AIMS has an internationally significant collection of long cores from long-lived massive corals collected from the Great Barrier Reef that represent coral growth histories over the past few hundred years and allow reconstructions of past tropical reef environments and climates before the availability of instrumental records (see previous Highlight). In 2010-11, the Institute collected complementary sets of cores from corals in Western Australia for the eventual purpose of creating a unified marine climatology for all of northern Australia.
The WA collections ranged from massive corals living at Ashmore Reef, 800km west of Darwin, to colonies living at the Houtman Abrolhos Islands, located 70 km offshore of Geraldton in Western Australia. The latter are the most southerly reefs in the Indian Ocean and, before the visit, were considered marginal for coral reef growth under prevailing ocean temperatures.
Preliminary analysis of calcification variations over the past 110 years, a time period covered by instrumental records of sea surface temperature (SST), has been completed for 27 cores from six reef sites between 17oS to 28oS.
The cores from Western Australia have shown no evidence of the decadal decline in calcification rates from 1980 that was previously reported in the same species of coral from the Great Barrier Reef (De'ath et al., 2009). Since 1900, calcification rates have shown no significant change at three sites (including the Rowley Shoals where the rate of SST warming has been relatively small). This means that that declining calcification observed among GBR corals is most likely due to the repeated heat stresses on this system experienced since the first mass coral bleaching episode observed in 1998 rather than due to changing ocean chemistry which would be expected to have a more even effect around the continent.
Cores from two sites (Coral Bay ~23oS and the Houtman Abrolhos ~28oS), have shown a significant increase in calcification rates over the past century that matches the observed warming of SSTs observed at these southerly locations.