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 experie nce broad environmental fluctuations in both salinity and temperature, para meters that can affect nearly all aspects of their physiological function. The routine rates of oxygen uptake of megalopa, first and fifth instar juve nile 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 20 deg rees C. At 10 degrees C there is no significant effect of salinity on the r ate of oxygen uptake of the megalopa. At 20 degrees C, however, the rate of oxygen uptake rises and is greater at 75 and 50% SW than in 100% SW The ra tes of oxygen uptake of the first instar juvenile, fifth instar juvenile an d adult are not affected by salinity at either 10 or 20 degrees C. The oxyg en uptake of the fifth instar juvenile is less temperature sensitive, at al l salinities, than the other stages examined. Weight specific cardiac outpu t is affected by both salinity and temperature. The effect of temperature o n cardiac output is especially pronounced for the first instar juvenile. Th e first instar juvenile is the first benthic stage and therefore is an impo rtant step in recruitment of crabs in the estuary. The differences in metab olic response between the stages indicate that the first instar juvenile, i n 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. (C) 1999 Elsevier Science B.V. All rights re served.