Assessing the effects of polychlorinated biphenyls (Aroclor 1254) on a scleractinian coral (Stylophora pistillata) at organism, physiological, and molecular levels
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Stylophora pistillata
Zooxanthellae
Pocillopora damicornis
Plant Physiology
Total amino-N content and glutamine to glutamate ratios (gin: glu) were determined in zooxanthellae freshly isolated from colonies of the coral Pocillopora damicornis (Linnaeus) incubated in ambient seawater orin seawater supplemented with ammonium to give a final concentration of 20 or 50 J.lM. Addition of ammonium did not change total amino-N content but did increase gin: glu from 0.25 to 0.47-0.48, suggesting that ammonium was di rectly utilized by the symbiotic zooxanthellae. Gin: glu in zooxanthellae from corals maintained in seawater stripped of ammonium fell to 0.18. Sizes of pools of most free amino acids in zooxanthellae from P. damicornis were roughly two to five times those of zooxanthellae from the temperate sea anenome Anemonia viridis, but the latter, which is not believed to be N-limited, exhibited higher gin: glu ratios. These data indicate that gin: glu is a sensitive measure of the response of symbiotic zooxanthellae to exogenous dissolved nitrogen, but despite an increase in gin: glu when seawater is supplemented with ammonium, it cannot be concluded that individual zooxanthellae are normally N-limited. tive of nitrogen-limited metabolism, but other parameters remain to be investigated. The Hawaii Institute of Marine Biology work shop provided the opportunity to measure both elemental composition of zooxanthellae (Muller-Parker et al. 1994a) and size and composition of zooxanthellar amino acid pools.
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Zooxanthellae
Artificial seawater
Stylophora pistillata
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Zooxanthellae
Pocillopora damicornis
Photoprotection
Coral bleaching
Stylophora pistillata
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Ultrastructural changes in the coral tissues and symbiotic zooxanthellae of the scleractinian coral, Pocillopora damicornis, after exposure to high temperature (HT), ultraviolet (UV) and far-red (FR) radiation were examined by transmission electron microscopy. In normal environmental conditions, the coral gastrodermis contained zero to two zooxanthellae and maintained well-defined cortical and intracellular structures. When corals were exposed to HT, UV and FR, the gastrodermal features changed remarkably depending on the duration of exposure. Treatment with HT for 15 min or exposure to UV and FR for 6 h induced the appearance of numerous, small, electron-dense granules in the gastrodermis. Autophagosomes and lysosomes in the gastrodermal cells also increased in number. The gastrodermal cells containing no zooxanthellae began to degrade and became vacuolated through the destruction and fragmentation of their cytoplasmic contents. Prolonged exposure to these stressors brought about the disintegration of the cells without zooxanthellae and led to the collapse of the gastrodermis. This resulted in the release of the other gastrodermal cells containing zooxanthellae from the gastrodermis to gastrovascular cavities. HT, UV and FR affected the gastrodermal cells without zooxanthellae more severely than the zooxanthellae themselves, although the thylakoids of the zooxanthellae were often destroyed when the coral was exposed to UV and FR. These results suggest that the coral receives the distinct stressors, HT, UV and FR, but has a common mechanism that promotes autolysis activities in the gastrodermis and discharges cells containing zooxanthellae.
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MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 352:137-144 (2007) - DOI: https://doi.org/10.3354/meps07159 Post-bleaching viability of expelled zooxanthellae from the scleractinian coral Pocillopora damicornis Ross Hill, Peter J. Ralph* Institute for Water and Environmental Resource Management and Department of Environmental Sciences, University of Technology, Sydney, PO Box 123, Broadway, New South Wales 2007, Australia *Corresponding author. Email: peter.ralph@uts.edu.au ABSTRACT: Coral bleaching events have been linked to elevated seawater temperatures in combination with intense light and can be characterised by the loss of symbionts (zooxanthellae, genus Symbiodinium) from the host tissue, as well as a reduction in photosynthetic pigments in these zooxanthellae. The long-term (days) viability of expelled zooxanthellae in the water column from the scleractinian coral Pocillopora damicornis was explored in this study through measurements of photosynthetic health and morphological condition. After initial expulsion, zooxanthellae were found to be photosynthetically competent and structurally intact. However, within 6 to 12 h following this time, photosystem II photochemical efficiency dramatically declined in these cells and photosynthetic damage was gradually manifested in the loss of structural integrity of the cell. The time of expulsion during bleaching exposure, as well as ambient water temperature, greatly influenced survivorship. Expelled zooxanthellae were collected at 4 different time intervals (0–6, 6–12, 12–24 and 24–36 h) following the onset of exposure to bleaching conditions (32°C and 400 µmol photons m–2 s–1) and then maintained at 28, 30 or 32°C and 100 µmol photons m–2 s–1 for up to 96 h. Those cells expelled within the first 6 h of bleaching and held at 28°C (lagoon temperature) had the greatest longevity, although even in this treatment, long-term photosynthetic viability was restricted to 5 d in the water column. This suggests that unless expelled zooxanthellae inhabit other environments of coral reefs (such as sediments) which may be more favourable for survival, their capacity for persistence in the environment is extremely limited. KEY WORDS: Coral bleaching · Chlorophyll a fluorescence · Effective quantum yield · Pulse amplitude modulated · PAM · Zooxanthellae · Symbiodinium Full text in pdf format PreviousNextCite this article as: Hill R, Ralph PJ (2007) Post-bleaching viability of expelled zooxanthellae from the scleractinian coral Pocillopora damicornis. Mar Ecol Prog Ser 352:137-144. https://doi.org/10.3354/meps07159 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 352. Online publication date: December 20, 2007 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2007 Inter-Research.
