Response of the diatom Encyonema evergladianum to environmental changes associated with sea level rise in the Caribbean Basin

Background/Question/Methods

The karstic, freshwater wetlands of the Everglades and Caribbean are threatened by saltwater intrusion due to sea level rise, a problem that is exacerbated by the lack of freshwater delivery from upstream due to water management practices. In the Everglades, saltwater intrusion has been linked to elevated phosphorus (P) levels due to the upside-down nature of this coastal landscape where the marine end-member is the major source of this limiting nutrient.

Calcareous periphyton mats are a ubiquitous and important component of karstic wetlands found throughout the Caribbean Basin and contain a characteristic diatom community that is reacting in diagnostic ways to these changes in water quality. Encyonema evergladianum is a keystone diatom species in these mats and may provide insight into the relationship between periphyton abundance and shifting water sources. We propose that this species is a potentially powerful indicator of water quality changes associated with saltwater intrusion into these wetlands and responds to these changes in ways that reflect whole periphyton community production trends. In this study, we explore the response of E. evergladianumabundance to periphyton mat TP, mat mineral content, and conductivity in the Florida Everglades and similar Caribbean wetlands. 

Results/Conclusions

We found that in both the Everglades and the Caribbean, E. evergladianum is highly sensitive to changes in the mineral content (calcareousness) of the periphyton mats in which they live and decreases in mat mineral weight are strongly correlated to TP concentration. Furthermore conductivity was positively correlated with TP and negatively correlated to the mineral content of the mats in the Everglades, but these relationships were not seen in the Caribbean. These results suggest that calcareous periphyton mats are the preferred niche of E. evergladianumand that loss of this mat structure is correlated to elevated TP which, in the Everglades, is coupled with elevated conductivity.

This study provides preliminary support for the use of E. evergladianum as an indicator species in karstic, freshwater wetlands threatened by elevated salinity and phosphorus associated with saltwater intrusion. Mesocosm experiments are underway to test the individual and synergistic effects of increased salinity and phosphorus on E. evergladianum abundance and periphyton mat calcareousness in order to disentangle the direct and indirect drivers of changes in E. evergladianum abundance.