Growth of Western Australian corals in the Anthropocene

Twenty-seven long cores were collected between October 2008 and September 2010 from massive Porites sp. colonies at six locations covering approximately 1000 km of the coast of Western Australia. The sampling locations included two reefs in the Rowley Shoals: Clerke Reef and Imperieuse Reef; three locations within the Ningaloo Reef Tract: Bundegi, Tantabiddi and Coral Bay; and the Houtman Abrolhos Islands.

All sampled colonies were <=2 m in height and selected from the leeward side of the reef or island at depths <6 m below the lowest astronomical tide. Spatial and temporal variations in three annual coral growth parameters; annual extension (linear distance between adjacent density minima (cm/y)), skeletal density (g/cm³) and calcification rate (the product of skeletal density and annual extension, g/cm²/y) were examined, as measured by gamma densitometry using standard procedures.

While some cores extended back to the 18th century, focus was on the period 1900-2010, which was common to the majority (70%) of cores, and provided sufficient replication at each location and overlap with instrumental SST observations. Average monthly SST were obtained from the HadISST 1.1 database, available from the British Atmospheric Data Centre.

Calcification anomalies were calculated for each core as the percent difference between the annual calcification rate and the long-term average for the period 1900-2010. Calcification anomalies were then averaged for each six locations and for all 27 cores. Linear regression (Generalized Linear Model (GLM) and non-linear regression (Generalized Additive models were used to examine the influence of time, SST and location on the calcification average and anomaly data. All models were analysed using the statistical package R.