The value of reefs
offshore coral communities
an asset to barbados
by Julia Rawlins-Bentham
Barbados’ coral reefs are perhaps the most important communities beneath the deep blue sea.
Their rainbow colours and reef fish attract many visitors to various sites on the ocean floor around Barbados. However, the reefs are under serious threat from pollution and effects of Global Climate Change such as higher than average sea surface temperatures.
While many people do not think of coral reefs in terms of their economic value, these numbers are actually quite vast. Economists are examining the value of the reefs in terms of their ability to protect shorelines, provide fish habitat and tourism.
The values are staggering. In Jamaica, they reach US$210 to US $630 million for Montego Bay alone, while in Tobago, their reefs are priced between US$43.5 to US$86 million, and in St. Lucia between US$68 to US$102 million. This gives some idea of the economic importance of these ecosystems.
The bank reefs (offshore) have historically been healthier than the near shore reefs, as impacts from land tend to be diluted by the time they reach these reefs and they are also not as accessible as the near shore reefs.
However, the once healthy bank reefs are now showing signs of deterioration; while the fringing reefs (near shore reefs) are showing very slight changes over the years.
Marine Biologist at the Coastal Zone Management Unit, Angelique Brathwaite, explained: “The average coral cover on the bank reefs is around 25 per cent, while in 1997 it was around 40 per cent. Average coral cover on the fringing reefs is between 13 per cent to 18 per cent, by comparison,” she said.
She added that approximately 50 per cent of the corals on the bank reefs of Barbados were lost within a decade.
Brathwaite said a study established in 1982 called Temporal Changes in Coral Reef Communities, was designed to track the changes in the island’s reefs over time. The study, which was carried out by the Office of Research at the University of the West Indies, on behalf of the CZMU, is repeated at five-year intervals.
“We are now in the process of carrying out the 2012 event, in which we are repeating studies carried out on the east coast of the island,” she said. The studies take note of the number (abundance) of corals on the reefs, the different species (diversity), Diadema antillarum (Cobblers) and the macro algal cover, among other indicators.
“It is normal, and part of the natural biodiversity on a reef is to have macro algae. However, with excessive nutrients and a reduction in grazers, macro algae proliferate tend to out-compete corals. They essentially take over, becoming the dominant organisms on the reefs,” she said.
Brathwaite noted that the CZMU also carried out water quality monitoring to determine how specific parameters change over time. The programme is two-fold, with one component focusing on the collection of samples in order to test for bacteriological and nutrient parameters.
The other component employs probes placed in the water at reef sites along the south and west coasts to allow officials to monitor water temperatures. “We leave them in the water and pull them up every quarter to download the information. It allows us to see what the temperatures were for that time period,” Brathwaite explained.
Although they are buried beneath the cooling waters of the ocean, the stinging rays of the sun are stripping away the rainbow colours of corals via a process called bleaching.
Bleaching refers to the process whereby under stressful conditions, the algae which live in a symbiotic relationship with the coral, are expelled. When this phenomenon occurs on a large scale it is called a mass bleaching event. These have occurred in the region during the years 1998, 2005 and 2010 so far.
“In order to fully appreciate the impact of bleaching, one has to understand a bit about coral nutrition,” the marine biologist pointed out.
In explaining how corals survive, she described them as animals which required food.
“Our sea is so clear and beautiful, partially because it is also quite barren, like a desert. The corals have solved this problem by having internal farms of plants called zooxanthellae; which use the sunlight (photosynthesis) and give up their carbohydrate rich products to the coral animal.
“In return the corals give up some of their by-products to the plants so they are helping each other,” Brathwaite explained.
But, if the corals become stressed, the zooxanthellae are expelled, taking with them much of the reef’s beautiful colours, allowing the white skeleton to show. Also gone is a system that provided up to 85 per cent of the animal’s nutritional needs.
“Once the zooxanthellae go it does not mean that the coral is dead, but if that condition persists they will die of starvation. If the stress is removed, that is, if cooler temperatures return, then the corals will get recolonised with the zooxanthellae,” she said.
Even if the animal survives, there could be impacts such as reduced reproductive ability and increased susceptibility to disease.
These rising temperatures have already had disastrous effects on coral reefs. Coral bleaching episodes have been monitored by the Marine Research Section at the CZMU and the Centre of Resource Management & Environmental Studies of the UWI, since the second regional mass coral reef bleaching event in 2005 and again in 2010.
Up to 80 per cent of the corals around the island were bleached during the 2005 event, and around 26 per cent of the corals died. The situation was slightly better during the 2010 event, when around 50 per cent of colonies were bleached and only four per cent of them died.
Brathwaite added that the CZMU also conducted research on coral diseases. It showed that while disease levels were low at this point, it already had a devastating effect on the reefs.
White band disease decimated the acroporids, elkhorn and staghorn corals on the near shore reefs, in the 1970s to the extent that they are hardly seen now. The entire face of the fringing reefs changed in less than a decade from reefs dominated by these magnificent corals to non-branching ones.
Brathwaite said that other diseases being seen on corals were the White Plague, Dark Spot Disease, Yellow Band Disease, Black Band Disease and Aspergillosis.
“What the research has shown is that disease abundance is extremely low in Barbados, averaging five per cent. However, the region had been identified as a disease ‘hot spot’.
“There is not a lot of it in Barbados, but it is quite pervasive and is found on all the reefs at all times during the year, so it is still something we need to look out for and take into consideration,” she added.
Reasons put forward for the increase in disease are all linked to humans, namely nutrient enrichment, and general pollution, in addition to other factors such as the influx of African dust from the Sahara.
“It has been proven that White band disease is caused by a bacterium found in the human gut, and Aspergillosis, by a fungus carried in African dust,” Brathwaite stated, noting that diseases seemed to be exacerbated by bleaching and high temperatures.
She however, cautioned that bleaching and coral diseases were having an impact on corals already weakened by man-made stressors such as nutrient enrichment, over fishing, unsustainable fishing and physical damage.
In fact, experts are warning that unless something is done to save the world’s corals most of the ecosystem services provided by coral reefs, such as shoreline protection and reef fish habitat could be lost in as few as another 70 years.
She added: “We have to work with all of the relevant sectors to do what we can. We can do better at cleaning up our waste water, reducing physical impacts to the reefs and stopping unsustainable fishing.”