Metabolic rates of epipelagic marine copepods as a function of body mass and temperature

Metabolic rates (oxygen consumption, ammonia excretion, phosphate excretion) have been calculated as a function of body mass (dry, carbon, nitrogen and phosphorus weights) and habitat temperature, using multiple regression. The metabolic data used for this analysis were species structured, collected from Arctic to Antarctic seas (temperature range: -1.7°C to 29.0°C). The data were further divided into geographical and/or seasonal groups (35 species and 43 data sets for oxygen consumption; 38 species and 58 data sets for ammonia excretion; 22 species and 31 data sets for phosphate excretion). The results revealed that the variance attributed to body mass and temperature was highest (93-96%) for oxygen consumption rates, followed by ammonia excretion rates (74-80%) and phosphate excretion rates (46-56%). Among the various body mass units, the best correlation was provided by the nitrogen unit, followed by the dry weight unit. The calculated Q₁₀ values varied slightly according to the choice of body mass units; overall ranges were 1.8-2.1 for oxygen consumption rates, 1.8-2.0 for ammonia excretion rates and 1.6-1.9 for phosphate excretion rates. The effects of body mass and temperature on the metabolic quotients (O:N, N:P, O:P) were insignificant in most cases. Although the copepod metabolic data used in the present analysis were for adult and pre-adult stages, possible applications of the resultant regression equations to predict the metabolic rates of naupliar and early copepodite stages are discussed. Finally, global patterns of net growth efficiency [growth (growth+metabolism)^-1] of copepods were deduced by combining the present metabolic equation with Hirst and Lampitt's global growth equation for epipelagic marine copepods.     

Metabolic rates of epipelagic marine zooplankton as a function of body mass and temperature

The metabolic rates (oxygen uptake, ammonia excretion, phosphate excretion) of epipelagic marine zooplankton have been expressed as a function of body mass (dry, carbon, nitrogen and phosphorus weights) and habitat temperature, using the multiple-regression method. Zooplankton data used for this analysis are from phylogenetically mixed groups (56 to 143 species, representing 7 to 8 phyla, body mass range: 6 orders of magnitude) from various latitudes (habitat temperature range:-1.4° to 30°C). The results revealed that 84 to 96% of variation in metabolic rates is due to body mass and habitat temperature. Among the various body-mass units, the best correlation was provided by carbon and nitrogen units for all three metabolic rates. Oxygen uptake, ammonia excretion and phosphate excretion are all similar in terms of body-mass effect, but differ in terms of temperature effect. With carbon or nitrogen body-mass units, calculated Q₁₀ values are 1.82 to 1.89 for oxygen uptake, 1.91 to 1.93 for ammonia excretion and 1.55 for phosphate excretion. The effects of body mass and habitat temperature on the metabolic quotients (O:N, N:P, O:P) are insignificant. The present results for oxygen-uptake rate vs body mass do not differ significantly from those reported for general poikilotherms by Hemmingsen and for crustaceans by Ivleva at a comparable temperature (20°C). The importance of a body-mass measure for meaningful comparison is suggested by the evaluation of the habitat-temperature effect between mixed taxonomic groups and selected ones. Considering the dominant effects of body mass and temperature on zooplankton metabolic rates, the latitudinal gradient of community metabolic rate for net zooplankton in the ocean is estimated, emphasizing the non-parallelism between community metabolic rates and the standing stock of net zooplankton.     

