Spatial, temporal and taxonomic variation in coral growth - implications for the structure and function of coral reef ecosystems
Growth is a fundamental biological trait, generally considered to have an important role in structuring populations and communities. Accordingly, many studies have quantifed growth rates of scleractinian corals, but using a variety of different methods and measures that may or may not be comparable. The purpose of this review is to compile extensive data on the growth of corals, to relate disparate methods of measuring coral growth, and to explore spatial, temporal, and taxonomic variation in growth rates. The most common metric of coral growth is linear extension, measured as unidirectional change in branch length or colony radius. Rates of linear extension vary greatly among corals, being highest among arborescent Acropora species. This is not unexpected given the limited carbonate investment in producing long, slender branches compared to solid hemispherical colonies. However, differences in the way that extension rates are actually measured (e.g., linear extension of individual branches vs. changes in the mean solid radius of massive corals) could potentially bias interspecifc comparisons of coral growth. The most comparable measure of growth, which gives unbiased estimates of growth across different growth forms, is average annual calcifcation or change in weight normalized to a measure of size. Surprisingly, even calcifcation rates appear to be much higher for branching Acropora compared to other coral genera, which contributes to the high extension rates recorded for this genus. Despite inconsistencies and incompatibilities among studies of coral growth, there is clear evidence that coral growth rates vary spatially and temporally, largely in response to light and water quality (e.g., turbidity), temperature, and aragonite saturation state. Ongoing changes in environmental conditions (e.g., due to climate change) are expected to have generally negative consequences for the growth of scleractinian corals, which may be further exacerbated by shifts in assemblage structure towards relatively slowgrowing species.