Posts Tagged 'Cnidaria'

Ocean acidification effects on mesozooplankton community development: Results from a long-term mesocosm experiment

Ocean acidification may affect zooplankton directly by decreasing in pH, as well as indirectly via trophic pathways, where changes in carbon availability or pH effects on primary producers may cascade up the food web thereby altering ecosystem functioning and community composition. Here, we present results from a mesocosm experiment carried out during 113 days in the Gullmar Fjord, Skagerrak coast of Sweden, studying plankton responses to predicted end-of-century pCO2 levels. We did not observe any pCO2 effect on the diversity of the mesozooplankton community, but a positive pCO2 effect on the total mesozooplankton abundance. Furthermore, we observed species-specific sensitivities to pCO2 in the two major groups in this experiment, copepods and hydromedusae. Also stage-specific pCO2 sensitivities were detected in copepods, with copepodites being the most responsive stage. Focusing on the most abundant species, Pseudocalanus acuspes, we observed that copepodites were significantly more abundant in the high-pCO2 treatment during most of the experiment, probably fuelled by phytoplankton community responses to high-pCO2 conditions. Physiological and reproductive output was analysed on P. acuspes females through two additional laboratory experiments, showing no pCO2 effect on females’ condition nor on egg hatching. Overall, our results suggest that the Gullmar Fjord mesozooplankton community structure is not expected to change much under realistic end-of-century OA scenarios as used here. However, the positive pCO2 effect detected on mesozooplankton abundance could potentially affect biomass transfer to higher trophic levels in the future.

Continue reading ‘Ocean acidification effects on mesozooplankton community development: Results from a long-term mesocosm experiment’

Entering the Anthropocene: How ocean acidification and warmer temperatures affect the symbiotic sea anemone Exaiptasia pallida

Here I report the effects of long-term elevated CO2 combined with two subsequent elevated temperature intervals on the model symbiotic anemone Exaiptasia pallida. A central goal of this thesis was to investigate how altered CO2 and temperature affect the symbiotic relationship while this anemone hosted three different strains of endosymbiotic dinoflagellates (Symbiodinium minutum, Symbiodinium A4a, and Symbiodinium A4b). Exposure to elevated CO2 (930μatm) alone for 42 days led to no significant changes in either the anemone or the algae physiological response, with the exception of some separation between the photosynthesis to respiration ratio of S. A4a and S. A4b control and treatment animals. Exposure to both elevated CO2 (930μatm) and a moderate  elevation in temperature (29°C) for 49 days led to a significant increase in the net maximal photosynthesis (normalized to algal cell density) between the treatment and controls of all three  holobionts. Exposure to both elevated CO2 (930μatm) and an even higher temperature (33°C) for up to 20 days led to a significant decrease in photobiology and algal cell density, along with visible bleaching in the S. minutum holobiont. All three holobionts displayed a significant decrease in the photosynthesis to respiration ratio, thereby providing evidence for temperature having a greater impact on the phototrophic response of these anemones. However, anemones harboring the two A4 Symbiodinium did not show as large of a negative response in photosystem II  photochemistry when compared to anemones with S. minutum. The high temperature treatment also resulted in juvenile mortality in all three holobionts, with the greatest mortality seen in the S. minutum holobiont. The differential response to both elevated CO2 and elevated temperature between the three holobionts highlights the thermal sensitivity of the S. minutum symbiosis, and the thermal tolerance of the S. A4 holobionts. Thermal tolerance may enable these anemones to survive and thrive in future climate change conditions, while the effects of higher CO2 appear to be more neutral.

Continue reading ‘Entering the Anthropocene: How ocean acidification and warmer temperatures affect the symbiotic sea anemone Exaiptasia pallida’

Effects of ocean acidification on benthic organisms in the Mediterranean Sea under realistic climatic scenarios: A meta-analysis

Ocean acidification is expected to cause significant changes in the marine environment over the coming century. The effects of acidification on organisms’ physiology have been studied over the past two decades. However, the experimental findings are not always easily comparable because of differences in experimental design, and comparable experiments do not always produce similar results. To rigorously integrate the current knowledge, we performed a meta-analysis of published studies focused on benthic organisms in the Mediterranean Sea, both in controlled manipulative experiments and in situ experiments near vent areas. In each experiment, the effect of acidification was calculated as the log-transformed response ratio (LnRR) of experimental versus control conditions. The quantitative results obtained by the meta-analysis highlight: (a) an increase in fleshy algae cover, which may lead to a competitive advantage over calcifying macroalgae; (b) a reduction of calcification by both algae and corals; (c) an increase in seagrass shoot density under low pH; and (d) a general increase in the photosynthetic activity of macrophytes.

Continue reading ‘Effects of ocean acidification on benthic organisms in the Mediterranean Sea under realistic climatic scenarios: A meta-analysis’

The stable microbiome of inter and sub-tidal anemone species under increasing pCO2

Increasing levels of pCO2 within the oceans will select for resistant organisms such as anemones, which may thrive under ocean acidification conditions. However, increasing pCO2 may alter the bacterial community of marine organisms, significantly affecting the health status of the host. A pH gradient associated with a natural volcanic vent system within Levante Bay, Vulcano Island, Italy, was used to test the effects of ocean acidification on the bacterial community of two anemone species in situ, Anemonia viridis and Actinia equina using 16 S rDNA pyrosequencing. Results showed the bacterial community of the two anemone species differed significantly from each other primarily because of differences in the Gammaproteobacteria and Epsilonproteobacteria abundances. The bacterial communities did not differ within species among sites with decreasing pH except for A. viridis at the vent site (pH = 6.05). In addition to low pH, the vent site contains trace metals and sulfide that may have influenced the bacteria community of A. viridis. The stability of the bacterial community from pH 8.1 to pH 7.4, coupled with previous experiments showing the lack of, or beneficial changes within anemones living under low pH conditions indicates that A. viridis and A. equina will be winners under future ocean acidification scenarios.

