WHILE Bermuda's coral reefs have not yet shown signs of the degradation that is afflicting reefs world-wide, they should be considered in a "high-risk" category.

Speaking last night at the Bermuda Biological Station For Research (BBSR), Associate Research Scientist Dr. Ross Jones outlined the causes and significance of increasingly frequent coral 'bleaching' events, with special reference to Bermuda's reefs.

When corals lose their symbiotic algae, they also lose their colour, Dr. Jones explained, and the loss of this microscopic algae, vital to coral health, slows the rate of growth and increases mortality.

"If you have a very large reef system like the Great Barrier reef in Australia, you can have quite high mortality in one area of it, but it will be 'seeded' or repaired by juvenile larvae from surrounding areas that weren't so badly hit," explained Dr. Jones.

"The ability of reefs to bounce back from these 'bleaching' events really depends on how good the population is on the periphery, on the 'outliers'."

Assessments to late 2000 are that 27 per cent of the world's reefs are effectively lost, about 16 per cent by a massive 'bleaching' event in 1998, in nine months of the largest El Ni?o and La Ni?a climate changes ever recorded, and 11 per cent due to pollution and other man-made causes. The reef systems off Florida and in the Caribbean have not escaped damage.

The significance of the decline of corals far to the south of us is that they are the "seed bed" of the Bermuda system. Bermuda's reefs have been seeded over aeons by coral larvae from Florida and the Caribbean, and borne here by the Gulf Stream, they have created reefs of global importance: the most northerly reefs in the Atlantic.

"We are highly isolated geographically, so our ability to recover from 'bleaching' does depend on the health and status of the reefs 'upstream'. The worrying thing is that the reefs 'upstream', in our case Florida and the Caribbean, are very degraded, so that means Bermuda getting more ecologically isolated, and the system has to rely on itself for recovery," he said.

Dr. Jones explained that the success of corals over geologic time-scales has been linked to their evolution alongside microscopic single-cell algae which live within the coral's cells and provide basic life-giving and life-enhancing powers: metabolism, respiration and especially, growth.

'Bleaching' is a physiological distress response of corals, thought to be caused principally by higher atmospheric carbon dioxide, and to global climate change. The symbiotic algae, which provide the kaleidoscope of colours associated with corals, abandon the corals, leaving the bleached white coral skeletons exposed.

"The 'bleaching' phenomenon is linked to elevated sea-water temperatures through climate change, not some change in ocean chemistry," advised Dr. Jones. "It's purely linked to these 'hot spots'. No one had seen those 'bleaching' events until the early Eighties, and they increased in size and frequency, when the average water temperature exceeded 29 degrees centigrade.

"Coral and algae have a symbiotic relationship, but when the water warms to that level, the algae 'dissociates', leaving the calcium carbonate skeleton visible through the relatively transparent animal tissues.

"The coral is still alive, and if you touch it, you don't touch the skeleton, you touch the coral polyp itself," explained Dr. Jones. "A 'bleached' reef looks like a snowfield underwater, like freshly fallen snow. We have had three or four small 'bleaching' events in the last 15 years, but the system recovered."

Bermuda reefs are likely to become more progressively isolated as localised extinctions to the south occur, through pollution, dredging, disease, hurricanes or bleaching. Limited genetic variations in isolated populations will make it difficult to recover from relatively rapid man-made environmental changes, and the decline in adult stocks in the Caribbean, and the resulting reduction in the genetic diversity and volume of coral larvae flowing north on the Gulf Stream will make Bermuda's reefs more isolated over time, and more susceptible to the effects of climate change.

Dr. Jones, an Englishman who graduated from the University of Southampton, began his career at the BBSR in 1989, and spent two years here as a research technician working on an environmental impact assessment associated with the Tynes Bay incinerator.

He then spent ten years working on Australia's Great Barrier Reef, receiving a PhD in coral physiology from James Cook University at Townsville in Queensland in 1996, and completing postdoctoral fellowships at both the University of Sydney's School of Biological Sciences and the University of Queensland's Centre for Marine Studies.

His major research theme is the biology of coral-algae symbiosis, and understanding how that relationship changes during different environmental conditions, both natural and man-made. He specialises in the study of corals: how they react to pollution and stress, and the nature and cause of bleaching and disease.

Dr. Jones explained that the risks to Bermuda's corals from isolation are exacerbated by local pollution, and hardly had to remind his local audience that Bermuda's population density is among the highest in the world.

The attendant problems flow principally from waste disposal, as most sewage is disposed of in cesspits and eventually leaches into the sea. The summer influx of tourists only adds to that problem.

"We are trying to get a feel for how 'closed' or 'open' the system is; a 'closed' system is self-reliant, and an 'open' system relies on regular infusions of new larvae from a gene pool 'upstream'," said Dr. Jones.

"We don't have a firm view yet as to whether Bermuda's reef system is 'open' or 'closed '. We know that, for example, lion fish will appear in local waters from Florida, but we don't know about frequency.

"We don't know if the larvae appear as a big settlement event where we get lots of larvae up from the Caribbean every 200 or 1,000 years, and they propagate and develop and become part of the gene pool.

"But we can certainly assume that they are coming from Florida and the Caribbean, and we can assume that what is happening there is dangerous, and as these systems go down hill, it becomes progressively more dangerous for us.

"That's the more pessimistic view, but offsetting that, is that the northern rim of our coral cover has not changed in 20 years. We have the same 25 per cent hard coral cover we had in 1984, and that may be due to regular tidal flushing of the system by crystal-clear oceanic sea-water.

"Bermuda can do nothing about the problems caused by carbon dioxide and global warming, but we can do everything possible to diminish any effects by local pollution. Corals survived mass extinctions at the end of the Triassic, over 200 million years ago, and at the end of the Cretaceous, 65 million years ago, when a few 'families' survived and re-populated reef systems, but we can't be sure they will survive man."