Increasing Food Concentration Research Articles

Biochemical proxies for growth and metabolism in Acartia bifilosa (Copepoda, Calanoida)

Biochemical proxies are becoming increasingly common for growth assessment in zooplankton. Their suitability is often unknown, however, and proper calibration is lacking. We investigated correlations between physiological variables (ingestion, egg production, and respiration rates) and biochemical indices related to protein synthesis (RNA content, RNA:DNA ratio, RNA:protein ratio, and protein specific aminoacyl‐tRNA synthetases [spAARS] activity) in copepods Acartia bifilosa exposed to different algal concentrations (0–1200 µg C L−1). All variables assayed increased with increasing food concentration either linearly (spAARS) or nonlinearly (all other variables). Egg production and ingestion rates were significantly and positively correlated with RNA content and RNA:protein ratio, whereas correlations with spAARS and RNA:DNA ratio were weaker or nonsignificant. However, when RNA:DNA ratio and spAARS activity were used as predictors of ingestion, together they had higher explanatory value than did either variable separately. As there were substantial differences in saturating food concentrations among the assayed variables, applicability of biomarkers as proxies of physiological rates will be more reliable if restricted to the nonsaturated phase of the functional response of either variable, unless both variables saturate simultaneously. These findings contribute to methodology of zooplankton growth assessment and to our understanding of biochemical processes underlying growth and metabolism in copepods.

Feeding and growth kinetics of the planktotrophic larvae of the spionid polychaete Polydora ciliata (Johnston)

We studied the effect of food concentration on the feeding and growth rates of different larval developmental stages of the spionid polychaete Polydora ciliata. We estimated larval feeding rates as a function of food abundance by incubation experiments with two different preys, presented separately, the cryptophyte Rhodomonas salina (ESD = 9.7 µm) and the diatom T. weissflogii (ESD = 12.9 µm). Additionally, we determined larval growth rates and gross growth efficiencies (GGE) as a function of R. salina concentration. P. ciliata larvae exhibited a type II functional response. Clearance rates decreased continuously with increasing food concentration, and ingestion rates increased up to a food saturation concentration above which ingestion remained fairly constant. The food concentration at which feeding became saturated varied depending on the food type, from ca. 2 µg C mL − 1 when feeding on T. weissflogii to ca. 5 µg C mL − 1 when feeding on R . salina. The maximum carbon specific ingestion rates were very similar for both prey types and decreased with increasing larval size/age, from 0.67 d − 1 for early larvae to 0.45 d − 1 for late stage larvae. Growth rates as a function of food concentration ( R. salina) followed a saturation curve; the maximum specific growth rate decreased slightly during larval development from 0.22 to 0.17 d − 1 . Maximum growth rates were reached at food concentrations ranging from 2.5 to 1.4 µg C mL − 1 depending on larval size. The GGE, estimated as the slope of the regression equations relating specific growth rates versus specific ingestion rates, were 0.29 and 0.16 for early and intermediate larvae, respectively. The GGE, calculated specifically for each food level, decreased as the food concentration increased, from 0.53 to 0.33 for early larvae and from 0.27 to 0.20 for intermediate larval stages. From an ecological perspective, we suggest that there is a trade-off between larval feeding/growth kinetics and larval dispersal. Natural selection may favor that some meroplanktonic larvae, such as P. ciliata, present low filtration efficiency and low growth rates despite inhabiting environments with high food availability. This larval performance allows a planktonic development sufficiently long to ensure efficient larval dispersion.

Appendicularian ecophysiology I: Food concentration dependent clearance rate, assimilation efficiency, growth and reproduction of Oikopleura dioica

