| Summary: | Spatial, temporal and taxonomic differences in coral growth play an important role in the ecology and dynamics of coral reef ecosystems, affecting reef productivity, heterogeneity, and growth. Moreover, climate change poses an increasing risk to the future status of coral reefs with increasing ocean temperature and acidification causing reductions in growth of reef-building corals, if not survivorship. The purpose of this study was to measure the growth rate of six scleractinian corals, Acropora yongei, Isopora cuneata, Pocillopora damicornis, Porites heronensis, Seriatopora hystrix and Stylophora pistillata, at Lord Howe Island, Australia's southernmost coral reef environment, during the 2010-11 summer growing season. Measurements were taken to compare growth rates of corals from other sub-tropical locations, and greatly increase understanding of the effects of climate change on coral growth. At high latitude locations (subtropical reefs), coral growth is currently limited by the cool winter temperatures and climate related increases in ocean temperature may extend the summer growing period. Conversely, aragonite saturation declines with increasing latitude and climateinduced ocean acidification may further reduce the capacity for growth of calcifying organisms at the latitudinal limits of reef growth. Coral growth (specifically, linear extension) was measured at North Bay and Horseshoe Reef using i) Alizarin staining, and ii) changes in length of individually tagged branches. Acropora displayed at least two fold higher growth rates, significantly greater than other genera, whereas Pocillopora had the lowest growth rate. There was limited evidence of recent increases in growth rates of corals, rather growth rates of Pocillopora were much lower than expected. While very preliminary, these findings suggest that declining aragonite saturation, which will have most pronounced effects on high latitude reefs, are already offsetting any positive effect of increasing temperature.
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