The heat production rate of the euryhaline isopod Idotea chelipes inhabiting two geographically and ecologically different regions, the Gulf of Gdansk (6.8 psu) (psu, practical salinity unit) and the Mecklenburg Bay (11.8 psu), was examined by direct calorimetry. The wet weights of specimens from the two regions varied from 0.005 to 0.030 g and between 0.004 and 0.036g for L chelipes from the Gulf of Gdansk and Mecklenburg Bay, respectively, and were not statistically different (P>0.05). Animals that exhibited locomotor activity were characterized by metabolic rates higher by 12-77% compared to those of inactive specimens. The mean specific metabolic rates of L chelipes from the Gulf of Gdansk and Mecklenburg Bay were 7.5 +/- 3.4 J h(-1) g(-1) ww (n=28) and 8.4 2.6J h(-1) g(-1) ww (n=28), respectively. Metabolic rates of males and females were not significantly different (P > 0.05). The statistically significant (P < 0.05) relationship between specific metabolic rate (SMR) and wet weight (ww) was described within the experimental mass range by the power functions SMR1 0.53 ww(1)(-0.56) (R = -0.48) for I. chelipes from the Gulf of Gdansk and SMR2 = 0.32ww(2)(-0.75) (R = -0.63) for those from Mecklenburg Bay. (C) 2005 Elsevier B.V. All rights reserved.