Tracking Hurricanes Hanna and Ike.

By Marlon Hibbert, Scientific Officer, DECR

Hurricane Ike engulfs the Turks & Caicos Islands

It is no secret that 2008 was an extraordinary year for the Turks & Caicos Islands. During a one week period we suffered the onslaught of two major hurricanes. They wreaked havoc on the people of the Islands and came at a time when the global economy, and indeed the economy of our Islands, were on a downward spiral. Fast forward to August 2009, almost a year later, and some people in the country have still not recovered.

Hurricanes are driven by warm temperatures and Hurricanes Hanna and Ike were no exceptions. It is published that over the last 20 years or so, the average sea surface temperatures of the TCI have risen (Goreau et al 2007). These data were obtained from the National Oceanic and Atmospheric Administration’s (NOAA) long term records.

Here in the TCI, since May 2008 we have had the opportunity to track sea temperatures for ourselves. Four  Onset Co./HOBO® Pendant temperature/light data loggers were placed in two underwater locations at different  depths off Providenciales and West Caicos. Two meters were also installed in Grand Turk, but unfortunately, after the hurricanes had passed. Placed at depths varying from 142 to 38 feet, the meters were well positioned to record the effects of the hurricanes on the sea temperatures. After the hurricanes, the Providenciales and West Caicos meters were retrieved and the information analyzed in graphical form.

The results were astounding: at the locations in Grace Bay at depths of 105 feet and at 38 feet, temperatures fell from approximate highs of 30ºC to lows of 25ºC, a drop of more than 4ºC. This was also the trend at West Caicos where meters had been placed at 141 feet and at 42 feet. A few days later the same trend was observed for Hurricane Ike at both sites. As soon as temperatures were returning to normal levels after the passing of Hanna, the heat was sucked from the water again, dropping temperatures by an approximate 3ºC. Corresponding light levels were also reduced but, interestingly, took much longer to return to normal levels, indicating that the sediments that had been stirred up took a much longer time to settle out of the water column.

What does this mean for the coral reefs that are so crucial to the Turks & Caicos Islands? Corals exist and thrive in a very narrow temperature range and deviation from these temperatures can cause shock, mainly expressed in the form of bleaching. Bleaching occurs when corals expel their algal tenants resulting in a white appearance. This usually occurs with extended periods of higher than normal sea surface temperatures. (It must be said that other factors also play a role in coral bleaching with elevated temperatures being just one, though a major one.) Depending on the length of time that the corals are exposed to these drastic changes in temperature, bleaching may be partial or complete. Complete bleaching usually leads to coral mortality and dead coral supports reduced life. Corals also need light to grow; reduced light levels reduce the productivity of the corals and the ability to produce food, and essentially they come to a standstill.

Just like trees, corals display banding as measures of growth, and would likely show a very narrow growth band for period 2008/2009. Coupled with the shock reduction in temperature, lowering of light levels and increased sedimentation due to the hurricanes, the coral reef system in the Turks & Caicos suffered just as badly as their terrestrial counterparts and people.

Just as we are struggling to regain normalcy to our lives after the disruption of these devastating natural occurrences, so too are the wounded reefs putting up a fight. It is this fact that makes it even more important for users of these resources — fishermen, boaters, divers and snorkelers — to act wisely and in a manner consistent with the laws. Extra care at this time will give our reefs the opportunity to help themselves to regenerate naturally without adding to their stress levels.

As we continue to gather more information we are able to correlate this information to events that we see occurring on the reefs. In some cases it may help us to predict what may happen (more like an educated guess) on our reefs during future events.

If you are diving and recognize the onset of bleaching or any abnormalities of the reefs, let us know by contacting www.environment.tc. And remember, when diving leave only bubbles and take nothing but memories.