Moderate seawater acidification does not elicit long-term metabolic depression in the blue mussel Mytilus edulis

Abstract

Marine organisms are exposed to increasingly acidic oceans, as a result of equilibration of surface ocean water with rising atmospheric CO 2 concentrations. In this study, we examined the physiological response of Mytilus edulis from the Baltic Sea, grown for 2 months at 4 seawater pCO 2 levels (39, 113, 243 and 405 Pa/385, 1,120, 2,400 and 4,000 latm). Shell and somatic growth, calcification, oxygen consumption and NH þ 4 excretion rates were measured in order to test the hypothesis whether exposure to elevated seawater pCO 2 is causally related to metabolic depression. During the experimental period, mussel shell mass and shell-free dry mass (SFDM) increased at least by a factor of two and three, respectively. However, shell length and shell mass growth decreased linearly with increasing pCO 2 by 6-20 and 10-34%, while SFDM growth was not significantly affected by hypercapnia. We observed a parabolic change in routine metabolic rates with increasing pCO 2 and the highest rates (?60%) at 243 Pa. NH þ 4 excretion rose linearly with increasing pCO 2 . Decreased O:N ratios at the highest seawater pCO 2 indicate enhanced protein metabolism which may contribute to intracellular pH regulation. We suggest that reduced shell growth under severe acidification is not caused by (global) metabolic depression but is potentially due to synergistic effects of increased cellular energy demand and nitrogen loss.

Pathogenic challenge reveals immune trade-off in mussels exposed to reduced seawater pH and increased temperature

“…In agreement with previous research (Beesley et al, 2008;Ellis et al, 2014;Ries et al, 2009;Thomsen and Melzner, 2010;, mussels in the present study were tolerant of a level of seawater acidification projected to occur in the open ocean over the next 300 years (pH 7.35; Caldeira and Wickett, 2005). Under these experimental conditions the antibacterial activity of cell-free haemolymph remained unaffected and survival was maintained above 90% at 12.5°C.…”

“…Miles et al, 2007;Spicer et al, 2007), metabolism (e.g. Michaelidis et al, 2005;Thomsen and Melzner, 2010), growth (Berge et al, 2006; and behaviour (e.g. Bibby et al, 2007;Nilsson et al, 2012) in a wide range of marine organisms, the investigation of host defence and its interaction with climate change stressors is still in its infancy.…”

Adaptation and acclimatization to ocean acidification in marine ectotherms: anin situtransplant experiment with polychaetes at a shallow CO2vent system

“…When exposed to elevated pCO 2 , a number of taxa exhibit a marked downregulation of their metabolic rate or 'metabolic depression' [11,[13][14][15][16][17] but this is not ubiquitous. There are examples of upregulation [18][19][20], and no change in metabolism in response to elevated pCO 2 [11,[21][22][23][24]. It has been proposed that metabolic depression evolved to enable organisms to maintain a balance between energy supply and demand when their physiological machinery may be impaired as a result of environmental challenges [25,26].…”

Tolerance of Hyas araneus zoea I larvae to elevated seawater PCO2 despite elevated metabolic costs

“…This may result in decreasing whole animal oxygen consumption (Pörtner et al 1998;Michaelidis et al 2005) or, if compensated for by the rise in energy demanding processes (e.g. calcification), an increase in whole organism oxygen demand (Thomsen andMelzner 2010, Lannig et al 2010;Stumpp et al 2011) and an associated shift in energy budgets. So far, it is not known to what extent these patterns also hold for early life stages of crustaceans, which have to allocate considerable amounts of energy to growth and morphological changes and may be the more sensitive life stages under ocean acidification (Walther et al 2010).…”