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Reefs Battle Bleaching

The Department of Environment (DoE) staff has confirmed significant amounts of coral bleaching on local reefs.

Following up on reports from the diving community as well as a 'bleaching potential' alert from the recently installed ICON monitoring station in Little Cayman, DoE staff conducted a rapid assessment of reefs on the north, west and south coasts of Grand Cayman.

The scientific diving team found that nearly all corals in the shallow reefs to about 30 ft showed signs of moderate to severe bleaching, while approximately 80% of corals in the deeper reefs to 120 ft exhibited the early signs of coral bleaching. Bleaching appeared more intense on the north coast although the reasons for this are not fully understood at this stage.

Coral bleaching is a stress related reaction whereby the coral colonies lose their colour and 'bleach' white either due to the loss of pigments by microscopic algae living in symbiosis with their coral hosts, or because the algae have been totally expelled. Bleaching is closely associated with sustained elevated water temperatures and UV light and has been linked to global climate change as the world's oceans heat up.

Corals can recover from less severe bleaching episodes although recovery is variable and in some instances entire reefs have been lost to single bleaching events. The last major bout of bleaching to impact the Cayman's reefs occurred in 1998 with significant mortality following. Minor bleaching events have been recorded in the warmer summer months with increasing frequency during the last decade.

The DoE has a Long Term Coral Reef Monitoring Programme, in place since 1997, to the track the health of Cayman's reefs and is well placed to monitor the current extent and severity of impact associated with the recent bleaching having only just completed an extensive video survey at 55 reef sites around all three islands. Monitoring efforts will be increased over the next few weeks to better quantify and assess the impact of this bleaching event and to determine levels of recovery.

The DoE expects this current bleaching episode to increase significantly in severity in the following weeks as water temperatures remain above the threshold 29.5 degrees Celsius.

However, past water temperature data collected since 1996 suggest that local waters start cooling down from mid-October, which hopefully may bring some relief for the heat stressed corals.