• cyanotoxins;
  • Everglades;
  • grazing;
  • periphyton;
  • secondary production

Production of toxic secondary metabolites by cyanobacteria, collectively referred to as cyanotoxins, has been well described for eutrophied water bodies around the world. However, cohesive cyanobacterial mats also comprise a significant amount of biomass in subtropical oligotrophic wetlands. As these habitats generally do not support much secondary production, cyanotoxins, coupled with other physiological attributes of cyanobacteria, may be contributing to the minimized consumer biomass. Periphyton from the Florida Everglades has a diverse and abundant cyanobacterial assemblage whose species produce toxic metabolites; therefore, by screening periphyton representative of the greater Everglades ecosystem, six different cyanotoxins and one toxin (domoic acid) produced by diatoms were identified, ranging in content from 3 × 10−9 to 1.3 × 10−6 (g · g−1), with saxitoxin, microcystin, and anatoxin-a being the most common. While content of toxins were generally low, when coupled with the tremendous periphyton biomass (3–3,000 g · m−2), a significant amount of cyanotoxins may be present. While the direct effects of the toxins identified here on the local grazing community need to be determined, the screening process utilized proved effective in showing the broad potential of periphyton to produce a variety of toxins.