida Fish and Wildlife Conservation Commission, Fish and Wildlife Research Institute's Fisheries-Independent Monitoring Program for the countless hours of data collection. We thank Phil Stevens and Dave Blewett for their constructive comments and contributions to the final manuscript. This study was supported in part by contract 25303 from the St. Johns Water Management District to the Florida Fish and Wildlife Conservation Commission and by funds collected from the State of Florida Recreational Saltwater Fishing License sales. The statements, findings, views, and conclusions are those of the authors and are not necessarily the views of the District.


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Copyright information

© Coastal and Estuarine Research Federation 2012

Authors and Affiliations

  1. 1.Florida Fish and Wildlife Research InstituteFlorida Fish and Wildlife Conservation CommissionSt. PetersburgUSA

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