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Metabolic rates were measured of the euryhaline amphipodsGammarus locusta (L.),G. oceanicusSegerstråle,G. salinusSpooner,G. zaddachiSexton, andG. duebeniLilljeborg at 15° C by means of flow-through polarographic respirometry. The relationships between oxygen consumption (y) and body weight (x), expressed by the equationy = a · xb, under the influence of two salinities (10‰ and 30 ‰) were investigated. The regression coefficients (b), which describe the slopes of the regression lines, reveal significant differences for the salinities tested. Except forG. duebeni, higher values were obtained in 30 ‰ than in 10 ‰. In the five species, metabolism as a function of size is characterized by regression coefficients ranging from 1 to 0.6. An interspecific comparison of the parametera, representing the intercept on they axis, exhibits a decrease in oxygen requirements in the orderG. locusta, G. oceanicus, G. salinus, G. zaddachi, G. duebeni. The respective values for 0.1 g (fresh weight) animals range from 17.1 to 7.1 mm3 O2/h (30 ‰). Experiments on the alterations in metabolic rates following osmotic stress were designed to provide information on time course and capacity of adaptation to salinity. Depending on the salinity tolerances of the species, the responses after abrupt transfers from 10 to 30 ‰, 30 to 45 ‰, 30 to 10 ‰ and 10 to 3 ‰ were recorded. Changes from more concentrated to more dilute media induce less extensive alterations in respiratory rates and lead to faster adaptation to new salinity levels than transfers in the opposite direction. A new steady state of metabolic rate following salinity stress may be reached after 3 to about 30 hours.G. duebeni exhibits higher capabilities for compensatory adjustments than the other species.G. locusta was shown to be least capable of compensating for salinity changes. Oxygen consumption declines during starvation and attains a fairly constant level, reduced by ca. 15 %, 20 to 24 hours after the beginning of fast, as demonstrated inG. oceanicus by long-term experiments over 6 days. In adult individuals, activity metabolism exceeds standard rates by about 2 1/2 to 3 times. Under basal conditions, distinct respiratory ventilation rhythms of pleopod beating may occur. In addition, the time course of respiratory alterations during moulting was measured. At exuviation, oxygen uptake increases the mean respiratory rates 2.2 to 3.9 times. Some physiological and ecological aspects are discussed, mainly with respect to salinity adaptation and the processes of osmotic and ionic regulation involved. Metabolic rates of gammarid species are compared and related to environmental requirements. The similarity in the functional responses of the sibling speciesG. zaddachi andG. salinus is emphasized.

Vergleichende Untersuchungen zur Atmungsphysiologie euryhaliner Gammariden unter besonderer Berücksichtigung der Salzgehaltsanpassung