A new study partially funded by the NCCOS Ecology and Oceanography of Harmful Algal Blooms (ECOHAB) Program describes the various stressors that have impacted South Florida ecosystems over the last decade, providing insight into how these ecosystems could be managed better.

Scientists from the University of Maryland, Mote Marine Laboratory, and South Florida Water Management District used a long-term water quality and physicochemical data set (2009–2019) to understand why episodic periods of seagrass loss and picocyanobacterial blooms have occurred in Florida Bay. Given the long record of the data set, the study was also able to investigate the impacts of distinct changes in managed flow, drought, El Niño related increases in precipitation, and intensive storms and hurricanes.

Generalized map of South Florida from the southern Everglades to the Florida Keys showing the present distribution of freshwater inflow to Florida Bay from Shark River Slough and Taylor Slough (red arrows). Restored flows from the C-111 spreader canal project are illustrated with blue arrows. Credit: Everglades Foundation.

The study documents that seagrass die-offs and picocyanobacterial blooms in Florida Bay are a result of a number of natural and anthropogenic stressors impacting South Florida ecosystems over the past decade. These stressors include altered water flow through the Everglades and a cascade of downstream biogeochemical changes. Increases in flow and precipitation from storms and hurricanes enhance the input of organic nutrients to Florida Bay. Alterations in flow and precipitation, combined with periods of drought and high salinity conditions, contribute to the favorability of picocyanobacteria relative to phytoplankton species, which make up a balanced aquatic ecosystem.

In Florida Bay, climatological pressures at varying spatial and temporal scales (hurricanes, regional droughts, and global weather patterns) overlap with ongoing local anthropogenic changes in the managed and altered South Florida regional ecosystem. Coastal development, flood control, and eutrophication further increase the complexities affecting management of water flow.

The study concludes that climate change and fluctuations in precipitation cycles will continue to enhance delivery of organic nutrients and material from the freshwater Everglades to Florida Bay, fueling cycles of seagrass die-offs and algal blooms within Florida Bay.

The study was supported in part by the NCCOS ECOHAB project Life and Death of Karenia brevis Blooms in the Eastern Gulf of Mexico.