Exploring the basis of thermotolerance in the reef coral Goniastrea aspera

Abstract

The shallow-water reef coral Goniastrea aspera Verill 1865 has previously been reported to demonstrate differences in within-colony susceptibility to bleaching at elevated sea temperatures; parts of the colony which are exposed to the highest solar radiation are more thermotolerant than areas which are less exposed. In this paper, we show that at elevated experimental sea temperature the 'high light' surfaces lose fewer symbiotic algae, have lower levels of oxidative stress, higher levels of host antioxidant-enzyme copper zinc superoxidase dismutase (CuZnSOD), and host heat-shock proteins 60 and 70, compared to the less exposed surfaces. In addition, 'high light' surfaces show less chronic photoinhibition and greater Photosystem II (PS II) recovery potential when exposed to high irradiance at ambient sea temperature. In contrast, no differences were noted in algal defences (e.g. antioxidant enzymes and stress protein production, and xanthophyll cycling) either at elevated or ambient temperatures. These results are noteworthy because they suggest that corals which acclimatise to high irradiance can, as a result, develop increased thermotolerance which may prevent bleaching at high sea temperatures. Importantly, they also demonstrate the significance of the host tissues in maintaining the intact symbiosis of G. aspera under thermal stress.

Coral-associated marine fungi form novel lineages and heterogeneous assemblages

“…Several factors may account for the high level of fungal community dissimilarity found within the pools and the Symbiodinium genotypes. Prior work has shown that physiology of conspecific corals can vary considerably over short distances (Brown et al, 2002a, b;Smith et al, 2007;Bay et al, 2009;Barshis et al, 2010), which could obscure fungal community patterns associated with our measured variables. Furthermore, stochastic recruitment of large numbers of planktonic, benthic or even terrestrial fungi could mask signatures of specialization or obligacy of a small number of taxa.…”

Evidence for rapid, tide-related shifts in the microbiome of the coral Coelastrea aspera

“…The physical conditions experienced by corals at the study site during low spring tides included elevated temperature, intense solar radiation, sub-aerial exposure and extreme tidal water movements. Temperature and solar radiation effects were maximal during the first two days of Table 4 p values resulting from the Monte Carlo simulations testing for significant differences between diversity indices (Chao1, Alpha and log H 0 ) of microbial communities on different days, within the two coral age groups (*4-and *10-yr-old) sub-aerial exposure, and their negative effects on the physiology of the western sides of colonies have been previously documented in C. aspera at this site (Brown and Dunne 2008;Brown et al 2002). The effects of sub-aerial exposure on increased mucus production have also been highlighted (Jatkar et al 2010).…”

“…All of the above physical factors have the potential to affect the composition of coral-associated bacteria. High temperatures and solar radiation are known to induce oxidative stress in C. aspera with high levels of oxidative damage and increased antioxidant enzyme levels (CuZn-SOD) being produced under such conditions (Brown et al 2002). It has been suggested that high reactive oxygen concentrations are a barrier to microbial colonization of intracellular sites and that they may also play a role in colonization of micro-organisms at other locations in the coral where active oxygen is produced (Thompson et al 2014).…”

“…Such exposure causes severe oxidative damage within coral tissues during extreme low tides (Brown et al 2002). In recent work, we have also highlighted age-related changes in the microbiome of C. aspera, with the highest microbial diversity in 4-to 12-yr-old corals (Williams et al 2015).…”

Investigating the Driving Mechanisms Behind Differences in Bleaching and Disease Susceptibility Between Two Scleractinian Corals, Pseudodiploria Strigosa and Diploria Labyrinthiformis

“…Encouragingly, it is becoming evident that some corals demonstrate a degree of thermotolerance (Brown et al 2002;Mydlarz et al 2009) and are capable of survival in acidified conditions (Fine and Tchernov 2007); thus corals may have innate resilience to these aspects of climate change.…”