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Rice University

Publication Date

Winter 2017

Program Name

Australia: Rainforest, Reef, and Cultural Ecology

Abstract

The scleractinian coral species that so heavily define tropical coral reefs are increasingly threatened by anthropogenic global warming. Rising sea surface temperatures in combination with light stress causes the photosynthetic breakdown of the coral’s algal symbiont, Symbiodinium. Corals have developed a number of physiological responses to handle acute stressors, such as the production of ultraviolet-protecting amino acids, heat shock proteins, the ability to shift symbionts, and the production of fluorescent proteins. The latter has been thought to play a photoprotective role in the coral holobiont, and studies have shown evidence that corals orient these pigments to divert harmful light away from their symbionts in shallow reefs that are at great risk of environmental stress. The biological role these proteins play is still largely speculative. This study is part of a larger study examining coral physiological responses to thermal stress.

In total, 170 Acropora tenuis colonies were tagged in reefs surrounding Pelorus and Orpheus Islands before the onset on the bleaching event of 2017 that affected the Central Sector of the Great Barrier Reef. In addition to studying the genetic differences between resilient and susceptible individuals, the fluorescent protein expression of these colonies was examined during the height (March) and end (April) of the bleaching event. Of 25 colonies that underwent analysis, 21 experienced extreme thermal stress and were nearly completely bleached in April and two colonies not only survived the bleaching, but increased their Symbiodinium counts. Fragments collected were split into top and bottom portions for analysis. Top fragments experienced greater rates of bleaching than bottom fragments at both the March and April time point, suggesting that exposure to light in addition to heat is more stressful than heat alone. Total protein content linearly decreased weakly, but significantly, with the loss of Symbiodinium (r2 = 0.3226; P-value = 4.292e^-10). Fluorescent protein expression between March and April in all 25 colonies did not significantly change (r2 = 0.0002365, P=0.3142), but the ratio in concentration of cyan fluorescent protein (475 nm) to green fluorescent protein (505 nm) was higher in top fragments of colonies that remained bleached than in top fragments of colonies that remained healthy throughout March and April (P < 0.05). The same ratio difference was not detected in the bottom fragments (P > 0.05). This pattern suggests variability in the effects light and heat have on coral’s physiological response to stress and that corals may downregulate energetically costly FPs during bleaching.

Disciplines

Biodiversity | Environmental Studies | Oceanography | Terrestrial and Aquatic Ecology

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