Satellite-Observed Black Water Events off Southwest Florida: Implications for Coral Reef Health in the Florida Keys National Marine Sanctuary

Jun Zhao,Ryan Smith,Brian Lapointe,Nelson Melo,Elizabeth Johns,Chuanmin Hu

doi:10.3390/rs5010415

Abstract

A “black water” event, as observed from satellites, occurred off southwest Florida in 2012. Satellite observations suggested that the event started in early January and ended in mid-April 2012. The black water patch formed off central west Florida and advected southward towards Florida Bay and the Florida Keys with the shelf circulation, which was confirmed by satellite-tracked surface drifter trajectories. Compared with a previous black water event in 2002, the 2012 event was weaker in terms of spatial and temporal coverage. An in situ survey indicated that the 2012 black water patch contained toxic K. brevis and had relatively low CDOM (colored dissolved organic matter) and turbidity but high chlorophyll-a concentrations, while salinity was somewhat high compared with historical values. Further analysis revealed that the 2012 black water was formed by the K. brevis bloom initiated off central west Florida in late September 2011, while river runoff, Trichodesmium and possibly submarine groundwater discharge also played important roles in its formation. Black water patches can affect benthic coral reef communities by decreasing light availability at the bottom, and enhanced nutrient concentrations from black water patches support massive macroalgae growth that can overgrow coral reefs. It is thus important to continue the integrated observations where satellites provide synoptic and repeated observations of such adverse water quality events.

Highlights

The Florida Keys National Marine Sanctuary (FKNMS) is a marine protected area designated in 1990 to protect the coral reef ecosystems adjacent to the Florida Keys (Figure 1)
January 2012, the black water patch extended from the region near the coast to the region to the north of the Florida Keys
The patch nearly disappeared around 12 April. These movement patterns of the black water patch were consistent with the results obtained from satellite-tracked surface drifters deployed between late October and December 2011 in this region (Figure 4)

Summary

Introduction

The Florida Keys National Marine Sanctuary (FKNMS) is a marine protected area designated in 1990 to protect the coral reef ecosystems adjacent to the Florida Keys (Figure 1). Mangrove-fringed islands, coral reefs, and more than 6,000 species of marine life within the boundaries of the FKNMS make the area outstanding in terms of conservational, recreational, commercial, ecological, historical, scientific, educational, and aesthetic values [1,2]. The increasing population and development in the Florida Keys, together with agriculture and other human activities on the mainland of South Florida, imperil the downstream FKNMS ecosystems. Between 1991 and 1995, extensive cyanobacterial blooms developed in Florida Bay and the FKNMS in response to increased flows of nitrogen-enriched water from the Everglades Agricultural Area via Shark River

Results

Discussion

Conclusion