Salinity Gradient Influence on the Tar-Pamlico River Fish Community Structure

Abstract

Saltwater intrusion is increasing in estuarine systems worldwide as a result of sea-level rise, altered freshwater inflows, and climate change impacts on the water cycle. Changes in salinity have the potential to alter fish community composition as some species experience physiological stress, barriers to reproduction and larval dispersal, alterations to migration patterns of adult fishes, and reductions in suitable habitat. However, estuarine species are known to be resilient to environmental changes. The saltwater-freshwater interface of the Tar-Pamlico River is understudied, since sampling efforts generally target only freshwater areas or downstream, saltier portions of the estuary. The purpose of this study is to investigate how salinity structures fish communities in the Tar-Pamlico River at this interface to better understand how fish communities may respond to future saltwater intrusion brought about by climate change. The results indicated that biodiversity generally increased as bottom salinity increased. This pattern was correlated with salinity variations more than other variables examined, such as dissolved oxygen, temperature, or spatial factors. Furthermore, salinity was found to be the most influential factor causing variance in fish community composition. In a Redundancy Analysis (RDA), we identified three key species contributing to differences in community composition: spot (Leiostomus xanthurus), Atlantic menhaden (Brevoortia tyrannus), and gizzard shad (Dorosoma cepedianum). Using quotient curves and a Regional Oceanographic Modeling System (ROMS), we were able to identify the preferred salinity range of these species and determine how the spatial extent of this range varied under future climate and sea-level rise scenarios. The results indicated that suitable habitat for all three species is projected to move upstream.