. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 274 A. C. BROWN AND N. B. TERW1LLIGER a. >* o. 123456 Medium potassium ion activity (mmol/L) Figure 4. Hemolymph potassium ion activity of Cancer magister as a function of medium potassium ion activity for #, megalopa (n = 1- 3); A, 1st instar juvenile (n = 2-3); •, 5th instar juvenile (n = 2-3); • adult (n = 8). Solid symbols, n > 2, standard error bars drawn; open symbols, n < 2, mean. earlier equilibrium studies reported, that the hemolymph of adult C. magister is weakly hyperosmoregulated in wa- ter less concent
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 274 A. C. BROWN AND N. B. TERW1LLIGER a. >* o. 123456 Medium potassium ion activity (mmol/L) Figure 4. Hemolymph potassium ion activity of Cancer magister as a function of medium potassium ion activity for #, megalopa (n = 1- 3); A, 1st instar juvenile (n = 2-3); •, 5th instar juvenile (n = 2-3); • adult (n = 8). Solid symbols, n > 2, standard error bars drawn; open symbols, n < 2, mean. earlier equilibrium studies reported, that the hemolymph of adult C. magister is weakly hyperosmoregulated in wa- ter less concentrated than normal ocean seawater; chlo- ride, sodium, and potassium are somewhat hyperregulated in reduced salinity, magnesium is very strongly hyporeg- ulated and calcium is strongly hyperregulated. Compared with adults of four other species within the genus Cancer for which data are available (see Charmantier and Char- mantier-Daures, 1991, for review), C. magister adults are the strongest osmoregulators. For example, Cancer an- tennahus has a hemolymph osmolality only 15 mOsm/ kg above ambient seawater osmolality in approximately 53% seawater at 15-20°C (Jones, 1941) compared with C. magister hemolymph osmolality of 250 mOsm/kg above ambient seawater in 50% seawater at 20°C. Ontogeny of osmoregulation Studies on the larvae, post-larvae, and juveniles of a number of decapod crustacean species indicate that most larvae and post-larvae can maintain hemolymph osmo- lality above that of ambient seawater, either by hyperos- moconforming or by weakly hyperosmoregulating (see Charmantier et al., 1988). In such cases, metamorphosis often marks a profound change in osmoregulation from larval to adult patterns. Many decapods that are hyperos- moconforming or weakly hyperosmoregulating over a wide range of salinities in the premetamorphic stages un- dergo a change to become either (a) strongly hyperos- moregulating in low salinity and osmoconforming in high salinity in the adult,
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