Mastogloia smithii var lacustris Grun.: A Structural Engineer of Calcareous Mats in Karstic Subtropical Wetlands

Mastogloia smithii var. lacustris Grun. is the dominant diatom in periphyton mats of the calcareous, freshwater to brackish wetlands of Caribbean coasts. Despite oligotrophy, frequent desiccation, high irradiance and temperatures, and occasional fire, periphyton communities in these wetlands can produce over 2000 g m-2 of organic biomass, prompting studies that examine stress resistance and maintenance of algal mats under extreme conditions. The diatom flora inhabiting periphyton mats from over 500 sites in the Florida Everglades and similar wetlands in Belize, Jamaica and Mexico was examined, and M. smithii var. lacustris was a persistent component, present in 97% of samples and comprising up to 80% of a diverse diatom assemblage. Valves at various stages of division were observed encased in extracellular polysaccharide that exceeded the cell volume; SEM observations confirm issuance from mantle pores resulting in suspension of the cell in a matrix dominated by cyanobacterial filaments. Using corresponding biophysical data from the collection sites, we define the optima for M. smithii var. lacustris along salinity, pH, phosphorus, and water depth gradients. Experiments revealed a collapse of M. smithii var. lacustris populations in the presence of above-ambient phosphorus concentrations and a rapid resurgence upon reflooding of desiccated mats. This widespread diatom taxon appears to play a critical role similar to that of cyanobacteria in microbial mats, and its disappearance in the presence of enrichment threatens biodiversity and the natural function in these systems that are increasingly influenced by urbanization

Spatiotemporal patterns in community structure of macroinvertebrates inhabiting calcareous periphyton mats

Calcareous floating periphyton mats in the southern Everglades provide habitat for a diverse macroinvertebrate community that has not been well characterized. Our study described this community in an oligotrophic marsh, compared it with the macroinvertebrate community associated with adjacent epiphytic algae attached to macrophytes in the water column, and detected spatial patterns in density and community structure. The floating periphyton mat (floating mat) and epiphytic algae in the water column (submerged epiphyton) were sampled at 4 sites (1 km apart) in northern Shark River Slough, Everglades National Park (ENP), in the early (July) and late (November) wet season. Two perpendicular 90-m transects were established at each site and 100 samples were taken in a nested design. Sites were located in wet-prairie spikerush-dominated sloughs with similar water depths and emergent macrophyte communities. Floating mats were sampled by taking cores (6-cm diameter) that were sorted under magnification to enumerate infauna retained on a 250-μm-mesh sieve and with a maximum dimension >1 mm. Our results showed that floating mats provide habitat for a macroinvertebrate community with higher densities (no. animals/g ash-free dry mass) of Hyalella azteca, Dasyhelea spp., and Cladocera, and lower densities of Chironomidae and Planorbella spp. than communities associated with submerged epiphyton. Densities of the most common taxa increased 3× to 15× from early to late wet season, and community differences between the 2 habitat types became more pronounced. Floating-mat coverage and estimated floating-mat biomass increased 20 to 30% and 30 to 110%, respectively, at most sites in the late wet season. Some intersite variation was observed in individual taxa, but no consistent spatial pattern in any taxon was detected at any scale (from 0.2 m to 3 km). Floating mats and their resident macroinvertebrate communities are important components in the Everglades food web. This community should be included in environmental monitoring programs because degradation and eventual loss of the calcareous periphyton mat is associated with P enrichment in this ecosystem.