Influence of water motion on resistance of corals to high temperatures: Evidence from a field transport experiment

Smith, Lance

Pocillopora damicornis and Porites cylindrica were transplanted between sites within the backreef moat of the National Park of American Samoa on Ofu Island, to investigate the effects of extrinsic factors such as water motion on resistance of corals to high temperatures. Coral transplants were obtained from a relatively deep Source Pool, dyed with Alizarin red S to measure linear extension, and transplanted into two shallower pools, Test Pool 1 and Test Pool 2, as well as back into the Source Pool. Test Pool 1 had the highest daily maximum temperatures, the greatest duration of high temperatures, and the greatest daily fluctuations of temperatures of the three study sites. However, both transplanted species grew more in Test Pool 1 than the other two sites. Mean flow speeds were highest in Test Pool 1, especially on adjacent reef flats. Transplants in Test Pool 1 were located only 1-5 m from the reef flat, whereas in the other two pools they were located >35 m from the reef flat, thus transplants in Test Pool 1 were more exposed to high flow speeds from the reef flat than the transplants in the other two pools. The greater coral transplant growth rates in Test Pool 1 suggest that water motion enhanced the resistance of the transplants to the relatively high temperatures at this site.