Tobago’s reefs are on their third consecutive year of coral bleaching

October 28, 2022

Trinidad and Tobago continue to be under Bleaching Alert Level Two for the period of October 23 for up to four weeks. Tobago’s reefs are now experiencing coral bleaching for the third consecutive year. The IMA Team has been observing pale and partially bleached corals in Charlotteville, northeast Tobago. We have also received reports of coral bleaching on many reefs in southwest Tobago, including Buccoo Reef, Store Bay Reef, Flying Reef and Mt Irvine Reef. Bleaching is occurring across many species – brain corals, mountainous star corals, staghorn corals, fire corals and even the soft corals.

Staghorn Bleaching in Buccoo, Tobago

What is coral bleaching?

Corals form a symbiotic relationship with microscopic algae that lives in its tissues. The algae photosynthesize using sunlight and then feeds the coral. The algae give the corals their amazing bright colours. In return, the coral provides the algae with all essential nutrients and removes the waste. The amount of food provided allows corals to grow to enormous rocky skeletons which are used by other marine organisms for shelter. However, if waters get too warm the relationships between the coral and the algae break down and the algae get expelled from the coral. This results in coral bleaching where the coral eventually turns white because they lose all their colour.

Boulder Brain in Charlotteville, Tobago

What causes coral bleaching?

Today, global warming is the main driver of coral bleaching and die off, but pollution and overexploitation limit natural reef recovery. In the last 40 years, coral reefs around the world have suffered from global and regional coral bleaching events, where large sections of reef turned white as summertime sea temperatures became too warm because of global warming. Coral reefs of Tobago have also suffered from multiple bleaching events in the past including 2005 and 2010, and these have significantly degraded reef health. Corals that survive coral bleaching become vulnerable to disease that also result in coral mortality.

Soft Coral Bleaching in Charlotteville, Tobago

What is Coral Reef Watch

Coral Reef Watch was developed by NOAA (National Oceanographic and Atmospheric Administration, USA) following the first major global coral bleaching event in 1997 /1998. They realized that coral reefs around the world were bleaching during the summer months as tropical water temperatures were simply getting too hot for the corals. This led to the corals bleaching and dying globally. Launched in 2000, Coral Reef Watch delivers alerts about coral bleaching threats using satellite information on sea surface temperatures and predicts the likelihood of bleaching based on the rate of thermal heating of the water.

Satellite observations were calibrated with direct observations of water temperatures and coral bleaching along tropical coastal waters. The metric to determine the risk of bleaching is measured in Degree Heating Weeks. This is the cumulative heat stress that corals experience over a twelve-week window. The accumulation of heat stress is calculated by the amount degrees above the thermal summer mean temperature and the number of days that it persists above the mean value. From this, NOAA can provide weekly bleaching alerts for areas where bleaching may be possible at specific locations. Here are the alert levels:

Bleaching Watch – Low-level heat stress present

Bleaching Warning – Heat stress is accumulating, possible coral bleaching

Bleaching Alert Level One – significant bleaching across species and over extended areas is likely

Bleaching Alert Level Two – severe bleaching and coral death are likely.

https://coralreefwatch.noaa.gov/product/vs/gauges/trinidad_tobago.php