Temporal and spatial variation in the growth parameters skeletal density, linear extension and calcification rate in massive Porites from two nearshore regions of the northern Great Barrier Reef (GBR) were examined over a 16-year study period. Calcification rates in massive Porites have declined by approximately 21% in two regions on the GBR $ 450 km apart. This is a function primarily of a decrease in linear extension ($ 16%) with a smaller decline in skeletal density ($ 6%) and contrasts with previous studies on the environmental controls on growth of massive Porites on the GBR. Changes in the growth parameters were linear over time. tures had no effect on skeletal density, but a modal effect on annual extension and calcification with maxima at $26.7 1C. There were minor differences in the growth parameters between regions. A decline in coral calcification of this magnitude with increasing seawater temperatures is unprecedented in recent centuries based on analysis of growth records from long cores of massive Porites. We discuss the decline in calcification within the context of known environmental controls on coral growth. Although our findings are consistent with studies of the synergistic effect of elevated seawater temperatures and pCO 2 on coral calcification, we conclude that further data on seawater chemistry of the GBR are required to better understand the links between environmental change and effects on coral growth.

Approximately one quarter of zooxanthellate coral species have a depth distribution from shallow waters (<30 m) down to mesophotic depths of 30-60 m. The deeper populations of such species are less likely to be affected by certain environmental perturbations, including high temperature/high irradiance causing coral bleaching. This has led to the hypothesis that deep populations may serve as refuges and a source of recruits for shallow reef habitats. The extent of vertical connectivity of reef coral species, however, is largely unquantified. Using 10 coral host microsatellite loci and sequences of the host mtDNA putative control region, as well as ribosomal DNA (rDNA) ITS2 sequences of the coral's algal endosymbionts (Symbiodinium), we examine population structure, connectivity and symbiont specificity in the brooding coral Seriatopora hystrix across a depth profile in both northwest (Scott Reef) and northeast Australia (Yonge Reef). Strong genetic structuring over depth was observed in both regions based on the microsatellite loci; however, Yonge Reef exhibited an additional partitioning of mtDNA lineages (associated with specific symbiont ITS2 types), whereas Scott Reef was dominated by a single mtDNA lineage (with no apparent host-symbiont specificity). Evidence for recruitment of larvae of deep water origin into shallow habitats was found at Scott Reef, suggesting that recovery of shallow water habitats may be aided by migration from deep water refuges. Conversely, no migration from the genetically divergent deep slope populations into the shallow habitats was evident at Yonge Reef, making recovery of shallow habitats from deeper waters at this location highly unlikely.

Tropical storms (cyclones, hurricanes, or typhoons) are the most severe form of mechanical disturbance of coral reefs. In 2005, severe tropical cyclone Ingrid crossed the far northern Great Barrier Reef, a region that had not been affected by a major disturbance for several decades, and where benthic data had been collected before the cyclone crossed. This storm provided a unique opportunity to improve understanding of the extent and type of damage inflicted on inshore and offshore coral reefs along a gradient of wind speeds. Modeled maximum wind speeds ranged from 46 m s 21 (equivalent to category 4) near the path to 22 m s 21 (category 1) ,70 km to either side of the path. Surveys of 82 sites on 32 reefs along the wind gradient showed that the types and intensity of disturbance were well explained by local maximum wind speed, and by spatial and biotic factors. While offshore reefs had the deepest depth of damage, inshore reefs had the greatest rates of coral breakage and dislodgement. On a severely affected inshore reef, hard coral cover decreased about 800%, taxonomic richness decreased 250%, the density of coral recruits decreased by 30%, while massive coral cover remained unaltered. Maximum winds ,28 m s 21 for ,12 h inflicted only minor damage on any reef, but winds .33 m s 21 and .40 m s 21 caused catastrophic damage on inshore and offshore reefs, respectively. Observations from this cyclone were used to predict potential changes in storm-related coral loss under altered cyclone-intensity scenarios.