Sewage nutrients fuel coral disease
Nutrient rich water damages Caribbean corals by encouraging the spread of infections, a marine study has found. This is the first experiment in the ocean to show how agricultural run off and sewage may nike air max 1 destroy coral.
It will also fuel debate about whether run off from Queensland’s sugar cane and cattle stations threatens the relatively pristine Great Barrier Reef, home to almost one fifth of the world’s coral reefs.
“We’ve found pretty convincing evidence of a nutrient effect. It’s really happening,” says John Bruno of the University of North Carolina, Chapel Hill, who was lead researcher on the study.
While nutrients may increase the severity of coral disease, the root cause of epidemics remains largely a mystery, says Bruno. Around 80 per cent of Caribbean coral has been lost to disease in the past 20 years, but the decimation occurred across the whole region, not just where pollution is a problem.
However, the nutrients from agricultural run off and untreated sewage, or even natural causes that bring deep water to the surface, may be making epidemics more severe in the Caribbean. And the problem could worsen.
In one experiment, the researchers grafted pieces of sea fan infected with aspergillosis onto healthy sea fans in reefs off Mexico’s Yucatn coast. Then, every week for three months, they attached a fresh bag of slow release garden fertiliser a few centimetres from the graft.
The bags increased the nutrient concentration to between two and 10 times background levels, equivalent to a mildly polluted reef. Exposed to extra nutrients, about nike air max 1 twice as much of the sea fan colony became infected with aspergillosis compared with colonies that received the graft but no extra nutrients.
Bruno and his colleagues also studied two species of the reef building hard coral Montastraea. This can take hundreds of years to grow, so rather than infect healthy coral, the team studied ones that were already infected with yellow band disease. Upsetting the nutrient balance on the reefs may damage coral in other ways, too. For example, some scientists argue that nutrients stimulate the growth of algae, which then take over space that would otherwise be occupied by coral.
“[Bruno’s] results are fairly conclusive,” says Peter Ridd of James Cook University in Townsville, Australia. But, he says, the nutrient level used in the study was generally higher than those seen on the Great Barrier Reef. What is more, although disease is a huge problem for the Caribbean reefs, the barrier reef is relatively disease free.
Conservationists claim that climate change and agricultural run off are already taking their toll on the barrier reef, and that some reefs closer to land have less coral coverage and less diversity than before. But some scientists, including Ridd, have argued th nike air max 1 at any run off is likely to be far too dilute to affect the coral, and that the relatively small changes that have been seen on the barrier reef so far may be due to natural fluctuations in coral growth (New Scie nike air max 1 ntist print edition, 4 January 2003).
But Clive Wilkinson, a coral expert at the Australian Institute of Marine Science in Townsville, says he is worried about the future of the barrier reef. “The nasty trilogy of disease, climate change and pollution are all acting together to knock out coral around the world. On the Great Barrier Reef, we’re not pressing the panic buttons yet. But we’re nervous.”