Monitoring coral reefs

SIR – Rodney Tate (Letters, April 16) quotes the BBC’s report on the danger posed to coral reefs by climate change.

I believe this relates to a recent aerial survey of the great barrier reef in Australia. In assessing the damage to reefs by bleaching, aerial photographs can be misleading since they give no indication of the depth to which the bleaching has occurred or of the actual cause. Bleaching could be down to a number of things besides water temperature, including storms, attacks by crown-of-thorns starfish or exposure to the air during abnormally low tides.

The only way truly to determine the amount and the cause of damage is by diving and examining the coral itself. For example, researchers in Indonesian waters in the Lizard Island region found the extent of dead coral tissue was mostly limited to the upper six inches of coral. Bleaching without mortality is not a worrying event, no matter how extensive. G H Glover Ferndown, Dorset