Impacts of temperature-induced maternal effects on larval phenotype, settlement and post-settlement growth of brooding scleractinian corals

Due to elevations in atmospheric CO2 caused by anthropogenic activity, global temperatures are projected to increase 1.8 °C by 2100. The rate and magnitude of this thermal change will have negative impacts on tropical corals and significantly alter reef community structure. It remains unclear how early life stages will be affected by increases in temperature. The goal of this thesis was to evaluate the role that maternal coral colonies play in modulating larval response to thermal stress. Chapter 2 describes exploratory research, the results of which demonstrate that the upper thermal threshold of Pocillopora damicornis is ~32 °C and Symbiodinium densities are not closely associated with larval mortality. Second, utilizing these results, I show that maternal colonies had differential offspring provisioning, but this did not alter larval energy content in sub-lethal temperatures of 31 °C over 6 d. Finally, I describe a significant maternal effect with colonies incubated in a high temperature of 30 °C during larval development exhibiting advanced release of ~1 day, a 52% increase in larval output, and larvae containing 34% less energy than those spawned from corals kept at ambient temperatures of 27 °C. Chapter 3 documents this temperature-induced maternal effect on offspring from larval development to post-settlement. In Taiwan, Seriatopora caliendrum colonies exposed to elevated temperatures of 28 °C during larval development produced larvae that were 19% smaller and had 15% less protein content than those from 26 °C. Larval cohorts were settled into recruits and growth was monitored over 18 d at 25 °C and 28 °C. Recruits from colonies exposed to 28 °C had significantly reduced protein content and planar area, but an 18% increase in polyp division. In general, recruits incubated at 28 °C had 11% higher polyp division rates than recruits grown at 25 °C. There was no effect of temperature or maternal temperature on calcification rates. In Japan, larvae from P. damicornis colonies maintained at 31 °C had significantly reduced protein content and underwent higher rates of mortality during settlement than colonies incubated at 29 °C. Recruits incubated at 29 °C for 21 d had 43% higher polyp division than those at 31 °C, while recruits grown at 31 °C that originated from colonies of the same temperature did not divide. Collectively, these results demonstrate that the temperature of the maternal environment during reproduction in brooding corals significantly impacts offspring by shaping larval phenotypes, altering spawning characteristics, and influencing the post-settlement growth of larvae primarily through polyp division.

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