Corals not helped by marine reserves

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Although marine reserves may perform wonders in preserving reef fish populations, they may not help much, if at all, in doing the same for coral, according to a study to be published in a forthcoming issue of the journal Coral Reefs.

Brittany Huntington, Mandy Karnauskas and Diego Lirman came to this conclusion after assessing whether no-take reserve designation induced positive effects on the patch reef coral communities at Glover’s Reef Marine Reserve in Belize ten years after reserve designation.

The authors surveyed 87 patch reefs inside and outside the marine reserve for coral cover and population structure, as well as fish diversity and abundance.  Of the 87 reefs surveyed, 51 had been similarly sampled ten years earlier.

Despite ten years of protection as a marine reserve, the authors detected no significant differences in percentage coral cover between reefs in the reserve and fished reefs outside the reserve.

More disturbingly, the percentage cover of broadcasting coral species decreased from 5% to 3% in the same reefs sampled ten years apart, while brooding coral species appear to have undergone little or no change in population.  

Four of the six most common coral species found in 1998–1999 also showed declining trends in abundance by 2008–2009.  There is thus no clear indication that reserve implementation benefits coral cover, coral colony size, or abundance of juvenile corals.

The authors found no difference in herbivorous fish abundances or macroalgal cover between reserve and fished sites, which may help explain the lack of benefits to the coral following reserve designation.

"The macroalgae is faster growing than corals, dominating the available free space on the reef and impeding coral growth and survival," according to Brittany Huntington. "Without greater numbers of herbivorous fishes in the reserve to consume the macroalgae that is dominating these reefs, corals have little chance at recovery."

The authors also hypothesise that Glover's Reef Marine Reserve did not appear to be successful for corals because it is located in a stressed, degraded, and frequently disturbed habitat. It is also possible that enough time has passed since reserve establishment for positive effects to be observed.

Whatever the case, the study demonstrates the limitations of reserve protection in increasing the resilience of the coral community in some areas and that additional strategies are required to improve local coral condition.

For more information, see the paper: Huntington, BE, M Karnauskas and D Lirman (2011) Corals fail to recover at a Caribbean marine reserve despite ten years of reserve designation. Coral Reefs doi:10.1007/s00338-011-0809-4

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