Coral Bleaching - What does it mean for the Reef?

Many people are currently very concerned with the health of the coral reef of Belize. It's no wonder, considering the environmental and economic foundation that it constitutes in this region. In the past year, the term "coral bleaching" has become the catch phrase used to describe the state of the reef. But, what is this phenomenon and what does it mean for the future of the reef?

Coral reef ecosystems are extremely sensitive, especially to changes in water temperature and generally are restricted to mean water temperatures between 22 and 30 degrees Celsius. When the temperature is outside this narrow window, problems arise. Coral polyps are animals very dependent on a plant called zooxanthellae to provide food and oxygen through photosynthesis. Coral bleaching may occur when there is a rapid increase or fall in water temperature, causing coral polyps to begin expelling its zooanthellae population, thus weakening the coral's capacity to survive. With the loss of zooanthellae, there is a lack of chlorophyll pigment leading the coral to lose its color and appear "bleached."

Reef Brief is a weekly column published in the San Pedro Sun
Elevated sea temperature due to global warming and an increased presence of UV radiation has been linked to most mass bleaching (over 25% mortality) events. Over the past 25 years, bleaching has occurred throughout the world. However, the reefs of Belize only began suffering widespread coral bleaching in 1995. At that time, 46% of coral colonies were affected in most areas surveyed. Since then, there have routinely been bleaching occurrences in Belize. The summer of 1998 proved to be particularly damaging to the reef, with high incidences of bleaching and mortality occurring in the Bacalar Chico area.

Recovery of bleached corals can occur with a gradual accumulation of zooxanthellae within the corals, usually taking six months. However, if the water temperatures continue to rise, as predicted, the corals may not have the chance to fully recover. Clearly, there is a need for adequate coral reef protection, both for the corals and the habitat. On the local level it is probably futile to attempt to control the sources of global climate change. Instead, the focus should be on controlling other factors that impact the reef, such as sand dredging, increased turbidity, over-fishing, pollution and land-use practices. Through our environmental education and reef monitoring programs, it is the mission of Green Reef to assist in achieving this conservation objective.

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