Long-term changes in spatially structured benthic diatom assemblages in a major subtropical wetland under restoration

Biological communities often comprise core species that are locally abundant and regionally common. Benthic diatoms are crucial primary producers in wetlands and reflect ecosystem responses to long-term hydrological and nutrient changes, yet few studies explicitly focus on patterns and drivers of diatom core species abundance in these ecosystems. We investigated how benthic diatom core species abundance varies over space, time, and environmental gradients in a major shallow wetland, the Florida Everglades, where environmental gradients and diatom assemblages are spatially structured by water diversion and nutrient loading. We analysed a long-term dataset of species and environmental data collected over 6 locations in 2 major Southern Everglades drainages. We hypothesized that (1) the abundance of 4 diatom core species (present in >90% of the samples with relative abundance >5%) and water depth, benthic algal mat mineral weight and organic content, and mat total phosphorus and total nitrogen would vary more across space than time; and (2) the cumulative diatom core species abundance would increase with decreasing nutrient concentrations and depth. We found that (1) the abundance of 2 of the core species and the environmental conditions varied more between sites than between seasons and years, and (2) the cumulative abundance of the 4 diatom core species increased with oligotrophic and shallow water conditions. This study shows how, on average, the 4 diatom core species comprise similar to 82% of the total diatom abundance in the Everglades' benthic algal mats because these species are adapted to nutrient limitation and water scarcity. Similar dynamics may be at play in other wetlands undergoing hydrological and nutrient changes, thus warranting future work to predict these primary producers' responses to such changes.