Mortality, growth and reproduction in five species of scleractinian corals following bleaching on the Great Barrier Reef in 1998

Study sites: These data were collected on the fringing reefs on the west side of Orpheus Island at Little Pioneer Bay (S18.594°, E146.485°), and the south-eastern side of Pelorus Island (S18.560°, E146.500°). Both islands are continental islands of the Palm Islands group in the Central Section of the Great Barrier Reef (GBR) Marine Park. These sites were amongst the worst affected by bleaching on the GBR following a sharp rise in sea surface temperature in the early months of 1998 (Berkelmans and Oliver 1999)

Species response to and recovery from high Sea Surface Temperature (SST): On 24 March 1998, all living colonies of Acropora millepora (n = 37) and A. hyacinthus (n = 28) in a 20 m × 40 m area between 3-4 m deep on the fringing reef of south-east of Pelorus Island were tagged to examine the patterns of response to, and recovery from, high SST. Similarly, all colonies of Seriatopora hystrix at 10 m depth within a 5 by 40 m area at this site were tagged (n=27). Platygyra daedalea (n = 28) and Porites lobata (n = 14) at 3-4 m depth in an area of approximately 50 m × 10 m were tagged at Little Pioneer Bay on Orpheus Island. The extent of colony bleaching was classified into 6 categories following Marshall and Baird (2000): 1 = no bleaching; 2 = uniformly pale; 3 = 1-50; 4 = 51-99; 5 = 100% bleached, and 6 = dead. Colonies that were fluorescent were categorized as 100% bleached. The extent of colony bleaching was estimated on six occasions following the initial report of bleaching at these sites on 10 February 1998 (Hoegh-Guldberg 1999).

Colony size: The size of P. daedalea colonies was determined from the maximum colony diameter of colonies at the initial census, which ranged from 10 to 40 cm. The projected area of the two species of Acropora was estimated from digitized photos of the colonies. The volume of Seriatopora hystrix was estimated by multiplying maximum diameter width x the perpendicular of maximum colony diameter x maximum colony height. All lengths were measured to the nearest cm with a tape measure.

Partial mortality: Partial mortality was estimated as the proportion of the pre-bleaching tissue lost within each colony, estimated to the nearest 5%. Values ranged from zero (escape from injury) through various amounts of injury (partial mortality) to 100% (whole-colony mortality). Alternatively, in Seriatopora hystrix a categorical scale identical to the bleaching categories described above was used.

References

Berkelmans R, Oliver JK (1999) Large-scale bleaching of corals on the Great Barrier Reef. Coral Reefs 18:55-60

Hoegh-Guldberg O (1999) Climate change, coral bleaching and the future of the world's coral reefs. Mar Freshwat Res 50:839-866

Marshall PA, Baird AH (2000) Bleaching of corals on the Great Barrier Reef: differential susceptibilities among taxa. Coral Reefs 19:155-163