Continue reading ‘The stable microbiome of inter and sub-tidal anemone species under increasing pCO2’

Responses of the sea anemone, Exaiptasia pallida, to ocean acidification conditions and zinc or nickel exposure

Ocean acidification, caused by increasing atmospheric carbon dioxide (CO2), is a growing concern in marine environments. Land-based sources of pollution, such as metals, have also been a noted problem; however, little research has addressed the combined exposure of both pollutants to coral reef organisms. In this study we examined tissue metal accumulation and physiological effects (activity of anti-oxidant enzymes, catalase and glutathione reductase) in the sea anemone, Exaiptasia pallida after exposure to increased CO2, as well as zinc (Zn) or nickel (Ni). After exposure to four concentrations (nominal values = control, 10, 50, 100 μg/L) of Zn or Ni over 7 days, both metals accumulated in the tissues of E. pallida in a concentration-dependent manner. Anemones exposed to elevated CO2 (1000 ppm) accumulated significant tissue burdens of Zn or Ni faster (by 48 h) than those exposed to the same metal concentrations at ambient CO2. No differences were observed in catalase activity due to Zn exposure; however, 50 μg/L Ni caused a significant increase in catalase activity at ambient CO2. No significant effect on catalase activity from CO2 exposure alone was observed. Glutathione reductase activity was affected by increased Zn or Ni exposure and those effects were influenced by increased CO2. Results of this study provide insight into the toxic mechanisms and environmental implications of CO2 and Zn or Ni exposure to the cnidarian E. pallida.

Continue reading ‘Responses of the sea anemone, Exaiptasia pallida, to ocean acidification conditions and zinc or nickel exposure’

Resilience to ocean acidification: decreased carbonic anhydrase activity in sea anemones under high pCO2 conditions

Non-calcifying photosynthetic anthozoans have emerged as a group that may thrive under high carbon dioxide partial pressure ( pCO2) conditions via increased productivity. However, the physiological mechanisms underlying this potential success are unclear. Here we investigated the impact of high pCO2 on the dissolved inorganic carbon (DIC) use in the temperate sea anemone Anemonia viridis. We assessed the impacts of long-term exposure to high pCO2, i.e. sampling in situ natural CO2 vents (Vulcano, Italy), and short-term exposure, i.e. during a 3 wk controlled laboratory experiment. We focused on photo-physiological parameters (net photosynthesis rates, chlorophyll a content and Symbiodinium density) and on carbonic anhydrase (CA) activity, an enzyme involved in the energy-demanding process of DIC absorption. Long-term exposure to high pCO2 had no impact on Symbiodinium density and chlorophyll a content. In contrst, short-term exposure to high pCO2 induced a significant reduction in Symbiodinium density, which together with unchanged net photosynthesis resulted in the increase of Symbiodinium productivity per cell. Finally, in both in situ long-term and laboratory short-term exposure to high pCO2, we observed a significant decrease in the CA activity of sea anemones, suggesting a change in DIC use (i.e. from an HCO3- to a CO2 user). This change could enable a shift in the energy budget that may increase the ability of non-calcifying photosynthetic anthozoans to cope with ocean acidification.

Continue reading ‘Resilience to ocean acidification: decreased carbonic anhydrase activity in sea anemones under high pCO2 conditions’

Survey of Cnidarian gene expression profiles in response to environmental stressors: summarizing 20 years of research, what are we heading for?

Coral research has come a long way since the pioneering coral biology studies of thermal tolerance dating back to the turn of the previous century. In great contrast, at the present time, the currently available in silico technologies enable the entire transcriptome to be surveyed in a high-throughput manner following an array of stress manipulations. Deep-sequencing is expected to revolutionize the way we study gene expression and holds the potential to answer prominent questions regarding cnidarian cellular pathways following global change scenarios. In this review we focus on cnidarian responses to environmental stressors in general and to global climate change in particular, focusing on the gene expression levels. A wide characterization of studies conducted in cnidarians following environmental stress revealed that most of the studies investigated a single stress factor and mostly thermal stress, were short-term and focused on branching corals. Subsequently, there is a lack of gene expression knowledge concerning massive corals that are known to be less susceptible to bleaching comparing to branching corals. In this review, we present a detailed list of differentially expressed genes in branching/massive corals under eight types of environmental stress. A conceptual model was constructed of the main processes occurring within the coral host cell under heat, ocean acidification and UV stress. The tables and the pathways of this review emphasize gaps in knowledge and can assist in guiding future research as they suggests which genes/processes one should look at in order to achieve a greater understanding of the cnidarians molecular processes affected by global anthropogenic stress.

Continue reading ‘Survey of Cnidarian gene expression profiles in response to environmental stressors: summarizing 20 years of research, what are we heading for?’

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Ocean acidification in the IPCC AR5 WG II

OUP book