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 excretion by oceanic salps

Rates of oxygen consumption and ammonium nitrogen excretion were measured on the solitary and/or aggregate generations of ten species of oceanic salps collected by SCUBA divers during cruises in the Atlantic Ocean (1982–1985). Species that were visibly more active had higher metabolic rates than did less active species. Rates were 1.5 to 2 times lower and O:N ratios were lower when salps were held before incubation than when incubation began at the time of collection. Respiration rate showed a better relationship to length than to weight, suggesting that metabolic activity may be connected mainly with swimming. O:N ratios were between 13 and 28 for most species and generations, but higher and more variable in Pegea spp. Exretion of urea was low or undetectable. Rates of metabolic demand (turnover) ranged from 9.7 to 99% body carbon d^-1 and 6.4 to 55.6% body nitrogen d^-1.Contribution No. 5988 from the Woods Hole Oceanographic Institution and No. 412 from the Allan Hancock Foundation     

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.     

Trophic impact, metabolism, and biogeochemical role of the marine cladoceran Penilia avirostris and the co-dominant copepod Oithona nana in NW Mediterranean coastal waters

In this work we studied the trophic ecology and feeding impact of the cladoceran Penilia avirostris and the cyclopoid copepod Oithona nana, the two dominant zooplankters in the summer communities of the coastal NW Mediterranean, on the naturally occurring microbial communities. In order to ascertain carbon surplus for growth and reproduction and the contribution to carbon and nitrogen recycling of these two species, we also determined their basal metabolism and excretion rates. The experiments conducted during summers 2002, 2003, and 2004 indicate that P. avirostris grazed mostly upon small flagellates, dinoflagellates, and diatoms, whereas O. nana had a narrower prey range, selecting motile organisms such as ciliates and occasionally dinoflagellates. The grazing impact of both species accounted, on average, for <10% of the standing stock of the microbial groups considered. In spite of the oligotrophic conditions, the feeding activity of P. avirostris is in general sufficient to compensate basal metabolism and allows a surplus for growth and reproduction. This was not the case for O. nana, its daily rations being often lower than the carbon basal demands. Regarding excretion rates, both species presented different N:P excretion ratios, the ones of O. nana falling within values typical for copepods, whereas the absence of detectable phosphorus excretion by P. avirostris implied an unbalance recycling with respect to typical Redfield ratio composition of marine seston.     

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 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).     

Etude de la respiration et de l'excrétion d'azote et de phosphore des populations zooplanctoniques de l'upwelling mauritanien (mars–avril, 1972)

Fiftysix experiments were run for 22 h on 200 μ-net zooplankton in non-filtered sea water. The equations of orthogonal regression lines between respiration, and mineral, total nitrogen, and phosphorus excretion rates have been computed for 14 stations in the upwelling Mauritanian area. Correlation coefficients are high: excretion values may be estimated from respiration values in order to follow the N and P flux through the Mauritanian zooplanktonic populations. O:N, O:P, N:P, mineral:total excretion ratios are calculated for each station and are not significantly different in the 3 areas of the upwelling area studied. On the average, 48% of excreted phosphorus is thoroughly oxidized into phosphate and needs 142.4 atoms in respiration per P atom. The remainder, excreted as organic phosphorus, requires the same amount of oxygen for its later mineralization. The O:P ratio thus obtained is close to the theoretical -276. Fiftyfour percent of the nitrogen excreted is mineral and the O:N-NH ₊ ⁴ ratio shows a dominant carbohydrate and fat catabolism. The N:P ratio is constant, and close to 10 for both mineral and total excretion.     

