Digestion rates and assimilation efficiencies of siphonophores fed zooplankton prey

Digestion times and assimilation efficiencies are critical factors used in calculations of carbon and nitrogen budgets. Digestion times of natural copepod prey differed significantly among 4 genera of siphonophores (P>0.001), from a minimum of 1.6 h to a maximum of 9.6 h. Assimilation efficiencies, in contrast, were uniformly high; 87 to 94% for carbon and 90 to 96% for nitrogen. Nitrogen assimilation was consistently greater than carbon assimilation. Assimilation efficiencies calculated according to dry weight substantially underestimated assimilation of carbon and nitrogen, while calculations using ash-free dry weights and ash-free to dry weight ratios approached values for carbon assimilation. These values are appreciably higher than most of the assimilation efficiencies previously measured for a few other planktonic carnivores. These results indicate very efficient digestion of food by siphonophores in oceanic environments where prey densities are low.     

Resource allocation in Mytilus edulis on the shore and in suspended culture

The annual cycle of carbon and nitrogen content of the flesh of wild and cultivated mussels (Mytilus edulis L.) in Killary Harbour, Ireland, was measured over two years, starting in February, 1980 and ending in November, 1981. The carbon and nitrogen contents of mussel gametes were determined and the allometry of growth of wild and cultured mussel shells was examined with respect to length, weight and organic content. The carbon and nitrogen contents of the organic fraction of the shell were determined. These data were combined with those we had previously published on growth rate, gametogenesis and the annual cycle of ash-free dry weight (AFDW) of mussels in the same locality. Estimates were made of fecundity, reproductive effort and the partitioning of carbon and nitrogen between soma, gametes and shell. In suspended culture, cumulative production after eighteen months is equal to cumulative production after six to seven years on the shore. For comparison, partitioning of carbon and nitrogen resources between soma, shell and gonad is estimated when total cumulative production by wild and cultivated mussels is approximately equal. Differences in resource allocation are considerable. Wild mussels allocate some 57% of their carbon budget and 52% of their nitrogen budget to gamete output. In culture, mussels allocate only 22% of their carbon budget and 19% of their nitrogen budget to gamete output. It is concluded that in response to a higher production rate, cultivated mussels increase allocation of resources to somatic growth.     

Calorific,ash, carbon and nitrogen content in relation to length and dry weight of Parathemisto gaudichaudi (Amphipoda: Hyperiidea) in the North East Atlantic Ocean

The calorific, ash, carbon and nitrogen content, length and dry weight were determined for the hyperiid Parathemisto gaudichaudi (Guerin). Regression equations for all these variables were determined so that they can be estimated by calculation from measurements of length of the hyperiid. Mean values for total nitrogen and carbon were 7.79±0.85% and 36.80±4.18% of the dry weight, respectively. The carbon to calorific equivalent for P. gaudichaudi was 10.37 kcal g^-1 carbon (9.13 kcal g^-1 when corrected for nitrogen). The calorific value for ash-free adult P. gaudichaudi was 5.138 kcal g^-1±1.309 (4.510 kcal g^-1 when corrected for nitrogen). This large variation in the calorific content (coefficient of variation of 25.84%) can be accounted for largely by variation in the ash content (coefficient of variation of 21.84%). The calorific value determined for P. gaudichaudi is similar to that measured for other carnivorous crustaceans and adds support to the hypothesis that animals with high calorific content have a low fecundity and an energy-rich store which can be used as a buffer during unfavourable periods in their life.     

Salps in the Lazarev Sea, Southern Ocean: II. Biochemical composition and potential prey value

Two species of salps, Salpa thompsoni and Ihlea racovitzai, were sampled during three cruises to the Lazarev Sea, Southern Ocean, in summer (December–January) 2005/2006, Autumn (April–May) 2004 and Winter (July–August) 2006. Dry weight, carbon, nitrogen, protein, lipid and carbohydrate contents were measured to characterize the potential value of salps as a food source for predators in the Antarctic ecosystem. Biochemical composition measurements showed that despite having a high percentage of water (~94% of wet weight), both species had relatively high carbon and protein contents in their remaining dry weight (DW). In particular I. racovitzai showed high carbon (up to 22% of DW) and protein (up to 32% of DW) values during all seasons sampled, compared to lower values for S. thompsoni (carbon content only about 15% of the DW, protein content about 10% of the DW). At the same time, carbohydrates (CH) and lipids (Lip) only accounted for a small portion of salp DW in both species (1.4% CH and 3.6% Lip for I. racovitzai; 2.1% CH and 2.9% Lip for S. thompsoni). There was little variability in the biochemical composition of either salp species between the seasons sampled. Both biochemical composition and life cycle characteristics suggest that Antarctic salps, especially I. racovitzai, may be important prey items for both cold and warm-blooded predators in an environment where food is often very scarce.     

