The Status of Coral Reefs in the Remote Region of Andavadoaka, Southwest Madagascar

Three reef systems (fringing, barrier and patch reefs) were surveyed in the regionof Andavadoaka, southwest Madagascar. Patch reefs had the highest coral cover and highestdensity of coral recruits (~45% and 1.8 m-2 recruits), followed by barrier reefs (~12% and 1.3m-2 recruits) and fringing reefs (~8% and 0.8 m-2 recruits). Sea urchin assemblages varied greatlybetween reef systems, with fringing reefs being dominated by Echinothrix sp., barrier reefs by therock-boring sea urchin Echinostrephus molaris and patch reefs by Diadema sp. On all reef types,algae grazing sea urchin densities were six times lower then on overfished reefs elsewhere. Thedensity of commercial invertebrates (e.g., sea cucumbers) did not differ significantly betweenthe relatively unexploited patch reefs versus barrier and fringing reefs, which suggests that theseare not yet over-fished in the region. Coral reef fish assemblages were significantly different oneach reef system. Reef fish densities were high on both patch and barrier reefs (~170 per 100 m2)compared to fringing reefs (~90 per 100 m2). These reefs are not directly threatened by terrigenoussedimentation, which is considered to be one of the principle causes of reef degradation elsewherein southwest Madagascar’s extensive reef system; instead, it is over-fishing that appears to bethe main threat to their existence.