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There is an increasing need to predict the effects of global climate change on ecologically important marine organisms and a demand for proactive solutions to reduce CO 2 emissions. CO 2 sequestration is one such method. While this offers a practical solution, recognition should be given to the potential for considerable localised effects on marine organisms in the event of leakage. This laboratory study quantifies the impact of exposure to elevated pCO 2 conditions on the physiological and behavioural responses of a relatively tolerant marine organism. Burrowing shrimps Upogebia deltaura were exposed to CO 2-enriched seawater for 35 d to treatments of 1396 μatm (pH 7.64), 2707 μatm (pH 7.35) and 14 110 μatm (pH 6.71). CO 2 levels represented scenarios which included coastal ocean acidification and extremely elevated CO 2 associated with geological CO 2 sequestration leaks. Results were compared with those from shrimps maintained in a control treatment (pH 7.99). U. deltaura appeared to be tolerant to elevated pCO 2 predicted to occur in the year 2100 (1396 μatm, pH 7.64). However, at 2707 μatm (pH 7.35) shrimps experienced extracellular acidosis, but no difference in haemolymph bicarbonate concentration, suggesting they have little or no buffering capacity, although there was no evidence of other physiological costs in terms of metabolism, osmotic regulation, shell mineralogy, growth and overall activity. At pH 6.71, before 100% mortality occurred, significant differences in activity were observed compared with shrimps in other pH treatments. Results suggest deleterious consequences for benthic ecosystems in the event of a CO 2 sequestration leakage. © Inter-Research 2012.

Ocean acidification may have far-reaching consequences for marine community and ecosystem dynamics, but its full impacts remain poorly understood due to the difficulty of manipulating pCO2 at the ecosystem level to mimic realistic fluctuations that occur on a number of different timescales. It is especially unclear how quickly communities at various stages of development respond to intermediate-scale pCO2 change and, if high pCO2 is relieved mid-succession, whether past acidification effects persist, are reversed by alleviation of pCO2 stress, or are worsened by departures from prior high pCO2 conditions to which organisms had acclimatized. Here, we used reciprocal transplant experiments along a shallow water volcanic pCO2 gradient to assess the importance of the timing and duration of high pCO2 exposure (i.e., discrete events at different stages of successional development vs. continuous exposure) on patterns of colonization and succession in a benthic fouling community. We show that succession at the acidified site was initially delayed (less community change by 8Âweeks) but then caught up over the next 4Âweeks. These changes in succession led to homogenization of communities maintained in or transplanted to acidified conditions, and altered community structure in ways that reflected both short- and longer-term acidification history. These community shifts are likely a result of interspecific variability in response to increased pCO2 and changes in species interactions. High pCO2 altered biofilm development, allowing serpulids to do best at the acidified site by the end of the experiment, although early (pretransplant) negative effects of pCO2 on recruitment of these worms were still detectable. The ascidians Diplosoma sp. and Botryllus sp. settled later and were more tolerant to acidification. Overall, transient and persistent acidification-driven changes in the biofouling community, via both past and more recent exposure, could have important implications for ecosystem function and food web dynamics.

Ocean acidification is predicted to have detrimental effects on many marine organisms and ecological processes. Despite growing evidence for direct impacts on specific species, few studies have simultaneously considered the effects of ocean acidification on individuals (e.g. consequences for energy budgets and resource partitioning) and population level demographic processes. Here we show that ocean acidification increases energetic demands on gastropods resulting in altered energy allocation, i.e. reduced shell size but increased body mass. When scaled up to the population level, long-term exposure to ocean acidification altered population demography, with evidence of a reduction in the proportion of females in the population and genetic signatures of increased variance in reproductive success among individuals. Such increased variance enhances levels of short-term genetic drift which is predicted to inhibit adaptation. Our study indicates that even against a background of high gene flow, ocean acidification is driving individual- and population-level changes that will impact eco-evolutionary trajectories.

