THE EFFECTS OF SEASONAL-VARIATIONS IN TEMPERATURE ON EXTRACELLULAR ACID-BASE STATUS IN A WILD POPULATION OF THE CRAYFISH AUSTROPOTAMOBIUS-PALLIPES

Between February 1990 and February 1991, a wild population of Austropo tamobius pallipes (L.) inhabiting a large, shallow, freshwater pool in Staffordshire, central England, experienced environmental fluctuation s in water temperature (1-21-degrees-C) and pH (8.2-9.5). Moulting was seasonal, with crayfish entering pre- and postmoult between May and A ugust. Haemolymph pHa levels declined in the spring when temperatures increased from 8 to 18-degrees-C (DELTApH/DELTAt=0.013 pH units degree s-C-1). This decrease was accompanied by a fall in [HCO3-] (of 4.12 mm ol l-1) and [lactate] (of 4.71 mmol l-1) and a premoult elevation in P (CO2) to 0.59 kPa. After ecdysis, when water temperatures and pH were at their maxima, pHa levels increased, they continued to increase as t emperature fell in late summer, reaching 7.97 in intermoult crayfish a t 13-degrees-C during September. This increase was accompanied by a de crease in P(CO2) to 0.22 kPa at constant [HCO3-] (5-6 mmol l-1). Betwe en September (13-degrees-C) and October (11-degrees-C) pHa fell to 7.8 7 with an elevation in P(CO2) (of 0.18 kPa) and [lactate] (of 1.84 mmo l l-1). As temperature continued to decrease (11-1-degrees-C), pHa rem ained unchanged despite an elevation in [HCO3-] by 2.4 mmol l-1 at con stant P(CO2). A mechanism accounting for the unvarying haemolymph pH v alues at low temperatures is proposed, stressing the importance of tem perature-related seasonal changes in CO2 Solubility and measured value s for pK1' in addition to adjustments in [HCO3-] and P(CO2). These wer e apparently unaffected by changes in collecting and holding protocols .