Posts Tagged 'temperature'

Ecophysiological responses to elevated CO2 and temperature in Cystoseira tamariscifolia (Phaeophyceae)

Ocean acidification increases the amount of dissolved inorganic carbon (DIC) available in seawater which can benefit photosynthesis in those algae that are currently carbon limited, leading to shifts in the structure and function of seaweed communities. Recent studies have shown that ocean acidification-driven shifts in seaweed community dominance will depend on interactions with other factors such as light and nutrients. The study of interactive effects of ocean acidification and warming can help elucidate the likely effects of climate change on marine primary producers. In this study, we investigated the ecophysiological responses of Cystoseira tamariscifolia (Hudson) Papenfuss. This large brown macroalga plays an important structural role in coastal Mediterranean communities. Algae were collected from both oligotrophic and ultraoligotrophic waters in southern Spain. They were then incubated in tanks at ambient (ca. 400–500 ppm) and high CO2 (ca. 1200–1300 ppm), and at 20 °C (ambient temperature) and 24 °C (ambient temperature +4 °C). Increased CO2 levels benefited the algae from both origins. Biomass increased in elevated CO2 treatments and was similar in algae from both origins. The maximal electron transport rate (ETRmax), used to estimate photosynthetic capacity, increased in ambient temperature/high CO2 treatments. The highest polyphenol content and antioxidant activity were observed in ambient temperature/high CO2 conditions in algae from both origins; phenol content was higher in algae from ultraoligotrophic waters (1.5–3.0%) than that from oligotrophic waters (1.0–2.2%). Our study shows that ongoing ocean acidification can be expected to increase algal productivity (ETRmax), boost antioxidant activity (EC50), and increase production of photoprotective phenols. Cystoseira tamariscifolia collected from oligotrophic and ultraoligotrophic waters were able to benefit from increases in DIC at ambient temperatures. Warming, not acidification, may be the key stressor for this habitat as CO2 levels continue to rise.

Continue reading ‘Ecophysiological responses to elevated CO2 and temperature in Cystoseira tamariscifolia (Phaeophyceae)’

Early life behaviour and sensory ecology of predatory fish under climate change and ocean acidification

The early life cycle of a fish species is presumed to be the most vulnerable to abiotic change. Their successful development and growth is key to sustaining and connecting existing populations and dispersal to new habitats. Larvae and juvenile fish have to progressively develop and fine tune their behavioural and sensory capabilities in order to successfully hunt and or forage for prey, avoid larger predators and find suitable habitat to reach maturity and reproduce. Their sensory capabilities typically involve multiple senses including, vision, olfaction and audition. Ocean warming and acidification alter the physiological performance and behaviour of many small bodied fish, however, the potential interactive effects of these stressors on large predatory fish has not been explored fully and may act synergistically or antagonistically. Predatory fish can have large effects on trophically-structured systems. The potential for altered predatory function through alterations in their metabolism as a result of temperature and behaviour from ocean acidification may not only affect their hunting ability but also the communities in which their prey live. In this thesis, I show that the combination of ocean warming with acidification can alter the metabolic function and hunting behaviour of a predatory shark leading to considerable reductions in growth rates. Laboratory experiments revealed faster embryonic development under elevated temperature, however elevated temperature and CO2 had detrimental impacts on sharks by increasing energetic demands. Subsequent mesocosm experiments showed reductions in growth rates under elevated CO2 either alone or in combination with elevated temperatures, where their metabolic efficiency was decreased and their ability to locate food through olfaction was reduced. Additionally, while elevated temperature increased the motivational drive to locate prey, elevated CO2 negated chemical and visual behavioural responses that enable effective hunting. I also found that ocean acidification alone altered the physicochemical sensing in a predatory teleost fish (Barramundi) such that cues for temperature and salinity were inhibited by reduced pH. This thesis reveals a more complex reality for predators where the combination of elevated temperature and CO2 reduces their ability to hunt effectively leading to smaller sharks, ultimately reduces their ability to exert strong top-down control over food webs. Furthermore, alterations to their perception and evaluation of environmental cues during the critical phase of dispersal have implications for ensuing recruitment and population replenishment. Alterations such as the ones brought about by ocean acidification and increased temperature far reaching consequences, not just for the individual predator population’s sustainability, but also the ecosystem food webs which they inhabit.

