Stony Coral Tissue Loss Disease (SCTLD) is the deadliest known coral disease to species with a hard skeleton (i.e., Scleractinians), causing rapidly-expanding, bare lesions to form across a coral’s skeleton until there is no more living tissue.
The pathogen or microbes leading to the spread of this disease have yet to be identified.
Yet scientists also investigate the impacts of environmental conditions like high sea surface temperatures and excessive nutrient concentrations on disease transmission – factors known to exacerbate the infection rate of other diseases.
In a new study funded by Florida’s Department of Environmental Protection (FDEP), scientists at AOML and the University of Miami’s Cooperative Institute for Marine and Atmospheric Sciences (CIMAS) that for one ESA-listed endangered coral species, the spread of the disease may be hindered by high sea surface temperatures. Using newly-developed robotic technology, this study may indicate the spread of SCTLD could be inhibited with temperatures typically observed at the peak of the summer months.
SCTLD has spread since it was first identified in 2014 in Virginia Key off of Miami to the Florida Keys, Puerto Rico, Mexico, and Latin America. Recent studies have already shown how coral diseases can be spread via ship’s ballast water, traveling long distances and complicating any solutions to control their spread.
Stony Coral Tissue Loss Disease (SCTLD) has spread across the Western Atlantic from Florida to the Greater and Lesser Antilles to Latin America. (From Kramer et al. 2022, FIELD GUIDE for Monitoring Coral Disease Outbreaks in the Mesoamerican Region: Location of countries/territories where SCTLD has been confirmed in the Wider Caribbean Region as of July 2022.
Higher sea surface temperatures and excessive nutrient levels have also been known to increase disease transmission and susceptibility.
However, in this new study led by Ana Palacio, Ph.D., a CIMAS Assistant Scientist with AOML’s Coral Program, they found that higher temperatures led to significantly decreased transmission of SCTLD.
In the Experimental Reef Lab located at the University of Miami’s Rosenstiel campus, fragments of the coral were exposed to the disease across isolated tanks with one of four combinations of average temperatures (28 degrees Celsius) and high temperatures (31 degrees Celsius) and with or without increased levels of ammonium.
Using two robotic systems programmed, designed, and integrated into the lab space by scientists at AOML, the team was able to finely manipulate and control the dosage of nutrients, temperature and disease inoculation for each coral fragment over the two month-long study.
“The use of robotic automation allowed us to precisely and independently treat 80 coral fragments with different nutrients and diseases, while keeping each fragment in its own isolated environment. This breakthrough ensures reliable, contamination-free results and opens new possibilities for high-replication marine disease research.” – Ana Palacio, Ph.D., lead author on the study.
While the study found varying levels of ammonium had no effect on the disease transmission, the team observed that increased concentrations led to a reduced calcification rate among the corals, especially when combined with higher temperatures.
Healthy fragment of Mountainous Star Coral (O. faveolata)
Diseased coral fragment after exposure to SCTLD.
However, SCTLD transmission was drastically reduced among the coral fragments exposed to high temperatures (31 degrees Celsius) – compared to those exposed to the lower temperature (28 degrees Celsius).
This could indicate that the transmission of SCTLD is lower during the peak of the summer months – when waters can climb to an estimated 31 degrees Celsius. And that’s the key to this study.
The Mountainous Star Coral is designated an essential reef-building species in the Caribbean from the Florida Keys to Puerto Rico and the US Virgin Islands, but like others, it’s listed as endangered.
By understanding how and when the impacts of coral diseases are reduced, inhibited by seasonal fluctuations in temperature and other conditions, scientists and managers can better strategize responses to the disease – enhancing predictions of when its likely to spread, what species are the most susceptible and how best to mitigate these impacts across miles of essential coral reefs.
In the Experimental Reef Lab, scientists at AOML are underway with a new series of experiments to identify how multiple environmental stressors – high sea surface temperatures, ocean acidification and hypoxia – impact crucial reef-building coral species.
As part of the larger four-year Florida Regional Ecosystems Stressors Collaborative Assessment (FRESCA), these experiments seek to identify thresholds of coral species to multiple different combinations of stressors that reefs are already experiencing – threats expected to rise in the future.
By investigating corals’ response to multiple stressors, scientists hope to understand what specific conditions entire reefs may face moving forward – and how we can most effectively mitigate the impacts of rising stressors while enhancing the resiliency of a natural barrier and ecosystem we depend on.