Temporal trends in estuarine-resident fishes: Functional traits and responses to environmental and climatic...

Extreme climatic events, such as El Niño, are becoming increasingly intense and frequent, driving hydrodynamic changes in estuaries and significantly affecting their structure and biodiversity. Using long-term data (22 years) obtained from standardized surveys, we analyzed the abundance of three estuarine-resident species (Atherinella brasiliensis, Jenynsia lineata, Ctenogobius shufeldti) with distinct functional traits (related to reproductive strategy, feeding, and habitat use) and their relationships with local, regional, and climatic environmental factors in a subtropical estuary. We investigated the following hypotheses: (i) there is a long-term declining trend in the abundance of these estuarine-resident species; (ii) reductions in their abundance are associated with El Niño events; (iii) the abundance of species with different functional traits responds similarly to the effects of El Niño events. The analysis revealed a consistent decline in the abundance of all three estuarine-resident species, driven by local and regional factors and climatic variations, despite differences in their functional traits. Generalized linear models showed that El Niño events impact species in distinct ways, with more pronounced effects on oviparous species (A. brasiliensis and C. shufeldti) compared to viviparous ones (J. lineata). These findings provide empirical evidence of decadal changes decline in the abundance of estuarine-resident fishes regardless of their distinct functional traits, raising concerns to the conservation of ecological functions and ecosystem services in subtropical estuaries under increasing anthropogenic and climatic pressures.