A FIELD VERSUS LABORATORY STUDY OF BLOOD-OXYGEN STATUS IN NORMOXIC CRABS AT DIFFERENT TEMPERATURES

The blood oxygen status of two species of active crabs (Carcinus maena s and Necora puber) was studied in the field and compared with the res ults of previous laboratory experiments performed on a wide spectrum o f physiologically different water-breathers. The aim was to determine whether, as in the laboratory, the functioning of the O-2 supply syste m in the field could be based on maintaining the arterial Po-2 (Pao(2) ) in the low range, 1-3 kPa. The O-2 partial pressures and concentrati ons in the arterial and venous blood, arterial blood pH, and blood res piratory pigment concentration were measured in normoxic water at vari ous temperatures ranging from 10 to 20 degrees C and in various season s. In the field, Pao(2) values in normoxic C. maenas and N. puber were in the low range, 1-3 kPa, independently of temperature, season, and blood haemocyanin concentration. It is concluded that in the field as in the laboratory, Pao(2) values mainly in the low range provide a hea d pressure sufficient to meet O-2 needs. The changes that appear to oc cur in other respiratory variables are discussed in relation to field versus laboratory conditions and temperature differences. The conseque nces for analysing problems of hypoxaemia in hypoxic waters or situati ons are discussed.