Synergistic effect of ocean acidification and elevated temperature on the physiological ecology of the intertidal crab Porcellana platycheles

Ongoing global environmental changes pose an unprecedented threat to global biodiversity; in particular increasing environmental temperatures and decreasing ocean pH (Ocean Acidification or OA, as a result of increased seawater pCO2−). The extent to which these two drivers will act synergistically, reducing the thermal tolerance window of individual species, and so potentially affect their large-scale distribution, is only beginning to be understood. Here we present a formal test on the potential synergistic effect of elevated temperatures and hypercapnic sea water on the rate of O2 uptake (as a proxy for metabolism), tolerance to heat, and the degree of exoskeleton calcification in the intertidal porcellanid crab Porcellana platycheles. Eighty individuals crabs were haphazardly assigned to one of four treatments, and kept for 40 days at either 15.0 °C (seasonal ambient) or 20.0 °C (+ 5 °C), and at either pH 8.0 (seasonal ambient) or 7.4. In Porcellana platycheles metabolic activity and tolerance to heat were positively affected by increasing temperature, whilst the degree of exoskeleton calcification was negatively affected. No effect of pH was detectable. It is therefore suggested that P. platycheles may not be affected by medium-term exposure to the predicted level of OA, but that acclimation to elevated temperatures may result in improved tolerance of high temperatures despite an increase in metabolic costs and a decrease of calcification. Our results are discussed within a broader ecological and evolutionary context, with particular emphasis on the idea that intertidal species may be to some extent exapted to hypercapnic exposure.

Impacts of hypercapnia and temperature on physiological performance of marine invertebrates from the Baltic Sea

Anthropogenic CO2 emissions cause rising ocean pCO2 and decreased ocean pH. This progressing ocean acidification has been shown to compromise physiological performance of many marine benthic organisms. In this study, Baltic blue mussel Mytilus edulis and common starfish Asterias rubens from Kiel Fjord were exposed to 6 different hypercapnic levels between 0.04 and 0.41 kPa pCO2 for 1–2 weeks, respectively, at 12 °C. The experiments revealed extracellular acidosis in both species with no active accretion of HCO3−. Even at moderate pCO2 levels (e.g. 0.08 kPa) pHe was significant decreased. Although shell dissolution occurred in the highest pCO2 treatment, no HCO3− or Ca2+ accumulation was observed in extracellular fluids. Gradients of pCO2 between body fluids and ambient sea water were stable at lower pCO2 levels and decreased at 0.41 kPa, which might indicate a metabolic depression. Ongoing metabolic rate and filtration rate determinations will resolve this issue. Calcification rates were only minorly impacted in the lower pCO2 treatments and became negative at 0.41 kPa pCO2. Field measurements conducted in Kiel Fjord revealed a large annual variability of surface pH and pCO2. During winter and spring, surface pH averaged 8.1 but mean summer pH values were < 7.8 and the highest measured pCO2 value exceeded 0.2 kPa (ca 2000 μatm), thus even the maximum average pCO2 values modelled for the surface ocean of the year 2300.

Experiments will be repeated at summer temperatures of 18–22 °C in June 2009 to clarify if thermal extremes increase the species' sensitivity towards hypercapnia.

Physiological and shell microstructural responses of an intertidal periwinkle Littorina littorea (Linnaeus, 1758) to ocean acidification and elevated temperature

Future changes in seawater temperature and pH could significantly affect marine biodiversity, yet there are still few studies that have addressed the combined influence of these environmental stressors. In this study, a laboratory experiment was used to investigate how the potential synergistic/additive effects of long-term exposure (30 days) to different levels of seawater pH (8.0, 7.8, 7.6, and 6.5) and temperature (ambient and + 4 °C) on the physiology and shell construction of the intertidal gastropod, Littorina littorea. To determine effects on physiological function, concentrations of ATP, ADP, AMP, succinic and lactic acid were measured, as well as rates of respiration and water loss. In addition, vertical and horizontal sections through the shell were taken and fragments of approximately 5 mm in length assessed for the growth form (thickness) and structural layers. The aim of this study is to identify whether the combined exposure to ocean warming and acidification at the levels predicted for the year 2100 and 2250, and for CO2 leakage from geological storage will exert a synergistic or additive effect on the fitness of this key intertidal grazing species as currently predicted under the simultaneous influence of both ocean acidification and temperature change.

