Alleviating impacts of anthropogenic activities by traditional conservation measures: can a small reef reserve be sustainedly managed?

Abstract

Zoning schemes that are becoming an important management tool in large marine reserves, are difficult to implement in small reef areas. At the 3.4 km long reef of Eilat (Red Sea), a small (ca. 350 m of coastline) enclosure strategy has been enforced since 1992, while the remaining reef was left open to intense human activities. Here we have investigated for 2.5 y three populations of the branching coral Stylophora pistillata (3605 colonies) in a locality within the enclosed area (site NR) and in two areas open to the public, by tossing random quadrats at the shallow lagoonar zone (0.5–1.5 m depth). In the two open sites we found significantly higher levels of colony breakage (14–34% vs. 4–9% in the enclosed site), lower partial mortality levels of colonies (in the first 1.5 y; 7–9% vs. 23–30% at NR), higher recruitment (up to 3.0 vs. up to 0.9 colonies/m 2), 50% reduction in coral life span (10 vs. 20 y) and an estimated extinction period of 9–10 y for new cohorts as compared to >20 y in the enclosed site. Average colony size and maximal colony size were about half in the open sites. Live coverage fluctuated widely in all sites but was 3 times higher in the enclosed area (1.0–3.0% vs. 0.3–1.1%). Log-transformed size frequency distributions revealed, at the open sites, a shift from small towards medium-size classes and at the enclosed site, a shift from larger to medium size classes. We conclude that the enclosure of a limited core zone, although improved some ecological parameters, was not sufficient to compensate for stress imposed by anthropogenic activities. It is suggested to employ active restoration approaches, such as the “gardening concept”, as supplementary management tools.