Effects of nutritional history on nitrogen assimilation in congeneric temperate and tropical scleractinian corals

The nutritional history of corals is known to affect metabolic processes such as inorganic nutrient uptake and photosynthesis, but little is known about how it affects assimilation efficiency of ingested prey items or the partitioning of prey nitrogen between the host and symbiont. The temperate scleractinian coral Oculina arbuscula and its tropical congener Oculina diffusa were acclimated to three nutritional regimes (fed twice weekly, starved, starved with an inorganic nutrient supplement), then fed Artemia nauplii labeled with the stable isotope tracer ¹⁵N. Fed corals of both species had the lowest assimilation efficiencies (36–51% for O. arbuscula, 38–57% for O. diffusa), but were not statistically different from the other nutritional regimes. Fed and starved corals also had similar NH₄⁺ excretion rates. This is inconsistent with decreased nitrogen excretion and reduced amino acid catabolism predicted by both the nitrogen recycling and conservation paradigms. In coral host tissue, ~90% of the ingested ¹⁵N was in the TCA-insoluble (protein and nucleic acids) and ethanol-soluble (amino acids/low molecular weight compounds) within 4 h of feeding. The TCA-insoluble pool was also the dominant repository of the label in zooxanthellae of both species (40–53% in O. arbuscula, 50–60% in O. diffusa). However, nutritional history had no effect on the distribution of prey ¹⁵N within the biochemical pools of the host or the zooxanthellae for either species. This result is consistent with the nitrogen conservation hypothesis, as preferential carbon metabolism would minimize the effects of starvation on nitrogen-containing biochemical pools.Communicated by P.W. Sammarco, Chauvin     

Effect of starvation on the energy budget of two Asian horseshoe crab species: <Emphasis Type="Italic">Tachypleus tridentatus</Emphasis> and <Emphasis Type="Italic">Carcinoscorpius rotundicauda</Emphasis> (Chelicerata: Xiphosura)

Energy budget is one of the most studied parameters in aquatic animals under environmental challenge. To examine how prolonged starvation would affect their energy budget, respiration rate (RR), ammonia excretion rate (ER), oxygen consumption to ammonia–nitrogen excretion (O:N) ratio and scope for growth (SfG) representing the balance between energy intake and metabolic output, two Asian horseshoe crab species, Tachypleus tridentatus and Carcinoscorpius rotundicauda, were investigated in two feeding regimes (fed and starved) over a period of 7 weeks. No significant effects of species and time course, as well as their interaction, on absorption efficiency were observed in the fed treatments. For both species, RR and ER of the starved treatments significantly decreased, while their O:N ratio significantly increased during the experiment. However, such values for the fed treatments remained relatively stable over the study period. A rapid reduction in SfG was only apparent in the first week of the starved treatments for both species; thereafter, their SfG remained relatively constant. In the fed treatments, SfG of T. tridentatus was significantly lower than that of C. rotundicauda throughout the experiment. In general, C. rotundicauda showed a greater decrease in SfG under starvation than T. tridentatus, suggesting that they may have a more competitive life-history strategy for adjusting to poor nutritional conditions.     

Fish distributions and nutrient cycling in streams: can fish create biogeochemical hotspots?

Rates of biogeochemical processes often vary widely in space and time, and characterizing this variation is critical for understanding ecosystem functioning. In streams, spatial hotspots of nutrient transformations are generally attributed to physical and microbial processes. Here we examine the potential for heterogeneous distributions of fish to generate hotspots of nutrient recycling. We measured nitrogen (N) and phosphorus (P) excretion rates of 47 species of fish in an N-limited Neotropical stream, and we combined these data with population densities in each of 49 stream channel units to estimate unit- and reach-scale nutrient recycling. Species varied widely in rates of N and P excretion as well as excreted N:P ratios (6-176 molar). At the reach scale, fish excretion could meet >75% of ecosystem demand for dissolved inorganic N and turn over the ambient NH4 pool in <0.3 km. Areal N excretion estimates varied 47-fold among channel units, suggesting that fish distributions could influence local N availability. P excretion rates varied 14-fold among units but were low relative to ambient concentrations. Spatial variation in aggregate nutrient excretion by fish reflected the effects of habitat characteristics (depth, water velocity) on community structure (body size, density, species composition), and the preference of large-bodied species for deep runs was particularly important. We conclude that the spatial distribution of fish could indeed create hotspots of nutrient recycling during the dry season in this species-rich tropical stream. The prevalence of patchy distributions of stream fish and invertebrates suggests that hotspots of consumer nutrient recycling may often occur in stream ecosystems.     

