The aftermath of coral bleaching on a Maldivian reef—a quantitative study

Abstract

Since the bleaching event of 1998, the development of the reef flat and upper reef slope on a Maldivian reef (the Komandoo house reef; Komandoo Island, Lhaviyani atoll or Fadiffolu atoll) is under detailed observation. We quantitatively recorded specific losses, re-colonisation by coral larvae on transects on the reef flat and on dead Acropora tables at the reef slope and regeneration of partly damaged large Porites and Diploastrea—colonies over the period from 1999 to 2004. The detrimental effects on the reef structure by bioerosion and hydrodynamics, as well as the overall status of the reef community were qualitatively assessed. Recruitment soon after the bleaching was more pronounced than in the following years, Pavona varians being a main constituent. The temporal re-colonisation pattern points at an emergency spawning of local Scleractinia just prior to the bleaching, whereas a sharp decrease of young settlers in 2001 and 2002 confirms a reduction of fertile colonies. The dominant species in the coral community shifted from acroporids and pocilloporids to agariciids. The skeletal deposition of recovering Diploastrea heliopora was equivalent to that before the bleaching, but much less than that of neighbouring Porites lobata colonies. The slow and scattered formation of new reef substance, which would structurally strengthen the reef, is however outweighed by the collapse of dead protruding and spacious colonies (e.g., Acropora tables). Six years after the bleaching, the formerly three-dimensional structure of the reef flat and upper reef slope presents as a levelled field of rubble, only partly consolidated by incrusting corals. Considering the recurrence of bleaching events (1987, 1998) and the results of the present study, one may assume a cascading deterioration of the status of the reef for the future.