Determination of average individual dry weights and ash-free dry weights in different sieve fractions of marine meiofauna

Individual dry weights and ash-free dry weights for different meiofauna taxa from two soft bottom localities (31 and 117 m depth) in Gullmar Fjord on the Swedish west coast were determined. Samples from August 1980 and February 1981 of about 100 to 600 formalin-preserved specimens of each of the different taxa from each of four sieve fractions were weighed on a microbalance. Individual dry weights ranging from 0.12 g (nematodes in the 0.040-mm fraction) to 172 g (polythalamous, arenaceous Foraminifera in the 0.500-mm fraction) and ash-free dry weights ranging from 0.10 g (nematodes in the 0.040-mm fraction) to 37 g (polychaetes in the 0.500-mm fraction) were obtained. Great similarities were noted between corresponding values from the two stations as well as between summer and winter values. The percentage of organic matter, determined by ashing, in the body weight differed greatly among taxa. Some standard individual dry weight and ash-free dry weight values, to be used for re-calculation of abundance values into biomass, are presented.     

Proximate and elemental composition and energy content of mesopelagic crustaceans from the Eastern Gulf of Mexico

The proximate and elemental chemical compositions of 25 species of pelagic decapod and mysid crustaceans collected from the eastern Gulf of Mexico (27°N; 86°W, 1984 to 1989) was examined. Water level ranged from 63 to 95% and increased slightly with species' increased depth of occurrence. Protein levels were generally high (1.5 to 18.3% wet wt, WW; 27.6 to 62.4% ash-free dry wt, AFDW) and comprised the primary organic component in the majority of species. Protein, both as % WW and % AFDW, decreased with increased depth of occurrence. In contrast to protein, lipid levels were low (0.5 to 8.9% WW; 5.7 to 60.9% AFDW), and increased with increased depth of occurrence. Carbon and nitrogen best mirrored measured lipid and protein levels when considered as non-protein carbon and non-chitin nitrogen, respectively. C:N ratios increased with increased depth, consistent with changes in protein and lipid with depth. Because of their compositional attributes, resident Gulf of Mexico species have a low total wet weight energy content relative to species from more productive regions. Energy content showed no significant trend with depth. Vertical migration patterns were distinctly different between shallow-and deep-living gulf species and these differences were largely responsible for the relationships observed between composition and depth. In migrating species, the protein and nitrogen content were higher, the lipid and carbon contents and C:N ratio lower, than in non-migrating species. Three deep-living species of the genus Acanthephyra were found to be compositionally atypical, resembling shallow, migrating types rather than other deep-living, non-migratory species.     

Dry weight, carbon and nitrogen components of caprellid amphipods (Crustacea) inhabiting the Sargassumyezoense community of Otsuchi Bay, northeastern Japan

Dry weight (DW), carbon (C) and nitrogen (N) contents in four species of caprellids, Caprella danilevskii, C. subinermis, C. penantis R-type, and C. verrucosa, inhabiting Sargassumyezoense (Yamada) in Otsuchi Bay, northeastern Japan, were measured based on live specimens. In all species males tend to grow larger than females in pereonite II length, which is used as an indicator of body length, and have greater dry weight, carbon and nitrogen contents. All three parameters (DW, C and N) had highly significant relationships against pereonite II length. Regressions of female pereonite II length against the three parameters significantly differed from males in the four species. Average percentages of carbon and nitrogen contents of the total dry weight ranged from 30.82 to 32.21% and 5.82 to 6.86%, respectively. The carbon/nitrogen ratio tended to decrease against increasing pereonite II length, e.g., 7.2 to 4.3 in C. danilevskii. Received: 25 November 1996 / Accepted: 31 July 1997     

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     

The tunicate Salpa thompsoni ecology in the Southern Ocean. II. Proximate and elemental composition

