Changes in quantum efficiency of Photosystem II of symbiotic dinoflagellates of corals after heat stress, and of bleached corals sampled after the 1998 Great Barrier Reef mass bleaching event

Abstract

Pulse–amplitude–modulation chlorophyll fluorometry was used to examine changes in dark-adapted Fv/Fm of endosymbiotic dinoflagellate microalgae within the tissues of the temperate coral Plesiastrea versipora exposed to elevated seawater temperature. The Fv/Fm was markedly reduced following exposure of corals to 28°C for 48 h. When corals were returned to ambient (24°C) conditions, Fv/Fm increased in an initial rapid and then secondary slower phase. Tissue discolouration (coral bleaching), caused by a significant decrease in the density of algae, was observed during the first 2–3 days of the recovery period. After 14 days, Fv/Fm was still significantly lower than in control corals. The recovery of Fv/Fm is discussed in terms of repair processes within the symbiotic algae, division of healthy algae and also the selective removal of photo-damaged dinoflagellates. Under field conditions, bleached corals sampled at Heron Island Reef during a bleaching event had significantly lower Fv/Fm than non-bleached colonies; four months after the bleaching event, there were no differences in F v /F m or algal density in corals marked as having bleached or having shown no signs of colour loss. The results of this laboratory and field study are consistent with the hypothesis that an impairment of photosynthesis occurs during heat-stress, and is the underlying cause of coral bleaching.

Photosynthetic responses of corals Mussismilia harttii (Verrill, 1867) from turbid waters to changes in temperature and presence/absence of light

“…This incubation time was sufficient to promote a dark adaptation of the samples and did not influence the physiological response, since distinct times used for dark adaptation are found in the literature. For instance, 20 and 120 min were used for Pocillopora damicornis (JONES et al, 1998;JONES et al, 2000;FRISCH et al, 2007), and a dark adaptation of from 20 to 60 min was used for calculating F v /F m in other coral species (BROWN et al, 1999;WARNER et al, 1999;JONES et al, 2000;HOEGH-GULDBERG, 2001). Experiments were carried out in open-topped glass aquaria kept at distinct temperatures (26.5 [control], 29.0, 31.0, 33.0, and 35.0 °C).…”

Photosynthesis and light utilization in the Caribbean coral Montastraea faveolata recovering from a bleaching event

“…Depending on the severity of the thermal stress, coral bleaching may be a reversible phenomenon or may result in massive coral mortality episodes with catastrophic ecological consequences (Hoegh-Guldberg 1999). Although there is controversy regarding the actual site of thermal damage (Warner et al 1999;Tchernov et al 2004;Smith et al 2005), coral bleaching appears to be initiated by the temperature-dependent inactivation of the photosynthetic function of the symbionts (Iglesias-Prieto et al 1992;Jones et al 1998). Once photosynthesis is impaired, light plays a major role in modulating the disruption of the symbiosis (Hoegh-Guldberg 1999).…”

“…The abilities of different symbionts to recolonize the host after bleaching may be critical in determining if a particular colony will be able to recover or experience mortality. Despite its importance, the physiological process of recovery from coral bleaching has received very little attention (Jones et al 2000;Nakamura et al 2003).…”

Upwelling linked to warm summers and bleaching on the Great Barrier Reef

“…4D-F). Of particular note at Magnetic Island is that the bleaching summers of 1997-1998-2002(Berkelmans et al 2004) stand out with . 25 d of upwelling compared to , 12 d during nonbleaching summers.…”

“…These same conditions also cause greatly enhanced local heating and stratification, the primary causal factors behind bleaching. In addition, doldrums conditions enhance settlement of particulate matter, increasing light penetration (visible and ultraviolet; Zepp et al 2008), which in turn accelerates bleaching in heat-impaired corals (Jones et al 1998(Jones et al , 2000. Doldrums conditions also provide the potential for a positive feedback.…”