Molecular identity and nutrient limitation of Lyngbya wollei mat communities in north Florida freshwater systems

Lyngbya wollei (Speziale ex Gomont) is a filamentous cyanobacterium that is capable of nitrogen fixation. Within Florida springs, L. wollei is an opportunistic invader that can smother both native and invasive submerged aquatic vegetation with its thick benthic mats (up to 1-1.5 kg dry weight m-2), and it has been shown to produce toxins (neurotoxins and hepatotoxins). Blooms of L. wollei persist in many recreational and drinking water supplies within the southeastern United States. The inability to find a statistically significant relationship between L. wollei biomass in Florida springs and nutrient concentrations (nitrogen, phosphorus) has led to the hypothesis that the present standard for identification of freshwater L. wollei may in fact encompass multiple species. There is a need to accurately identify this cyanobacterium and identify limiting nutrients, the input of which may be controlled by water managers in an effort to reduce L. wollei biomass. We sequenced partial 16S rDNA and nifH genes from L. wollei mats that were identified using the current taxonomic description for L. wollei. The 16S and nifH datasets contained diverse sequences. The majority of sequences were found to be from L. wollei filaments and unidentified cyanobacteria. Of the unidentified cyanobacteria, six 16S sequences corresponded (>98% similarity) to a known toxin-producing Phormidium sp. The combined phylogenetic analyses of the 16S rDNA and nifH genes, in conjunction with morphological analysis (cell width and length), indicates that the current L. wollei description in the literature represents two or possibly three species. No correlation was found between the species divisions and dissolved inorganic nitrogen concentration and N:P for the collection sites. To determine limiting nutrients for effective mitigation of L. wollei biomass in Florida springs, four dissolved inorganic nutrient addition bioassays were employed over the course of one year. Primary productivity results showed that L. wollei primary productivity was limited by both nitrogen and phosphorus. Therefore, L. wollei biomass will most likely be reduced by lowering nitrogen and phosphorus loading in affected springs