Continue reading ‘Early life behaviour and sensory ecology of predatory fish under climate change and ocean acidification’

Ocean acidification increases the sensitivity and variability of physiological responses of an intertidal limpet to thermal stress

Understanding physiological responses of organisms to warming and ocean acidification is the first step towards predicting the potential population, community and ecological impacts of these stressors. Increasingly, physiological plasticity is being recognized as important for organisms to adapt to the changing microclimates. Here, we evaluate the importance of physiological plasticity for coping with ocean acidification and elevated temperature, and its variability among individuals from the same population, of the limpet Cellana toreuma. Heart rates (as a proxy for metabolic performance) and genes encoding heat-shock proteins were measured at different heat shock temperatures (26, 30, 34, 38 °C) in individuals acclimated under combinations of different pCO2 (400 ppm, 1000 ppm) and temperature (20 °C, 24 °C) regimes. Analysis of heart rate showed significantly higher temperature coefficients (Q10 rates) for limpets at 20 °C than at 24 °C and lower post-acclimation thermal sensitivity of limpets at 400 ppm than at 1000 ppm. hsp70 expression linearly increased with the increasing heat-shock temperatures, with the largest slope occurring in limpets under a future scenario (24 °C and 1000 ppm pCO2). These results suggested that limpets will have increased sensitivity and energy consumption under future conditions. Furthermore, the increased variation in physiological response under the future scenario indicated that some individuals were better to cope physiologically with these conditions. Therefore, while ocean acidification decreases the ability of many individuals to respond to thermal stress, physiological plasticity and variability seem to be crucial in allowing some intertidal animals to survive in a rapidly changing environment.

Continue reading ‘Ocean acidification increases the sensitivity and variability of physiological responses of an intertidal limpet to thermal stress’

Mediterranean versus Red sea corals facing climate change, a transcriptome analysis

The anthropogenic increase in atmospheric CO2 that drives global warming and ocean acidification raises serious concerns regarding the future of corals, the main carbonate biomineralizers. Here we used transcriptome analysis to study the effect of long-term gradual temperature increase (annual rate), combined with lowered pH values, on a sub-tropical Red Sea coral, Stylophora pistillata, and on a temperate Mediterranean symbiotic coral Balanophyllia europaea. The gene expression profiles revealed a strong effect of both temperature increase and pH decrease implying for synergism response. The temperate coral, exposed to a twice as high range of seasonal temperature fluctuations than the Red Sea species, faced stress more effectively. The compensatory strategy for coping apparently involves deviating cellular resources into a massive up-regulation of genes in general, and specifically of genes involved in the generation of metabolic energy. Our results imply that sub-lethal, prolonged exposure to stress can stimulate evolutionary increase in stress resilience.

Continue reading ‘Mediterranean versus Red sea corals facing climate change, a transcriptome analysis’

The acclimation process of phytoplankton biomass, carbon fixation and respiration to the combined effects of elevated temperature and pCO2 in the northern South China Sea

We conducted shipboard microcosm experiments at both off-shore (SEATS) and near-shore (D001) stations in the northern South China Sea (NSCS) under three treatments, low temperature and low pCO2 (LTLC), high temperature and low pCO2 (HTLC), and high temperature and high pCO2 (HTHC). Biomass of phytoplankton at both stations were enhanced by HT. HTHC did not affect phytoplankton biomass at station D001 but decreased it at station SEATS. HT alone increased net primary productivity by 234% at station SEATS and by 67% at station D001 but the stimulating effect disappeared when HC was combined. HT also increased respiration rate by 236% at station SEATS and by 87% at station D001 whereas HTHC reduced it by 61% at station SEATS and did not affect it at station D001. Overall, our findings indicate that the positive effect of ocean warming on phytoplankton assemblages in NSCS could be damped or offset by ocean acidification.

Continue reading ‘The acclimation process of phytoplankton biomass, carbon fixation and respiration to the combined effects of elevated temperature and pCO2 in the northern South China Sea’

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’

Acidification and warming affect prominent bacteria in two seasonal phytoplankton bloom mesocosms

In contrast to clear stimulatory effects of rising temperature, recent studies of the effects of CO2 on planktonic bacteria have reported conflicting results. To better understand the potential impact of predicted climate scenarios on the development and performance of bacterial communities, we performed bifactorial mesocosm experiments (pCO2 and temperature) with Baltic Sea water, during a diatom dominated bloom in autumn and a mixed phytoplankton bloom in summer. The development of bacterial community composition (BCC) followed well-known algal bloom dynamics. A principal coordinate analysis (PCoA) of bacterial OTUs (operational taxonomic units) revealed that phytoplankton succession and temperature were the major variables structuring the bacterial community whereas the impact of pCO2 was weak. Prokaryotic abundance and carbon production, and organic matter concentration and composition were partly affected by temperature but not by increased pCO2. However, pCO2 did have significant and potentially direct effects on the relative abundance of several dominant OTUs; in some cases, these effects were accompanied by an antagonistic impact of temperature. Our results suggest the necessity of high-resolution BCC analyses and statistical analyses at the OTU level to detect the strong impact of CO2 on specific bacterial groups, which in turn might also influence specific organic matter degradation processes.

Continue reading ‘Acidification and warming affect prominent bacteria in two seasonal phytoplankton bloom mesocosms’

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Ocean acidification in the IPCC AR5 WG II

OUP book