Monday, June 13, 2011

Coral Bleaching Alert as Sea Temperatures Rise

It seems like Bonaire is having an extremely warm and early summer, as temperatures are already at higher points than normal for this year, and, with the high temperatures, there comes a rise in sea water temperatures.  The Caribbean region is already seeing a rapid rise in water temperatures, and with it comes the possibilities for coral bleaching events like the one the region experienced in 2010. 

Coral bleaching is the whitening of corals, due to stress-induced expulsion or death of their symbiotic protozoa. The corals that form the structure of the reef ecosystem of tropical seas depend upon a symbiotic relationship with this unicellular organism, called zooxanthellae. Zooxanthellae give coral its coloration.  Under stress, corals may expel their zooxanthellae, which leads to a lighter or completely white appearance, hence the term “bleached.”

According to the NOAA Coral Reef Watch monitoring system, coral bleaching is likely in the Caribbean in 2011. With temperatures above-average, the National Oceanic and Atmospheric Administration’s (NOAA) models show a strong potential for bleaching in the southern and southeastern Caribbean that could be as severe as in 2010.

The Bonaire National Marine Park just receive the first Coral Bleaching Alert for the 2011 season from NOAA. Coral Bleaching Alerts are delivered when the sea water temperature exceeds the Maximum Monthly Mean (MMM) of Sub Surface Temperature (SST) at the site. This condition is called a “Hot Spot.” The stress produced by a Hot Spot over the coral is measured in Degree Heating Weeks (DHW). One DHW equals 1°C over the MMM for one week, 0.5°C for two weeks or any other combination. Our DHW for the last season was 9.9 which corresponded to the highest Bleaching Alert Level.

Definitions of Alert Levels:
No Stress: No thermal stress (HotSpot <= 0)
Watch: Low-level thermal stress (0 < HotSpot < 1)
Warning: Thermal stress is accumulating (HotSpot >= 1 and 0 < DHW < 4)
Alert Level 1: Bleaching expected (HotSpot >= 1 and 4 <= DHW < 8)
Alert Level 2: Significant bleaching expected (HotSpot >= 1 and DHW >= 8)

Bonaire’s current MMM is 28.5°C and the present temperature is 29°C since June 9, 2011, which puts Bonaire into a Bleaching Watch. For more information about NOAA’s Coral Bleach Watch, click here.

Be aware that coral reefs under these conditions are highly vulnerable to external factors and extreme care should be given during this time. Since corals are more susceptible to illness by losing their protective mucus by abrasion, divers should exercise all caution to avoid coming in contact with the reef by practicing good buoyancy skills.  (Source:  Bonaire National Marine Park)