Effects of long-term moderate hypercapnia on acid-base balance and growth rate in marine mussels Mytilus galloprovincialis

Abstract

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.

Temperature and CO2additively regulate physiology, morphology and genomic responses of larval sea urchins,Strongylocentrotus purpuratus

“…Previous research has attributed the inhibitory effect of pCO 2 on skeletogenesis to developmental delay [50], metabolic depression [51,52] and/or a decreased capacity for calcification [53]. Our data show that although highly sensitive to temperature, development was not delayed by pCO 2 and larvae from both pCO 2 treatments reached obvious developmental landmarks synchronously.…”

Abiotic conditions in cephalopod (Sepia officinalis) eggs: embryonic development at low pH and high pCO2

“…However, high pCO 2 /low pH may be important factors as well, as they could also elicit reductions in respiration rates: Metabolic depression, in combination with reduced growth and calcification performance, has recently been observed in mussels (Mytilus galloprovincialis) exposed to sea water of similar pCO 2 (ca. 0.5 kPa, Michaelidis et al 2005).…”

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

“…There is also evidence that an uncompensated drop in extracellular pH has a depressing effect on aerobic energy metabolism of some tissues like muscle (Reipschläger and Pörtner 1996) and isolated liver cells (Langenbuch and Pörtner 2003), through effects on the mode and rate of proton equivalent ion exchange (Pörtner et al 2000) and a decrease in protein synthesis (Langenbuch et al 2006). 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.…”