Decadal-Scale Changes in Subtidal Nekton Assemblages in a Warm-Temperate Estuary
Coincidental long-term changes in estuarine nekton assemblages and environmental conditions are widely reported. In this study, from a warm-temperate, high salinity, salt marsh-dominated estuary in the southeastern USA, decreases in overall abundance, shifts in species and life stage composition, and changes in seasonal patterns of occurrence coincided with increased water temperature. Biweekly trawl collections in a subtidal creek were made during two 4-year periods separated by more than 30 years. Of the total 111 taxa in the North Inlet estuary, South Carolina, 64% (71) occurred during both the historic (1981–84) and recent (2013–16) periods. The top five species and their proportions of the total annual catches changed between periods. In the recent study period, near-bottom species (Lagodon rhomboides, Bairdiella chrysoura, Litopenaeus setiferus) increased, and pelagic species (Anchoa spp. and Lolliguncula brevis) decreased. The mean abundance of total nekton in the recent period was approximately 50% of historic abundance. Large, but temporary increases in nekton abundance occurred when salinity decreased after major storms. In the recent study period, shifts in the timing of peak abundances from spring to fall, the occurrence of juveniles during winter, and increased diversity suggested responses to significantly warmer winters and summers. Over the 30 year period, the subtidal nekton assemblage transitioned to a state of lower abundance and different composition. Future increases in water temperature, incidences of major storms, and modifications of estuarine habitats due to rising sea level could lead to additional changes in the fauna of warm-temperate estuaries.
KeywordsClimate change Fish assemblages Long-term changes Local-scale effects Salt marsh Shrimp Tidal creeks
Special thanks go to (in alphabetical order) W. Allen, L. Barker, T. Buck, K. Dean, K. Gruenhagen, E. Haffey, M. Mace, B. McCutchen, W. Michener, C. Ryan, T. Swanson, T. Swatzel and the many dozens of other staff, students, and volunteers who assisted with field collections, sample processing, and data management.
The historic period study was supported by National Science Foundation grant DEB 8012165 and the recent period study was supported by the North Inlet-Winyah Bay National Estuarine Research Reserve.
Compliance with Ethical Standards
This research was conducted in accordance with the guidelines set forth in the University of South Carolina IACUC Animal Care and Use Protocol no. 2338-101197-030317.
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