Detailed determination of Salpa thompsoni elemental composition has been carried out on specimens collected in the Eastern Bellingshausen Sea and at the northern edge of the Weddell Gyre during austral autumn (April and May) of 1996 and 2001. More than 170 Antarctic tunicates S. thompsoni were analysed to determine wet weight (WW), dry weight (DW), ash-free dry weight (AFDW) and elemental composition (C, N content, proteins, carbohydrates and lipids) of different sizes and stages. Dry weight comprised 6.4% (aggregate form) to 7.7% (solitary form) of the WW. AFDW amounted to ~44% of the DW. Carbon and nitrogen contents (Carbon: 17–22%, Nitrogen: 3–5% of the DW) of both aggregate and solitary forms were found to be high relative to data reported in the literature. Although some unidentified organic compounds are not included in our carbon budget, the findings of this study show higher than previously reported nutritional values of S. thompsoni. In spite of this, a shift from a krill-dominated towards a salp-dominated ecosystem would have dramatic consequences for organisms at higher trophic levels.     

Brood size and chemical composition of Pareuchaeta norvegica (Crustacea: Copepoda) in Loch Etive,Scotland

Brood size and chemical composition (carbon, nitrogen, and ash) of Pareuchaeta norvegica in Loch Etive, Scotland have been determined. From 23 to 37 eggs were found in each egg mass (mean=30 eggs). The eggs are oval; the mean size of the longer axis is 438 m. Variation in egg mass (as dry weight) is related to increase in dry weight of the maternal body. an increase of 1 mg in maternal body dry weight produces an increase of 0.03 mg dry weight in the egg mass. Carbon content increases with increasing body dry weight both in pre-spawning and spent females, but nitrogen content decreases with increasing body weight. Thus, the carbon:nitrogen ratio increases with increasing body dry weight. The carbon content of an egg mass ranges from 61.4 to 65.3%, and nitrogen content from 9.6 to 13.2% of the total dry weight. Some examples of partitioning of chemical components of the maternal body into the egg mass are also described.     

Fatty acid composition of the triacylglycerols of the cypris larva of the barnacle Balanus balanoides during metamorphosis

In the free-swimming cypris larva of Balanus balanoides, the mean level of triacylglycerols (triglycerides) was 8% of the ash-free dry weight. During metamorphosis into the juvenile barnacle, the triacylglycerol level in the newly settled non-feeding cypris larva fell to a mean of 2% of the ash-free dry weight. The ratio of fatty acids in the triacylglycerols remained constant throughout metamorphosis, indicating that all species of fatty acids were used as energy sources. There was no evidence for the selective utilisation of particular fatty acids.     

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.     

Effects of preservation on wet weight,dry weight,nitrogen and carbon contents of Calanus helgolandicus (Crustacea: Copepoda)

The lengths, wet and dry weights, nitrogen and carbon contents of fresh, frozen and formaldehyde-fixed specimens of Calanus helgolandicus (Claus) were determined. Samples were collected during May 1980 in the Celtic Sea. Individual Copepodite Stages 3, 4, 5, and Adult Male and Female Stage 6 were measured and analysed, and 36 linear regression equations derived for these variables together with mean values, standard deviations and 95% confidence limits. The range of nitrogen values in the fresh material, expressed as a percentage of dry weight, ranged from 8.08%±0.80 (Copepodite Stage 3) to 10.89%±0.27 (adult female); carbon values changed from 41.6%±3.05 (mean ±95% confidence limits) for Copepodite Stage 3 to 50.97%±2.63 in Copepodite Stage 5. The adult females had a high nitrogen and relatively low carbon content, while the converse was true for Stage 5 copepodites. There was a loss of dry weight from the frozen samples (57%) and the fixed samples (38%) compared with the mean of the fresh dry weight of all stages. The material lost from the copepods was rich in nitrogen, thus, artificially high percentage carbon values were determined from the frozen and fixed samples (52.0 to 60.3% and 44.7 to 58.5%, respectively).     

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.     

Significance of ATP,carbon, and caloric content of meiobenthic nematodes in partitioning benthic biomass

Benthic, free-living marine nematodes from two stations, one subtidal, one intertidal, in the North Inlet Estuary, South Carolina, USA, have been characterized by measurement of adenosine triphosphate (ATP), carbon, caloric content, and ash-free dry weight. Two methods of extracting the organisms from the sediment were used. Resulting carbon to ATP ratios and population density data from ongoing North Inlet meiofauna studies show that the nematodes account for 0.11 to 6.33 g ATP per g dry weight of sediment, varying seasonally. The percentage of nematode ATP/g sediment is higher in the winter and lowest in the summer, and accounts for 68% to over 90% of the total sediment ATP. The findings of this study indicate that meiofauna, particularly nematodes, can no longer be overlooked as a separate entity in attempts to partition benthic systems.Contribution No. 173 from the Belle W. Baruch Institute for Marine Biology and Coastal Research. Research supported by Oceanography Section, National Science Foundation, NSF Grant DES 72-01573 AO1.     

