Changes in zooplankton community, and seston and zooplankton fatty acid profiles at the freshwater/saltwater interface of the Chowan River, North Carolina

Abstract

The variability in zooplankton fatty acid composition may be an indicator of larval fish habitat quality as fatty acids are linked to fish larval growth and survival. We sampled an anadromous fish nursery, the Chowan River, during spring of 2013 in order to determine how the seston fatty acid composition varied in comparison with the zooplankton community composition and fatty acid composition during the period of anadromous larval fish residency. The seston fatty acid profiles showed no distinct pattern in relation to sampling time or location. The mesozooplankton community composition varied spatially and the fatty acid profiles were typical of freshwater species in April. The Chowan River experienced a saltwater intrusion event during May, which resulted in brackish water species dominating the zooplankton community and the fatty acid profile showed an increase in polyunsaturated fatty acids (PUFA), in particular eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). The saltwater intrusion event was followed by an influx of freshwater due to high precipitation levels in June. The zooplankton community composition once again became dominated by freshwater species and the fatty acid profiles shifted to reflect this change; however, EPA levels remained high, particularly in the lower river. We found correlations between the seston, microzooplankton and mesozooplankton fatty acid compositions. Salinity was the main factor correlated to the observed pattern in species composition, and fatty acid changes in the mesozooplankton. These data suggest that anadromous fish nursery habitat likely experiences considerable spatial variability in fatty acid profiles of zooplankton prey and that are correlated to seston community composition and hydrodynamic changes. Our results also suggest that sufficient prey density as well as a diverse fatty acid composition is present in the Chowan River to support larval fish production.

Multiple Trophic Tracer Analyses of Subarctic Rhodolith (Lithothamnion glaciale) Bed Trophodynamics Uncover Bottom-Up Forcing and Benthic-Pelagic Coupling

“…This is in accordance with Bec et al (2010) who concluded phytoplankton only explains 27% of the variance in seston. Because of our study site's proximity to riverine input, some proportions of 18:1ω9 and 18:2ω6 (5.3%) could also be influenced by conifer pollen found in large quantities during spring (Masclaux et al, 2013;Lichti et al, 2017). Regardless, diatoms help support a rich infaunal community living underneath rhodoliths, which likely depends on deposition of organic material at the rhodolith-sediment interface (Steller et al, 2003;Grall et al, 2006;Berlandi et al, 2012).…”

Essential Biomolecules in Food Webs

“…Humic substances in dystrophic lakes may shield susceptible LC-PUFA from UV, but also exert direct toxic effects to consumers, such as daphnids (CasaNova et al, 2018 and references therein). Salinity gradients structuring estuaries can affect trophic dynamics of LC-ω3PUFA, especially in larval fish (Litchi et al, 2017).…”

The effects of temperature on Bosmina longirostris susceptibility to microcystin-LR acute toxicity

“…Microcystin-LR can cause direct mortality [16–18], eliminating susceptible zooplankton from the food web, and thereby reduce the prey available to larval and juvenile fish. Bosmina longirostris is a ubiquitous species of herbivorous, freshwater zooplankter that is dominant in abundance within the Chowan River system in the spring months of April through June [19]. B .…”