Physiological responses of Mediterranean corals to temperature and pH perturbations

Understanding coral responses to environmental change is critical to predicting their health and future distribution. While tropical and subtropical corals generally experience limited environmental changes, temperate corals undergo pronounced seasonal cycles in irradiance, temperature and nutrients. Their ability to cope with environmental changes makes temperate organisms an ideal model to investigate the effects of global change on coral physiology.

Using the two symbiotic Mediterranean corals, Cladocora caespitosa and Oculina patagonica, we studied the effects of natural changes in light and temperature on their physiological responses both in laboratory and in situ. Temperature was shown to be the major factor affecting coral metabolism. Photosynthetic and growth rates were maximal under normal summer temperatures up to a physiological threshold after which very high temperatures induced, in both coral species, a severe decrease in the rates of photosynthesis and growth. Coral response to high temperatures was species-specific, and highly dependent on the amplitude and length of the temperature stress. These results, together with the observations of recurrent mass-mortalities during recent summers suggest that endemic Mediterranean corals are living near their upper thermal limits. A second study assessed the effects of seasonality, thermal stress (+ 3 °C) and ocean acidification (700 μatm; end-of-century prediction) on the coral C. caespitosa. Corals were collected at 30 m depth and maintained in aquaria over a one-year period under experimental conditions. Surprisingly, calcification and photosynthetic rates were not affected by the high pCO2 conditions, while the seasonal change in temperature had significant effects.

Physiological performance of Baltic Sea blue mussels, Mytilus edulis, under CO2 induced stress: Cardiac performance, activity and filtration rate

Anthropogenic CO2 emissions will lead to an increased ocean pCO2 level of possibly 1900 ppm in the year 2300. Previous studies depicted that bivalves might react very sensitively towards increased seawater pCO2 with decreased rates of calcification, metabolism and growth. In order to assess the impacts of simulated ocean acidification on a Baltic Sea M. edulis population, we simultaneously monitored heart rate variability, filtration and activity patterns, as well as extracellular acid base status and calcification.

Adult mussels were kept in flow through aquaria for two weeks at six different CO2 concentrations between 380 ppm and 4000 ppm. Mussels were fed continuously with a mixed phytoplankton concentrate. Measurements of heart rate, heart rate variability, valve and siphon opening revealed no effect of pCO2 on cardiac performance and activity, even though significant extracellular acid–base disturbances and decreases in calcification rate were recorded. Filtration rates, on the other hand, were significantly depressed at 4000 ppm. In an ongoing study, mussels are continuously being fed with Rhodomonas sp. at a concentration of 1000–4000 cells/ml in order to study filtration efficiency in more detail.

Physiological changes might not only affect the mussel’s health but the whole ecosystem, since filter feeding bivalves act as ecosystem engineers, not only changing the inorganic nutrient pool available to phytoplankton, but also producing faeces and pseudofaeces, which can reduce erosion by 10-fold in some areas. Being the dominant benthic invertebrate, dense mussel beds even provide an important settling ground for various other organisms.

Ecosystem impacts of climate change and ocean acidification: A case for “global” conservation physiology

Climate change causes ocean warming and acidification on global scales. In contrast to well established effects of warming, evidence for the effects of rising carbon dioxide (CO2) on marine ecosystems is only just emerging. However, future scenarios indicate threats to marine life through combinations of rising CO2, warming and more frequent hypoxia events. For realistic future climate effect scenarios, key physiological mechanisms and their responses to combined stressors require identification. These are physiological mechanisms which define species performance, including their capacity to interact, e.g. in food webs (1). Many ecosystem changes likely occur when temperature drifts beyond species-specific limits and causes a shift in phenology or fitness. High sensitivity to elevated CO2 levels may involve a low capacity for acid–base regulation, as seen in lower marine invertebrates (2). The disturbed extracellular acid–base status affects processes involved in growth, calcification, neural functions, blood gas transport and behavioural capacities (2). Current evidence indicates elevated sensitivity to elevated CO2 levels towards the extremes of thermal windows (3). The ultimate consequence may be a narrowing of thermal tolerance windows and associated ranges of geographical distribution and of the performance at ecosystem level. Thus, CO2 may exacerbate warming effects on marine ecosystems. Future research will have to test these concepts under realistic climate and ocean acidification scenarios and in various marine ecosystems between the tropics and the poles.