Zooxanthellae
Pocillopora damicornis
Symbiodinium
Coral bleaching
Stylophora pistillata
Hermatypic coral
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Increased ocean temperatures are thought to be triggering mass coral bleaching events around the world. The intracellular symbiotic zooxanthellae (genus Symbiodinium) are expelled from the coral host, which is believed to be a response to photosynthetic damage within these symbionts. Several sites of impact have been proposed, and here we probe the functional heterogeneity of Photosystem II (PSII) in three coral species exposed to bleaching conditions. As length of exposure to bleaching conditions (32 degrees C and 350 micromol photons m(-2) s(-1)) increased, the QA- reoxidation kinetics showed a rise in the proportion of inactive PSII centers (PSIIx), where QB was unable to accept electrons. PSIIx contributed up to 20% of the total PSII centers in Pocillopora damicornis, 35% in Acropora nobilis and 14% in Cyphastrea serailia. Changes in Fv/Fm and amplitude of the J step along fast induction curves were found to be highly dependent upon the proportion of PSIIx centers within the total pool of PSII reaction centers. Determination of PSII antenna size revealed that under control conditions in the three coral species up to 60% of PSII centers were lacking peripheral light-harvesting complexes (PSIIbeta). In P. damicornis, the proportion of PSIIbeta increased under bleaching conditions and this could be a photoprotective mechanism in response to excess light. The rapid increases in PSIIx and PSIIbeta observed in these corals under bleaching conditions indicates these physiological processes are involved in the initial photochemical damage to zooxanthellae.
Zooxanthellae
Pocillopora damicornis
Coral bleaching
Symbiodinium
Stylophora pistillata
Scleractinia
P700
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Stylophora pistillata
Zooxanthellae
Pocillopora damicornis
Propagule
Scleractinia
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The unique mutualism between corals and their photosynthetic zooxanthellae (Symbiodinium spp.) is the driving force behind functional assemblages of coral reefs. However, the respective roles of hosts and Symbiodinium in this endosymbiotic association, particularly in response to environmental challenges (e.g., high sea surface temperatures), remain unsettled. One of the key obstacles is to produce and maintain aposymbiotic coral hosts for experimental purposes. In this study, a simple and gentle protocol to generate aposymbiotic coral hosts (Isopora palifera and Stylophora pistillata) was developed using repeated incubation in menthol/artificial seawater (ASW) medium under light and in ASW in darkness, which depleted more than 99% of Symbiodinium from the host within 4∼8 days. As indicated by the respiration rate, energy metabolism (by malate dehydrogenase activity), and nitrogen metabolism (by glutamate dehydrogenase activity and profiles of free amino acids), the physiological and biochemical performances of the menthol-induced aposymbiotic corals were comparable to their symbiotic counterparts without nutrient supplementation (e.g., for Stylophora) or with a nutrient supplement containing glycerol, vitamins, and a host mimic of free amino acid mixture (e.g., for Isopora). Differences in biochemical responses to menthol-induced bleaching between Stylophora and Isopora were attributed to the former digesting Symbiodinium rather than expelling the algae live as found in the latter species. Our studies showed that menthol could successfully bleach corals and provided aposymbiotic corals for further exploration of coral-alga symbioses.
Stylophora pistillata
Symbiodinium
Zooxanthellae
Pocillopora damicornis
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Stylophora pistillata
Zooxanthellae
Pocillopora damicornis
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Pocillopora damicornis
Tadpole (physics)
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