Articles | Volume 14, issue 24
Research article
21 Dec 2017
Research article |  | 21 Dec 2017

Impact of diurnal temperature fluctuations on larval settlement and growth of the reef coral Pocillopora damicornis

Lei Jiang, You-Fang Sun, Yu-Yang Zhang, Guo-Wei Zhou, Xiu-Bao Li, Laurence J. McCook, Jian-Sheng Lian, Xin-Ming Lei, Sheng Liu, Lin Cai, Pei-Yuan Qian, and Hui Huang

Abstract. Diurnal fluctuations in seawater temperature are ubiquitous on tropical reef flats. However, the effects of such dynamic temperature variations on the early stages of corals are poorly understood. In this study, we investigated the responses of larvae and new recruits of Pocillopora damicornis to two constant temperature treatments (29 and 31 °C) and two diurnally fluctuating treatments (28–31 and 30–33 °C with daily means of 29 and 31 °C, respectively) simulating the 3 °C diel oscillations at 3 m depth on the Luhuitou fringing reef (Sanya, China). Results showed that the thermal stress on settlement at 31 °C was almost negated by the fluctuating treatment. Further, neither elevated temperature nor temperature fluctuations caused bleaching responses in recruits, while the maximum excitation pressure over photosystem II (PSII) was reduced under fluctuating temperatures. Although early growth and development were highly stimulated at 31 °C, oscillations of 3 °C had little effects on budding and lateral growth at either mean temperature. Nevertheless, daytime encounters with the maximum temperature of 33 °C in fluctuating 31 °C elicited a notable reduction in calcification compared to constant 31 °C. These results underscore the complexity of the effects caused by diel temperature fluctuations on early stages of corals and suggest that ecologically relevant temperature variability could buffer warming stress on larval settlement and dampen the positive effects of increased temperatures on coral growth.

Short summary
The negative effects of elevated temperature (31 °C) on larval settlement of P. damicornis was greatly tempered by diurnal temperature fluctuations, whilst diel oscillations in temperature reduced the heat stress on photo-physiology of coral recruits. Although elevated temperature greatly stimulated the growth of recruits, the daytime encounters with the maximum temperature of 33 °C in the fluctuating treatment elicited a notable reduction in calcification.
Final-revised paper