Three aspects of the appendicularian O. dioica' s ecophysiology were measured here: 1) morphological parameters over a wide range of appendicularian sizes, including mature animals in order to document the morphological characteristics inducing reproduction; 2) clearance rate and assimilation efficiency using feeding incubations with different algal concentrations and 3) the effect of food concentration on growth, mortality and reproduction. The relationship between the body carbon weight and the clearance rate follows a power function, with an exponent of 0.91 (± 0.07). The rate of particles retention increases with the food concentration following a Michaelis–Menten relationship (half-saturation constant = 151 ± 22 µg C l − 1 , maximum clearance rate = 12 ± 1 µg C µg C − 1 d − 1 ). The carbon assimilation efficiency decreases with the increasing food concentration. As a result, appendicularian growth which is limited in concentrations lower than 50 µg C l − 1 is saturated above 100 µg C l − 1 . In immature animals the gonad represents less than 30% of the body volume whereas in mature individuals, its volume varies between 50% and 87% (mean 63%) suggesting that gonad/total volume ratio can be used as indicator of the maturation stages. The gonad weight in mature animals represents 70.3 (± 4.6)% of the total body carbon weight. Two major maturity stages can explain the changes in energy allocation: i) the somatic growth, when less energy is invested in gonad growth when compared to the rest of the body and ii) the maturation phase where most of the assimilated matter is invested in gonad maturation. This process is rapid, lasting only few hours. For this reason we measured completely mature organisms that are generally not measured during the experimental work with appendicularians. In food-limited conditions, the gonad maturation process starts with smaller individuals and ends with smaller reproductive animals having the same gonad to total volume ratio than in unlimited food conditions. The results obtained in this study were used to model the life cycle of O. dioica (see Lombard, F., Sciandra, A. and Gorsky, G., 2009-this volume. Appendicularian ecophysiology. II. Modeling nutrition, metabolism, growth and reproduction of the appendicularian Oikopleura dioica.).

Effects of toxic Alexandrium minutum strains on the feeding and survival rates of pelagic marine copepods Acartia grani and Euterpina acutifrons

Feeding and survival experiments with three different toxic strains of Alexandrium minutum (AL1V, AL2V, and AMINAR1) revealed that copepods Acartia grani and Euterpina acutifrons were able to consume all A. minutum strains to a similar extent at which they fed on the non-toxic and similar-sized Scrippsiella trochoidea (strain S. T.). Feeding of both copepod species showed a typical satiation response to increasing food concentrations. Ingestion rates of A. grani on the four dinoflagellate strains were always higher than those observed for E. acutifrons. Significant differences (P < 0.05) were found between these rates for the most toxic strain (AL1V) when comparing both copepod species. For carbon concentrations higher than 800 μg C copepod−1 h−1, ingestion rates of both copepod species on AL1V were higher than those found for S. T., and such behaviour could probably be linked to digestive dysfunction or to the use of part of the accumulated energy in detoxification processes. Survival rates and physiological condition index data suggest that A. grani is more sensitive to A. minutum PSP toxins than E. acutifrons. A long-term exposure experiment (288 h) resulted in 0% survival of A. grani when exposed to AL1V, whereas survival of E. acutifrons was greater than 50% for this strain. For the less toxic AMINAR1 strain, the survival rate of E. acutifrons was 80% compared to 95% survival feeding on S. trochoidea. Our results suggest that both A. grani and E. acutifrons can act, to a different extent, as A. minutum PSP-toxin vectors through the food web.

Predator-induced shifts in Daphnia life-histories under different food regimes

Abstract: Patterns of growth and reproduction (first, second and third broods) of aDaphnia magna clone were studied in a life-table experiment with and without chemi-cal signals from fish predators, under three different food regimes (0.2, 0.5 and 2.0mgCl –1 ).At high resource levels, predation played a role as a factor synchronizing repro-ductive events. Somatic growth rates increased with increasing food concentration andwere lower under the presence of fish than in the control treatments. Smaller femalesize in the fish treatments was accompanied by reduced number of eggs released in thesecond and third (but not the first) clutch. The effect of decreased cumulative numberof offspring was counterbalanced by the gain in the second fitness component –decreased age in releasing successive broods, which eventually resulted in equivalentintrinsic rates of increase (r) in both, the fish and fish-free environments. Conse-quently, Daphnia life-history performance under the presence of predator cues, with-out accompanying mortality, did not incur fitness costs, across the studied range offood concentrations.Key words: Daphnia magna , phenotypic plasticity, growth rate, predation, reproduc-tive synchrony.

