Declining Coral Calcification on the Great Barrier Reef

Abstract

Reef-building corals are under increasing physiological stress from a changing climate and ocean absorption of increasing atmospheric carbon dioxide. We investigated 328 colonies of massive Porites corals from 69 reefs of the Great Barrier Reef (GBR) in Australia. Their skeletal records show that throughout the GBR, calcification has declined by 14.2% since 1990, predominantly because extension (linear growth) has declined by 13.3%. The data suggest that such a severe and sudden decline in calcification is unprecedented in at least the past 400 years. Calcification increases linearly with increasing large-scale sea surface temperature but responds nonlinearly to annual temperature anomalies. The causes of the decline remain unknown; however, this study suggests that increasing temperature stress and a declining saturation state of seawater aragonite may be diminishing the ability of GBR corals to deposit calcium carbonate.

A corrosive concoction: The combined effects of ocean warming and acidification on the early growth of a stony coral are multiplicative

“…In adult corals, elevated temperatures can actually increase calcification rates (Clausen and Roth, 1975), probably due to the higher metabolic rates, but when combined with more acidic conditions, calcification decreases significantly (Reynaud et al, 2003). There is evidence that corals are already responding to the changing conditions: In vivo cores from adult Porites colonies reveal that calcification has reduced since 1990 by 14.2% (De'ath et al, 2009).…”

Bioindicators of changes in water quality on coral reefs: review and recommendations for monitoring programmes

“…For example, the skeletal density of massive Porites increases (Risk and Sammarco 1991), but the rate of linear extension and calcification decreases, with increasing distance from the coast (Lough and Barnes 1992; Table 2). However, coral growth is also influenced by variation in other parameters such as temperature, thermal stress and ocean acidification (Lough and Barnes 2000;Cooper et al 2008a;De'ath et al 2009) indicating a moderate specificity to changes in water quality. Coral growth ranked a medium-priority bioindicator for use in long-term monitoring, but was of low priority for short-term monitoring because of its slow response time (Table 3).…”

On the surface circulation in the western Coral Sea and residence times in the Great Barrier Reef

“…Furthermore, the GBR may be facing unprecedented consortia of threats from the rise of global ocean temperatures, changes in ocean pH, continued fishing pressure and the impact of land use changes since European settlement [Hoegh-Guldberg, 1999;Pandolfi et al, 2003;Wolanski et al, 2003;De'ath et al, 2009]. Therefore, a better understanding of the water movement within the GBR and between the GBR and the adjacent Coral Sea, by the evaluation of its residence time, would provide valuable information for management of the GBR and its catchments, and shed new light on the connectivity of the region.…”