White plague (coral disease)

White plague is a suite of coral diseases of which three types have been identified, initially in the Florida Keys. They are infectious diseases but it has proved difficult to identify the pathogens involved. White plague type II may be caused by the gram negative bacterium Aurantimonas coralicida in the order Hyphomicrobiales but other bacteria have also been associated with diseased corals and viruses may also be implicated.

History

In 1977, a disease of scleractinian corals appeared on reefs off the Florida Keys in the United States and was termed white plague. It caused white lesions and was shown to be an infectious disease, being particularly prevalent in Mycetophyllia ferox. This disease caused little mortality and occurred sporadically, but was still present in the area in 1984. It is now known as white plague type 1.^[1]

In 1995, a new coral disease was described as an

Dichocoenia stokesi and cultured in the laboratory, subsequently being used to inoculate two healthy colonies which then developed the disease.^[3] In the next few months, it had spread over 200 km (124 mi) of reef and was killing seventeen species of coral. Over the next four years, it spread further, but was most severe in different regions each year.^[1]

White plague is an enigmatic disease. Further research cast into doubt the role of A. coralicida as a causative agent by finding that bacterium on healthy parts of colonies of Orbicella annularis affected by white plague disease but absent from diseased parts. In these diseased colonies, an α-proteobacterium similar to one which causes a disease in juvenile oysters has been implicated, being found on the diseased parts of the coral but not on the sound tissues. These anomalous findings may be caused by the fact that there are two or more diseases with similar symptoms, both known as white plague.^[3]

In 1999, a third and still more virulent variant appeared in the northern Florida Keys. White plague type III mostly affected

Colpophyllia natans and Orbicella annularis.^[4]

A white-plague like disease reported from the

Thalassomonas loyana. Further research has shown that viruses may be involved in white plague infections, the coral small circular ssDNA viruses (SCSDVs) being present in association with diseased tissue. This group of viruses is known to cause disease in plants and animals.^[5]