Declining Coral Calcification on the Great Barrier Reef

TLDR

Reef‑building corals are under increasing physiological stress from a changing climate and ocean absorption of rising atmospheric CO₂. We investigated 328 colonies of massive Porites corals from 69 reefs of the Great Barrier Reef in Australia. Skeletal records from these colonies show a 14.2 % decline in calcification since 1990—primarily driven by a 13.3 % drop in linear extension—an unprecedented change in four centuries, with calcification rising linearly with large‑scale sea‑surface temperature but responding nonlinearly to annual anomalies, suggesting temperature stress and decreasing aragonite saturation are likely contributors.

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.