Coralline Lethal Orange Disease

Given the importance of coralline algae in contributing material to the reef framework, it was particularly disturbing when a disease of coralline algae was discovered by Mark and Diane Littler in 1993 on reefs of the Cook Islands, Fiji, and the Solomon Islands. This disease is known as coralline lethal orange disease (CLOD), because of its characteristic orange color.

Coralline lethal orange disease Photo by M. and D. Littler
Appearance	A "band" of bright orange slimy material spreads across the algal surface, leaving behind the bare skeletal carbonate remains of the coralline algae. When this material reaches the margin of the algal thallus, it forms upright filaments and globules, similar to those formed by terrestrial slime molds. The globules can be caught by waves and easily spread to nearby corallines.
Globule formation in CLOD Photo by M. and D. Littler
Cause	Microscopic examination of the orange material revealed motile gliding rods of a colonial bacterium in a mucilaginous matrix. The orange globules can be experimentally transferred to other coralline algae and cause the same disease and loss of algal tissue. Additional studies of this bacterium associated with CLOD are under way.
Distribution	Western Indo-Pacific and spreading
Impact	The recent appearance of this disease in the Indo-Pacific could potentially affect the structure and function of many reef sites, since dead corallines, like dead corals, no longer contribute to productivity and carbonate accretion processes and filamentous and fleshy algae overgrow the bare skeletons, inhibiting the settlement and growth of reef-building corals.