Date of Award
Sok Kean Khoo
Coral reefs are under increasing pressure from global climate change. In particular, ocean warming is having a deleterious effect on many of the world’s shallow reefs. Some authors suggest that acute exposure is more detrimental than chronic, versus others who indicate the opposite. However, little knowledge exists regarding heat induced stress on deeper mesophotic reefs. Here, I examined the effect of acute (72 hrs.) and chronic (480 hrs.) heat stress using laboratory experiments on coral Montastraea cavernosa (Linnaeus 1767) collected from an upper mesophotic (~30 m) reef off Islamorada Florida. I examined a variety of putative immune and stress genes as a proxy for response to heat stress. The acute experiment (Heat and Heat + Oil (Deep Horizon Oil) increased from 27 °C to 33 °C over six hours whereas the chronic experiment (Heat) increased from 27 °C at 1.5 °C increments every 72 hours until temperatures reached 33 °C. Quantitative real-time polymerase chain reaction (qRT-PCR) was performed on six genes including RpL9, RpS7, BCL-2, HSP90, catalase, and cathepsin L1, resulting in two distinct gene expression profiles (rapid transcript upregulation and variable transcript expression). A generalized linear mixed model (GLMM) with a Markov chain Monte Carlo (MCMC) sampling scheme was used to model the expression of genes under treatment conditions. Acute heat exposure resulted in an increase in catalase, BCL-2, and HSP90 at all time points whereas Heat + Oil yielded a strong increase in catalaseactivity from hour 24 to 48. Fewer genes were up-regulated in the chronic experiment until hour 28 (30 °C) where 5 of 6 genes were up-regulated, three of which were significantly up-regulated. Overall, both acute and chronic heat stress elicited a significant response in gene expression relative to control samples. Acute exposure resulted in the activation and upregulation of an oxidative protective enzyme, molecular chaperone, and anti-apoptotic protein. Chronic heat exposure elicited a physiological response at 30 °C which I propose as a heat-stress threshold for M. cavernosa at this depth. In conclusion, M. cavernosa at the upper mesophotic zone is susceptible to increased ocean temperature and should be regarded as a sensitive ecosystem.
Skutnik, John, "Examining the Effect of Climate Change on the Upper Mesophotic Coral Montastrea cavernosa (Linnaeus 1767)" (2016). Masters Theses. 815.