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- Faxneld, Suzanne, 1978-
(author)
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Coral reefs in the Anthropocene : The effects of stress on coral metabolism and symbiont composition
- 2011
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Doctoral thesis (other academic/artistic)abstract
- 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.
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| 2. |
- Faxneld, Suzanne, et al.
(author)
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Differences in physiological response to increased seawater temperature in nearshore and offshore corals in northern Vietnam
- 2011
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In: Marine Environmental Research. - : Elsevier BV. - 0141-1136 .- 1879-0291. ; 71:3, s. 225-233
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Journal article (peer-reviewed)abstract
- 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.
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| 3. |
- Faxneld, Suzanne, et al.
(author)
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Effects of elevated water temperature, reduced salinity and nutrient enrichment on the metabolism of the coral Turbinaria mesenterina
- 2010
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In: Estuarine, Coastal and Shelf Science. - : Elsevier BV. - 0272-7714 .- 1096-0015. ; 88:4, s. 482-487
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Journal article (peer-reviewed)abstract
- 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.
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| 4. |
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| 5. |
- Hellström, Micaela, 1965-
(author)
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Sex and symbionts : New discoveries in local and regional patterns of coral ecology and reproduction
- 2011
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Doctoral thesis (other academic/artistic)abstract
- Coral reefs belong to the most diverse and the most threatened ecosystems on earth. Anthropogenic stressors and climate change have led to mortalities at levels unprecedented in modern times. The aims of this thesis are to investigate aspects of the corals’ ability to reproduce, disperse, adapt and survive. Papers I-III study reproduction in a common soft coral species, Sarcophyton elegans, with previously unknown reproductive modes. Paper IV investigates genetic distribution of coral-symbiont associations in Galaxea fascicularis focusing on adaptation to the environment along the coastline of Vietnam. Sarcophyton elegans is a gonochoric broadcast spawner with a 1:1 sex ratio. Reproduction is strictly size dependent. Oogenesis takes 19-24 months, with a new cycle commencing every year. Spermatogenesis takes 10-12 months. The majority of gametes were released during the annual austral mass spawning event after full moon in November, but spawning also occur between August and February. The polyps at the outer edge of the colonies released their gametes first, followed by polyps situated closer to the center during subsequent months. Colonies upstream in the prevailing current spawn earlier than those downstream. The colonies were arranged in clusters of alternating males and females, which spawned simultaneously and were of the same genotype. Fission and buddying is a common mode to expand locally. Additionally, females undergoing fission divided into the most fecund size classes. 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. The study highlights the importance of protecting resilient coral and algal genotypes in stressed areas and the need to understand reproductive modes for coral conservation.
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| 6. |
- Mena, F., et al.
(author)
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Use of cholinesterase activity as a biomarker of pesticide exposure used on Costa Rican banana plantations in the native tropical fish Astyanax aeneus (Gunther, 1860)
- 2014
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In: Journal of environmental biology. - 0254-8704. ; 35:1 (SI), s. 35-42
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Journal article (peer-reviewed)abstract
- In Costa Rica, thousands of tones of agricultural pesticides have been used for decades and their use is continuously increasing due to intensive and expanding production of coffee, pineapple, rice, ornamental plants and bananas. The objective of this study was to evaluate whether choline esterase (ChE) activity could be used as a biomarker of exposure to pesticides in the Costa Rican native fish Astyanax aeneus (characidae). Three methods used in order to evaluate the ChE biomarker were as follows: Laboratory studies where A. aeneus was exposed to organophosphate pesticide (ethoprophos); In situ 48 hr exposure assessment using caging experiments with fish exposed upstream and downstream of banana plantations and ChE activity estimation of in fish captured directly at sites with different degrees of pesticide exposure. Results from the laboratory studies showed that ChE activity in both brain and muscle tissue was significantly lower in fish exposed to ethoprophos than in controls. Fish from the caging experiments showed no difference in ChE activity neither in brain nor in muscle tissue between the four tested sites and was attributed to the short duration of the exposure. A significant difference in ChE activity was determined in muscle of fish captured from Laguna Madre de Dios compared to fish from Canal Batan. Although our laboratory results revealed that ChE activity in A. aeneus was highly responsive to ethoprophos, results from field experiments were less conclusive and showed that the captured fish showed large variability in ChE activity and that more research is needed before ChE activity can be used as reliable biomarker of pesticide exposure.
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