Suspended clay reduces Daphnia feeding rate

SUMMARY. 1. Suspended sediments often reduce cladoceran abundance in the field, and reduce the algal feeding rates of cladocerans in the laboratory. This paper explores the behavioural mechanisms by which suspended clay reduces Daphnia feeding rates. Feeding experiments using radiolabelled Cryptomonas cells showed that 50–200 mg 1-^?1 coarse suspended clay (particle size<2 μm) reduced the algal ingestion rate of Daphnia ambigua by 29–87%, but fine suspended clay (<1 μm) had no effect. Suspended clay decreased feeding rate by 60–70% at low algal concentrations (≤5×10³ cells ml^?1), but by only 27% at high algal concentrations (20×10³ cells ml^?1). Thus, the inhibitory effects of suspended clay are greater at low algal concentrations. The sudden addition (or removal) of suspended clay caused immediate reductions (or increases) in algal ingestion rate. 2. Observations of the feeding behaviour of tethered D.pulex showed that the frequency of postabdominal rejections increased greatly in the presence of suspended clay. The rejected boluses contained both algae and clay. Thoracic feeding appendage beat frequency decreased in the presence of suspended clay, decreasing the volume of water searched for food particles. 3. These behavioural responses indicate that clay reduces cladoceran feeding rate by mechanically interfering with both the collection and ingestion of algal cells. Both inhibitory effects are caused because cladocerans collect and ingest suspended clay particles. The behavioural mechanisms by which cladocerans regulate their feeding rate in very high concentrations of algal cells (rejection of excess food and reduction in thoracic limb pumping movements) are the same mechanisms responsible for the inhibition of algal ingestion rate in the presence of high concentrations of suspended clay particles.     

Body size and food thresholds for zero growth in Dreissena polymorpha: a mechanism underlying intraspecific competition

1. Dreissena polymorpha is an extraordinarily successful invasive species that shows high recruitment of small juvenile mussels on established mussel banks. Such juvenile settlement on, and overgrowth of, large adult mussels; however, leads to competition with adults, and often at high densities and low‐food concentrations. 2. The concept of food thresholds for zero growth has been a powerful approach to explaining size‐related exploitative competition in different zooplankton species. We applied it to investigate whether food threshold concentrations for zero growth (C₀) differ between juvenile and adult zebra mussels. 3. By determining body mass growth at various concentrations of a diet mixture (Nannochloropsis limnetica and Isochrysis aff. galbana) we demonstrate that the threshold food concentration for growth of juvenile mussels (C₀ = 0.08 mg C L⁻¹) is substantially lower than that for adults (C₀ = 0.36 mg C L⁻¹). 4. This indicates that, at low food availability, juvenile zebra mussels are competitively superior to their larger conspecifics. Within zebra mussel banks plankton food is substantially depleted and so the observed mechanism might ensure juvenile success and therefore the regeneration of mussel banks in nature.     

QUANTITATIVE STUDIES OF PHAGOCYTOSIS : Kinetic Effects of Cations and Heat-Labile Opsonin

Kinetic analysis of the initial ingestion rate of albumin-coated paraffin oil particles by human granulocytes and rabbit alveolar macrophages was undertaken to study the mechanism of action of cations and of heat-labile opsonin on engulfment. The rate of uptake of the particles was stimulated by Ca⁺⁺, Mg⁺⁺, Mn⁺⁺, or Co⁺⁺. At high concentrations (> 20 mM) Ca⁺⁺ and Mg⁺⁺ inhibited the rate of ingestion. Treatment of the particles with fresh serum (heat-labile opsonin) also stimulated the rate of ingestion. ¹²⁵I-labeled C3 was bound to the particles during opsonization. C3-deficient human serum lacked opsonic activity, which was restored by addition of purified C3. Normal, C2-deficient, and hereditary angioneurotic edema sera had equivalent opsonic activity. The serum opsonic activity thus involved C3 fixation to the particles by means of the properdin system. Although Mg⁺⁺ and heat-labile opsonin both accelerated the maximal rates of ingestion of the particles, neither altered the particle concentrations associated with one-half maximal ingestion rates. Opsonization of the particles markedly diminished the concentrations of divalent cations causing both stimulatory and inhibitory effects on ingestion rates and altered the shapes of the cation activation curves. ⁴⁵Ca was not bound to the particles during opsonization. The results are consistent with a mechanism whereby divalent cations and heat-labile opsonin activate ingestion by stimulating the work of engulfment rather than by merely enhancing cell-particle affinity, and whereby heat-labile opsonin acts by potentiating the effects of divalent cations.     

