Developmental changes in oxygen uptake in Cancer magister (Dana) in response to changes in salinity and temperature

The various life stages of the Dungeness crab, Cancer magister, may experience broad environmental fluctuations in both salinity and temperature, parameters that can affect nearly all aspects of their physiological function. The routine rates of oxygen uptake of megalopa, first and fifth instar juvenile and adult C. magister were measured, using closed vessel respirometry over 8 h during acute exposure to 100, 75 and 50% seawater at 10 and 208C. At 108C there is no significant effect of salinity on the rate of oxygen uptake of the megalopa. At 208C, however, the rate of oxygen uptake rises and is greater at 75 and 50% SW than in 100% SW. The rates of oxygen uptake of the first instar juvenile, fifth instar juvenile and adult are not affected by salinity at either 10 or 208C. The oxygen uptake of the fifth instar juvenile is less temperature sensitive, at all salinities, than the other stages examined. Weight specific cardiac output is affected by both salinity and temperature. The effect of temperature on cardiac output is especially pronounced for the first instar juvenile. The first instar juvenile is the first benthic stage and therefore is an important step in recruitment of crabs in the estuary. The differences in metabolic response between the stages indicate that the first instar juvenile, in particular, may be very near the limit of its respiratory and circulatory capacities as a result of tidal changes in salinity and temperature in the intertidal estuarine habitat.  1999 Elsevier Science B.V. All rights reserved.