Variation in periphyton biomass and species composition in Lake Okeechobee, Florida (USA): Distribution of algal guilds along environmental gradients

Many environmental factors (disturbance, resources, grazing pressure) collectively interact to influence periphyton abundance and species composition, particularly in large lakes where environmental gradients are commonplace. We assessed the link between variation in key environmental factors and changes in periphyton biomass and taxonomic composition in Lake Okeechobee, Florida, USA. Epiphyton and epipelon were collected quarterly from plant grab samples (10 sites) and sediment cores (15 sites) at fixed locations during 1994-95 (n = 98) in the lake. Samples were analyzed microscopically to estimate periphyton biomass and species composition, and physical and chemical conditions at each site were measured. Periphyton biovolume was high throughout the year (range epiphyton: 0.05-175 mm³/g and epipelon: 0.03-16 mm³/cm²) and was dominated by diatoms and cyanobacteria (30-50 % on average), with chlorophytes being subdominant (4-20 %). Although epipelic cyanobacteria were more abundant during the wet season (June-October), limited seasonal variation was observed for other groups, and this was attributed to the relatively constant climate characteristic of this subtropical geographic region. Both epiphyton and epipelon biovolume were greatest in protected inner marsh sites, while epipelon was also abundant in the pelagic zone where a meroplankton assemblage was dominant. Functional groups of species (guilds) were formed according to their adaptive response to changing resources and disturbance. In turn, algal guilds in Lake Okeechobee (flocculent, metaphyton, adnate, meroplankton mats) reflected local nitrogen and phosphorus inputs as mediated by strong lake-wide gradients in light penetration and physical disturbance.