ECOLOGICAL ASSESSMENT OF A COMPLEX NATURAL SYSTEM: A CASE STUDY FROM THE GREAT BARRIER REEF

Abstract

Ecological assessments of habitats are an integral part of the process of developing management plans for the use and conservation of large natural ecosystems. Using coral reefs in the Whitsunday region of the Great Barrier Reef, Australia, as a case study, we show that a two-tiered approach of rapid ecological assessment can provide a highly informative basis for assigning a range of conservation values. Visual assessments of extent of reef development and benthic cover (Tier I), combined with taxonomic inventories (Tier II), provide the basis for evaluating specific areas in the following terms: (1) their faunistic and floristic composition (as a basis for assigning representative “types” of reefs); (2) the degree to which reef development has progressed through the Holocene; (3) their current status or “quality” in terms of attributes widely perceived as desirable (i.e., high species richness and diversity, high coral cover, low dead coral cover, and low macro-algal cover); and (4) their importance as reservoirs of biodiversity, including representation of rare taxa. Cluster analysis defined four community types (two shallow and two deep) and five quality groups, interpretable as successional stages within the four community types. A discriminant variable provided a useful index for quality of individual sites. The quality index was also useful in predicting the occurrence of rare species within a site’s species complement. Simple indexes of coral cover, species richness and abundance, and taxonomic rarity proved useful in rating sites in terms of their conservation value. The indexes were correlated with the quality ranking, providing useful alternatives to the more complex multivariate analysis. We present maps that highlight the locations of sites of high conservation value based on these several criteria and note the extent to which they are congruent, in terms of representativeness, protection of the unusual, and identification of “better” examples within equivalent types.