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Coral cover's deadly decline

By Dave Armstrong - 10 Sep 2012 13:23:54 GMT
Coral cover's deadly decline

Montastrea coral from the relatively unaffected Curacao area plays host to many organisms such as this tiny sharknose goby - Boulder star coral image; Credit: © Shutterstock

From starfish to vertebrates, the International Union for Conservation of Nature (IUCN) and the Global Coral Reef Monitoring Network (GCRMN) have published a number of reports on the Caribbean coral fauna recently. Using masses of accumulated data and the handiwork of more than 36 researchers, heavily involved in the region, the preliminary report has been finalised. By 2016, they hope to have covered the global situation. In their September update the Panamanian Report from May is improved and conclusions drawn such as:

"Caribbean reefs with the highest surviving coral cover and least macro-algae tend to be characterized by little land-based pollution, some degree of fisheries regulations and enforcement, moderate economic prosperity and lower frequency of hurricanes, coral bleaching and disease."

Geographical coverage by country of data, sizes of circles are proportional to the number of data sets for benthos (pink) and fish (blue)

Geographical coverage by country of data, sizes of circles are proportional to the number of data sets for benthos (pink) and fish (blue); Credit: © IUCN

Caribbean coral reefs have declined since the 1970s from a 50% cover of live corals to 8%. The rate of decline is quite fast, as the graph below illustrates very well:

Decline in percent coral cover on Caribbean coral reefs from 1963 to present

Decline in percent coral cover on Caribbean coral reefs from 1963 to present based on data compiled for this report (yearly averages weighted by the area surveyed per study) compared to Gardner et al. 2003 (yearly averages weighted by the inverse of a study's sample variance); Credit: © IUCN

The trends for all stony corals, dominant coral groups, algae, octocorals, sponges, zoanthids were combined with density information on the starfish, Diadema antillarum and fish. 40 years of such data were combined, with some recently acquired sets from Curacao and Bonaire being particularly useful, because of the high level of coral cover there. Even today, it remains at a high 25-30%, though in slow decline. In contrast, the Florida keys data showed severe degradation, even as far back as the early 70s.

Regional analysis begins to give some fascinating differences between parts of the Caribbean.

Percent cover by region for (a) Acropora, (b) Poritidae, (c) Agariciidae, and 9d) the Montastrea annularis species complex

Percent cover by region for (a) Acropora, (b) Poritidae, (c) Agariciidae, and 9d) the Montastrea annularis species complex; Credit: © IUCN

These graphs illustrate the various Caribbean areas relative decline. Disease seems a determinant of several losses (and there are very few recoveries, unfortunately.) Natural disasters can have an effect on coral cover too, for example, Hurricane Allen was responsible for Acropora collapse in Jamaica. However, "the major causes of coral decline are well known and include overfishing, pollution, disease and bleaching caused by rising temperatures resulting from the burning of fossil fuels," says Carl Gustaf Lundin, Director of IUCN's Global Marine and Polar Programme.

As far as fish were concerned, Cuba recorded the greatest biomass before 2000, with Jamaica the lowest. Apex predators were basically absent in four island areas. Large groupers have virtually disappeared since 1991, coinciding with a increase in the smaller grouper Cephalopholis up until 2011. Some large parrotfish have also disappeared, this time, since 2001. As they remove dead coral and perform several other substrate preparations, their loss is to be regretted (by all species.)

parrotfish

The business end of the parrotfish removes encrusting algae and prepares substrates for new coral - Parrotfish image; Credit: © Shutterstock

Next, IUCN move on to the eastern Pacific. We look forward to their erudite approach, if not to the conclusions they may be forced to draw!

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Topics: Coral