Size-structure patterns of juvenile hard corals in the Maldives

In April 2006 and May 2007 abundance data of small coral colonies were collected in the central atolls of the Maldives (N3835.9–4826.6 E72847.3–73857.5) in order to evaluate variability in hard coral recruitment and post-settlement success. Visual quadrats were randomly placed in two reef typologies (oceanic reef and lagoonal reef) at three different depths. Colonies were conventionally defined as ‘recruits’ when smaller than 5 cm in diameter, whereas the term ‘juveniles’ was reserved for colonies ranging between 5 and 15 cm. Clear differences in the relative importance of the two size-classes across the three different depths and the two reef typologies were found. A size-structure index (SsI%), based on abundance data, was calculated in order to evaluate the percentage of ‘recruits’ out of the total juvenile hard corals. SsI% values differed between reef typologies and according to depth zones with a higher percentage of ‘recruits’ found in shallow oceanic reefs. Physical and ecological differences between the two reef typologies according to depth are presumed to cause different success in the settlement of new colonies and their survival during growth. Coupled with the usual estimates of hard coral cover, SsI% may represent a useful tool for monitoring, and be effective for the quick assessment of coral reef recovery after disturbances.