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Impacts of temperature and other environmental factors on the early life stages of a scleractinian coral
As a result of anthropogenic increases in atmospheric CO2 concentrations, mean global temperature has increased 0.5 °C since the 1970s, with a further expected increase of 2.6 - 4.8 °C by 2100. If realized, rising temperatures will negatively impact many species including scleractinian coral, which already live near their upper thermal limit. In addition, other abiotic factors (e.g., light and pCO2) have the potential to exacerbate the impacts of high temperature on coral. Much less is known about the effects of these abiotic factors on larvae and recently settled recruits, which are critical life stages that are more sensitive than adults. The goal of this thesis was to study the effects of temperature in conjunction with other biotic and abiotic factors on coral recruitment under current and predicted future environmental regimes. Chapter 2 assesses how the relationship between crustose coralline algae (CCA, a facilitator of coral settlement and post-settlement processes) and the early life stages of Pocillopora damicornis is affected by temperature. P. damicornis larvae settled preferentially onto CCA regardless of temperature; and P. damicornis recruits that had settled onto CCA exhibited higher survivorship at 30 °C than those that had settled onto rock at the same temperature. However, while recruits that had settled on CCA exhibited higher survival, this facilitation was uncoupled when documenting growth with 55% lower growth rates of coral settled to CCA than to rock, regardless of temperature. Chapter 3 documents the effects of temperature and pCO2 on P. damicornis settlement and post-settlement processes. P. damicornis larvae exposed to high temperatures of 30 °C settled 4x faster than those at 26.5 °C. After settlement, recruits in high temperature treatments exhibited high fission rates and a trend toward faster growth (basal tissue area). Elevated pCO2 depressed fission rates, mirroring an antagonistic effect reported previously between high temperature and high pCO2. Survivorship was 30% higher at elevated pCO2 than in ambient pCO2. Collectively, the results of my research demonstrate that temperature, pCO2, and settlement substratum can impact the early life stages of coral by affecting settlement and post-settlement success, two critical early life processes responsible for sustaining coral populations.