Spring bloom succession, grazing impact and herbivore selectivity of ciliate communities in response to winter warming

This study aimed at simulating different degrees of winter warming and at assessing its potential effects on ciliate succession and grazing-related patterns. By using indoor mesocosms filled with unfiltered water from Kiel Bight, natural light and four different temperature regimes, phytoplankton spring blooms were induced and the thermal responses of ciliates were quantified. Two distinct ciliate assemblages, a pre-spring and a spring bloom assemblage, could be detected, while their formation was strongly temperature-dependent. Both assemblages were dominated by Strobilidiids; the pre-spring bloom phase was dominated by the small Strobilidiids Lohmaniella oviformis, and the spring bloom was mainly dominated by large Strobilidiids of the genus Strobilidium. The numerical response of ciliates to increasing food concentrations showed a strong acceleration by temperature. Grazing rates of ciliates and copepods were low during the pre-spring bloom period and high during the bloom ranging from 0.06 (Delta0 degrees C) to 0.23 day(-1) (Delta4 degrees C) for ciliates and 0.09 (Delta0 degrees C) to 1.62 day(-1) (Delta4 degrees C) for copepods. During the spring bloom ciliates and copepods showed a strong dietary overlap characterized by a wide food spectrum consisting mainly of Chrysochromulina sp., diatom chains and large, single-celled diatoms.

Transgenerational retention and maternal transfer of selenium in Daphnia magna

We examined transgenerational retention and maternal transfer of selenium (Se) in three consecutive generations (F0, F1, and F2) of Daphnia magna. The F0 generation was exposed to dietary selenium (as selenite) only, and the F1 and F2 generations received only the maternally derived selenium from F0 and F1, respectively. Algal food Scenedesmus obilquus was radiolabeled with 0.56 microM Se, and the finial Se concentration in the algae was 115.6 microg Se/g dry weight. After 10 d feeding, the initial Se concentration in the F0 prior to depuration was 0.72 microg Se/g wet weight. The Se retention within the same generation was comparable at different food concentrations, but it increased across the consecutive generations regardless of the food concentration, suggesting that Se elimination was dependent on the source of Se accumulation (dietary vs maternally derived). Retention was also comparable among different batches of offspring within the same generation. Reproduction rate increased with increasing food concentration but decreased across the successive batches in F1. The 10-d overall maternal transfer efficiency increased with increasing food concentration in all generations. Approximately 19 to 24% of Se in F0 was transferred maternally to F1 during reproductive events, but the-efficiency decreased considerably from F1 to F2. Maternal transfer also decreased in the later batches of F1. The transfer efficiency to each neonate showed a negative relationship with food concentration in both F0 and F1, suggesting that the Se transfer to the offspring was compromised by the reproduction rate. We concluded that dietary-derived Se (from F0) was more efficiently transferred to the offspring (F1) than the maternally derived Se (from F1) transferred to F2; thus it is necessary to separate the dietary and maternal contributions to the overall Se accumulation in Daphnia.

Daphnia growth is hindered by chemical information on predation risk at high but not at low food levels

Daphnia hyalina x galeata (Dhg) and D. pulicaria (Dp) are ready to pay greater costs in terms of predation risk avoidance at high rather than at low food levels. Such costs are easier to assess in Daphnia than in large long-lived and difficult-to-handle herbivores, since they can be precisely determined in a few-day experiment as the reduced growth (P=A-R) resulting from diminished assimilation (A) and/or increased respiration (R). In experiments with Daphnia grown for six days from the neonate to the first clutch of eggs, which were given different levels of algal food (Scenedesmus at concentrations from 0.05 to 1.60 mg C l(-1)), individual growth was lower in the presence of fish kairomone (chemical information on fish predation; present at a concentration that induces antipredator defensive behavior and life histories) than in the absence of kairomone (control). The difference from the control was negligible at the lowest food levels, and gradually increased with increasing food concentration. At a food concentration of 1.6 mg C l(-1), growth was reduced by 9-32 and 0-8% in Dhg and Dp, respectively, compared to the controls. A similar reduction was observed in the body length of six-day-old animals (Dhg 6-19%, Dp 0-14%), but not in the first clutch reproductive effort (clutch volume). Daphnia had a greater number of eggs per clutch in the presence of the kairomone, but smaller eggs, so that the total volume of eggs in a clutch was the same with and without kairomone. The amplification of the effect of the kairomone due to high food levels was weaker in Dp, a species that rarely coexists with planktivorous fish in natural habitats.