Oxygen uptake,ammonia excretion and phosphate excretion by krill and other Antarctic zooplankton in relation to their body size and chemical composition

Oxygen uptake, ammonia excretion and phosphate excretion were measured in 14 Antarctic zooplankton species, including various size classes of krill (Euphausia superba), during a cruise to the Antarctic Ocean adjacent to Wilkes Land in the summer of 1980. Elemental composition (C, N and P) was also determined on the specimens used in these metabolic rate measurements. The values obtained for C, N and P were 4.7 to 47.5%, 1.2 to 12.5% and 0.09 to 1.23% of dry weight, respectively. Regression analyses of metabolic rates on different measures of body weight (fresh, dry, C, N and P) were made on krill, salps and other zooplankton as arbitrarily defined groups and also on the combined groups to determine the best measure of body weight for intra- and interspecific comparison of metabolic rates. The correlations were highly significant in all regressions, although no common measure of body weight provided the best correlation for the three groups of animals. Except for the regression of ammonia excretion on C and N weight, all other regressions of metabolic rates and body weights were significantly different within these three groups. In the combined group, oxygen uptake and ammonia excretion were better correlated to C and N weights than to dry and P weights. For phosphate excretion in the combined groups, dry weight gave the best correlation. Despite these results, the choice of a particular measure of body weight was shown to be important in a comparison of the rates between krill and salps because of their widely different chemical compositions. Our results of rate measurements are compared with those of previous workers for some Antarctic zooplankton, particularly krill. Some of the previous data are in good agreement with ours, while others are not. Possible contributing factors are considered in the latter case. The ratios between the rates (O:N, N:P and O:P) fell within the general ranges reported for zooplankton from different seas. The O:N ratio was consistently low (7.0 to 19.8, by atoms) in all species, suggesting the importance of protein in their metabolic substrates. Protein-oriented metabolism was also supported by the results of C and N analyses which indicated no large deposition of lipid in these animals. From the results of metabolic rate measurements and elemental analyses, daily losses in bodily C, N and P for Antarctic zooplankton in summer were estimated as 0.4 to 2.8%, 0.6 to 2.5% and 1.3 to 19.4%, respectively. These values are approximately one order of magnitude lower than those reported for subtropical and tropical zooplankton.     

Metabolism and elemental composition of zooplankton from the Barents Sea during early Arctic summer

Rates of oxygen consumption, ammonia excretion and phosphate excretion were measured on a hydromedusae (Aglantha digitale), pteropods (Limacia helicina, Clione limacina), copepods (Calanus finmarchicus, C. glacialis, C. hyperboreus, Metridia longa), an amphipod (Parathemisto libellula), a euphausiid (Thysanoessa inermis) and a chaetognath (Sagitta elegans), all of which were dominant species in the Barents Sea during early summer 1987. Water and ash contents and elemental composition (C and N) were also analysed on the specimens used in these metabolic experiments. Between species variations were 67.8% to 94.7% of wet weight in water content, 6.4% to 56.5% of dry weight in ash content, 16.7% to 61.0% of dry weight in carbon content, and 4.3% to 11.2% of dry weight in nitrogen content. Oxygen consumption rates ranged from 0.33 to 13.8 l O₂ individual^-1 h^-1, ammonia excretion rates, from 0.0072 to 0.885 gN individual^-1 h^-1 and phosphate excretion rates, from 0.0036 to 0.33 g P individual^-1 h^-1. In general, higher rates were associated with larger species, but considerable differences were also seen between species. The ratios between the rates (O : N, N : P, O : P) exhibited a wide species-specific variation, indicating differences in dominant metabolic substrates. Typical protein oriented metabolism was identified only in S. elegans. From the results of metabolic rate measurements and elemental analyses, daily losses of body carbon and nitrogen were estimated to be 0.50 to 4.15% and 0.084 to 1.87%, respectively, showing faster turnover rates of carbon than that of nitrogen. Comparison of daily loss of body carbon of the Barents Sea zooplankton with that of the Antarctic zooplankton indicated reduced rates of the former (63% on average).     

