Temperature tolerance of the coral Porites lutea exposed to simulated large amplitude internal waves (LAIW)

Large-amplitude internal waves (LAW) cause intense drops in sea water temperature (6-9 degrees C) and acidity (0.6 pH units) within minutes, posing a major disturbance factor for shallow water corals in the Andaman Sea. During periods of elevated temperatures, however, they may provide a vital source of relief to heat-stressed corals. To assess the effect of LAIW on the thermal tolerance of the massive coral Porites lutea, we carried out a onemonth reciprocal LAIW simulation experiment with coral nubbins collected from the LAIW-exposed and LAIW-sheltered sides of the Similan Islands, an offshore archipelago near the Thai Andaman shelf break (distance of sampling locations <3 km). Corals from either origin were subjected to (1) ambient (29 degrees C, pH 839) vs. elevated (31.5 degrees C) temperatures; and (2) ambient temperatures with simulated LAIW (30 minute drops to 23.8 degrees C, pH 7.9, twice per day) vs. elevated temperatures with LAIW (30 minute drops to 24.9 degrees C, pH 7.9, twice per day). Simulated LAIW reduced heat stress responses in all corals. However, nubbins from the LAIW-exposed site showed a higher tolerance to the heat stress than sheltered corals, i.e. lower bleaching- and mortality rates, higher photosynthetic performances and higher protein contents at the end of the experiment, despite identical algal symbiont genotypes (ITS-2, C15). Our results suggest that LAIW-induced nutrient availability, enhanced heterotrophic feeding and thermal variability increased the upper thermal resistance of P. lutea, supporting the notion that LAIW-exposed reefs might be important refugia for coral survival in a warming ocean. (C) 2015 Elsevier B.V. All rights reserved.