White syndrome (WS) destroys our coral reefs, but how?
The loss of corals like Montipora capitata is a rapid, disgusting and irreversible phenomenon of recent times. First in the Atlantic, then the Caribbean and Pacific coral reefs, more and more are being affected. Thierry M. Work, Robin Russell and Greta S. Aeby of the US Geological Survey and the Kaneohe based Hawaii Institute of Marine Biology are out to locate the many causes. They publish today in the Proceedings of the Royal Society B: Biological Sciences.
Montipora White Syndrome and that of many Acripora and many other corals, is caused or rather associated with multiple infections of ciliates, helminth worms and together they cause multiple lesions and a horrific loss of cells and biomass.
In February and March, Hawaiian Montipora were labelled and the monitoring of lesions begun. Gross lesions of various types and the invasive organums were recorded, as well as repair. Single celled ciliates were found in association with necrosis (premature death of cells) while helminths were found with necrosis and where wounds were repairing, predominating at the lesions.
No viruses or bacteria were seen or suspected, despite the tissue loss. Host response is given the responsibility of some lesions, even though only one organism was found in each of the "gross" lesions. If the immune-response of corals is disturbed, it could allow these invaders into the coral lesions, both small and gross. The analogy is with sea turtles that have heavy infections of bacteria and parasites, due to immune-suppression. Perhaps easier to understand is our own AIDS association with fungal and bacterial diseases.
Credit: © Proceedings of the Royal Society B: Biological Sciences
Above: Gross lesions of WS in Montipora capitata - Top to bottom - (a to c) Scale bars, 17 cm
(a) Multifocal; note lesions indicated by white arrows
(b) Locally extensive; note central area of tissue loss revealing bare white skeleton (small white arrow) surrounded by an ill-defined band of pale tissues (block arrow)
(c) Diffuse; note extensive area of tissue loss revealing intact bare white skeleton with some green colouring indicating overgrowth of algae
Light is being shed at last on the potential causes of WS in coral and its responses. There is certainly a slow response and another almost opposite response which is temporary but rapidly destructive. There is a "new" kind of parasitic chimaera called IGMS (intragastrovascular multicellular structures, if you really want to know) which was associated with necrosis.
This may be symptomatic of some loss of the immune response or a clue as to how to prevent further loss of coral. Its genetic origins are known and perhaps genetics is the next tool to locate the original cause of WS.
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