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Coral reefs in the Anthropocene: The effects of stress on coral metabolism and symbiont composition
Stockholm University, Faculty of Science, Department of Systems Ecology.
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Coral reefs constitute some of the most prolific and diverse ecosystems on our planet, but also among the most threatened.

This thesis investigates the effects of environmental stressors on corals’ metabolism and symbiont diversity. Paper I shows that the coral Turbinaria mesenterina withstood a single stressor while a combination of two stressors (decreased salinity and increased seawater temperature) lead to decreased metabolism. Increased seawater temperature in combination with two stressors (enhanced nutrients and decreased salinity) lead to rapid mortality of all specimens. Paper II shows that chronic stress in combination with increased seawater temperature affects coral species differently. Porites lutea did not show any difference in response to temperature increase, regardless of environmental disturbance history, while Galaxea fascicularis’ metabolism was negatively affected in chronically disturbed corals but not in corals from less disturbed areas. The main explanation for the difference in response between the two species is different compositions of endosymbionts as found in paper III. P. lutea only harboured the symbiont C15, regardless of environment, whilst D1a dominated the nearshore G. fascicularis and C1 dominated offshore corals. In paper IV there was a clear inshore-offshore pattern of D1a along the whole coast of Vietnam, where D1a dominated inshore. In contrast, the five symbionts belonging to group C displayed a strong latitudinal gradient, with diversity increasing from north to south. The coral host showed higher diversity offshore than inshore.

The thesis emphasizes the importance of improving water quality (paper I and II) and protecting marginal areas since tolerant coral hosts and symbionts can be found there (paper III and IV), as well as safeguarding areas with high symbiont diversity (paper IV) to increase the ability of corals to withstand future environmental changes.

Place, publisher, year, edition, pages
Stockholm: Department of Systems Ecology, Stockholm University , 2011. , 53 p.
Keyword [en]
Corals, Disturbance, Galaxea fascicularis, ITS2, Metabolism, mtDNA, Pollution, Porites lutea, Symbiodinium, Temperature, Turbinaria mesenterina, Vietnam
National Category
Natural Sciences
Research subject
Marine Ecotoxicology
Identifiers
URN: urn:nbn:se:su:diva-62867ISBN: 978-91-7447-383-4 (print)OAI: oai:DiVA.org:su-62867DiVA: diva2:445323
Public defence
2011-11-18, William-Olssonsalen, Geovetenskapens hus, Svante Arrhenius väg 14, Stockholm, 13:30 (English)
Opponent
Supervisors
Note
At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: Manuscript. Paper 4: Manuscript. Available from: 2011-10-27 Created: 2011-10-03 Last updated: 2011-10-26Bibliographically approved
List of papers
1. Effects of elevated water temperature, reduced salinity and nutrient enrichment on the metabolism of the coral Turbinaria mesenterina
Open this publication in new window or tab >>Effects of elevated water temperature, reduced salinity and nutrient enrichment on the metabolism of the coral Turbinaria mesenterina
2010 (English)In: Estuarine, Coastal and Shelf Science, ISSN 0272-7714, E-ISSN 1096-0015, Vol. 88, no 4, 482-487 p.Article in journal (Refereed) Published
Abstract [en]

Water quality is declining in many coastal areas, which has caused coral degradation worldwide. In addition, reduced water quality may aggravate the impacts of seawater temperature. In this study the effects of increased temperature (31 degrees C), nitrate enrichment (+5 mu M NO3-), low salinity (20) and combinations of these stressors were investigated compared to ambient water (25 degrees C, 30, 0.3 mu M NO3-) on the metabolism and survival of the coral Turbinaria mesenterina from the Tonkin Gulf, Vietnam. The results showed that all specimens exposed to a combination of all three stressors (i.e. high temperature + high nitrate + low salinity) died after 24 h exposure, while those that had been exposed to high nitrate + low salinity at ambient temperature did not show any effects on the metabolism or survival. Furthermore, corals exposed to low salinity + high temperature displayed a decrease in gross primary production/respiration (GP/R) ratio and the mortality rate was 50%. In addition, all corals exposed to increased temperature, alone or in combination with another stressor, displayed a GP/R-24h ratio below 1.0, suggesting that they depend on stored energy to cover their metabolic requirements. The results showed that corals may tolerate short-term exposure to stressors such as low salinity + high nitrate concentration in ambient temperature, while additional increased temperature lead to rapid mortality, hence suggesting a synergistic effect. Thus, the effect of climate change might be more severe in nearshore coastal areas where corals already are exposed to several disturbances.

