Resilient nekton composition in the face of climate-driven foundation species shifts

Climate-driven range expansions of individual species are well-documented, but corresponding community shifts are not. This lack of widespread community change may indicate communities can resist wholesale change with the arrival of new species. In the northern Gulf of Mexico, climate change is driving the expansion of black mangroves (Avicennia germinans) into areas traditionally dominated by smooth cordgrass (Spartina alterniflora). This study investigates the effects of these changes on the species composition of animals and habitat structure in Louisiana, USA, with implications for how species expand their range under shifting climactic regimes. Using quantitative nekton sampling and satellite imagery analysis over two decades, we observed a substantial increase in winter temperatures of 3.5°C and a regime shift from marsh to mangrove habitats. Despite these remarkable environmental changes, the composition of nekton remained stable. We expected that warming temperatures and the expansion of black mangroves would shift nekton community composition in our system by favoring warm-adapted species and facilitating the arrival of new climate migrants. However, based on the community temperature index and species-level analysis of relative abundances, thermal tolerance, and latitudinal range, we found no detectable increase in thermal affinity or establishment of new warm-adapted taxa in Port Fourchon since 2002. Given that many systems experiencing comparable climate forcing have undergone marked compositional shifts, our findings suggest that local biotic interactions and species adaptability may buffer this community from the broader range expansions observed elsewhere. Our findings highlight the resilience of estuarine communities to rapid environmental changes and emphasize the need for further research on the indirect effects of habitat shifts on food web dynamics.