Examining the Effect of Heat Stress on Montastraea cavernosa (Linnaeus 1767) from a Mesophotic Coral Ecosystem (MCE)

Sango Otieno,Sok Kean Khoo,John E Skutnik,Kevin B Strychar

doi:10.3390/w12051303

Abstract

Coral reefs are under increasing pressure from global warming. Little knowledge, however, exists regarding heat induced stress on deeper mesophotic coral ecosystems (MCEs). Here, we examined the effect of acute (72 h) and chronic (480 h) heat stress on the host coral Montastraea cavernosa (Linnaeus 1767) collected from an upper MCE (~30 m) in Florida, USA. We examined six immune/stress-related genes: ribosomal protein L9 (RpL9), ribosomal protein S7 (RpS7), B-cell lymphoma 2 apoptosis regulator (BCL-2), heat shock protein 90 (HSP90), catalase, and cathepsin L1, as a proxy for coral response to heat stress. Quantitative real-time polymerase chain reaction (qRT-PCR) was performed to evaluate the gene expression. Overall, both acute and chronic heat stress treatments elicited a response in gene expression relative to control samples. Acute heat exposure resulted in up-regulation of catalase, BCL-2, and HSP90 at all time points from hour 24 to 48, suggesting the activation of an oxidative protective enzyme, molecular chaperone, and anti-apoptotic protein. Fewer genes were up-regulated in the chronic experiment until hour 288 (30 °C) where catalase, RpL9, and RpS7 were significantly up-regulated. Chronic heat exposure elicited a physiological response at 30 °C, which we propose as a heat-stress threshold for Montastraea cavernosa (M. cavernosa) collected from an MCE.

Highlights

Global warming is a natural component of the Earth’s history, shifting between warming and cooling over thousands and millions of years driven by orbital and axial variations as it circles the sun [1]
When exposed characterize heat stress in Differential gene expression was observed across all treatments to heat, expression of ribosomal protein L9 (RpL9) decreased −2.11-fold after 24 h (p = 0.05; Table 3)
The pattern of gene expression produced by the host coral fluctuated, likely due to normal physiological homeostasis

Summary

Introduction

Global warming is a natural component of the Earth’s history, shifting between warming and cooling over thousands and millions of years driven by orbital and axial variations as it circles the sun (described as Milankovitch cycles) [1]. Revolution (~1850), atmospheric concentrations of CO2 have steadily increased warming rather than cooling [7]. Following this logic, when the Earth cycles out of a cooling trend, Earth’s heating trend will be compounded by temperatures already above the expected “normal”. Such warming has considerable implications for reef communities by stressing host corals and their associated symbiont’s

Results

Discussion

Conclusion