180 A
.C. Brown, N.B. Terwilliger J. Exp. Mar. Biol. Ecol. 241 1999 179 –192
1. Introduction
The Dungeness crab, Cancer magister, goes through a complex combination of morphological, physiological, and distributional changes during development. The larval
stages are planktonic and are found up to and beyond 150 km offshore Lough, 1976; Hobbs et al., 1992, while metamorphosis from megalopa to juvenile, and recruitment of
juveniles occurs in coastal and estuarine waters. The young of the year juvenile crabs can be found in large numbers on the intertidal mudflats in the Coos River estuary 43
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9N, 1248 189W throughout their first summer. Adult C. magister occur primarily in deeper estuarine and nearshore waters. The maximum dredged depth of the Coos River
is about 14 m at the entrance. Despite their different distributions and utilization of different habitats, estuarine megalopas, juveniles and adults are exposed to regimes of
changing environmental salinity and temperature due to the tides.
These types of changes in salinity and temperature, essentially acute exposure for the 6–8 h of a tidal cycle, typically cause changes in the aerobic metabolism of crustaceans.
There are data available on metabolic response to salinity and or temperature for adults of many species of decapod crustaceans. These include Hemigrapsus nudus and
Hemigrapsus oregonensis Dehnel, 1960, Panopeus herbstii Dimock and Groves, 1975, Carcinus maenas Taylor, 1977, Callinectes sapidus Findley et al., 1978, and
Ilyoplax gangetica Savant and Amte, 1995. This topic has also been reviewed by Scholander et al., 1953; Kinne, 1964; Vernberg, 1983 and Morris, 1991.
Data on the effects of salinity and or temperature on the oxygen consumption rates of early life stages of decapod crustaceans are also available, including studies on Uca spp.
Vernberg and Costlow, 1966, Callinectes sapidus Leffler, 1972, Carcinus maenas Klein Breteler, 1975, Cancer magister Gutermuth and Armstrong, 1989, and
Callinectes similis Guerin and Stickle, 1997. The temperature and salinity sensitivity of metabolic rates of different developmental stages may vary greatly. Changes in
sensitivity to temperature and salinity between the life stages in a given species tend to correspond to such ecological factors as changes in habitat utilization or seasonal shifts
in environmental salinity and or temperature.
An important developmental change in C . magister is the stage specific difference in
ionic regulation Brown and Terwilliger, 1992. In megalopas first and fifth instar juveniles and adults of C
. magister exposed to 50, 75 and 100 seawater SW at 10 and 20
8C, all stages can be characterized as weak hyperosmoregulators. However, the hemolymph magnesium concentrations in megalopas and juveniles acclimated to 100
SW were twice that of the adults. After 8 h exposure to 50 SW the adults had maintained constant hemolymph magnesium levels, while the hemolymph magnesium
levels in the megalopas and juveniles had decreased to the same level as the adult hemolymph magnesium concentration. Hemolymph calcium ion is regulated by both
megalopas and adults in all salinity exposures. On the other hand, hemolymph calcium is much less well regulated in the juvenile stages.
An additional physiological contrast among the developmental stages of C . magister
is the difference in hemocyanin structure and function. When the subunit composition of the hemocyanin from megalopa and early juveniles is compared to that of the adult, the
larval juvenile hemocyanin shows a different stoichiometry of the first five subunits and
A .C. Brown, N.B. Terwilliger J. Exp. Mar. Biol. Ecol. 241 1999 179 –192
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lacks subunit six, which is present in the adult Terwilliger and Terwilliger, 1982. Functionally, the intrinsic oxygen affinity of the larval juvenile 25S hemocyanin is half
the oxygen affinity of the adult 25S hemocyanin under identical experimental conditions Terwilliger et al. 1986. The oxygen affinities of the stage specific 25S hemocyanins
show differential sensitivity to the effects of calcium and magnesium ion concentrations Terwilliger and Brown, 1993. In the whole hemolymph of animals from 100 SW and
normal temperatures ¯ 108C, however, the apparent oxygen affinity is indistinguish- able between the stages Brown and Terwilliger, 1998, due at least in part to differences
in hemolymph ion concentrations.
All of these factors, developmental stage, habitat, ionic and osmotic regulatory patterns, and hemocyanin oxygen transport function, will affect the overall metabolism
of an animal exposed to changes in salinity and temperature. Measurement of oxygen uptake, as an estimate of metabolism of an organism, assuming aerobic metabolism, is a
valid method of assessing the organismal response to changes in the environment Cameron, 1989. In order to determine the extent of physiological stress that a certain
combination of external parameters imposes on an organism it is useful to look at oxygen uptake and some of the functional features of the respiratory protein in oxygen
transport. This study examines oxygen uptake of four life stages of C
. magister exposed to various salinities and temperatures that were determined to mimic the habitat changes
experienced by the life stages due to semidiurnal tides. The results are discussed in conjunction with C
. magister hemocyanin oxygen dissociation properties Terwilliger and Brown, 1993; Brown and Terwilliger, 1998 and blood gas parameters Johansen et
al., 1970. Estimated cardiac output necessary to fuel the apparent oxygen uptake is also discussed as a measure of performance of the circulatory system of the different
developmental stages.
2. Materials and methods
