Excess sediment in waters bad for coral health

October 9th, 2008 - 3:13 pm ICT by ANI  

Canberra, Oct 9 (ANI): A new research has suggested that a lot of sediment in the water is bad for corals, and may even prevent them from ever re-establishing.

Thats the latest startling evidence to emerge from research into the likely fate of reefs under climate change and rising sea levels, at the ARC Centre of Excellence for Coral Reef Studies (CoECRS) in Australia.

The killer blow for a degraded coral reef is a thick mat of sand and weeds that shrouds the rocky surfaces on which the corals would normally grow, preventing them from re-establishing.

This gritty algal turf has shown itself to be remarkably hardy and, once in place, makes it almost impossible for the corals to return.

According to Professor David Bellwood of CoECRS, if sea levels rise, then the smothered reef drowns and never recovers.

We know this from geological history, at the time of previous sea level rises. The reason we are doing the work is to see whether or not coral reefs will be able to keep up with rising sea levels under climate change, he said.

But, Professor Bellwood and colleague Dr Chris Fulton from the Australian National University have also uncovered a remarkable link in the chain that explains why the algal turf can win in its turf war with the corals.

When the water is thick with sediment and it settles on the seaweeds, herbivorous reef fish turn up their noses at the gritty food, much as humans disdain a sandwich that has been dropped on a sandy beach.

Remarkably we found that when there is little sediment around and plenty of fish, the fish mowed the weeds very fast, eating two thirds of their length in about 4 hours. This action by fish in keeping the algal turf down gives the corals a chance to re-establish, said Dr Fulton.

But if there is a lot of sediment in the water, the fish go off their feed, the weeds grow, more sand settles and the murky shroud that smothers the reef becomes more stable, often permanent. Then, when sea levels rise, the reef drowns, he added.

If there is enough sediment in the water to settle on the seaweed, it turns the weed-eating fish off their meal.

Were not entirely sure why this is. It may be that the sediment acts as an antacid and gives the fish indigestion by preventing their stomach acids digesting their food. Or it may simply be that fish, like people, dont appreciate a mouthful of sand and mud, said Professor Bellwood. (ANI)

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