Coral Bleaching - A Major Threat to Coral Reef Health

Coral bleaching is often regarded as one of he greatest threats to the health of coral reefs. Due to the relatively fragile nature of the coral-zooxanthellae symbiosis, a small change in environmental conditions can cause the symbiosis to collapse and the zooxanthellae to be expelled, leading to bleaching. Although corals can usually recover over a period of years, by re-forming a symbiosis with zooxanthellae, in extreme cases the coral polyps will die which can have more serious knock-on effects for the whole ecosystem. Coral bleaching events have been occurring since records began, but what is worrying is that bleaching events seem to be occurring at a more frequent rate than in the past. The highest SSTs ever recorded were in 1998, and with this the most widespread coral bleaching events recorded. The rising SSTs over the last fifty years correlate with the amount of bleaching events being seen around the world, and in turn subsequent death to the coral. Figure 5 shows recent bleaching events, the majority took place in the West Atlantic and East Pacific.