Seasonal variations in food web dynamics of floodplain lakes with contrasting hydrological connectivity in the Southern Gulf of Mexico

Abstract

Floodplains are some of the most productive and diverse ecosystems on Earth. The Usumacinta River Basin, in the Southern Gulf of Mexico, hosts several floodplain lakes, whose integrity is threatened by water resource development. We aimed to investigate how food webs in these ecosystems vary in relation to their hydrological connectivity and seasonal flood cycles. To do this, we combined analysis of water quality and stable isotopes in two lakes with permanent connection to the Usumacinta River and two isolated lakes during dry, early rainy and late rainy season. Significant differences in chlorophyll-a, nutrients and suspended solids were reflected in distinct trophic dynamics among lakes. Stable isotope analysis revealed that fish from all lakes relied predominantly on autochthonous primary production, but while phytoplankton was the dominant resource for fish in the isolated lakes, aquatic macrophytes made the highest contribution to consumers’ production in the connected lakes. Fish tended to have broader isotopic niches during the early rainy season, likely reflecting consumption of a wider range of resources following the first flow pulses of the year. Our study highlights the importance of hydrological connectivity and natural flow regimes to maintain the outstanding biodiversity and fishery yield of these floodplain ecosystems.