Experimental evaluation of the energy balance in Octopus vulgaris, fed ad libitum on a high-lipid diet

A complete energy balance equation was estimated for the common octopus Octopus vulgaris at a constant temperature of 20°C, fed ad libitum on anchovy fillet (Engraulis encrasicolus). Energy used for growth and respiration or lost with faeces and excreted ammonia was estimated, along with total energy consumption through food, for six specimens of O. vulgaris (with masses between 114 and 662 g). The energy balance equation was estimated for the specimens at 10-day intervals. During each 10-day interval, food consumed, body mass increase and quantity of faeces voided were measured. The calorific values of octopus flesh, anchovy flesh and faeces were measured by bomb calorimetry. Oxygen consumption and ammonia excretion rates were monitored for each specimen during three 24-h experiments and daily oxygen consumption and ammonia excretion were estimated. It was found that 58% of the energy consumed was used for respiration. The amount of energy invested in somatic and gonadal growth represented 26% of the total energy budget. The energy discarded through faeces was 13% of consumed energy. The estimated assimilation efficiency (AE) values of O. vulgaris feeding on anchovy (80.9–90.7%) were lower than the AE values estimated for other cephalopod species with different diets of lower lipid content such as crabs or mussels. Specific growth rates (SGR) ranged 0.43–0.95 and were similar to those reported for other high-lipid diets (bogue, sardine) and lower than SGR values found for low-lipid, high-protein diets (squid, crab, natural diet). Ammonia excretion peak (6 h after feeding) followed the one of oxygen consumption (1 h after feeding). The values of atomic oxygen-to-nitrogen (O:N) ratio indicated a protein-dominated metabolism for O. vulgaris.     

Respiration and excretion rates of Calanus glacialis in arctic waters of the Barents Sea

The respiration and excretion rates of Calanus glacialis (Jaschnov) Copepodite Stages III, IV, V, and adult females from the drift-ice area east of Svalbard (Barents Sea) were measured in shipboard experiments during the period from 27 May to 13 June, 1983. The phytoplankton biomass and abundance varied considerably between localities, but these variations were not generally reflected in the respiration and excretion rates of the copepod. The respiration and excretion rates of C. glacialis at the ambient temperature of-1.8°C (average respiration rates of 0.95, 0.73, 0.57, and 0.60 l O₂ mg^-1 dry wt h^-1 for Copepodite Stage III, IV, V, and adult females, respectively) were similar to those previously reported for other large-sized copepods from cold or temperate areas. Average respiration and excretion rates tended to decrease with incubation time or time after capture. Measurements on ten occasions within a period of 27 h after capture revealed excretion rates of ammonium ranging between 2.9 and 16.8 for C III, 3.7 and 21.1 for C IV, 1.3 and 28.4 for C V, and 1.6 and 18.7 for adult females, all expressed as nmol mg^-1 dry wt h^-1. In all experiments, excretion rates of inorganic phosphate varied between 0.7 and 1.5 (C III), 0.5 and 1.1 (C IV), 0.2 and 0.8 (C V), and 0.3 and 1.0 (adult females) nmol mg^-1 dry wt h^-1. Ratios of O:N, O:P, and N:P indicated that much of the metabolic energy was derived from catabolism of proteins. Comparison of the turnover rate of carbon and nitrogen showed, however, that nitrogen turnover was between 2.6 and 8.9 times higher than that of carbon. This may indicate that the copepods deaminate ingested protein, with the carbon skeleton of the amino acids subsequently being used in the synthesis of lipid compounds, possibly wax esters.     

Metabolic activity and elemental composition of krill and other zooplankton from Prydz Bay,Antarctica, during early summer (November–December)

