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Changes in metabolic rate and N excretion in the marine invertebrate Sipunculus nudus under conditions of environmental hypercapnia : identifying effective acid—base variables

M. Langenbuch and H. O. Pörtner^*

Alfred-Wegener-Institut für Polar- und Meeresforschung, Ökophysiologie und Ökotoxikologie, Postfach 120161, D-27515 Bremerhaven, Germany

View larger version (19K): [in a new window]   Fig. 1. (A) Steady-state intracellular pH values of Sipunculus nudus isolated body wall tissue under normo- and hypercapnia, measured after long-term exposure to media of different pH. *pHi significantly different from the control value at pHe 7.9. (B) Intracellular bicarbonate concentrations of isolated tissue exposed to media of different pH and bicarbonate concentrations. Values are means ± S.D., N=5-6, except for extracellular bicarbonate levels, which are media concentrations, used to set the specific pHe, and therefore given without S.D.

View larger version (18K): [in a new window]   Fig. 2. Oxygen consumption rates of Sipunculus nudus isolated body wall musculature measured at different values of extracellular (A) and intracellular (B) pH during normocapnic or hypercapnic incubation. *Oxygen consumption rate significantly different from the respective control value at pHe 7.9. Values are means ± S.D., N=5-6.

View larger version (19K): [in a new window]   Fig. 3. Relationship between oxygen consumption rates of Sipunculus nudus isolated body wall musculature and extracellular bicarbonate concentrations ([HCO3-]). Bicarbonate levels in hypercapnic media cover a broad range of concentrations while normocapnic levels are all very low (0.27-0.015 mmol l-1 HCO3-). *Oxygen consumption rate significantly different from the respective control value at pHe 7.9. Values are means ± S.D., N=5-6.

View larger version (19K): [in a new window]   Fig. 4. The effect of changing extracellular (A) and intracellular (B) pH on ammonia excretion rates of Sipunculus nudus isolated body wall musculature. Tissue samples were analysed after long-term exposure to normocapnic or hypercapnic media of different pH. *Ammonia excretion rate significantly different from the respective control value at pHe 7.9. Values are means ± S.D., N=5-6.

View larger version (21K): [in a new window]   Fig. 5. O/N ratios of Sipunculus nudus body wall musculature, calculated from oxygen consumption and ammonia excretion rates under normo- and hypercapnia, versus different values of extracellular (A) and intracellular (B) pH. *O/N ratio significantly different from the respective control value at pHe 7.9. Values are means ± S.D., N=5-6.

View larger version (19K): [in a new window]   Fig. 6. Correlated changes in O/N ratios and intracellular bicarbonate concentrations determined in Sipunculus nudus isolated body wall tissue. Data were measured after long-term exposure to normocapnic and hypercapnic media of different pH and bicarbonate content. *O/N ratio significantly different from the respective control value at pHe 7.9. Values are means ± S.D., N=5-6.