Kings Bay is a large, tidally influenced artesian springs complex that forms the headwaters of Crystal River on Florida’s gulf coast. Internationally known as one of the most world’s important refuges for the West Indian manatee (Trichechus manatus), in recent decades Kings Bay has seen progressive declines of native submersed aquatic vegetation, reductions of water clarity, and increased coverage of potentially toxic filamentous cyanobacteria. In 2012, a pilot study called the Kings Bay Adaptive Management (KBAM) project established in situ treatment and control plots to document ecosystem processes associated with increased coverage by two floating aquatic plants: water hyacinth (Eichhornia crassipes) and water lettuce (Pistia stratiotes). The overall purpose of this project was to begin answering the question as to whether increased populations of these floating plants, both of which are listed as Class 1 invasive species and typically managed through aggressive herbicidal control, might facilitate long-term recovery of native submersed plant communities. Longitudinal comparisons of water quality, surveys of aquatic animal diversity and abundance, and observations of manatee grazing pressure were undertaken over the four-year study period in an attempt to quantify novel ecosystem self-organization associated with increased floating plant coverage.
Results/Conclusions
The KBAM study provided a series of key findings. First, stratification of the freshwater/saltwater interface at the semi-estuarine study site allowed for survival and growth of water hyacinth and water lettuce, both of which are relatively intolerant to sustained saltwater exposure. Second, manatee grazing pressure provided a natural control on floating plant populations, to the point that water hyacinth and water lettuce could not be established in the treatment area without manatee exclusion. Third, floating plant areas that were protected from manatee herbivory quickly formed into complex habitat structures that supported much higher abundances and diversities of macro-invertebrates and small fish than control sites dominated by filamentous algae. Consistent with previous studies of floating plant ecology in Florida, especially high densities of odonates, grass shrimp (Palaemonetes paludosus), peninsula crayfish (Procambarus paeninsulanus), least killifish (Heterandria Formosa), and bluefin killifish (Lucania goodei) were recorded in water hyacinth patches. Water quality measures indicated reductions of turbidity and some differences in oxygen profile within floating plant mats as compared to the control site, but – likely due to the small size of the treatment area – were otherwise inconclusive. Larger field studies coupled with laboratory experiments of floating plant and cyanobacteria competition dynamics provide logical next steps to this study.