The production and secreton of digestive enzymes in the purple seastar Pisaster ochraceus

The purple seastar Pisaster ochraceus contains clearly measurable protease and amylase activity. Centrifuged supernatants of pyloric caeca homogenates undergo a spontaneous threefold increase in protease activity when incubated under toluene for 50 h at 25°C. Amylase activity remains nearly constant over this period. Bovine trypsin at a 1 to 100 ratio (trypsin to supernatant protein) induces a twofold increase in protease activity over that of the control supernatant while having virtually no effect on amylase activity over the control. The data indicate a specific interaction of trypsin with a protease zymogen rather than a conspecific hydrolysis of membrane components or vesicles by trypsin. Two percent Triton X-100 used as a diluent in place of distilled, deionized water causes a sevenfold increase in protease activity and a twofold increase in amylase activity in pyloric caeca supernatants. The use of Triton as a diluent in the preparation of a stomach-tissue supernatant allows quantitative measurement of both protease and amylase activity in that tissue.     

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.     

Effect of bryozoan colonization on inorganic nitrogen acquisition by the kelps Agarum fimbriatum and Macrocystis integrifolia

The effect of bryozoan colonization on inorganic nitrogen acquisition by Agarum fimbriatum Harv. and Macrocystis integrifolia Bory., collected from the west coast of Vancouver Island, British Columbia, Canada, was examined in laboratory experiments during June and July 1992. Pieces of kelp blades that were completely covered on one side by the bryozoans Lichenopora novae-zelandiae Busk or Membranipora membranacea, L., or uncolonized (clean treatment), were used to estimate the rate at which nitrate and ammonium were removed from the surrounding seawater. In addition, the rate of ammonium excretion by bryozoans isolated from their associated kelp was measured and also estimated from the results of the uptake experiments. Values obtained were used to estimate the contribution of ammonium excreted by bryozoans to the total amount of inorganic nitrogen available to the associated kelp. Both bryozoan species reduced the ability of the associated kelp to remove nitrate and ammonium from seawater but provided a source of ammonium to the kelp through excretion. The nitrogen status of colonized and clean kelp disks was determined from the ratio of total particulate carbon to total particulate nitrogen (C:N ratio). The C:N ratios for A. fimbriatum colonized with either L. novae-zelandiae or M. membranacea were similar (C:N=12 to 14), and differences between colonized and clean treatments were not significant. For A. fimbriatum, therefore, the C:N ratio indicates that this species was not nitrogen limited at the time of the present study. In contrast, both colonized and clean disks of M. integrifolia were nitrogen limited, but colonized disks (C:N=19) were significantly less limited by nitrogen than clean disks (C:N=29). Results are discussed in relation to the different environments inhabited by both kelp species and are consistent with the hypothesis that ammonium excreted by bryozoans was an important source of inorganic nitrogen to M. integrifolia, but not to A. fimbriatum, at the time of the study.     

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.     

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).     

Linking abundance and diversity of sponge-associated microbial communities to metabolic differences in host sponges

Many sponge species contain large and diverse communities of microorganisms. Some of these microbes are suggested to be in a mutualistic interaction with their host sponges, but there is little evidence to support these hypotheses. Stable nitrogen isotope ratios of sponges in the Key Largo, Florida (USA) area grouped sponges into species with relatively low δ¹⁵N ratios and species with relatively high δ¹⁵N ratios. Using samples collected in June 2002 from Three Sisters Reef and Conch Reef in the Key Largo, Florida area, transmission electron microscopy (TEM) and denaturing gradient gel electrophoresis were performed on tissues of the sponges Ircinia felix and Aplysina cauliformis, which are in the low δ¹⁵N group, and on tissue of the sponge Niphates erecta, which is in the high δ¹⁵N group. Results showed that I. felix and A. cauliformis have large and diverse microbial communities, while N. erecta has a low biomass of one bacterial strain. As the low δ¹⁵N ratios indicated a microbial input of nitrogen, these results suggested that I. felix and A. cauliformis were receiving nitrogen from their associated microbial community, while N. erecta was obtaining nitrogen solely from external sources. Sequence analysis of the microbial communities showed a diversity of metabolic capabilities among the microbes of the low δ¹⁵N group, which are lacking in the high δ¹⁵N group, further supporting metabolic differences between the two groups. This research provides support for hypotheses of mutualisms between sponges and their associated microbial communities.     

