FWRI Scientist Publications on Stony Coral Tissue Loss Disease

*Authors in bold are FWC researchers

Authors: Erinn Muller, Constance Sartor, Nicholas Alcaraz, and Robert van Woesik

How was Stony Coral Tissue Loss Disease spread on large scales? How contagious is it? What may have influenced the spread of the outbreak? A team of researchers including one from the FWRI Information Science and Management Group wanted to answer these questions. By looking at data collected from a number of sources, including the FWC’s Coral Reef Evaluation and Monitoring Project (CREMP), researchers were able to pick out patterns from the dataset. They found that the spread of the disease was linear and moved fast – up to 300 feet a day. Because the disease spread slightly faster to the north than it did south, scientists propose that the Gulf Stream drove the spread north, and back eddies coming off the Gulf Stream helped spread the disease south. Based on the patterns of spread and how the disease clustered on nearby reefs, the disease is highly contagious. Higher diversity, deeper reefs were at greater risk of this disease than shallower, lower diversity reefs. Although the disease started during a major global bleaching event, its linear mode of movement suggests there is little seasonal influence. It also doesn’t seem to be affected by water temperature, as scientists noticed no relationship between rate of spread and temperature. This study shed light on the movement patterns of this disease, which will be important for Caribbean countries as they start responding to it.

Citation: Muller EM, Sartor C, Alcaraz NI and van Woesik R (2020) Spatial Epidemiology of the Stony-Coral-Tissue-Loss Disease in Florida. Front. Mar. Sci. 7:163. doi: 10.3389/fmars.2020.00163

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Authors: Stephanie Rosales, Abigail Clark, Lindsay Huebner, Rob Ruzicka, and Erinn Muller

In this study, scientists from the University of Miami, Mote Marine Laboratory, and the FWRI Coral Research Program wanted to learn if bacteria are playing a role in the stony coral tissue loss disease outbreak. They identified bacteria taken from samples of healthy and diseased corals, water, and sand from three different zones. These zones included where the outbreak was active, where the outbreak was past its peak, and areas where the disease had yet to arrive. They found different types of bacteria depending on the zone and coral species sampled. They also found that bacteria from the orders Rhodobacterales and Rhizobiales were always higher in abundance in diseased coral tissue in all coral species studied. These bacteria were also present in higher numbers in water and sand samples from diseased reefs. These bacteria may not be the main cause of the disease, but it is likely they are still playing a role in the disease. For example, they may be taking advantage of an already sick coral and making it worse. How exactly are the bacteria impacting the diseased corals? How are they spreading through the environment? Further research is needed to fully tease out their findings and better understand the role these bacteria have in the outbreak.

Citation: Rosales SM, Clark AS, Huebner LK, Ruzicka RR and Muller EM (2020) Rhodobacterales and Rhizobiales Are Associated With Stony Coral Tissue Loss Disease and Its Suspected Sources of Transmission. Front. Microbiol. 11:681. doi: 10.3389/fmicb.2020.00681

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Authors: Bill Sharp, Colin Shea, Kerry Maxwell, Erinn Muller, and John Hunt

How does stony coral tissue loss disease move across a reef? The FWRI Restoration Ecology team based out of Marathon’s South Florida Regional Lab set out to answer this question by watching how the disease moved across four reef sites in the Middle Florida Keys. SCTLD first hit the study reefs in February 2018 and moved from east to west. The disease appears to be spread mainly by water movement – how close corals were to each other had no impact on the spread. However, the size of the coral did, as larger corals were more likely to become infected. Corals in the Families Meandrinidae (including maze and flower corals) and Faviidae (including brain corals) fared the worst, with half of the colonies of these species dying. Inshore sites fared better than offshore sites, with a smaller loss of living coral tissue and slower rate of disease spread. These findings indicate that corals at inshore reefs may have some natural resilience to the disease – of great interest to those working to combat the effects of this disease.

Citation: Sharp WC, CP Shea, KE Maxwell, EM Muller, and JH Hunt. 2020. Evaluating the small-scale epidemiology of the stony-coral -tissue-loss disease in the middle Florida Keys. PLoS ONE 15(11): e0241871.

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Authors: Jan Landsberg, Yasunari Kiryu, Esther Peters, Patrick Wilson, Noretta Perry, Yvonne Waters, Kerry Maxwell, Lindsay Huebner, and Thierry Work

What does stony coral tissue loss disease look like on a cellular level? What can this tell us about the cause of the disease? The FWRI Fish and Wildlife Health team teamed up with scientists from the Coral Research Program and Restoration Ecology Team to answer these questions. By looking at coral tissue through microscopes, researchers found that the disease appears to affect the coral’s relationship with its zooxanthellae – the tiny beneficial algae that lives inside coral. The coral provides zooxanthellae with a safe place to live, and the zooxanthellae shares the “food” it creates from photosynthesis. The disease first appears deep inside the coral, close to the skeleton. This is where most of the corals’ zooxanthellae are found. The zooxanthellae start to die, along with coral cells. These changes make their way through the coral tissue, until it can be seen as living tissue sloughing off the coral skeleton. Even in some corals showing no outward signs of the disease at reefs having an outbreak, the scientists found microscopic evidence of the disease. The cause of the disease remains a mystery for now - no obvious causes, such as bacteria, were found within the diseased tissue. Regardless of cause, reducing sources of stress, like pollution, will help corals resist disease.

Citation: Landsberg JH, Kiryu Y, Peters EC, Wilson PW, Perry N, Waters Y, Maxwell KE, Huebner LK and Work TM (2020) Stony Coral Tissue Loss Disease in Florida Is Associated With Disruption of Host–Zooxanthellae Physiology. Front. Mar. Sci. 7:576013. doi: 10.3389/fmars.2020.576013

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