Post-bleaching viability of expelled zooxanthellae from the scleractinian coral Pocillopora damicornis
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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.Keywords:
Zooxanthellae
Pocillopora damicornis
Symbiodinium
Coral bleaching
Stylophora pistillata
Hermatypic coral
Stylophora pistillata
Pocillopora damicornis
Hermatypic coral
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Pocillopora damicornis
Hermatypic coral
Zooxanthellae
Coral bleaching
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Symbiodinium
Zooxanthellae
Hermatypic coral
Dinoflagellate
Anthozoa
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1. The hermatypic coral, Pocillopora damicornis was incubated in the laboratory and in its reef habitat with Na214CO3 for 1-24 hours. Controls were incubated in darkness. 14C fixation in light exceeded that in darkness. 2. Fractionation of corals labeled on the reef for 24 hours revealed that 35-50% of the total 14C fixed appeared in the animal tissue lipid (as 14C-glycerol) and protein. From a comparison with dark controls it is concluded that photosynthetic products of zooxanthellae are translocated to host coral tissue. The skeletal organic matrix also acquires 14C. 3. Zooxanthehellae isolated from corals and incubated in a homogenate of host coral tissue selectively release glycerol and traces of other organic material including glucose, alanine, and glycolic acid confirming previous observations.
Pocillopora damicornis
Zooxanthellae
Hermatypic coral
Darkness
Tentacle (botany)
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Zooxanthellae
Pocillopora damicornis
Symbiodinium
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Zooxanthellae
Stylophora pistillata
Hermatypic coral
Autotroph
Scleractinia
Degradation
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Stylophora pistillata
Hermatypic coral
Zooxanthellae
Light intensity
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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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