Proximate composition and energy content of mesopelagic fishes from the eastern Gulf of Mexico

The proximate composition of 33 species of mesopelagic fishes collected from the eastern Gulf of Mexico during May–June 1984, July–November 1985 and January 1986 was determined. Water level increased and ash-free dry weight (% dry weight) and protein level (% wet weight) decreased with increasing species' minimum depth of occurrence (that depth below which 90% of a species' population lives). Lipid level (% wet weight or % ash-free dry weight), did not change with species' minimum depth of occurrence. Skeletal ash level (% wet weight) generally decreased with minimum depth of occurrence, whereas carbohydrate level did not change with depth. The variable water level, low lipid level, and high protein level in eastern Gulf of Mexico fishes resulted in a low energy content. These results are generally characteristic of fishes from warm, stable regions of low productivity, such as the eastern North Pacific Gyre. The constant food supply provided by a stable environment may obviate the need for large lipid reserves, in contrast to colder waters at higher latitudes where food availability is seasonal. In addition, the large energy requirements for diel excursions into high-temperature surface waters by the many vertically migrating fishes of this region may influence lipid deposition. The relatively high protein level found in migrators compared to that in non-migrators or weak migrators indicates that locomotory demands influence the percentage of protein found in Gulf fishes. The lack of a positive correlation between protein level and the food availability of a zoogeographic region, suggested in previous studies, is supported here.     

Weight and chemical composition of some important oceanic zooplankton in the North Pacific Ocean

Wet and dry weight, total carbon, nitrogen, hydrogen, and ash contents were determined on 33 species of zooplankton distributed predominantly in the open sea region of the North Pacific. Sampling covered the waters from 44°N to the equator. Average percentage of dry weight to wet weight was about 19% of all samples from the whole area. Percentage dry weight of carbon in copepods was on an average 51.5%. The highest value, 66.6%, was obtained in eggs of the copepod Pareuchaeta sarsi. Mixed zooplankton was assumed to contain carbon comprising about 35 to 45% of the dry weight. Carbon contained in the zooplankton biomass existing in the upper 200 m in the western parts of the northern North Pacific and Bering Sea during spring and summer was estimated to range from 20 to 85 mg C/m³. Nitrogen content varied considerably with localities. Average ratio of carbon to nitrogen was 8.5 in subarctic copepods, and 4.1 in subtropic-tropic copepods. This ratio also varied with season. In the copepod Calanus cristatus the ratio was highest (10.0) in May, immediately after the spring bloom of phytoplankton, when the animals contained much fat. The ratio fell to 5.1 in December. There seemed to be a large seasonal variation in boreal zooplankton due to great fluctuations of environmental conditions, especially the amount of food available; in tropical species the range was small because of environmental uniformity. Average hydrogen content was about 6 to 10%. The percentage of ash to dry weight amounted to 39.3% in pteropods and 3.4% in copepods.     

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.     

Influence du mode de conservation sur la composition chimique élémentaire de Pontella mediterranea (Copepoda: pontellidae)

A comparative study of the elementary chemical composition (C, H, N) of Pontella mediterranea (males, females and copepodites) was carried out in two series: in Series 1, live copepods were briefly rinsed with distilled water, dried for one night (12 h) at 60°C, and then stored in a desiccator; in Series 2, the copepods were preserved in a 5% formalin-freshwater solution neutralized with borax; they were then rinsed with distilled water, and subsequently dried and stored in a desiccator as in Series 1. The results reveal that the dry weight of preserved copepods (Series 2) is 20 to 25% less than that of fresh, dried individuals. Carbon loss was estimated as about 10% in males and 17% in females, hydrogen loss as 14% in males and 23% in females, and nitrogen loss as 20% in males and 21% in females. The organic compounds lost seem to be mainly proteinaceous. Nevertheless, relative carbon content expressed as percent dry weight, and C:N and C:H ratios were all significantly higher in the preserved specimens. These results are compared with literature data on two other crustancean species.     

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.