Oxygen binding characteristics of haemocyanin in the Baltic isopod Saduria entomon

The brackish water isopod Saduria entomon has a haemocyanin oxygen carrying capacity of 1.15 vol%. The physically dissolved oxygen corresponds to 0.66 vol% giving a total normoxic carrying capacity of 1.8 vol% (0.56 mmol.l(-1)). The haemocyanin shows a very high affinity for oxygen; at 6 degrees C and pH of 8.1 and 7.7 P-50 values were 1.7 and 8 Torr. Haemocyanin oxygen affinity was increased at 12 degrees C compared to 6 degrees C. In vivo pH values were 7.65 in normoxia and 7.93 in hypoxia 10-20% air saturation. Exposure to hypoxia (10-20% air saturation) for up to 18 days did not change the oxygen affinity of the haemocyanin. The metabolism of S. entomon remained aerobic during this hypoxic period, no metabolic endproduct like lactate or endproducts of nitrogen metabolism like urate accumulated. The influence of these affinity modulating factors on the blood pigment of S. entomon is thus negligible during environmental hypoxia. In vitro studies on pH in relation to PCO2 showed that pH was always higher in oxygenated compared to deoxygenated haemolymph. The capacity for CO2 transport was rather low, around 5 mmol.l(-1). The results are discussed in relation to the ecology of S. entomon as this species for very long periods can be exposed to hypoxic conditions in the Baltic.