Bioaccumulation and transfer of benzo(a)pyrene in a simplified marine food chain

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 312:101-111 (2006) - doi:10.3354/meps312101 Bioaccumulation and transfer of benzo(a)pyrene in a simplified marine food chain Xinhong Wang, Wen-Xiong Wang* Department of Biology, The Hong Kong University of Science and Technology (HKUST), Clear Water Bay, Hong Kong, SAR *Corresponding author. Email: wwang@ust.hk ABSTRACT: We examined the toxicokinetics of benzo(a)pyrene (BaP) and the trophic transfer in a marine planktonic food chain comprising phytoplankton, copepods, and fish. Kinetic parameters including the uptake rate from the dissolved phase, the assimilation efficiency (AE) from the ingested food, and the elimination rate were quantified. Influences of food quality and quantity and different routes of exposure (aqueous and food) on the biokinetics were also examined. The uptake rate constants were 390 to 1090 ml mg–1 h–1 in different species of phytoplankton, 1.2 ml mg–1 h–1 in the copepods, and 0.157 ml mg–1 h–1 in the fish, respectively. The assimilation efficiencies were 2 to 24% in the copepods and 32 to 51% in the fish ingesting different prey types. Increasing food concentration significantly reduced the AEs, whereas the AEs varied little among the different food diets tested at the same biomass. The elimination rate constants by the copepods were 0.8 to 1.7 d–1, and comparable following uptake from the aqueous phase and the dietary phase. A kinetic modeling calculation suggests that more BaP accumulated in the copepods originates from the dietary intake than the aqueous intake. For fish, both trophic transfer and aqueous uptake are important in BaP bioaccumulation. Feeding rates contribute to the differences in the relative proportion of accumulated BaP in the fish. KEY WORDS: PAHs · Bioaccumulation · Kinetic modeling · Food chain Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 312. Online publication date: April 24, 2006 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2006 Inter-Research.

Enzymatic and feeding behaviour of Argopecten purpuratus under variation in salinity and food supply

Argopecten purpuratus is a bivalve filter feeder inhabiting protected areas of the Peruvian coastline and northern and central Chile. The species is commercially valuable and the natural stocks are over-exploited in Chile, mainly in the central region. Expansion of aquaculture farms to the geographically protected coastline of southern Chile is a potential solution to this problem. So, the objective of the present study was to determine the acute feeding and digestive response of A. purpuratus in relation to short acclimation periods (1, 3 and 7days) and exposure to variable salinity (24‰, 27‰ and 30‰) with two different diets. The feeding behaviour of A. purpuratus follows that described for other species of bivalves whereby the decrease in salinity produces a reduction in the clearance and ingestion rates. This behaviour is not affected by the diet type or the 7 day acclimation period. Lower values of absorption efficiency are associated with increasing food concentration. The response of the AE at 24‰ salinity and low organic content diet indicates that the interaction of low salinity and low organic content diet reduces the AE to values approaching zero. The enzymatic investment of A. purpuratus at low salinity (24‰) is similar for both diets and more reduced than for 30‰ and 27‰ salinity. The results show that osmotic stress leads to a reduction of the enzymatic response capacity. The multiple regression analysis indicates that different responses are observed as a function of the enzymatic activity and the organ. A reduction of the carbohydrase activities in the digestive gland was observed to low salinity (24‰), specifically amylase and celullase. The results of this study are ecophysiologically relevant and highlight a relationship between digestive enzymatic activity and salinity, and may explain the possible differences in the energetic balance of A. purpuratus in response to changes in salinity.

Relationship between the energy status of Daphnia magna and its sensitivity to environmental stress

This work tested the hypothesis that animals with a high energy status are more successful in dealing with stress than animals with a low energy status. Daphnids ( Daphnia magna) were reared for 2 weeks in four different concentrations of food. Survival was not affected by food supply, and growth and reproduction increased with increasing food ration. This increase correlated well with the energy status, as was measured by scope for growth on day 15. After 2 weeks, the daphnids in the four different food ration groups were exposed for another 2 weeks to a range of increased salinities or cadmium concentrations, while remaining in their respective food concentrations. In the salinity groups, survival, growth, or reproduction were not influenced at low salinities. Exposure to higher salinity significantly decreased survival and reproduction, but this decrease was more pronounced in the highest food concentrations. In the cadmium exposed daphnids, cadmium content increased with increasing exposure concentrations, but accumulation was independent of food rations. Cadmium exposure significantly decreased survival, growth, and reproduction and this decrease again was more pronounced with increasing food concentration. Thus, the high energy status of the daphnids from the high food concentrations at the start of the exposure did not provide an increased capacity to cope with additional stress. Instead, the sensitivity of the daphnids to stress increased with increasing food ration. This increased sensitivity is likely to be the result of a change in life history from emphasizing survival at low food supply to stressing reproduction at high food supply.

