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.     

A comparison of carbon based ammonia excretion rates between gelatinous and non-gelatinous zooplankton: Implications and consequences

About 560 literature data on weight-specific ammonia excretion rates of gelatinous zooplankton (cnidarians, ctenophores and salps) and non-gelatinous zooplankton (mainly crustacea) were converted to carbon based units to enabel a better comparison between both groups. If carbon is used as body-mass unit ammonia excretion rates of gelatinous zooplankton are in the same range as values obtained for other zooplankton taxa, indicating a similar nitrogen output per unit of organic matter in both groups. These results suggest nutrient regeneration potential to be the same in gelatinous and non-gelatinous zooplankton, and that nutrient regeneration within the pelagic system depends more upon the carbon biomass ratio between gelatinous and other zooplankton than on physiological differences.     

Respiration and ammonia excretion by marine metazooplankton taxa: synthesis toward a global-bathymetric model

For thirteen representative taxa of metazooplankton from various depth horizons (<4,200 m) of the world’s oceans, respiration rate (681 datasets on 390 species) and ammonia excretion rate (266 datasets on 190 species) are compiled and analyzed as a function of body mass (dry mass, carbon or nitrogen), habitat temperature, habitat depth and taxon. Stepwise-regression analyses reveal that body mass is the most important parameter, followed by habitat temperature and habitat depth, whereas taxon is of lesser importance for both rates. The resultant multiple regression equations show that both respiration rate and ammonia excretion rate (per individual) increase with increase in body mass and habitat temperature, but decrease with habitat depth. Some taxa are characterized by significantly higher or lower rates of respiration or ammonia excretion than the others. Overall, the global-bathymetric models explain 93.4–94.2 % of the variance of respiration data and 80.8–89.7 % of the variance of ammonia excretion data. The atomic O:N ratios (respiration/ammonia excretion) are largely independent of body mass, habitat temperature, habitat depth and taxon, with a median of 17.8. The present results are discussed in light of the methodological constraints and the standing hypotheses for the relationship between metabolic rate and temperature. Perspectives for model improvement and possible application of it to plankton-imaging systems for rapid assessment of the role of metazooplankton in C or N cycles in the pelagic ecosystem are briefly discussed.     

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.     

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.     

Respiration and ammonia excretion of euphausiid crustaceans: synthesis toward a global-bathymetric model

Respiration and ammonia excretion rates of 19–24 euphausiids from the epipelagic through bathypelagic zones of the world’s oceans were compiled. Body mass (expressed in terms of dry mass, carbon or nitrogen), habitat temperature and sampling depth were designated as parameters in multiple regression analysis. Results suggested that the three parameters were highly significant, contributing 71–89 % of the variance in respiration rates and 69–81 % of the variance in ammonia excretion rates. Atomic O:N ratios derived from simultaneous measurements of respiration and ammonia excretion rates ranged from 11 to 90 (median: 27), and no appreciable effects of the three parameters on O:N ratios were detected. If global-bathymetric models for the metabolism and chemical composition of copepods and chaetognaths are compared with those of euphausiids, it becomes evident that euphausiids are unique in that they maintain high metabolic rates and accumulate moderate amounts of energy reserves (lipids).     

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.     

Influence of temperature changes on oxygen uptake and ammonia and phosphate excretion,in relation to body size and weight,in Oikopleura dioica (Appendicularia)

The relationship between the rates of oxygen consumption, ammonia and phosphate excretion of a pelagic tunicate, the larvacean Oikopleura dioica Fol, 1872 were assessed as a function of size, dry weight and ash-free dry weight at 15°, 20° and 24°C. O. dioica has higher respiration and excretion rates than copepods of similar weight, but the weight exponent of the allometric power function: Y=aX ^b is similar to that of other poikilotherms. Temperatures above 20°C have a depressing effect on respiration and ammonia excretion. 90% of the variance in metabolic rates is explainable by body mass and temperatures Q₁₀ values for oxygen consumption, ammonia and phosphate excretion, respectively, are 2.45, 1.86 and 1.75 between 15° and 20°C, and 3.75, 2.90 and 3.60 between 20° and 24°C. Metabolic quotients (O:N, O:P, N:P) indicate a protein-oriented diet. The results of this study suggest weak metabolic regulation in O. dioica, an energetic strategy which allows an immediate response to favourable changes in feeding conditions.     

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).     