Oxygen uptake and ammonia excretion rates, and body carbon and nitrogen contents were measured in krill (Euphausia superba) and eight other zooplankton species collected during November–December 1982 in the Prydz Bay, Antarctica. From these data, metabolic O:N ratios (by atoms), body C:N ratios (by weight) and daily metabolic losses of body carbon and nitrogen were calculated as a basis from which to evaluate seasonal differences in metabolism and nutritional condition. Comparison of the present data with mid-summer (January) data revealed that early-summer E. superba were characterized by higher metabolic O:N ratios (58.7 to 103, compared with 15.9 to 17.5 for mid-summer individuals). Higher O:N ratios of early-summer E. superba resulted largely from reduced ammonia excretion rates and, to a lesser degree, from slightly increased oxygen uptake rates. Body C:N ratios of E. superba were low in early-summer (3.8 to 4.2) compared with mid-summer krill (4.1 to 4.7) due to lowered body-carbon contents in the former (42.6 to 43.6% compared with 43.2 to 47.5% dry weight of midsummer individuals); gravid females formed an exception, since no seasonal differences in body elemental composition were detected for these. No significant changes in water content (75.3 to 81.4% wet wt) and nitrogen content (9.9 to 11.1% dry wt) in E. superba were evident between the two seasons. Seasonal differences in metabolic rates and elemental composition were less pronounced in a salp (Salpa thompsoni), but a higher metabolic O:N ratio occurred in early-summer individuals. Interspecific comparison of the seven remaining zooplankton species studied with twelve species from mid-summer zooplankton investigated in an earlier study indicated that higher metabolic O:N ratios in early-summer are characteristic not only of herbivore/filter-feeders, but also of some carnivores/omnivores. No relationship between metabolic O:N ratios and body C:N ratios was apparent either intraspecifically or interspecifically, within or between early-summer and mid-summer seasons.     

Metabolic responses of the sympagic amphipodsGammarus wilkitzkii andOnisimus glacialis to acute temperature variations

Acutely elevated seawater temperatures had pronounced metabolic effect on the Arctic under-ice amphipodsGammarus wilkitzkii andOnisimus glacialis, collected in May 1986 and 1988 in the Barents Sea. An increased rate of oxygen consumption vs temperature was observed for both species. In the range from 0° to 10 °CG. wilkitzkii andO. glacialis exhibit Q₁₀ values of 3.4 and 3.6, respectively. The results also indicate increased ammonia excretion rates forG. wilkitzkii andO. glacialis by an elevation of temperature from 0° to 10°C, with an overall Q₁₀ of 1.9 and 2.3, respectively. The present study demonstrates an increased O:N ratio with ambient temperature elevation from 0° to 10°C forG. wilkitzkii andO. glacialis, with overall Q₁₀ values of 2.0 and 1.6, respectively. This indicates a temperature-induced change in the metabolic substrate towards lipids.     

Metabolism of epipelagic tropical ctenophores

Measurements of respiration and excretion at 25°C were made for five species of ctenophores collected during five cruises to the Bahamas (1982–1984). The mean element-specific respiration and ammonium excretion rates of freshly collected specimens of all species ranged from 4 to 16% d^-1, the mean atomic O:N ratios were 10 to 16, and ammonium averaged 60 to 90% of the total dissolved nitrogen excreted. For adult ctenophores, the carbon content ranged from 0.6% carbon (as percent of dry weight) for Bolinopsis vitrea to 3.7% carbon for Beroë ovata. There was a marked increase in the organic content (% carbon of dry weight) of small Bolinopsis vitrea with tentacles compared to fully lobate adults. B. vitrea had increasingly higher metabolic rates when held at food concentrations up to 100 copepods 1^-1 (about 250 g C 1^-1). The overall range between starved and well-fed B. vitrea was about two times for respiration and a factor of three for ammonium excretion. B. vitrea decreased from well-fed to a starved metabolic rate in about a day after removal from food. The metabolic rate of Eurhamphaea vexilligera was not measurably affected by short-term starvation or feeding (maximum 25 copepods 1^-1). In feeding experiments, E. vexilligera of 20 to 56 mm length fed at rates equivalent to clearance rates of 250 to 1 800 ml h^-1.     

