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modern-coral-growths


AIMS is custodian of the world's largest and most comprehensive collection oftaken from massivePorites.Density bands within these cores are laid down annually, providing an historical record of growth rates and environmental conditions stretching back, in some cases, hundreds of years. The longest core in the AIMS collection has been dated back to 1300 A.D.Previous AIMS research has shown that growth inPoritesis directly proportional to average sea surface temperature: corals in warmer water grow faster. On that basis, the general warming of the ocean over the last century (about 0.4 °C for theGreat Barrier Reef) suggests that (in the absence of other factors) growth of modern corals should be increasing. Consequently, it was a surprise when analyses ofPoritescolonies from two inshore regions of theGreat Barrier Reef(450 km apart) showed evidence to the contrary.Although restricted to a 16-year window in the recent past, the corals collected from the Wet Tropics region and Princess Charlotte Bay showed that calcification rates in massivePoriteshave declined linearly by around 21% in both regions since 1988: this decline was mainly due to slower linear extension (~16%) with a smaller decline in skeletal density (~6%). The corals also showed a non-linear response to increasing seawater temperatures: calcification was highest around 26.7 °C in the study regions, and declined above and below this point. This finding indicated that corals grow best up to an optimal temperature of 26.7 °C but growth is affected when temperatures exceed this point. Possible causes of the observed decline in coral growth since 1988 despite warming waters are now being investigated. Causes under investigation focus on a combination of increasing temperature stress and changes in seawater chemistry ("ocean acidification") due to rising atmospheric CO2 concentrations.