Most studies assessing the impacts of ocean acidification (OA) on benthic marine invertebrates have used stable mean pH/pCO2 levels to highlight variation in the physiological sensitivities in a range of taxa. However, many marine environments experience natural fluctuations in carbonate chemistry, and to date little attempt has been made to understand the effect of naturally fluctuating seawater pCO2 (pCO2sw) on the physiological capacity of organisms to maintain acid–base homeostasis. Here, for the first time, we exposed two species of sea urchin with different acid–base tolerances, Paracentrotus lividus and Arbacia lixula, to naturally fluctuating pCO2sw conditions at shallow water CO2 seep systems (Vulcano, Italy) and assessed their acid–base responses. Both sea urchin species experienced fluctuations in extracellular coelomic fluid pH, pCO2, and [HCO3−] (pHe, pCO2e, and [HCO3−]e, respectively) in line with fluctuations in pCO2sw. The less tolerant species, P. lividus, had the greatest capacity for [HCO3−]e buffering in response to acute pCO2sw fluctuations, but it also experienced greater extracellular hypercapnia and acidification and was thus unable to fully compensate for acid–base disturbances. Conversely, the more tolerant A. lixula relied on non-bicarbonate protein buffering and greater respiratory control. In the light of these findings, we discuss the possible energetic consequences of increased reliance on bicarbonate buffering activity in P. lividus compared with A. lixula and how these differing physiological responses to acute fluctuations in pCO2sw may be as important as chronic responses to mean changes in pCO2sw when considering how CO2 emissions will affect survival and success of marine organisms within naturally assembled systems.

Increased atmospheric CO2 concentration is leading to changes in the carbonate chemistry and the temperature of the ocean. The impact of these processes on marine organisms will depend on their ability to cope with those changes, particularly the maintenance of calcium carbonate structures. Both a laboratory experiment (long-term exposure to decreased pH and increased temperature) and collections of individuals from natural environments characterized by low pH levels (individuals from intertidal pools and around a CO2 seep) were here coupled to comprehensively study the impact of near-future conditions of pH and temperature on the mechanical properties of the skeleton of the euechinoid sea urchin Paracentrotus lividus. To assess skeletal mechanical properties, we characterized the fracture force, Young's modulus, second moment of area, material nanohardness, and specific Young's modulus of sea urchin test plates. None of these parameters were significantly affected by low pH and/or increased temperature in the laboratory experiment and by low pH only in the individuals chronically exposed to lowered pH from the CO2 seeps. In tidal pools, the fracture force was higher and the Young's modulus lower in ambital plates of individuals from the rock pool characterized by the largest pH variations but also a dominance of calcifying algae, which might explain some of the variation. Thus, decreases of pH to levels expected for 2100 did not directly alter the mechanical properties of the test of P. lividus. Since the maintenance of test integrity is a question of survival for sea urchins and since weakened tests would increase the sea urchins' risk of predation, our findings indicate that the decreasing seawater pH and increasing seawater temperature expected for the end of the century should not represent an immediate threat to sea urchins vulnerability.

Excessive CO 2 in the present-day ocean-atmosphere system is causing ocean acidification, and is likely to cause a severe biodiversity decline in the future, mirroring effects in many past mass extinctions. Fossil records demonstrate that organisms surviving such events were often smaller than those before, a phenomenon called the Lilliput effect. Here, we show that two gastropod species adapted to acidified seawater at shallow-water CO 2 seeps were smaller than those found in normal pH conditions and had higher mass-specific energy consumption but significantly lower whole-animal metabolic energy demand. These physiological changes allowed the animals to maintain calcification and to partially repair shell dissolution. These observations of the long-term chronic effects of increased CO 2 levels forewarn of changes we can expect in marine ecosystems as CO 2 emissions continue to rise unchecked, and support the hypothesis that ocean acidification contributed to past extinction events. The ability to adapt through dwarfing can confer physiological advantages as the rate of CO 2 emissions continues to increase.