Egg production of the copepod Acartia tonsa: The influence of hypoxia and food concentration

Low dissolved oxygen conditions, or hypoxia, occur in estuaries and impact more than just the obvious commercially important species. Copepods are an important link in the food web, and the influence of hypoxia upon them is relatively unstudied. Using the copepod Acartia tonsa, a study of the impact of hypoxia on egg production was conducted. A. tonsa had reduced egg production at low dissolved oxygen concentrations (DO), with the lowest egg production occurring at 0.53-ml/l O 2 concentration. Another experiment was conducted to determine if, by increasing food concentration, the affect of hypoxia could be mitigated. The results indicate that increased food did not offset the impact that hypoxia had on egg production of A. tonsa. These results suggest that as A. tonsa experiences hypoxia in the wild, population numbers will decrease. Thus, if hypoxic conditions increase in scope and duration, declines in copepod abundance may lead to a decline in the abundance of species that depend on them as food. These species may be of commercial importance (e.g., fish, crabs, and oysters).

Numerical and functional responses of choreo- and oligotrich planktonic ciliates

A total of 6 planktonic naked ciliates were isolated from the Oslofjord, Norway. Numer- ical and functional responses were investigated using bottle incubations at 11 to 14°C, with the prasinophyceae Nephroselmis pyriformis and cryptophyceae Hemiselmis sp. as food. Growth rates followed hyperbolic curves, which levelled off at about 15 000 algal cells ml -1 (152 µg C l -1 ). Highest growth rate was recorded for the large heterotroph Strobilidium spiralis (μmax = 1.38 ± 0.08 d -1 (mean ± SE). A small mixotroph, Strombidium vestitum, displayed high growth rates (μmax = 1.04 ± 0.05 d -1 ), compared to the larger strombidiids Strombidium conicum, S. acutum and Strombidium sp. (μmax = 0.55 to 0.80 d -1 ). Food thresholds for positive net growth rates were estimated to be in the range of 600 to 3300 algal cells ml -1 , or 6 to 34 µg C l -1 . Specific ingestion rates increased at increasing food concentrations, and maximum measured rates were generally in the range of 2 to 4 d -1 . S. spiralis increased its clearance rate to a maximum of 18.3 ± 0.69 µl h -1 as algal concentrations were enhanced from 900 to 2600 algal cells ml -1 . Gross growth efficiency ranged from 7 to 52% above threshold food levels, with a mean and median of 22 and 23%, respectively.

The effect of the quality of food patches on larval vertical distribution of the sea urchins Lytechinus variegatus (Lamarck) and Strongylocentrotus droebachiensis (Mueller)

Although most invertebrate larvae are weak swimmers and act as passive particles on horizontal scales, they may be able to regulate their vertical position in response to different factors, including increased food concentration. We examined the effect of the quality of food patches on larval vertical distribution for the sea urchins Lytechinus variegatus and Strongylocentrotus droebachiensis, and determined the effect of dietary conditioning on that response in the laboratory. We reared larvae on a mixed algal diet of Dunaliella tertiolecta and Isochrysis galbana under low (500 cells ml −1) and high (5000 cells ml −1) rations. Food patches were maintained in Plexiglas rectangular columns (30×10×10 cm) using a density gradient, where practical salinity in the bottom layer was 33, in the middle layer 30, and in the top layer 27. We examined the magnitude and mechanism of a behavioural response of larvae of L. variegatus in the four-arm stage, and on two developmental stages of S. droebachiensis (four- and six-arm), by manipulating patch quality. In the absence of a patch, larvae of both species and developmental stages swam through to the surface of the experimental columns. In the presence of algae, fewer larvae were present above the patch and more were at the patch than in control columns. More larvae swam through patches of “unflavoured” algal mimics than algal patches, and aggregated at the surface. Larval distribution relative to patches of algal filtrate without algal cells or of “flavoured” algal mimics in algal filtrate was not consistently different from that in either control or algal patches; thus, the magnitude of larval response to filtrate (with or without particles) was intermediate between that to control and algal patches. For L. variegatus, more larvae crossed the patches when reared on low than high rations, indicating that poorly conditioned larvae may be less responsive to environmental cues. Our results suggest that larvae can actively aggregate and maintain a vertical position in response to a food patch that depends on the quality and quantity of food. The response appears to be based mostly on a chemosensory rather than a mechanosensory mechanism.