Metabolism and elemental composition of a giant chaetognath Sagitta gazellae from the Southern Ocean

Oxygen consumption, ammonia excretion and phosphate excretion rates were measured on Sagitta gazellae Ritter-Zahony, in conjunction with body composition analyses (water, ash, carbon, hydrogen, nitrogen and phosphorus). Both water content (94.7% of wet weight) and ash content (53.0% of dry weight) recorded on S. gazellae were the highest and the lowest, respectively, among the chaetognath data being reported. Contents of carbon, hydrogen and nitrogen of S. gazellae were the lowest among published values of chaetognaths. Metabolic comparison with other chaetognaths living in similar subzero water temperature revealed reduced rates in S. gazellae, while no appreciable differences were seen in the metabolic quotients (O:N, N:P and O:P ratios). The O:N atomic ratios were 10.5 to 15.9 indicating protein oriented metabolism. Reduced metabolic activity of S. gazellae is not due to their body composition as calculated daily metabolic losses of body carbon (0.50%), body nitrogen (0.38) and body phosphorus (1.6%) were also found to be lower than respective values reported on other congeners and even those of other zooplankton living in the Antarctic waters.     

The effect of laboratory conditions on the extrapolation of experimental measurements to the ecology of marine zooplankton. IV. Changes in respiration and excretion rates of boreal zooplankton species maintained under fed and starved conditions

Herbivorous zooplankton species (Calanus plumchrus, Paracalanus parvus and Euphausia pacifica) and carnivorous species (Parathemisto pacifica and Pleurobrachia pileus) collected from Saanich Inlet, British Columbia, Canada, were maintained in the laboratory under fed and starved conditions. Respiration rate and excretion rates of ammonia and inorganic phosphate were measured successively on the same batch populations of each species in different feeding conditions. Respiration rate remained at a constant level or increased during the feeding experiment but decreased progressively in starved individuals. Herbivorous, but not carnivorous, species showed a rapid decrease in both excretion rates for the first few days of an experiment irrespective of feeding conditions. However, the general level of excretion rates of fed specimens was higher than that of starved ones. The O:N, N:P and O:P ratios were calculated from respiration, ammonia excretion and phosphate excretion and discussed in relation to metabolic substrates of animals during the experiment. A marked difference was shown in the O:N ratio between fed hervivores (>16) and fed carnivores (7 to 19), suggesting highly protein-oriented metabolism in the latter. One unknown factor causing variation in excretion rates is speculated to be the physiological stress on animals during sampling from the field. It is suggested that the laboratory measurement of realistic excretion rates of zooplankton is difficult owing to their large fluctuations, but this is not the case with respiration rate.     

Oxygen consumption and ammonia excretion of<Emphasis Type="Italic"> Octopus vulgaris</Emphasis> (Cephalopoda) in relation to body mass and temperature

The common octopus, Octopus vulgaris Cuvier, is of great scientific and commercial importance and its culture is becoming an area of increasing interest. In this study, the combined effects of temperature (T) and body mass (M) on the routine oxygen consumption rate (R) and ammonia excretion rate (U) in O. vulgaris were quantified. The experiments were conducted in a closed seawater system, and great care was taken to reduce handling stress of the animals. Temperature, salinity, pH and ammonia, nitrite, nitrate and phosphate concentrations were monitored and controlled during the experiment. The following predictive equations were evaluated: at temperatures between 13°C and 28°C and at temperatures between 15.5°C and 26°C (T_a is degrees Kelvin and M in gram). O/N ratios showed that O. vulgaris has a protein-dominated metabolism. No significant relationship between the O/N ratio and body mass or temperature was found. Sex had no significant effect on the oxygen consumption rate or on the ammonia excretion rate. For other octopod species, the dependence of metabolic rate on temperature does not differ with that for O. vulgaris.Communicated by O. Kinne, Oldendorf/Luhe     

Metabolic characteristics of midwater zooplankton: Ammonia excretion,O:N rations,and the effect of starvation

