Life's been hard for coral of late. Scarcely a week goes by without dire news for the charismatic ocean invertebrates.

Take the coral depicted above, for example. The first picture, taken August 20th, 2014, shows a healthy colony going about its business just off Florida's Virginia Key. Only a month later (picture B), the coral was left bleached and vulnerable as high water temperatures forced symbiotic algae to vacate. These symbionts, called zooxanthellae, returned roughly six weeks later when temperatures dropped, but by then, the coral colony was imperiled by a new, far more dangerous threat: white plague. You can see its first traces on the colony's lower right side in picture C. Less than a month later (picture D), the coral was dead and buried by sea sediments.

This story was all too common within Florida's coral reefs between September 2014 and September 2015. During that time, an unprecedented and highly lethal outbreak of white plague struck corals situated off Miami-Dade County. Researchers just revealed the extent of the outbreak in the journal Scientific Reports.

White plague deserves any and all comparisons to the bubonic plague that fueled Europe's Black Death from 1346 to 1353. Once a coral is infected, the disease spreads rapidly. Small lesions or blemishes at the base or surface of the colony quickly blossom into an expanding ring of necrotic tissue. A small colony can be engulfed in less than a week, with only a bare, white skeleton left behind.

The variety of white plague that struck off Florida in 2014 and 2015 was likely caused by a bacterium. Another version -- there are two total -- might be viral in origin.

The researchers surveyed a total of 14 sites all along the coast of Miami-Dade County and found that 61% of coral species were infected. Moreover, virtually all infected coral colonies died. That prevalence is unprecedented, the researchers say. Also remarkable is the fact that most of the colonies were spread over a wide area of more than 130 kilometers with limited coral cover, indicating that this strain of white plague could travel in water and was highly contagious.

Eight species of coral were particularly devastated by the outbreak. The figure below shows the number of colonies surveyed (n) and the proportion infected.

The researchers believe that a prior temperature-induced coral bleaching event greatly enhanced the severity of the outbreak, and further suggest that as climate change raises ocean temperatures, coral disease outbreaks will grow more common, more widespread, and more deadly. What occurred in Florida between September 2014 and September 2015 is merely a preview.

"The high prevalence of disease, the number of susceptible species, and the high mortality of corals affected suggests this disease outbreak is arguably one of the most lethal ever recorded on a contemporary coral reef," the researchers say.

Source: Precht, W. F. et al. Unprecedented Disease-Related Coral Mortality in Southeastern Florida. Sci. Rep. 6, 31374; doi: 10.1038/srep31374 (2016).