Keyword
temperature increase, salinity, nutrients, corals, metabolism, stress
National Category
Biological Sciences
Research subject
Marine Ecotoxicology
Identifiers
urn:nbn:se:su:diva-49476 (URN)10.1016/j.ecss.2010.05.008 (DOI)000279860800006 ()
Note

authorCount :3

Available from: 2010-12-14 Created: 2010-12-14 Last updated: 2017-12-11Bibliographically approved
2. Differences in physiological response to increased seawater temperature in nearshore and offshore corals in northern Vietnam
Open this publication in new window or tab >>Differences in physiological response to increased seawater temperature in nearshore and offshore corals in northern Vietnam
Show others...
2011 (English)In: Marine Environmental Research, ISSN 0141-1136, E-ISSN 1879-0291, Vol. 71, no 3, 225-233 p.Article in journal (Refereed) Published
Abstract [en]

Effects of elevated seawater temperature show high spatial heterogeneity and variation within and among coral species. The objective of this study was to investigate how two coral species, Porites lutea and Galaxea fascicularis, from two high latitude reefs differently exposed to chronic disturbance, respond to elevated seawater temperatures. Corals were collected from reefs nearshore (i.e. subjected to high sediment load, higher chlorophyll α concentrations, turbidity etc.) and offshore (i.e. less exposed). The corals were exposed in the lab to gradually increasing temperatures (25.5–33.5 °C) for 72 h after which they were allowed to recover to ambient temperature (25.5 °C) for 24 h. Production and respiration were measured after 24, 48, 72 and 96 h. The results show that P. lutea from nearshore reefs suffered an initial decrease in gross primary production/respiration (GP/R) ratio after 24 h, after only a moderate temperature increase (+2 °C, from 25.5 to 27.5 °C), while there was no difference in GP/R ratio between heat-exposed and controls the other days, indicating that the chronic disturbance in the nearshore reef had no effect on their thermotolerance. Furthermore, P. lutea from the offshore reef showed a decrease in GP/R ratio both after 24 h and 72 h (33.5 °C) of exposure.

In comparison, G. fascicularis showed a decrease in GP/R ratio after 48 h, 72 h and 96 h of exposure for the nearshore corals. Also, after 72 h these corals had withdrawn their polyps. There were no differences between heat-treated and controls for the offshore G. fascicularis. This implies that the chronically disturbed G. fascicularis had lower thermotolerance when exposed to a temperature increase.

This study, hence, shows that the response of corals to elevated seawater temperature varies with species and environmental background history.

Keyword
Increased water temperature, Galaxea fascicularis, Porites lutea, Disturbance, Physiological responses, High latitude reefs, Vietnam
National Category
Natural Sciences
Research subject
Marine Ecotoxicology
Identifiers
urn:nbn:se:su:diva-62845 (URN)10.1016/j.marenvres.2011.01.007 (DOI)000288780400010 ()
Available from: 2011-10-03 Created: 2011-10-03 Last updated: 2017-12-08Bibliographically approved
3. Symbiodinium spp. composition in nearshore and offshore Porites lutea and Galaxea fascicularis in northern Vietnam
Open this publication in new window or tab >>Symbiodinium spp. composition in nearshore and offshore Porites lutea and Galaxea fascicularis in northern Vietnam
(English)Manuscript (preprint) (Other academic)
National Category
Natural Sciences
Research subject
Marine Ecotoxicology
Identifiers
urn:nbn:se:su:diva-62846 (URN)
Available from: 2011-10-03 Created: 2011-10-03 Last updated: 2011-10-06Bibliographically approved
4. Symbiodinium spp. diversity in a single host species, Galaxea fascicularis, Vietnam: Impact of environmental factors, host traits, and diversity hot spots
Open this publication in new window or tab >>Symbiodinium spp. diversity in a single host species, Galaxea fascicularis, Vietnam: Impact of environmental factors, host traits, and diversity hot spots
Show others...
(English)Manuscript (preprint) (Other academic)
Abstract [en]

We determined the distribution of zooxanthellate ITS2 types within one broadcast spawning coral species,

Galaxea fascicularis with horizontal symbiont uptake, in both inshore and offshore reef habitats over a 3200 km range along the coast of Vietnam, covering 11 degrees of latitude. Host traits (mtDNA genotype) and environmental factors (visibility, sea surface temperatures and Chlorophyll a derived from satellite data, regional measures of coral species diversity and distance from land (inshore/offshore)) were measured to test whether symbiont type distribution was determined by host characteristics or by environmental factors. The G. fascicularis and their associated symbionts were not genetically coupled to each other but to environmental factors The host displayed an inshore-offshore zonation, with higher diversity offshore. The D1a symbiont exhibited an inshore- offshore zonation. In contrast; the 5 different C symbiont types showed a latitudinal distribution gradient, which shifted in dominance north to south. We found regional differences in symbiont type; these were related to environmental differences and not to genetic characteristics in the coral G. fascicularis.

National Category
Natural Sciences
Research subject
Marine Ecotoxicology
Identifiers
urn:nbn:se:su:diva-57221 (URN)
Available from: 2011-05-09 Created: 2011-05-04 Last updated: 2014-03-04Bibliographically approved

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