Feeding selectivities of the marine cladocerans Penilia avirostris, Podon intermedius and Evadne nordmanni

We conducted grazing experiments with the three marine cladoceran genera Penilia, Podon and Evadne, with Penilia avirostris feeding on plankton communities from Blanes Bay (NW Mediterranean, Spain), covering a wide range of food concentrations (0.02–8.8 mm3 l−1, plankton assemblages grown in mesocosms at different nutrient levels), and with Podon intermedius and Evadne nordmanni feeding on the plankton community found in summer in Hopavagen Fjord (NE Atlantic, Norway, 0.4 mm3 l−1). P. avirostris and P. intermedius showed bell-shaped grazing spectra. Both species reached highest grazing coefficients at similar food sizes, i.e. when the food organisms ranged between 15 and 70 µm and between 7.5 and 70 µm at their longest linear extensions, respectively. E. nordmanni preferred organisms of around 125 µm, but also showed high grazing coefficients for particles of around 10 µm, while grazing coefficients for intermediate food sizes were low. Lower size limits were >2.5 µm, for all cladocerans. P. avirostris showed upper food size limits of 100 µm length (longest linear extension) and of 37.5 µm particle width. Upper size limits for P. intermedius were 135 µm long and 60 µm wide; those for E. nordmanni were 210 µm long and 60 µm wide. Effective food concentration (EFC) followed a domed curve with increasing nutrient enrichment for P. avirostris; maximum values were at intermediate enrichment levels. The EFC was significantly higher for P. intermedius than for E. nordmanni. With increasing food concentrations, the clearance rates of P. avirostris showed a curvilinear response, with a narrow modal range; ingestion rates indicated a rectilinear functional response. Mean clearance rates of P. avirostris, P. intermedius and E. nordmanni were 25.5, 18.0 and 19.3 ml ind.−1 day−1, respectively. Ingestion rates at similar food concentrations (0.4 mm3 l−1) were 0.6, 0.8 and 0.9 μg C ind.−1 day−1.

Feeding selectivities and food niche separation of Acartia clausi, Penilia avirostris (Crustacea) and Doliolum denticulatum (Thaliacea) in Blanes Bay (Catalan Sea, NW Mediterranean)

Selectivity-size spectra, clearance and ingestion rates and assimilation efficiencies of Acartia clausi (Copepoda), Penilia avirostris (Cladocera) and Doliolum denticulatum (Doliolida) from Blanes Bay (Catalan Sea, NW Mediterranean) were evaluated in grazing experiments over a wide range of food concentrations (0.02-8.8 mm 3 L -1 plankton assemblages from Blanes Bay, grown in mesocosms at different nutrient levels). Acartia clausi reached the highest grazing coefficients for large algae >70 μm (longest linear extension), P. avirostris for intermediate food sizes between 15 and 70 μm, and D. denticulatum for small sizes from 2.5 to 15 μm. Penilia avirostris and D. denticulatum acted as passive filler-feeders. Acartia clausi gave some evidence for a supplementary raptorial feeding mode. Effective food concentration (EFC) decreased linearly with increasing nutrient enrichment for D. denticulatum and followed domed curves for A. clausi and for P. avirostris with maximum values at intermediate and high enrichment levels, respectively. Clearance rates of crustacean species showed curvilinear responses with narrow modal ranges to increasing food concentration. Clearance rates of D. denticulatum increased abruptly and levelled into a plateau at low food concentrations. Mean clearance rates were 13.9, 25.5 and 64.1 mL ind. -1 day -1 , respectively. No clearance could be detected for A. clausi at food concentrations <0.1 mm 3 L -1 and for P. avirostris at food concentrations <0.02 mm 3 L -1 . Ingestion rates indicate a rectilinear functional response for A. clausi and for P. avirostris and showed a sigmoidal curve for D. denticulatum. Mean ingestion rates were 1.3, 2.8 and 7.7 μg C μg C ind . -1 day -1 , respectively. Conversion of ingested carbon to tissue was 30-80% for the investigated crustaceans and 20-50% for doliolids. Food niche calculations suggest that food niche separation may explain the coexistence of the three species in summer in Blanes Bay.