Submit abstracts to PICES 2009 Annual Meeting in Jeju, Korea

The PICES 2009 Annual Meeting will be held October 23 – November 1, 2009 in Jeju, Korea, We are soliciting abstracts for a session on “Anthropogenic perturbations of the carbon cycle and their impacts in the North Pacific”. Abstract deadline is July 12.

The effect of pCO2 on carbon acquisition and intracellular assimilation in four marine diatoms

The effect of pCO2 on carbon acquisition and intracellular assimilation was investigated in the three bloom-forming diatom species, Eucampia zodiacus (Ehrenberg), Skeletonema costatum (Greville) Cleve, Thalassionema nitzschioides (Grunow) Mereschkowsky and the non-bloom-forming Thalassiosira pseudonana (Hust.) Hasle and Heimdal. In vivo activities of carbonic anhydrase (CA), photosynthetic O2 evolution, CO2 and HCO3− uptake rates were measured by membrane-inlet mass spectrometry (MIMS) in cells acclimated to pCO2 levels of 370 and 800 μatm. To investigate whether the cells operate a C4-like pathway, activities of ribulose-1,5-bisphosphate carboxylase (RubisCO) and phosphoenolpyruvate carboxylase (PEPC) were measured at the mentioned pCO2 levels and a lower pCO2 level of 50 μatm. In the bloom-forming species, extracellular CA activities strongly increased with decreasing CO2 supply while constantly low activities were obtained for T. pseudonana. Half-saturation concentrations (K1/2) for photosynthetic O2 evolution decreased with decreasing CO2 supply in the two bloom-forming species S. costatum and T. nitzschioides, but not in T. pseudonana and E. zodiacus. With the exception of S. costatum, maximum rates (Vmax) of photosynthesis remained constant in all investigated diatom species. Independent of the pCO2 level, PEPC activities were significantly lower than those for RubisCO, averaging generally less than 3%. All examined diatom species operate highly efficient CCMs under ambient and high pCO2, but differ strongly in the degree of regulation of individual components of the CCM such as Ci uptake kinetics and extracellular CA activities. The present data do not suggest C4 metabolism in the investigated species.

Just add lime (to the sea) – the latest plan to cut CO2 emissions

• Project ‘could turn back clock’ on carbon dioxide
• Guardian conference will select top 10 climate ideas

Putting lime into the oceans could stop or even reverse the accumulation of CO2 in the atmosphere, according to proposals unveiled at a conference on climate change solutions in Manchester today.

According to its advocates, the same technique could help fix one of the most dangerous side effects of man-made CO2 emissions: rising ocean acidity.

The project, known as Cquestrate, is the brainchild of Tim Kruger, a former management consultant. “This is an idea that can not only stop the clock on carbon dioxide, it can turn it back,” he said, although he conceded that tipping large quantities of lime into the sea would currently be illegal.

A last resort against global warming?

Summary — Global warming is accelerating, and although engineering the climate strikes most people as a bad idea, it is time to take it seriously.

Each year, the effects of climate change are coming into sharper focus. Barely a month goes by without some fresh bad news: ice sheets and glaciers are melting faster than expected, sea levels are rising more rapidly than ever in recorded history, plants are blooming earlier in the spring, water supplies and habitats are in danger, birds are being forced to find new migratory patterns.

The odds that the global climate will reach a dangerous tipping point are increasing. Over the course of the twenty-first century, key ocean currents, such as the Gulf Stream, could shift radically, and thawing permafrost could release huge amounts of additional greenhouse gases into the atmosphere. Such scenarios, although still remote, would dramatically accelerate and compound the consequences of global warming. Scientists are taking these doomsday scenarios seriously because the steady accumulation of warming gases in the atmosphere is forcing change in the climate system at rates so rapid that the outcomes are extremely difficult to predict.