Excretion of ammonia by zooplankton and its potential contribution to nitrogen requirements for primary production in the Catalan Sea (NW Mediterranean)

Excretion of ammonia by mesozooplankton (>200 m zooplankton) and its potential contribution to the nitrogen requirement for phytoplankton growth has been estimated for different hydrographical situations along a transect across the Catalan Sea (Northwestern Mediterranean). The nitrogen excreted as ammonia was estimated from mesozooplankton biomass and specific excretion rates. Nitrogen requirements of phytoplankton were estimated by means of carbon fixation rates and C:N ratios of <200 m particulate organic matter. Minimum C:N ratios and maximum primary production, zooplankton biomass, phytoplankton nitrogen requirements, and nitrogen excretion of zooplankton occurred near the Catalan density front. On average, the nitrogen regenerated by the mesozooplankton accounted for 43% of the nitrogen requirements of the phytoplankton. The specific excretion rates of ammonia and the percentage of phytoplanktonnitrogen requirements supplied by excreted nitrogen were higher at coastal stations. In some coastal and frontal stations, the ammonia excreted exceeded the phytoplanktonnitrogen demand. Bacteria competing for nutrient supply and the possible uncoupling between rate processes and standing stocks of phyto- and zooplankton could explain the apparent excess of regenerated ammonia.     

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.     

Metabolism and body composition of two euphausiids (Euphausia superba and E. crystallorophias) collected from under the pack-ice off Enderby Land,Antarctica

Oxygen consumption, ammonia excretion and phosphate excretion rates were measured for Euphausia superba and E. crystallorophias captured under the pack-ice off Enderby Land, Antarctica, during November 1985. Water, ash, carbon, nitrogen and phosphorus composition were also determined. Compared with summer data, body composition of E. superba at this time of year was characterized by low carbon (40.2 to 40.7% of total dry wt), high nitrogen (11.8 to 12.0%), high phosphorus (1.2%) and high water (80.6 to 81.7% of total wet wt) content. Metabolic rates, expressed as percentage daily losses of body carbon, nitrogen and phosphorus were 1.3 to 1.6%, 0.38 to 0.42% and 1.9 to 2.2%, respectively; these fall within the ranges of summer data. E. superba fed on algae growing on the bottom of the ice, but body compositional features of this species suggest limited contribution of ice-algae to nutrition. Compared to E. superba, E. crystallorophias displayed greater metabolic rates and much higher body carbon content (40.9 to 45.0%), implying that feeding conditions under the ice were better suited to the requirements of E. crystallorophias. The only gravid females found belonged to E. crystallorophias.     

Respiration and excretion by the ctenophore Mnepiopsis leidyi

Respiration (dissolved oxygen and carbon dioxide) and excretion (dissolved organic carbon, inorganic and organic nitrogen and phosphorus) rates were measured for a variety of sizes of Mnemiopsis leidyi over a temperature range of 10.3° to 24.5°C. Both respiration and excretion rates were a direct linear function of animal weight and very temperature sensitive (Q₁₀4). Oxygen uptake ranged from 155 to 489 g at O/(g dry weight) day^-1 and carbon dioxide release from 43 to 166 M. Organic carbon made up about 38% of the total carbon released. Inorganic nitrogen excretion, exclusively in the form of ammonium, comprised 54% of the total nitrogen release and ranged from 10 to 36 M NH₄/(g dry weight) day^-1. Average release of dissolved primary amines (expressed as glycine equivalents) equaled 43% of the organic nitrogen fraction. Inorganic phosphorus release ranged from 2.0 to 4.9 M/(g dry weight) day^-1 and made up about 72% of the total phosphorus loss. The turnover of elements in the body was calculated as 5 to 19% per day for carbon and nitrogen, depending on the temperature, and an even higher 20 to 48% per day for phosphorus. These values are comparable to rates observed for small, active zooplankton.     

Metabolic maintenance costs of the suspension feeder Styela plicata

The bioenergetic basis of the biannual reproductive cycle of the solitary tunicate Styela plicata was investigated in order to evaluate hypotheses concerning the lack of larval settlement in summer. The rate of ingestion and absorption efficiency were measured in order to provide an estimate of the rate at which material was made available for maintenance, growth, and reproduction. At a given temperature the rate of ingestion was proportional to the 0.7 power of wet mass. the ingestion rate increased rapidly with increasing temperature between 12° and 18°C (Q₁₀3), but was independent of temperature between 18° and 28°C. Absorption efficiency was independent of temperature and body size and averaged approximately one-third for both carbon and nitrogen. Metabolic maintenance costs were estimated from measurements of oxygen consumption and excretion of ammonia and urea reported for s. plicata. These require only 18±11% of the carbon and 37±22% of the nitrogen absorbed from the gut of S. plicata over the temperature range 12° to 28°C. Metabolic maintenance makes no excessive demands on the material absorbed in the gut at a particular time of year, and a surplus of carbon and nitrogen substrate is available throughout the year for growth and reproduction. Predation on larvae and young adults may be responsible for the low rate of settlement observed in summer months.     

