We introduce a global data bank on body composition of aquatic organisms that is available at http://www. thomas-brey.de/science/virtualhandbook. It covers ratios between body mass (wet, dry, ash free dry mass), body composition (protein, lipid, carbohydrate), macro-elements (C, N, P) and energy content (J). Sofar, data for 3158 different taxa (animals, plants, bacteria) were collected from 725 different sources. The principal purpose of the data bank is mining for conversion factors, as necessary in ecological studies that require a common energetic currency. The data bank can be used to explore general ecological principles, too: among all animals, carnivorous swimmers have the highest energy density, presumably an across-taxon selection for propulsion power and handling force. Plants and animals do not only differ in their C/N and C/P ratios, but these ratios change with temperature in opposite directions. In plants, C/N and C/P increase with temperature, most likely a response to the higher levels of N and P in polar waters. In animals C/N and C/P decrease with temperature, an indicator for selection towards lower activity and larger lipid stores in polar animals.

Anthropogenic climate change confronts marine organisms with rapid trends of concomitant warming and CO 2 induced ocean acidification. The survival and distribution of species partly depend on their ability to exploit their physiological plasticity during acclimatization. Therefore, in laboratory studies the effects of simulated future ocean acidification on thermal tolerance, energy metabolism and acid-base regulation capacity of the North Sea population of the blue mussel Mytilus edulis were examined. Following one month of pre-acclimation to 10°C and control CO 2 levels, mussels were exposed for two weeks to control and projected oceanic CO 2 levels (390, 750 and 1120 μatm) before being subjected to a stepwise warming protocol between 10°C and 31°C (+3°C each night). Oxygen consumption and heart rates, anaerobic metabolite levels and haemolymph acidbase status were determined at each temperature. CO 2 exposure left oxygen consumption rate unchanged at acclimation temperature but caused a somewhat stronger increase during acute warming and thus mildly higher Q 10 -values than seen in controls. Interestingly, the thermally induced limitation of oxygen consumption rate set in earlier in normocapnic than in hypercapnic (1120 μatm CO 2 ) mussels (25.2°C vs. 28.8°C), likely due to an onset of metabolic depression in the control group following warming. However, the temperature induced increase in heart rate became limited above 25°C in both groups indicating an unchanged pejus temperature regardless of CO 2 treatment. An upper critical temperature was reached above 28°C in both treatments indicated by the accumulation of anaerobic metabolites in the mantle tissue, paralleled by a strong increase in haemolymph PCO 2 at 31°C. Ocean acidification caused a decrease in haemolymph pH. The extracellular acidosis remained largely uncompensated despite some bicarbonate accumulation. In all treatments animals developed a progressive warming-induced extracellular acidosis. A stronger pH drop at around 25°C was followed by stagnating heart rates. However, normocapnic mussels enhanced bicarbonate accumulation at the critical limit, a strategy no longer available to hypercapnic mussels. In conclusion, CO 2 has small effects on the response patterns of mussels to warming, leaving thermal thresholds largely unaffected. High resilience of adult North Sea mussels to future ocean acidification indicates that sensitivity to thermal stress is more relevant in shaping the response to future climate change.

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