Stromatolitic mats are highly productive in subtropical, calcareous wetlands, with biomass estimates ranging from 50-1200 g m^-2. These values often exceed biomass of plant counterparts, so in these systems stromatolites regulate water concentrations of gases and nutrients, fuels detrital and consumer food webs and influence soil formation and quality.  Mats are inhabited by a diverse microbial consortium that maintains high rates of production despite very low nutrient concentrations inherent to calcitic wetlands.  We sampled freshwater stromatolites in 4 wetland complexes in South Florida, USA, Black River Morass, Jamaica, New River Lagoon, Belize and Sian Ka’an, Mexico during dry and wet seasons of 2005-2008. 

Results/Conclusions

We found comparable ranges of production among the 4 widely separated marshes, with highest values at all sites occurring during the wet season.  Compositional overlap in algal assemblages was high, with all sites containing the same dominant 21 taxa, many of which were previously considered endemic to the Florida Everglades. Spatial patterns of production and composition were related to phosphorus (P) availability in the stromatolitic matrix. Patterns in all 4 wetland complexes showed the same perplexing relationship described for the Everglades, with increased P availability being associated with declining primary productivity. We discuss ramifications of nutrient enrichment to carbon sequestration and food web structure in subtropical habitats dominated by stromatolites.