Topic
Zooxanthellae
About: Zooxanthellae is a research topic. Over the lifetime, 1355 publications have been published within this topic receiving 80732 citations.
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TL;DR: Evaluated data on temperature and irradiance-induced bleaching, including long-term data sets which suggest that repeated bleaching events may be the consequence of a steadily rising background sea temperature that will in the future expose corals to an increasingly hostile environment, are evaluated.
Abstract: It has been over 10 years since the phenomenon of extensive coral bleaching was first described. In most cases bleaching has been attributed to elevated temperature, but other instances involving high solar irradiance, and sometimes disease, have also been documented. It is timely, in view of our concern about worldwide reef condition, to review knowledge of physical and biological factors involved in bleaching, the mechanisms of zooxanthellae and pigment loss, and the ecological consequences for coral communities. Here we evaluate recently acquired data on temperature and irradiance-induced bleaching, including long-term data sets which suggest that repeated bleaching events may be the consequence of a steadily rising background sea temperature that will in the future expose corals to an increasingly hostile environment. Cellular mechanisms of bleaching involve a variety of processes that include the degeneration of zooxanthellae in situ, release of zooxanthellae from mesenterial filaments and release of algae within host cells which become detached from the endoderm. Photo-protective defences (particularly carotenoid pigments) in zooxanthellae are likely to play an important role in limiting the bleaching response which is probably elicited by a combination of elevated temperature and irradiance in the field. The ability of corals to respond adaptively to recurrent bleaching episodes is not known, but preliminary evidence suggests that phenotypic responses of both corals and zooxanthellae may be significant.
1,431 citations
TL;DR: It is shown that adult corals, at least in some circumstances, are capable of acquiring increased thermal tolerance and that the increased tolerance is a direct result of a change in the symbiont type dominating their tissues from Symbiodinium type C to D.
Abstract: The ability of coral reefs to survive the projected increases in temperature due to global warming will depend largely on the ability of corals to adapt or acclimatize to increased temperature extr...
1,047 citations
TL;DR: Unusual symbionts normally found only in larval stages, marginal environments, uncommon host taxa, or at latitudinal extremes may prove critical in understanding the long-term resilience of coral reef ecosystems to environmental perturbation.
Abstract: ▪ Abstract Reef corals (and other marine invertebrates and protists) are hosts to a group of exceptionally diverse dinoflagellate symbionts in the genus Symbiodinium. These symbionts are critical components of coral reef ecosystems whose loss during stress-related “bleaching” events can lead to mass mortality of coral hosts and associated collapse of reef ecosystems. Molecular studies have shown these partnerships to be more flexible than previously thought, with different hosts and symbionts showing varying degrees of specificity in their associations. Further studies are beginning to reveal the systematic, ecological, and biogeographic underpinnings of this flexibility. Unusual symbionts normally found only in larval stages, marginal environments, uncommon host taxa, or at latitudinal extremes may prove critical in understanding the long-term resilience of coral reef ecosystems to environmental perturbation. The persistence of bleaching-resistant symbiont types in affected ecosystems, and the possibilit...
995 citations
TL;DR: It is found that the ecologically dominant Caribbean corals Montastraea annularis and M. faveolata can act as hosts to dynamic, multi-species communities of Symbiodinium, implying that physiological acclimatization is not the only mechanism by which corals cope with environmental heterogeneity.
Abstract: Reef-building corals are obligate, mutualistic symbioses of heterotrophic animals and phototrophic dinoflagellates (Symbiodinium spp)1 Contrary to the earlier, widely accepted belief that corals harbour only one symbiont, we found that the ecologically dominant Caribbean corals Montastraea annularis and M faveolata can act as hosts to dynamic, multi-species communities of Symbiodinium Composition of these communities follows gradients of environmental irradiance, implying that physiological acclimatization2,3,4 is not the only mechanism by which corals cope with environmental heterogeneity The importance of this diversity was underlined by analysis of a natural episode of coral bleaching Patterns of bleaching could be explained by the preferential elimination of a symbiont associated with low irradiance from the brightest parts of its distribution Comparative analyses of symbionts before and after bleaching from the same corals supported this interpretation, and suggested that some corals were protected from bleaching by hosting an additional symbiont that is more tolerant of high irradiance and temperature This ‘natural experiment’ suggests that temporal and spatial variability can favour the coexistence of diverse symbionts within a host, despite the potential for destabilizing competition among them5,6
754 citations
TL;DR: A model for coral bleaching is proposed whereby the primary site of heat damage in S, pistillata is carboxylation within the Calvin cycle, as has been observed during heat damageIn higher plants, Damage to PSII and a reduction in F-v/F-m are secondary effects following the overwhelming of photoprotective mechanisms by light.
Abstract: The early effects of heat stress on the photosynthesis of symbiotic dinoflagellates (zooxanthellae) within the tissues of a reef-building coral were examined using pulse-amplitude-modulated (PAM) chlorophyll fluorescence and photorespirometry. Exposure of Stylophora pistillata to 33 and 34 degrees C for 4 h resulted in (1) the development of strong non-photochemical quenching (qN) of the chlorophyll fluorescence signal, (2) marked decreases in photosynthetic oxygen evolution, and (3) decreases in optimal quantum yield (F-v/F-m) of photosystern II (PSII), Quantum yield decreased to a greater extent on the illuminated surfaces of coral branches than on lower (shaded) surfaces, and also when high irradiance intensities were combined with elevated temperature (33 degrees C as opposed to 28 degrees C), qN collapsed in heat-stressed samples when quenching analysis was conducted in the absence of oxygen, Collectively, these observations are interpreted as the initiation of photoprotective dissipation of excess absorbed energy as heat (qN) and O-2-dependent electron flow through the Mehler-Ascorbate-Peroxidase cycle (MAP-cycle) following the point at which the rate of light-driven electron transport exceeds the capacity of the Calvin cycle. A model for coral bleaching is proposed whereby the primary site of heat damage in S, pistillata is carboxylation within the Calvin cycle, as has been observed during heat damage in higher plants, Damage to PSII and a reduction in F-v/F-m (i.e. photoinhibition) are secondary effects following the overwhelming of photoprotective mechanisms by light. This secondary factor increases the effect of the primary variable, temperature. Potential restrictions of electron flow in heat-stressed zooxanthellae are discussed with respect to Calvin cycle enzymes and the unusual status of the dinoflagellate Rubisco, Significant features of our model are that (1) damage to PSII is not the initial step in the sequence of heat stress in zooxanthellae, acid (2) light plays a key secondary role in the initiation of the bleaching phenomena.
641 citations