Sci. Adv. 2, e1600825 (2016)

Credit: Ryan Lowe

Warming ocean temperatures due to climate change will affect marine biota, as has been seen this year with the mass global coral bleaching. Shallow reef systems will have increased vulnerability to thermal stress as temperatures increase. However, local variations in sea surface temperatures, including those due to the depth of the reef, may offer some protection.

To discover the interactions between solar warming and reef depth, Ryan Joseph Lowe and colleagues from the University of Western Australia study a reef with a large tidal range at Tallon Island, northwestern Australia. The large twice daily (semi-diurnal) tidal range permits study of how reef water depths determine maximum temperatures in the reef. Reef water temperature combined with heat exchange data was used to construct a heat budget model.

The authors find that the monthly semi-diurnal tidal cycle leads to 15-day cycles of daily temperature extremes. Application of the model to six example reefs shows that reefs with tidal ranges comparable to their depth experience the greatest temperature fluctuations, and when considered with projections these reefs would experience a 7–65% reduction in daily temperature fluctuations with 0.7 m of sea level rise. Therefore moderate sea level rise may alleviate some of the extreme termperatures and thermal stress in many shallow tide-dominated reefs.