Exposure to elevated sea-surface temperatures below the bleaching threshold impairs coral recovery and regeneration following injury.

Joshua Louis Bonesso,William Leggat,Tracy Danielle Ainsworth

doi:10.7717/peerj.3719

Joshua Louis Bonesso, William Leggat + Show 1 more

Open Access

https://doi.org/10.7717/peerj.3719

Copy DOI

Abstract

Elevated sea surface temperatures (SSTs) are linked to an increase in the frequency and severity of bleaching events due to temperatures exceeding corals’ upper thermal limits. The temperatures at which a breakdown of the coral-Symbiodinium endosymbiosis (coral bleaching) occurs are referred to as the upper thermal limits for the coral species. This breakdown of the endosymbiosis results in a reduction of corals’ nutritional uptake, growth, and tissue integrity. Periods of elevated sea surface temperature, thermal stress and coral bleaching are also linked to increased disease susceptibility and an increased frequency of storms which cause injury and physical damage to corals. Herein we aimed to determine the capacity of corals to regenerate and recover from injuries (removal of apical tips) sustained during periods of elevated sea surface temperatures which result in coral stress responses, but which do not result in coral bleaching (i.e., sub-bleaching thermal stress events). In this study, exposure of the species Acropora aspera to an elevated SST of 32 °C (2 °C below the bleaching threshold, 34 °C) was found to result in reduced fluorescence of green fluorescent protein (GFP), reduced skeletal calcification and a lack of branch regrowth at the site of injury, compared to corals maintained under ambient SST conditions (26 °C). Corals maintained under normal, ambient, sea surface temperatures expressed high GFP fluorescence at the injury site, underwent a rapid regeneration of the coral branch apical tip within 12 days of sustaining injury, and showed extensive regrowth of the coral skeleton. Taken together, our results have demonstrated that periods of sustained increased sea surface temperatures, below the corals’ bleaching threshold but above long-term summertime averages, impair coral recovery from damage, regardless of the onset or occurrence of coral bleaching.

Highlights

Sea surface temperatures (SSTs) have increased in recent decades and are projected to continue to increase at a rate of, on average, 0.12 ◦C per decade (Steig et al, 2009)
The regenerative and wound healing response of experimentally injured A. aspera to the synergistic impacts of thermal stress was documented by a time-series of micrographs of the apical tips of colonies held under temperature stressed and ambient conditions
More than 50% of regrowth of the apical tip had occurred by day 8 and complete regrowth of the apical tip was evident by experimental day 12

Summary

Introduction

Sea surface temperatures (SSTs) have increased in recent decades and are projected to continue to increase at a rate of, on average, 0.12 ◦C per decade (Steig et al, 2009). Storm and disease events are projected to increase in frequency and intensity (Hoegh-Guldberg et al, 2007; Hughes et al, 2003) and predation by crown of thorns starfish is predicted to increase in areas with decreasing water quality (De’arth et al, 2012; Brodie et al, 2005). These events in isolation, and where occurring together, will result in a far greater frequency of stress and injury to reef-building corals. This reformation of both skeleton and tissue at lesion sites is essential for colony survival, growth, reproduction and the prevention of disease (Oren, Benayahu & Loya, 1997; Van de Water et al, 2015a; Van de Water et al, 2015b)

Objectives

Methods

Results

Discussion

Conclusion