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

ABSTRACT

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 ∼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.

KEYWORDS:

• benthic mats
• core species
• diatoms
• long-term data
• wetlands

Acknowledgements

We especially thank Franco Tobias for identifying and counting diatoms and for developing and maintaining the taxonomic database. We also gratefully acknowledge Lara Panayotoff, Christine Taylor, Sylvia Lee, Nicholas Schulte, Emily Nodine, and Josette La Hée for identifying and counting diatoms; Rafael Travieso for collecting the samples; Mike Rugge for GIS assistance on Figure 1, Heather Henkel and Bryan McCloskey (USGS) for assistance with EDEN data; John Kominoski for advice on statistical analyses; and John Kominoski, Viviana Mazzei, and Nicholas Schulte for providing useful comments on manuscript drafts. This research was funded by the Florida Coastal Everglades Long Term Ecological Research program under Cooperative Agreements #DEB-1237517, #DBI-0620409, and #DEB-9910514. This is contribution number 876 from the Southeast Environmental Research Center in the Institute of Water & Environment at Florida International University.

ORCID

L. Marazzi http://orcid.org/0000-0002-3098-7059