A community change in the algal endosymbionts of a scleractinian coral following a natural bleaching event: field evidence of acclimatization

Abstract

The symbiosis between reef-building corals and their algal endosymbionts (zooxanthellae of the genus Symbiodinium) is highly sensitive to temperature stress, which makes coral reefs vulnerable to climate change. Thermal tolerance in corals is known to be substantially linked to the type of zooxanthellae they harbour and, when multiple types are present, the relative abundance of types can be experimentally manipulated to increase the thermal limits of individual corals. Although the potential exists for this to translate into substantial thermal acclimatization of coral communities, to date there is no evidence to show that this takes place under natural conditions. In this study, we show field evidence of a dramatic change in the symbiont community of Acropora millepora, a common and widespread Indo-Pacific hard coral species, after a natural bleaching event in early 2006 in the Keppel Islands (Great Barrier Reef ). Before bleaching, 93.5% (nZ460) of the randomly sampled and tagged colonies predominantly harboured the thermally sensitive Symbiodinium type C2, while the remainder harboured a tolerant Symbiodinium type belonging to clade D or mixtures of C2 and D. After bleaching, 71% of the surviving tagged colonies that were initially C2 predominant changed to D or C1 predominance. Colonies that were originally C2 predominant suffered high mortality (37%) compared with D-predominant colonies (8%). We estimate that just over 18% of the original A. millepora population survived unchanged leaving 29% of the population C2 and 71% D or C1 predominant six months after the bleaching event. This change in the symbiont community structure, while it persists, is likely to have substantially increased the thermal tolerance of this coral population. Understanding the processes that underpin the temporal changes in symbiont communities is key to assessing the acclimatization potential of reef corals.

Investigating the causes and consequences of symbiont shuffling in a multi-partner reef coral symbiosis under environmental change

“…R. Soc. B 282: 20141725 particular conditions of disturbance and recovery, and that differences in these factors may explain variable reports of symbiont community stability or dynamism in the literature [8,9,[17][18][19][20][21][23][24][25][26]43]. Furthermore, these data illustrate that quantitative community metrics, rather than qualitative identification of the dominant symbiont, are necessary to evaluate symbiont shuffling responses.…”

“…In particular, recovery with heat-tolerant symbionts can increase resistance to future thermal bleaching [8], but at a potential energetic cost [13][14][15][16]. Investigations of the ABH have revealed that, although corals sometimes change their symbionts [8,9,[17][18][19][20][21], this does not always occur: sometimes corals recover with the same symbiont community they had prior to stress [22][23][24][25][26]. These conflicting reports have generated controversy surrounding the ABH and the potential role of partner-switching in coral responses to climate change.…”

Lipid biomarkers in Symbiodinium dinoflagellates: new indicators of thermal stress

“…Ecological and environmental parameters such as the history of thermal exposure and Symbiodinium-coral association (Baker 2003;Cooper et al 2011;Jones et al 2008;LaJeunesse et al 2010) may additionally impact the overall thermal stress response.…”

“…Repeated thermal stress may therefore result in a population with more heat-tolerant types of Symbiodinium (Jones et al 2008). …”

Corals from the Persian/Arabian Gulf as models for thermotolerant reef-builders: Prevalence of clade C3 Symbiodinium, host fluorescence and ex situ temperature tolerance

“…Yet another strategy might be to host symbiont communities dominated by thermotolerant symbionts, either by the uptake of new symbionts after a bleaching event or by changing the relative abundance of symbiont types already present in the host (symbiont shuffling) (Baker, 2001;Baker et al, 2004;Berkelmans and van Oppen, 2006;Buddemeier and Fautin, 1993;Jones et al, 2008;Rowan et al, 1997). However, it is not yet established whether the observed acclimatisation will allow the corals to survive in the long run since only 23% of coral species may be able to change their symbionts (Goulet, 2006(Goulet, , 2007.…”