The nature of protein catabolism in a wide range of species of midwater zooplankton was investigated. The weight-specific ammonia excretion rates (g NH₃–N g^–1 dry wt h^–1, y) decline exponentially with minimum depth of occurreece (MDO, x), y=163.4 x^{–0.479±0.212} (95%ci) (CI=confidence interval), when temperature is held constant. The change in ammonia excretion can be partially explained by the decrease in percent protein (%P) with MDO, %P=80.17 MDO^{–0.148±0.122 (95%ci)} The atomic O:N ratio of freshly caught zooplankters ranged from 9.1 to 91, with most measurements between 9 and 25. Detailed studies were carried out on the response of one of the species studied (Gnathophausia ingens) to starvation (28 d). After 14 d of starvation the average ammonia excretion rate declined by more than 75% to less than 1 g NH₃–N g^–1 wet wt h^–1, although the average oxygen consumption declined by only 13% within the first 7 d of starvation and then remained stable. This differential response of oxygen consumption and ammonia excretion to starvation resulted in an increase in the average O:N ratio of starved animals from an initial 33 to 165 after 21 d. The average O:N ratios of fed mysids remained below 38 during the experiment. G. ingens maintains a relatively uniform metabolic rate during starvation by relying more heavily on its large lipid stores than when being fed.     

Anaerobic heat production of bivalves (Polymesoda caroliniana andModiolus demissus) in relation to temperature,body size,and duration of anoxia

Anaerobic heat-production rates of two co-occurring species of estuarine bivalves (a clam and a mussel) were measured with double-twin heat-flow calorimeters, one at 20°C, the other at 30°C. There is no significant difference between the two species in metabolic rates. There is evidence of initial aerobic metabolism in some individuals, as shown by high initial rates exponentially decreasing with time, while others had fluctuating but stable average metabolic activity from the beginning. During aerobic as well as anaerobic metabolism, the bivalves showed rhythmic periods of activity and quiescence. The two species differed in their rhythmic pattern of active and resting metabolism. In the case ofPolymesoda caroliniana, periods of resting metabolism tend to be longer and periods of active metabolism shorter at 30°C than at 20°C. There is a similarity between thermograms ofModiolus demissus at 20° and 30°C. Following acute temperature changes from 5° to 20° and 30°C, the bivalves showed stable metabolic rates in a matter of hours. The stabilized average rates [pooled averages for both species of 1.34×10^-4 (standard error of the mean=0.17×10^-4) W g^-1 dry weight of tissue at 20°C and 2.10×10^-4 (SE=0.20×10^-4) W g^-1 at 30°C] signify a temperature coefficient (Q₁₀) of 1.56 between 20° and 30°C, or partial temperature acclimation. Subtracting heat production as a result of physical activity, i.e., considering only resting metabolism, the corresponding means and standard errors of the means are 1.24×10^-4 and 0.14×10^-4 W g^-1 at 20°C and 1.91×10^-4 and 0.077×10^-4 W g^-1 at 30°C. Anaerobic heat production rate at 20°C is proportional to body size (r=0.84, 9 degrees of freedom, DF). ForM. demissus, measured anaerobic heat production is on the order of 7.5% of the level of aerobic respiration reported in the literature.     

How size relates to oxygen consumption,ammonia excretion,and ingestion rates in cold (<Emphasis Type="Italic">Enteroctopus megalocyathus</Emphasis>) and tropical (<Emphasis Type="Italic">Octopus maya</Emphasis>) octopus species

