Resilience and acclimatization potential of reef corals under predicted climate change stressors

Abstract

Coral reef ecosystems are among the most diverse and productive in the world. The basis for this productivity is the symbiosis between cnidarian hosts and single-celled dinoflagellates (Symbiodinium) that together structure the reef. Coral reefs are currently under threat locally from a variety of stressors, as well as globally from increasing temperature and CO2-induced ocean acidification. While rates of adaptation are anticipated to be slower than the rate of climate change, rapid acclimatory processes, such as trans-generational acclimatization and other epigenetic mechanisms may contribute to the maintenance of coral reefs in the future. The goal of this dissertation was to advance our understanding of the processes involved in coral response to climate change. In particular, I focused on identifying the variability in physical setting (temperature, pH, pCO2) for coastal reefs in Kaneohe Bay, Hawaii, and developing the experimental infrastructure with which to test the effects of increasing temperature and ocean acidification on the reef building coral Pocillopora damicornis. This brooding coral provides the ideal model to test life-stage specific response and the connection between adults and brooded larvae in a trans-generational context. In a 9-day factorial experimental exposure to either ambient (25°C) and high temperature (29°C) and ambient (~415 μatm) and high CO2 (~635 μatm), P. damicornis larvae displayed strong metabolic suppression and decline in Rubiso protein expression (ribulose-1,5-bisphosphate carboxylase/oxygenase, a rate-limiting enzyme in the Calvin cycle) at high temperatures regardless of CO2 concentration, likely resulting in energetic debt with negative fitness implications. When adult corals were preconditioned to ambient (26.5°C and ~ 415 μatm) or high temperature and CO2 (29°C and ~800 μatm) for 1.5 months prior to larval release, adults in high conditions displayed significant declines in productivity while maintaining metabolic rate and calcification, with reproductive consequences. Coral larvae from adults exposed to high conditions (29°C and ~800μatm) were significantly affected by adult environment resulting in smaller larvae with lower metabolic rates. However, positive trans-generational acclimatization was documented in a secondary reciprocal exposure in larvae from adults with a high history displaying higher sizenormalized metabolic rates, with implications for protein turnover, energetics, and fitness. This work highlights the necessity of considering rapid acclimatization, or epigenetic processes (i.e., trans-generational acclimatization) in our examination of the response of coral to climate change in order to best inform our predictions for the future of coral reefs.