Analysis of recovery patterns of Indian Ocean coral reefs through examination of Scleractinian communities and populations

This thesis examines the colony size structure and taxonomic composition of coral communities from eight regions of the Indian Ocean approximately 10 years after thermal stress-induced mass mortality events. Coral community composition and population structure differed widely within and between regions, reflecting the different climatic and anthropogenic impacts experienced by each over the past decade. Coral communities in most areas started from a similarly depleted condition but after 1998 their recovery trajectories varied significantly, reflecting different surviving adult communities and continuing, different local stressors; some have remained highly depleted, while others have shown marked recovery. Profound differences between coral communities at intra and inter-regional spatial scales are identified and related to diversity and taxonomic composition, colony abundance, surface area, size frequency distributions, and population demographic parameters within taxa. These are analysed through multivariate techniques and univariate graphical representations to illustrate the significantly different size frequency distributions, taxonomic composition, taxonomic richness and dominance patterns at different spatial scales. A novel technique is assessed for surveying juvenile coral communities, using ultraviolet light, which causes new, growing tissue to fluoresce. This method significantly increases detected juveniles, with important consequences to size frequency patterns and to some previously published views on juvenile densities. The surveying methodologies used are far more revealing than most commonly-used conventional benthic assessments such as intercept surveys, cover values and diversity, which rarely capture discriminatory information on overall composition of coral communities, let alone the structure of populations within them. These colony size-based studies of individual genera are extremely sensitive for interpreting spatial and temporal variations in reefs and greatly enhance understanding of coral reef condition and complexity. The spatial differences demonstrate the applicability of the methods for advising reef management, specifically in identifying areas where ecological resilience is impeded by recruitment failure. Long-term consequences of changes in coral communities may include reduced ecological functional redundancy, reduced structural complexity, reduced carbonate accretion and reef growth, and impaired recovery potential.
Harris Alasdair .
Scleractnia (hard corals)