Bioconcentration and redeposition of polychlorinated biphenyls by zebra mussels ( Dreissena polymorpha) in the Hudson River

The potential impact of zebra mussel infestation on the dynamics of polychlorinated biphenyls (PCBs) in the Hudson River was determined by investigating the biodeposition and bioconcentration of PCBs, using algal food contaminated with 2,5,2′- and 2,4,2′,4′-chlorobiphenyls (CBPs) in the laboratory. Approximately 46–90% of the total food was ingested depending on the supply rate. The highest proportion of ingested congeners was found in biodeposits (64±11% for 2,5,2′-CBP, and 52±6% for 2,4,2′,4′-CBP), followed by tissues (17±3% for 2,5,2′-CBP, and 23±5% for 2,4,2′,4′-CBP), and the lowest in shells. The clearance rate decreased with increasing food concentration, but increased with dilution rate. On the other hand, ingestion rate (IR) increased with food concentration and dilution rate. IR also increased with food supply rate (food concentration×dilution rate) following the same linear function whether the supply rate was varied through food concentration or dilution rate. Therefore, the dilution rate- or food concentration-dependent variation in IR was due to the change in the food supply rate. IR was independent of the kind of PCB congeners. The trend of bioaccumulation in mussel tissues from food ingestion was similar to that of IR; bioaccumulation increased linearly with food supply rate, whether the supply rate was varied through the dilution rate or the food concentration. The bioaccumulation of 2,4,2′,4′-CBP was significantly higher than that of 2,5,2′-CBP ( p<0.05). The bioaccumulation was linearly related to the IR or to the total amount of food ingested. Assimilation efficiency, PCB incorporated in the tissue per total ingested PCB, was higher for 2,4,2′,4′-CBP than for 2,5,2′-CBP ( p<0.05). The congener concentration in biodeposits increased with food supply rate. However, the concentration of 2,5,2′-CBP was significantly greater than that of 2,4,2′,4′-CBP in a mirror image of bioaccumulation. These results indicate that zebra mussels may significantly alter PCB dynamics in the Hudson River through redeposition from the water column and through bioconcentration.

Combined effects of food quantity and quality on Cd, Cr, and Zn assimilation to the green mussel, Perna viridis

We examined the assimilation of Cd, Cr, and Zn by the green mussel Perna viridis under complicated food conditions, including combinations of different compositions and concentrations of food (diatom and sediment), and variable food quantity and quality during particle digestion. At different combinations of food composition and quantity (5 mg l −1 and 20 mg −1, below and above the pseudofeces production), the Cd assimilation was significantly dependent on the food composition. The Cd assimilation efficiency (AE) decreased with increasing proportions of sediments in the diets, but its assimilation was not significantly affected by food concentration. In contrast, the assimilation of Cr and Zn decreased significantly with increasing food concentrations, whereas food composition did not significantly affect their AEs. Variations in metal gut passage time accounted partially for the difference in AEs among different combinations of food composition and quantity. By changing the type of particles during metal digestion, their AEs were maintained comparably at a low particle load (1 mg l −1), suggesting that variation of food quality during digestion did not affect metal assimilation. At a higher particle load (5 mg l −1), variation of food type during digestion affected the AEs of Cr and Zn. An increase in food concentrations from 1 to 15 mg l −1 during digestion resulted in a significant decrease in the AEs of Cr and Zn bound with either sediments or diatoms. Conversely, decreasing the food concentrations from 15 to 1 mg l −1 did not affect the AEs of metals, except for Zn bound with diatoms. Overall, our results highlighted the metal-specificity in their assimilation as influenced by complicated food environments, probably caused by different metal geochemical and biological behavior in the mussels. Feeding selectivity may have a greater control on the influx rate into the mussels than metal assimilation.

