Damage and recovery of Photosystem II during a manipulative field experiment on solar bleaching in the coral Goniastrea aspera

Abstract

The solar radiation regime on differently oriented surfaces of the shallow-water coral Goniastrea aspera is markedly different Field experiments involving rotation of small (20 cm diameter) hemispherical colonies exposed hitherto protected surfaces of the colonies to high levels of photosynthetically active radiation (PAR) whilst reducing PAR on the opposite surface. Photodamage and recovery, respectively, were recorded in the symbiotic algae using non-invasive chlorophyll fluorescence techniques. Measurements of photochemical efficiency (FJF,) indicated that the Photosystem I1 (PSII) reaction centres of algae in previously protected surfaces suffered 'chronic' photoinhibition, probably on a timescale of 3 h, as a result of exposure to elevated solar PAR. Furthermore, evidence from this study corroborates earlier findings that this photodamage is a function of high PAR irradiance for short periods rather than a similar dose accumulated more slowly. Sin~ultaneously, algae on the opposite surfaces were observed to recover their photochemical efficiency, but this recovery was at a much slower rate involving several days at reduced PAR. The photodamage was sufficiently severe to lead to the formation of visible lesions (bleached areas). Observations of coral polyp retraction and nleasurements of the protective xanthophyll pigments in the algae showed behavioural and photoprotective mechanisms being deployed to mitigate the photodamage.

Membrane lipids of symbiotic algae are diagnostic of sensitivity to thermal bleaching in corals

“…These two phenomena are diagnostic of an energetically uncoupled system in which the transmembrane proton gradient, established by the photochemical reactions in the functional reaction centers, is dissipated without generating ATP (23). This fluorescence kinetic pattern, uniquely found in thermally sensitive zooxanthellae, qualitatively differs from photoinhibition (24)(25)(26), with which the time constant for electron transfer increases as the reaction centers become increasingly impaired (27). Moreover, in thermally sensitive clones of zooxanthellae, the pattern of change in photochemical energy conversion occurs over a very narrow thermal window of Ͻ2°C.…”

Responses to iron limitation in two colonies of Stylophora pistillata exposed to high temperature: Implications for coral bleaching

“…Although the depletion of pigmentation also occurred at elevated temperature in the absence of DFB, as reported in other experimental studies of coral bleaching, iron limitation exacerbated the effect and caused substantial increases in DT/(DD + DT) at high temperature. In corals this increase in the conversion of DD to the photoprotective deepoxidated form, DT (Ambarsari et al 1997;Brown et al 1999;Warner and Berry-Lowe 2006), results in higher quenching of singlet chlorophyll by NPQ in the algae, typically to avert photo-oxidative damage (Casper-Lindley and Bjö rkman 1998).…”

Mechanisms of Thermal Tolerance in Reef-Building Corals across a Fine-Grained Environmental Mosaic: Lessons from Ofu, American Samoa

“…More recently, focus has shifted toward understanding the plasticity of thermal tolerance in corals, and numerous studies have identified a direct link between thermal preconditioning and bleaching susceptibility from both field observations (Castillo and Helmuth, 2005;Maynard et al, 2008;Thompson and van Woesik, 2009;Castillo et al, 2012;Shuail et al, 2016) and experimental manipulation (Brown et al, 2000(Brown et al, , 2002Dove et al, 2006;Middlebrook et al, 2008;Bellantuono et al, 2012b;Bay and Palumbi, 2015). For example, Acropora, Pocillopora, and Porites from the Great Barrier Reef showed lower rates of bleaching during the 2002 bleaching event than the 1998 event, despite more intense conditions during the 2002 event (Maynard et al, 2008).…”