Ingestion of natural particulate organic matter and subsequent assimilation,respiration and growth by tropical lagoon zooplankton

Rates of ingestion of natural particulate organic matter and subsequent assimilation and respiration by zooplankton at Enewetak Atoll lagoon (Marshall Islands) were measured using a flow-through system. Maximum daily ingestion rates of carbon and nitrogen, expressed as a percentage of the body content, were 79 and 37%, respectively, for the large copepod Undinula vulgaris; 112 and 65%, respectively, for a group of mixed small copepods; and 61 and 34%, respectively, for the pteropod Creseis acicula. Daily metabolic carbon losses, expressed as above, were 63% for U. vulgaris, 88% for the small copepods, and 50% for C. acicula. Assimilation efficiences of carbon and nitrogen ranged from about 86 to 91%. The above rates are generally higher than in previous reports for similar sized zooplankton in temperate waters, while the daily growth increments, expressed as a percentage of the body carbon content (4.8% for U. vulgaris, 8.6% for the small copepods, and 2.6% for C. acicula), are comparable. It appears that the high rates of ingestion and assimilation of organic matter are compensated by high metabolic losses. These results indicate that at least for carbon, tropical zooplankton may have low growth efficiencies ranging from 4 to 9%.     

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.     

Nitrogen regeneration by the surf zone penaeid prawn Macropetasma africanus

Nitrogen excretion of individual Macropetasma africanus (Balss) from an exposed beach/surf zone in Algoa Bay, South Africa was monitored under laboratory and field conditions in relation to body mass, temperature and feeding during 1985. Excretion rate experiments were performed on starved prawns at 15°, 18°, 20° and 25°C, as well as on individuals fed on four different diets (mussel, fish, shrimp and natural diet) at 15° and 20°C. The ratios of the excreted compounds to total nitrogen excreted were similar for the four diets despite differences in their nitrogen content and in the amount of food consumed. At 15° and 20°C, ammonia excretion rates of fed individuals were four to seven times higher than in starved prawns. the excretion rates were not correlated with nitrogen content of diets. M. africanus recycles 1 557 g NH₄–N per metre strip per year or 1 832 g total nitrogen m^-1 yr^-1, which constitute 12 and 14%, respectively, of total phytoplankton requirements of the surf zone. This study indicates that large motile crustaceans, when abundant, can play an important role in nutrient recycling in turbulent marine environments.     

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     

Energetics of Euphausia pacifica. I. Effects of body carbon and nitrogen and temperature on measured and predicted production

Laboratory production during the life span of Euphausia pacifica was measured directly (as the sum of growth, molting and reproduction) and indirectly (as assimilation minus metabolism and leakage) to test the hypothesis that weight-specific production is a constant for all sizes. Euphausiids were collected in Puget Sound, Washington State, USA, from September 1973 to March 1978. Equations were determined (in terms of carbon and nitrogen at 8° and 12° C) expressing the relationships between body weight and the daily rates of growth, molting, reproduction, ingestion and metabolism. The allometric equation (R=aW ^b ) best related body weight (W) to the rate (R) for growth, molting, ingestion, respiration and excretion for life stages from late larvae through adults. As predicted by the original above hypothesis, the weight-specific coefficient (b) was close to 1.0 for ingestion and excretion; in contrast, b was 0.62 for growth, and 0.77 to 0.85 for molting and respiration. The Q₁₀ s also varied: 3.5 for growth, 2.4 for molting, about 3.0 for ingestion, and 2.0 for respiration and excretion. Assimilation efficiencies, for all weights and at both temperatures, were 81.3% of carbon and 85.9% of nitrogen ingested. The relationships between rate and body weight of early larvae for growth and molting were linear, as was the relationship for reproduction in adults. Weight-specific production was higher by I to 2% at 12° than 8° C for all life stages, and was 2 to 4% for carbon and 2 to 6% for nitrogen in adults, but 13 to 17% for carbon and 14 to 15% for nitrogen in early furcilia larvae. The null hypothesis was rejected for production measured directly, but would have been accepted if only an indirect measurement of nitrogen production had been considered. Clearly, indirect measurement incorporates all errors of measurement and assumption and makes interpretation difficult.     

Energetics of Euphausia pacifica. II. Complete carbon and nitrogen budgets at 8° and 12° C throughout the life span

Complete carbon and nitrogen budgets at 8° and 12° C over the life span of Euphausia pacifica were constructed from data published in the foregoing publication. The relative magnitudes of physiological functions such as metabolism and growth for the different life history stages were compared. The carbon net growth efficiency (NGE) for E. pacifica increased to a maximum of 60 to 74% at Calyptopis 3 (a larval stage) and then decreased rapidly to a level of 10 to 12% for adults. The cumulative amount of assimilated carbon or nitrogen in reproductive products was equal to that in growth. The cumulative net production efficiency (tissue plus molts plus reproductive products) is 24 to 29%, and is slightly higher for nitrogen than for carbon. For juveniles and adults, the largest proportion (40 to 65%) of assimilated material is used in metabolism, and is about 10% higher at 8° than 12° C. The difference between measured and predicted ingestion (the sum of metabolism, leakage, defecation, growth, molting and reproduction) probably results from poorly understood aspects of zooplankton physiology (e.g. the effect of body weight on leakage). Nitrogen budgets at 8° C for furcilia bulanced the best, with deviations of less than 10%. In general, predicted ingestion was increasingly less than measured ingestion as body weight and temperature increased. Possible omissions or errors in assumptions or methods that may cause the imbalances are discussed.