Feeding and energy budgets of larval Antarctic krill Euphausia superba in summer

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 257:167-178 (2003) - doi:10.3354/meps257167 Feeding and energy budgets of larval Antarctic krill Euphausia superba in summer Bettina Meyer1,*, Angus Atkinson2, Bodo Blume1, Ulrich V. Bathmann1 1Alfred Wegener Institute for Polar and Marine Research, Department of Pelagic Ecosystems, Handelshafen 12, 27570 Bremerhaven, Germany 2British Antarctic Survey, Natural Environment Research Council, High Cross, Madingley Road, Cambridge CB3 0ET, United Kingdom *Email: bmeyer@awi-bremerhaven.de ABSTRACT: The physiological condition and feeding activity of the dominant larval stages of Euphausia superba (calyptopis stage III, furcilia stages I and II) were investigated from February to March 2000 at the Rothera Time Series monitoring station (67°34¹S, 68°07¹W, Adelaide Island, Western Antarctic Peninsula). A dense phytoplankton bloom (5 to 25 µg chl a l-1) occupied the mixed layer throughout the study period. The feeding of larvae was measured by incubating the animals in natural seawater. Food concentrations ranged from 102 to 518 µg C l-1 across experiments, and the mean daily C rations were 28% body C for calyptosis stage III (CIII), 25% for furcilia stage I (FI) and 15% for FII. The phytoplankton, dominated by diatoms and motile prey taxa, ranged from 8 to 79 µm in size. Across this size spectrum of diatoms, CIII cleared small cells most efficiently, as did FI to a lesser degree. FII, however, showed no clear tendency for a specific cell size. Across the measured size spectrum of the motile taxa, all larvae stages showed a clear preference towards the larger cells. Estimated C assimilation efficiencies were high, from 70 to 92% (mean 84%). Respiration rates of freshly caught larvae were 0.7 to 1.1 µl O2 mg DM-1 h-1. The calculated respiratory C loss showed a significant increase with increasing food concentration in all larval stages, ranging from 0.9 to 2.4% body C d-1. These respiratory losses, combined with the high assimilation efficiencies, thus give the larvae ample capacity for growth at these food concentrations. Critical concentrations of food to achieve maximum daily rations were in the range of 100 to 200 µg C l-1 (~2 to 4 µg chl a l-1). Thus productive shelf sites along the Antarctic Peninsula, such as Rothera, may act as good Œnursery¹ areas for krill larvae. KEY WORDS: Antarctic krill · Euphausia superba · Larval krill · Energy budget Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 257. Online publication date: August 07, 2003 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2003 Inter-Research.

Comparative population growth and life table demography of the rotifer Asplanchna girodi at different prey (Brachionus calyciflorus and Brachionus havanaensis) (Rotifera) densities

Population growth and life table demography of the predatory rotifer A. girodi using spineless Brachionus calyciflorus and spined Brachionus havanaensis as prey at densities of 1, 2, 4 and 8 ind. ml−1 at 25 °C were studied. Regardless of the prey species, the population of A. girodi increased with increasing availability of Brachionus in the medium. At any given prey density, A. girodi fed B. calyciflorus showed consistently better growth than when fed B. havanaensis. The maximum population densities of A. girodi varied from 0.28 to 1.8 ind. ml−1 depending on the prey species and the density. The rate of population increase observed in population growth studies varied from 0.17 to 0.43 day−1 when fed B. calyciflorus and 0.09 to 0.27 day−1 when fed B. havanaensis. Male population of A. girodi was closely related to female density. The lowest average lifespan was observed for A. girodi when fed B. havanaensis at 1 ind. ml−1, while the converse was the case when fed B. calyciflorus at comparable prey concentration. Net reproductive rates varied from 16 to 26 offspring female−1 lifespan−1 depending on the prey species and concentration. Generation time of A. girodi decreased with increasing food concentrations for both the prey species. The rates of population increase obtained from life table demography were lower for A. girodi when fed B. havanaensis than when fed B. calyciflorus.