The scaling of metabolic rates with body mass is one of the best known and most studied characteristics of aquatic animals. Herein, we studied how size is related to oxygen consumption, ammonia excretion, and ingestion rates in tropical (Octopus maya) and cold-water (Enteroctopus megalocyathus) cephalopod species in an attempt to understand how size affects their metabolism. We also looked at how cephalopod metabolisms are modulated by temperature by constructing the relationship between metabolism and temperature for some benthic octopod species. Finally, we estimated the energy balance for O. maya and E. megalocyathus in order to validate the use of this information for aquaculture or fisheries management. In both species, oxygen consumption and ammonia excretion increased allometrically with increasing body weight (BW) expressed as Y = aBW ^b . For oxygen consumption, b was 0.71 and 0.69 for E. megalocyathus and O. maya, respectively, and for ammonia excretion it was 0.37 and 0.43. Both species had low O/N ratios, indicating an apparent dependence on protein energy. The mean ingestion rates for E. megalocyathus (3.1 ± 0.2% its BW day⁻¹) and O. maya (2.9 ± 0.5% its BW day⁻¹) indicate that voracity, which is characteristic of cephalopods, could be independent of species. The scope for growth (P = I − (H + U + R) estimated for E. megalocyathus was 28% higher than that observed in O. maya (320 vs. 249 kJ day⁻¹ kg⁻¹). Thus, cold-water cephalopod species could be more efficient than tropical species. The protein and respiratory metabolisms of O. maya, E. megalocyathus, and other octopod species are directly dependent on temperature. Our results offer complementary evidence that, as Clarke (2004) stated, the metabolic response (R and U) cannot be determined mechanistically by temperature, as previously proposed (Gillooly et al. 2002).     

Metabolism and body composition of a copepod (<Emphasis Type="Italic">Neocalanus cristatus</Emphasis>: Crustacea) from the bathypelagic zone of the Oyashio region,western subarctic Pacific

Metabolism [respiratory oxygen consumption, electron-transfer-system (ETS) activity] and body composition [water, ash, carbon (C), nitrogen (N), carbon/nitrogen (C/N) ratio] of stage C5/C6 Neocalanus cristatus from 1000 to 2000 m depth of the Oyashio region, western subarctic Pacific, were determined during the period of July 2000 through June 2003. Compared with the C5 specimens from shallow depths (<250 m), those from 1000 to 2000 m were characterized by quiescent behavior, reduced respiration rates (30% of the rates at active feeding), very low water content (61–70% of wet weight), but high C content (56–64% of dry weight) and C/N ratios (7.2–10.6, by weight). Artifacts due to the recovery of live specimens from the bathypelagic zone appeared to be unlikely in this study, as judged by the consistent results between re-compression (100 atm) and non-compression (1 atm) respiration experiments, and between ETS activities and respiration rates directly measured. In addition, the respiration rates of C6 males and females of N. cristatus from the same 1000–2000 m depth were two to three times higher than the rates of C5 individuals, but were similar to the rates of a bathypelagic copepod, Paraeuchaeta rubra. Combining these results with literature data, C budgets of: (1) diapausing C5 specimens, weighing 6–10 mg dry weight; (2) molt to C6 females; and (3) the complete the life span were established, taking into account assorted losses in respiration during diapause at stages C5 and C6, molt production and egg production. Respiratory C losses by C5 and C6 specimens were estimated on the basis of body N as adjusted metabolic rates [AMR; µl O₂ (mg body N)^–0.843 h^–1], then N budgets were also computed subtracting N lost in the form of cast molts and eggs from the initial stock. Calculations revealed that allocation of the C stock was greatest to egg production (34–57%), followed by respiration (27%) and cast molts (3%), leaving residual C of 13–36% in spent C6 females. The present results for N. cristatus from the North Pacific are compared with those of Calanus spp. in the North Atlantic.Communicated by O. Kinne, Oldendorf/Luhe     

Oxygen consumption of midwater fishes and crustaceans from the eastern Gulf of Mexico

Oxygen consumption was measured as a function of temperature, oxygen partial-pressure (P_O2)and species depth of occurrence for twenty-three species of midwater fishes and crustaceans collected from the eastern Gulf of Mexico from June 1981 to July 1985. Q₁₀s (7° to 20°C) of 3.90 and 3.24 were recorded for myctophid and non-myctophid fish groups, respectively, while values of 2.22, 2.19, 2.19 and 2.54 were calculated for sergestid, penaeid, carid and euphausiid crustacean groups, respectively. Q₁₀s were consistent for species within each group. All of the species tested regulated their oxygen consumption to P_O2levels normally encountered within the eastern Gulf. Values of critical partial pressure (P_c) ranged from 20 to 40mm Hg and increased slightly with increasing temperature and respiration rate. Declining respiration with increasing minimum depth of occurrence was primarily a function of temperature alone. Changes in size, dry weight and water content contributed only a small fraction to the observed decrease. This finding contrasts with studies from the eastern Pacific Ocean, where temperature is a minor contributor to changes in respiration rate with depth.     

