During the summer and fall of 2015, the Florida Reef Tract (FRT) experienced widespread coral bleaching and an unprecedented level of coral disease. In coordination with many partners, the Florida Department of Environmental Protection’s Coral Reef Conservation Program (CRCP) conducted a significant response effort to better understand the prevalence and impacts of these stressors.
Large-scale mass coral bleaching events are driven by extreme sea temperatures (warm or cold) and are intensified by sunlight stress associated with calm, clear conditions. The warmest water temperatures usually occur between August–October. However, the water can start heating up as early as June and last as late as November. The summer of 2015 proved to be another unusually warm season for the FRT with flat, clear, calm conditions that resulted in warmer water temperatures that favored coral bleaching.
Coral bleaching is a stress reaction of the coral animals that happens when they expel their symbiotic algae, zooxanthellae, which is their main food source. Bleached corals are still living but are less likely to reproduce, are more susceptible to disease, predation and mortality, and are less able to resist or recover from other stressors. If stressful conditions subside soon enough, the corals can regain their zooxanthellae and survive the bleaching event; however, if stresses are severe or persist, bleaching can lead to the death of corals.
While records show that coral bleaching events have been occurring for many years throughout South Florida, the National Oceanic and Atmospheric Administration (NOAA) indicates that bleaching events have steadily increased in frequency and severity during the last few decades, and that the Caribbean region (which includes Florida) is in the middle of a three-year bleaching cycle. The CRCP monitors bleaching events through the SEAFAN BleachWatch program (a citizen-driven early warning network for coral bleaching) and by teaming up with The Nature Conservancy and many partners that conduct Florida Reef Resilience Program Disturbance Response Monitoring (DRM) surveys at sites throughout the FRT, documenting coral bleaching and disease. Preliminary DRM results classified the 2015 bleaching event as “moderate to severe.”
In addition to the bleaching events of the summer, a wide-spread coral disease event also affected the southeast Florida region, particularly in Miami-Dade and Broward counties. CRCP staff first observed disease at sites in Miami-Dade County in April, with later reports confirming disease at locations as far north as Broward County, and south through Biscayne National Park. Multiple diseases were observed including black band, dark spot, and the most prevalent: the white plague or white plague-like disease that affected multiple species of coral, including some listed as “Threatened” under the Endangered Species Act (Orbicella annularis/Boulder Star Coral, Dendrogyra cylindrus/Pillar Coral).
Coral diseases can be viral or bacterial, although the origin is difficult to determine. A certain amount of microbes (pathogens) are always present in an ecosystem and a background level of disease is not unusual in southeast Florida, however elevated microbial levels can lead to an increased prevalence of coral disease. NOAA’s Coral Disease and Health Consortium dictates that diseases and other stressors have dramatically increased over the past ten years, resulting in unprecedented losses of live coral tissue. These losses disrupt the delicately balanced marine ecosystem.
The CRCP coordinated a multi-tiered, multi-partner response effort to characterize the prevalence of the disease outbreak and understand potentially contributory environmental factors by performing DRM surveys. Tissue samples were collected to try to determine the likely pathogens. Partners included the Nature Conservancy, Florida Fish and Wildlife Conservation Commission, the National Park Service, Florida Park Service, Broward, Miami-Dade, and Palm Beach counties, Nova Southeastern University, the University of Miami, NOAA, and the Florida Keys National Marine Sanctuary. Preliminary results showed high disease prevalence at DRM sites, and observations outside of the DRM surveys reported as much as 80-100% of corals infected with disease. The disease moved so quickly that some corals died in as little as two weeks. Additional monitoring will continue this winter with results available in the spring of 2016.
Coral recovery is possible by reducing the impacts of local stressors. Boaters, divers, and snorkelers can reduce physical impacts to corals by using mooring buoys instead of anchoring, and being aware of their buoyancy to avoid kicking or touching the corals. If divers observe disease, they should take care not to dive elsewhere as to avoid potential disease transmission. Divers and snorkelers can learn how to identify coral bleaching and submit reports through the SEAFAN BleachWatch program. For more information or to request a SEAFAN BleachWatch class for your group, please email email@example.com.[PF1] [ZA2]