In the context of future scenarios of progressive accumulation of anthropogenic CO 2 in marine surface waters, the present study addresses the effects of long-term hypercapnia on a Mediterranean bivalve, Mytilus galloprovincialis. Sea-water pH was lowered to a value of 7.3 by equilibration with elevated CO 2 levels. This is close to the maximum pH drop expected in marine surface waters during atmospheric CO 2 accumulation. Intra-and extracellular acid -base parameters as well as changes in metabolic rate and growth were studied under both normocapnia and hypercapnia. Long-term hypercapnia caused a permanent reduction in haemolymph pH. To limit the degree of acidosis, mussels increased haemolymph bicarbonate levels, which are derived mainly from the dissolution of shell CaCO 3 . Intracellular pH in various tissues was at least partly compensated; no deviation from control values occurred during long-term measurements in whole soft-body tissues. The rate of oxygen consumption fell significantly, indicating a lower metabolic rate. In line with previous reports, a close correlation became evident between the reduction in extracellular pH and the reduction in metabolic rate of mussels during hypercapnia. Analysis of frequency histograms of growth rate revealed that hypercapnia caused a slowing of growth, possibly related to the reduction in metabolic rate and the dissolution of shell CaCO 3 as a result of extracellular acidosis. In addition, increased nitrogen excretion by hypercapnic mussels indicates the net degradation of protein, thereby contributing to growth reduction. The results obtained in the present study strongly indicate that a reduction in sea-water pH to 7.3 may be fatal for the mussels. They also confirm previous observations that a reduction in sea-water pH below 7.5 is harmful for shelled molluscs.

Frederich, Markus, and Hans O. Pö rtner. Oxygen limitation of thermal tolerance defined by cardiac and ventilatory performance in spider crab, Maja squinado. Am J Physiol Regulatory Integrative Comp Physiol 279: R1531-R1538, 2000.-Geographic distribution limits of ectothermal animals appear to be correlated with thermal tolerance thresholds previously identified from the onset of anaerobic metabolism. Transition to these critical temperatures was investigated in the spider crab (Maja squinado) with the goal of identifying the physiological processes limiting thermal tolerance. Heart and ventilation rates as well as PO 2 in the hemolymph were recorded on-line during progressive temperature change between 12 and 0°C (1°C/h) and between 12 and 40°C (2°C/h). Lactate and succinate were measured in tissues and hemolymph after intermediate or final temperatures were reached. High levels of hemolymph oxygenation suggest that an optimum range of aerobic performance exists between 8 and 17°C. Thermal limitation may already set in at the transition from optimum to pejus (pejus ϭ turning worse, progressively deleterious) range, characterized by the onset of a decrease in arterial PO 2 due to reduced ventilatory and cardiac performance. Hemolymph PO 2 values fell progressively toward both low and high temperature extremes until critical temperatures were reached at ϳ1 and 30°C, as indicated by low PO 2 and the onset of anaerobic energy production by mitochondria. In conclusion, the limited capacity of ventilation and circulation at extreme temperatures causes insufficient O 2 supply, thereby limiting aerobic scope and, finally, thermal tolerance. aerobic capacity; anaerobic metabolism; optodes; partial pressure of oxygen CRITICAL TEMPERATURES (T c ) have been defined for different marine invertebrate and fish species as being characterized by the onset of anaerobic metabolism, which is caused by a mismatch of O 2 demand and O 2 supply (for review, see Refs. 35 and 36). Extended exposure to temperatures above high T c or below low T c finally leads to death of the animal unless thermal acclimation, i.e., a shift of T c values, occurs (40, 51). One hypothesis is that the adjustment of mitochondrial density and capacity is involved in setting thermal tolerance limits and is therefore related to geographic distribution (35, 36). As a consequence, the relationship between O 2 availability to tissues and O 2 demand appears to be crucial for survival of exposure to temperature extremes. Study of the processes of O 2 uptake by ventilation and O 2 distribution by circulation therefore appear important to further our understanding of the O 2 limitation of thermal tolerance. Therefore, we chose to study these systemic aspects of thermal tolerance, selecting a crustacean, Maja squinado (Herbst), as a model organism. As yet, physiological studies of crustaceans have addressed temperature effects on O 2 consumption, heart and ventilatory performance, or growth (12-14, 16, 23, 34, 44). In most of these studies, temperatures were chosen wit...

The Paris Agreement target of limiting global surface warming to 1.5-2 • C compared to pre-industrial levels by 2100 will still heavily impact the ocean. While ambitious mitigation and adaptation are both needed, the ocean provides major opportunities for action to reduce climate change globally and its impacts on vital ecosystems and ecosystem services. A comprehensive and systematic assessment of 13 global-and local-scale, ocean-based measures was performed to help steer the development and implementation of technologies and actions toward a sustainable outcome. We show that (1) all measures have tradeoffs and multiple criteria must be used for a comprehensive assessment of their potential, (2) greatest benefit is derived by combining global and local solutions, some of which could be implemented or scaled-up immediately, (3) some measures are too uncertain to be recommended yet, (4) political consistency must be achieved through effective cross-scale governance mechanisms, (5) scientific effort must focus on effectiveness, co-benefits, disbenefits, and costs of poorly tested as well as new and emerging measures.

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Future scenarios for the oceans project combined developments of CO 2 accumulation and global warming and their impact on marine ecosystems. The synergistic impact of both factors was addressed by studying the effect of elevated CO 2 concentrations on thermal tolerance of the cold-eurythermal spider crab Hyas araneus from the population around Helgoland. Here ambient temperatures characterize the southernmost distribution limit of this species. Animals were exposed to present day normocapnia (380 ppm CO 2), CO 2 levels expected towards 2100 (710 ppm) and beyond (3000 ppm). Heart rate and haemolymph PO 2 (P e O 2) were measured during progressive short term cooling from 10 to 0 • C and during warming from 10 to 25 • C. An increase of P e O 2 occurred during cooling, the highest values being reached at 0 • C under all three CO 2 levels. Heart rate increased during warming until a critical temperature (T c) was reached. The putative T c under normocapnia was presumably >25 • C, from where it fell to 23.5 • C under 710 ppm and then 21.1 • C under 3000 ppm. At the same time, thermal sensitivity , as seen in the Q 10 values of heart rate, rose with increasing CO 2 concentration in the warmth. Our results suggest a narrowing of the thermal window of Hyas araneus under moderate increases in CO 2 levels by exacerbation of the heat or cold induced oxygen and capacity limitation of thermal tolerance.