Marine diatoms grown in chemostats under silicate or ammonium limitation. III. Cellular chemical composition and morphology of Chaetoceros debilis,Skeletonema costatum,and Thalassiosira gravida

Three marine diatoms, Skeletonema costatum, Chaetoceros debilis, and Thalassiosira gravida were grown under no limitation and ammonium or silicate limitation or starvation. Changes in cell morphology were documented with photomicrographs of ammonium and silicate-limited and non-limited cells, and correlated with observed changes in chemical composition. Cultures grown under silicate starvation or limitation showed an increase in particulate carbon, nitrogen and phosporus and chlorophyll a per unit cell volume compared to non-limited cells; particulate silica per cell volume decreased. Si-starved cells were different from Si-limited cells in that the former contained more particulate carbon and silica per cell volume. The most sensitive indicator of silicate limitation or starvation was the ratio C:Si, being 3 to 5 times higher than the values for non-limited cells. The ratios Si:chlorophyll a and S:P were lower and N:Si was higher than non-limited cells by a factor of 2 to 3. The other ratios, C:N, C:P, C:chlorophyll a, N:chlorophyll a, P:chlorophyll a and N:P were considered not to be sensitive indicators of silicate limitation or starvation. Chlorophyll a, and particulate nitrogen per unit cell volume decreased under ammonium limitation and starvation. NH₄-starved cells contained more chlorophyll a, carbon, nitrogen, silica, and phosphorus per cell volume than NH₄-limited cells. N:Si was the most sensitive ratio to ammonium limitation or starvation, being 2 to 3 times lower than non-limited cells. Si:chlorophyll a, P:chlorophyll a and N:P were less sensitive, while the ratios C:N, C:chlorophyll a, N:chlorophyll a, C:Si, C:P and Si:P were the least sensitive. Limited cells had less of the limiting nutrient per unit cell volume than starved cells and more of the non-limiting nutrients (i.e., silica and phosphorus for NH₄-limited cells). This suggests that nutrient-limited cells rather than nutrient-starved cells should be used along with non-limited cells to measure the full range of potential change in cellular chemical composition for one species under nutrient limitation.Contribution No. 943 from the Department of Oceanography, University of Washington, Seattle, Washington 98195, USA.     

Composition biochimique des copépodes de l'hyponeuston de Méditerranée Nord occidentale. Poids sec et analyse élémentaire du carbone,de l'hydrogène et de l'azote

Dry weight, total carbon, hydrogen and nitrogen contents were studied in Anomalocera patersoni, Pontella mediterranea, P. lo biancoï and Labidocera wollastoni as a function of sex and developmental stage. 629 individuals were analysed over the year. Protein content was calculated from the nitrogen values, and results are presented as percent dry weight. C:H and C:N ratios were also determined. The lowest contents of carbon (32.4%) and nitrogen (9.3%) were determined for female L. wollastoni, the highest carbon content (43.3%) for female P. lo biancoï, and the highest nitrogen content (11.5%) for female P. lo biancoï and male A. patersoni. This range agrees with the data in the literature for marine copepods. According to available data on biochemical composition of zooplankton in relation to depth, the Pontellidae contain a high amount of proteins. The carbon:nitrogen ratio displays great stability within a species, indicating a constant elementary composition during development from copepodite to adult. Nevertheless, there is a statistically significant discrepancy between the C:N ratios for A. patersoni and P. mediterranea which is due to a higher rate of increase in carbon content in A. patersoni. As a whole, interspecific variations were small (C:N ranged between 3.4 and 3.8) compared to those recorded in true planktonic species. This appears to be an important characteristic of the Pontellidae, in contrast with other, more widely distributed copepods, and probably is related to the peculiarities of their biotope, the ultrasuperficial layer.     

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 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.