Abstract

Marine protected areas (MPAs) are widely considered to aid resiliency to hard-coral/macroalgal phase shifts. To determine the effectiveness of an established marine reserve in Grand Cayman, algal biomass was compared within and outside the reserve. Between November-December 2010, macroalgae was extracted from five 0.25m2 quadrats at 12 shallow reef sites at an 8 - 10m depth (4 sites MPA, 8 non-MPA), samples identified to genus and weighed to attain mean biomass measures per site. A total dry- weight of 544.45g was collected (mean biomass at sites ranged from 3.47 - 6.26g West-MPA; 3.80 - 5.90g North-non-MPA; and 6.82 - 26.05g South-non-MPA), with Dyctiota, Halimeda, Lobophora, filamentous turf algae and other turfing algae comprising total biomass at most sites. Reserve effect was not detected (p > 0.05), though variability between sites based on aspect differentials were observed. Bio-mass was significantly higher in the South than North and West (p < 0.05), which exhibited similar biomass values (p > 0.05). Species composition varied between sites with southern sites displaying a significantly different algal community structure (p < 0.05), driven by comparatively minimal biomass of Lobophora, consistently large proportion of Halimeda and a greater biomass of turf algae than the North and West. Differences in biomass around the island may indicate natural variation between reefs of different exposures determining habitat complexity, reef fish populations, nu-trient levels and available spores for algal recruitment. Intra-habitat variation may be responsible for concealing re-serve effect in the West. Similarly, algae around the island may have reached a “size refuge? whereby keystone herbivores no longer graze upon them and thus minimal “effect? would be evident.

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