Coral mortality and recovery in response to increasing temperature in the southern Arabian Gulf

Analysis of a new data set for sea surface temperature shows that the seawater temperature rise in 1998 in the southern Arabian Gulf was the largest since 1870; it also showed that there is an underlying rising trend of sea surface temperature across the whole of the measured area spanning 5 degrees longitude and 3 degrees latitude. Over the last 50 years, sea surface temperature rise was about 0.2°C per decade, though this has accelerated to about 0.45°C per decade in the last 20 years. The pattern in temperature values in each 1 degree 'cell' are used to show that, at any one time, temperature rises towards the east of this area, which supports the concept of a general anti-clockwise circulation in the southeastern half of the Arabian Gulf. Spatial and temporal patterns in sea surface temperature rises also show that the mean temperature field at any location is similar to that which existed in the one degree cell immediately to its east approximately 30 years earlier. Coral cover in shallow water (<3 m depth) was <1 percent immediately following the 1998 event, due to near total mortality of vast areas of shallow Acropora (stagshorn) corals. Deeper than 3 m there was increasing survival of the large Porites (boulder) corals, survival increasing with depth. Coral survival improved towards the east, though overall, less than twenty coral species were found altogether. Juvenile recruitment also increased towards the east, and at any one site, recruitment increased with increasing depth. The identity of new juveniles was mainly faviid corals, not the Acropora or Porites which dominated these reefs before the 1998 event. This suggests that there may be a phase shift to a different stable state in terms of coral communities. We also speculate that, because the Arabian Gulf contains an extreme warm-tolerant subset of the Indian Ocean coral fauna, the changes seen in the Gulf may reflect future patterns across a greater part of the Indian Ocean.