Influence of environmental salinity on oxygen consumption and ammonia excretion of the arctic under-ice amphipodOnisimus glacialis

Changes in salinity affect the metabolic rate of the sympagic amphipodOnisimus glacialis collected from the Barents Sea in 1986 and 1988. When transferred from 35 to 5 ppt S, oxygen consumption and ammonia excretion both increase three-fold during the first 5 h of exposure, and they remain high throughout the rest of the experimental period (26 h). During 24-h acclimation to various salinities (5 to 45 ppt), the amphipods exhibit a respiratory and excretory response to hyper- and hypoosmotic stress; however, a rather constant O:N atomic ratio (around 15) was obtained at the experimental salinities, indicating protein/lipids as metabolic substrate. Both rates of oxygen consumption and ammonia excretion increased with an increasing osmotic difference (0 to 650 mOsm) between the haemolymph and the environmental medium, indicating higher energy requirements for osmotic and ionic regulation at low salinities. In amphipods abruptly transferred from 35 to 5 ppt, a minor decrease of the haemolymph sodium concentrations together with an increased ammonia excretion output indicate a counter-ion regulation of NH ₄ ⁺ and Na⁺ during hyposmotic stress.     

Biologie d'un copépode des mares temporaires du littoral méditerranéen français: Eurytemora velox

The respiration and excretion (ammonia and phosphate) of Eurytemora velox, a brackish copepod from temporary lakes of the south of France, were studied in 1978–1979 in relation to food ingestion, temperature and salinity. Suspensions of Tetraselmis maculata were used as food. Respiration was closely dependent on the quantity of the ingested food, displaying a linear relationship with a strong positive-slope coefficient. In most cases, the temperature effect on respiration and excretion was well described by a power-type equation (M=a b ^T , where M=metabolism and T=temperature) over a rather large temperature range. In some experiments, metabolism curves displayed a maximum at 20°C. The metabolismtem-temperature curves differed between successive experiments, depending on season and/or sampling area, perhaps as a result of different acclimatization processes developing in individuals from different generations and/or among geographically isolated populations. Salinity variations significantly affected respiration, but not excretion. Respiration increased in individuals placed in hypo- or hyper-salinity conditions for a period of 24 h. This inability for complete metabolic regulation is unexpected in a species from a habitat subjected to variable salinity, and may have resulted from a too short acclimatization time in the experiments.     

Chemical composition,metabolic rates and feeding behavior of the midwater ctenophore Bathocyroe fosteri

Individuals of the midwater ctenophore Bathocyroe fosteri (0.01 to 1.6 g dry weight, DW) were collected from Bahamian waters by the submersible Johnson-Sea-Link during May and September/October 1983 and October/November 1984 from 530 to 700 m depth. Metabolic rates were measured and showed oxygen consumption to be in the range of 0.01 to 0.18 mg O₂ g^-1 DW h^-1 at temperatures ranging from 9° to 12°C. Ammonium excretion (0.01 to 0.14 g-at N g^-1 DW h^-1) was typically low. Energy expenditures estimated from respiration data (ca. 7% body C d^-1) indicated that one to three midwater crustacean prey (ca. 150 g C d^-1) could provide the daily maintenance ration required by a 40 mm ctenophore. These metabolic characteristics complemented in situ observations of poor locomotor ability and passive feeding behavior.