Effects of dietary fatty acid composition and salinity on copepod reproduction in a eutrophic estuary

Estuarine ecosystems are critical for fisheries and biodiversity, with copepods serving as essential trophic links. Accurate prediction of copepod reproductive success, measured via egg production rate (EPR), is vital for ecosystem management. Traditional monitoring relies on biomass indicators like chlorophyll-a, but emerging evidence underscores the importance of dietary biochemical quality, particularly polyunsaturated fatty acids (PUFAs) as indicators of dietary biochemical quality. This study, conducted during seasonal cruises in the Pearl River Estuary in May (spring), August (summer), and November (autumn) 2015, and January (winter) 2016, tested a hierarchical framework where PUFA availability is the primary regulator of EPR, modulated by environmental factors like salinity. Generalized Additive Models revealed that PUFA variability were the strongest predictor of EPR, exhibiting nonlinear responses that reflect complex nutritional trade-offs. Salinity influenced reproduction indirectly by shaping phytoplankton community composition and subsequent PUFA quality, rather than through direct physiological stress. In contrast, chlorophyll-a showed limited explanatory power. These findings advocate for a paradigm shift from biomass-based to mechanism-driven assessments, with the PUFA-salinity relationship serving as a sensitive diagnostic tool for early detection of ecosystem degradation. This framework enables proactive management before population declines manifest and has implications for sustainable fisheries. Future research should validate causal links through controlled experiments and develop cost-effective PUFA monitoring methods.