Florida’s coral reefs are currently experiencing a multi-year outbreak of coral disease that have resulted in the mortality of millions of corals across southeast Florida, Biscayne National Park, and the Upper and Middle Florida Keys. In early September 2017, Hurricane Irma impacted the entire FRT. The purpose of this project was to conduct field surveys to identify the current state of the coral reefs in southeast Florida and coordinate with other concomitant reef tract efforts to improve the regional understanding of the extent of the disease outbreak and identify recent hurricane injury to direct future restoration. Through a broader partner network, 62 sites from Key Biscayne to St. Lucie Reef were targeted for survey. Twenty-nine sites were chosen based on previous data that indicated high coral values of richness, density, and/or cover at those locations. Thirty-three sites were chosen with FDEP reef managers where there were previous data gaps. A new protocol was developed, which was a modification of the Florida Reef Resilience Program (FRRP) Disturbance Response Monitoring (DRM) methodology. This included collecting additional disease and injury metrics in transects and by rover diver to prioritize sites for triage and restoration activities.
The analyses showed that hurricane impacts on corals were quite low where 82.3% (51/62) of the sites were listed as Tier 3 (minimal impact/triage not needed). There were nine sites listed with at least some Tier 2 damage (moderate impact/secondary priority if resources allow). Site 33 was listed as 100% Tier 2 and Site 30 was 100% Tier 1 (triage recommended). Site 30 had some impressive impacts including large (2 - 5 m) slabs of fractured hardbottom lifted and thrown several meters eastward atop other hardbottom affecting a ~ 2 m Orbicella faveolata colony that was mostly covered leaving only the very top exposed. One day of triage was conducted at a dense Acropora cervicornis patch to stabilize many coral fragments and collect loose debris (mostly gorgonians). Lack of capacity and weather deterred further triage attempts for several months. It was eventually decided that triage efforts were not a priority for SE Florida because of the ongoing disease. Coral disease prevalence was high. The rover diver surveys found 11.4% total disease prevalence across all sites (243/2130) infecting 43.3% of the species found, and prevalence at the southern sites was higher. Mean density and richness at sites with previous relatively high values were considerably lower than their historic values with a 57.2% and 42.2% decrease respectively, indicating profound changes in the coral populations. Perhaps the most striking result was the low density of Eusmilia fastigiata, Meandrina meandrites, Dichocoenia stokesi, Colpophyllia natans, Pseudodiploria strigosa, Diploria labyrinthiformis, and Orbicella annularis. We found 36 individuals of all these species combined out of 1,165 colonies (3.1%). A comparison of the percentages of each species to the total in the southern sites to those of the 2004 annual monitoring data in Broward County showed drastic differences in the populations that likely go beyond any bias in survey differences.
These data support the idea that the Florida Reef Tract is becoming more homogenous and dominated by eurytopic, generalist species that can tolerate a wider range of environmental conditions. However, this disease event contradicts the notion that the present assemblages are stable because they have “withstood a number of recent perturbations, including thermal stress and disease”. After moving through the more vulnerable species, the disease is now affecting hardier species thought to be more resistant to stress like Montastrea cavernosa and Siderastrea siderea. It is important that actions are taken to curtail this disease quickly so that the remaining population can stabilize and recovery and restoration efforts can begin. There should be continued focus on the remaining corals because they are apparently resistant to the disease and perhaps better acclimated to the stressful conditions over the past several years.
Brian K. Walker. 2018. Southeast Florida Reef-Wide Post-Irma Coral Disease Surveys : 1 -37. https://nsuworks.nova.edu/occ_facreports/128.