Epiphytes support aquatic consumers of a large floodplain lake ecosystem in the southern Gulf of Mexico

Floodplain lakes are highly productive and biodiverse ecosystems whose food webs depend on a variety of autochthonous and allochthonous resources. Thus far, the role of attached algae, and epiphytes in particular has been understudied, although often high densities of macrophytes in these lakes may provide extensive substrate for attached algal growth. Our goal was to evaluate spatial and temporal variability in food web dynamics of three floodplain lakes permanently connected to the Usumacinta River, with emphasis on the role of epiphytes as a carbon source for upper trophic levels. To achieve this, we analyzed the physicochemical properties of water and stable isotopes of fish and invertebrate consumers and potential autochthonous (macrophytes, phytoplankton, epiphytes, epipelon) and allochthonous (terrestrial organic matter) basal resources during the rainy and dry seasons. The mixing model output highlighted the crucial role of epiphytes as the main energy pathway supporting secondary production year-round, while aquatic macrophytes were of secondary importance. The contribution of terrestrial organic matter to consumers was low, mostly limited to invertebrates, and overall increased from the rainy to the dry season, countering expectations of higher allochthony following strong seasonal flow pulses. Community-wide metrics further revealed higher trophic diversity among invertebrates as compared to fish. Our findings highlight the importance of preserving epiphytic energy pathways and macrophyte-periphyton linkages, as they provide key support to food webs of these vital fishery ecosystems.