CONSERVATION:

Reef Heterogeneity Can Mask No-Take Marine Reserve Efficacy

Do no-take marine reserves protect the life within them? It's hard to conclusively answer this question when the reserve doesn't have "before and after" data, or when there's intrinsic and/or managerial heterogeneity between a reserve and a control site.

Studies of marine reserve efficacy are not as well-developed as those of terrestrial reserve efficacy. Brittany Huntington (University of Miami, United States) and coworkers have begun to fill in this gap in our knowledge with a novel assessment of the efficacy of a coral reef marine reserve near Belize.

This marine conservation research compliments the recent (2007) surprising observation that hurricanes can benefit damaged coral reefs. There's clearly much more remaining to be learned about conserving the marine environment.

Measuring fish and corals.

The scientists' study site is a no-take reserve within Glover's Reef Atoll, 30 kilometers off the coast of Belize. The atoll is 560 square kilometers in area, its depth is from 6 to 18 meters, and possesses 850 reefs from 20 square meters to 10,000 square meters in area.

The no-take reserve is in the south of the atoll. The scientists devised a method to quantify and classify reef heterogeneity, identify the variables correlated with fish and coral variability, and evaluate reserve efficacy while taking into account reef heterogeneity.

They randomly sampled 87 sites (56 non-reserve and 31 reserve) in underwater reefs from 2008 to 2009. Some extra repeat sampling was undertaken to check for possible 10-month variability (none was detected).

Five standard visual surveys were performed at each site to check for fish species, number, and length. Coral composition was measured via digital photography (100 randomly selected points in each of the 20 randomly selected images from the 25 to 100 taken per reef patch).

Satellite imagery and software was used to calculate reef patch area, perimeter, and edge-to-area ratio, while patch volume was based on depth and GPS data. Reef structural complexity was given a score from 0 (no vertical relief) to 3 (highest vertical relief), and statistical analysis was undertaken to determine correlations between reef heterogeneity and either fish or coral composition.

Correlations between reef heterogeneity and reserve efficacy.

The three features of the reef that most significantly explained variability among the fish were nearest neighbor distance, reef area, and distance from a channel. The three features of the reef that most significantly explained variability among the coral were reef structural complexity (complex or dome morphology), reef size, and distance from a channel.

The highlight of this research was to show that different segments of the overall reef respond more positively to protection than others. In comparison to outside the reserve, enhanced connectivity between reef patches (referring to patch density and distance between patches) facilitated enhanced fish diversity and abundance (up to 75%), but not fish species richness, and small reefs comprised of complex corals close to a channel exhibited enhanced coral-to-macroalgal ratios (80%) and coral cover (68%).

Importantly, the scientists found that when the reef as a whole was considered, no clear benefit of conservation was apparent. This research establishes that specific segments of the reef benefit more than others; consequently, reef heterogeneity should be taken into consideration when evaluating reserve efficacy.

Implications.

Marine conservation scientists need to consider reef heterogeneity when arguing the case for reef protection, and for identifying reefs most likely to respond positively to protection. Otherwise, heterogeneity within the reef may mask the benefits which do occur, undermining the case for conservation and hindering monetary allocation to sites of greatest conservation need.

NOTE: The scientists' research was funded by the Pew Institute for Ocean Science, the University of Miami, and the Explorers' Club.

for more information:

Huntington, B. E., Karnauskas, M., Babcock, E. A., & Lirman, D. (2010). Untangling Natural Seascape Variation from Marine Reserve Effects Using a Landscape Approach PLoS ONE, 5 (8) DOI: 10.1371/journal.pone.0012327