Effects of food concentration on clearance rate and energy budget of the Arctic bivalve Hiatella arctica (L) at subzero temperature

The influence of food concentration on clearance rate, respiration, assimilation, and excretion at −1.3 °C was studied on individuals of the bivalve Hiatella arctica (L.) from Young Sound, NE Greenland. Clearance rate, assimilation efficiency, respiration, and excretion rates were determined over a range of food concentrations using the microalga Rhodomonas baltica as food source. Physiological rates were generally low but responded significantly to increased food levels. Clearance rates and assimilation efficiency were reduced at increased food levels, whereas respiration and excretion increased. Assimilation efficiency was generally high, which may be an adaptation to the low food concentration during most of the year in NE Greenland. Low filtration rates limited ingestion rates and resulted in a low maximum assimilation of 3 J h⁻¹. Despite the low food intake, very low food concentrations were required for individual specimens to obtain a positive energy budget. Predicted growth based on rates of assimilation and respiration were compared to published estimates of annual growth in Young Sound. We estimate that 3 weeks of growth in the laboratory under optimal food conditions could match annual growth in situ. We interpret this as evidence that food limitation is the primary impediment to growth in this Arctic population.     

Phagotrophic phytoflagellates in microbial food webs

Phagotrophy by pigmented flagellates is known from the literature but has recently been rediscovered in the context of microbial food webs. Particle ingestion rates were found to be equivalent for pigmented and nonpigmented microflagellates in both field and laboratory studies. Ingestion rates of the chrysophytes Ochromonas danica, O. minuta, and Poterioochromonas malhamensis, the dinoflagellate Peridinium inconspicuum, and the cryptophytes Cryptomonas ovata and C. erosa were compared with those of two nonpigmented Monas species using 0.57 μm polystyrene beads as a food source. Ingestion rates were 0.31 to 3.17 beads/cell/h and filtration rates were 10⁻⁷ to 10⁻⁸ ml/cell/h with no detectable difference between pigmented and nonpigmented forms. Ingestion rates in unpigmented Monas species showed a linear increase with increasing particle concentration from 1.9 × 10⁶ to 1.6 × 10⁷ beads/ml. Light and DOC levels in the range of those encountered by phytoflagellates in the field also influenced laboratory measurements of bead ingestion by Poterioochromonas malhamensis. Ingestion rates decreased and photosynthesis increased over the natural PAR light range from 0 to 1800 microeinsteins/s/m². At 40 microeinsteins/s/m² maximum ingestion rates and high rates of photosynthesis occurred simultaneously. Ingestion rates decreased above 4 mgC/l supplied as glucose. DOC levels commonly occurring in Lake Oglethorpe range from 3.5 to 10.0 mgC/l. These studies suggest that mixotrophy, the trophic utilization of particulate food and dissolved organic matter as well as photosynthetically fixed organic matter, is a balanced process that can be regulated by environmental conditions. In field studies during a chrysophyte bloom, phytoflagellate grazing exceeded heterotrophic microflagellate grazing and constituted up to 55% of the bactivory of all microflagellates, ciliates, rotifers, and crustaceans combined. Neither bacterial abundance, light nor temperature were good predicters of grazing rates for the phagotrophic phytoflagellate association as a whole during this unstratified period. Phagotrophs are often most abundant at the metalimnetic plate during stratification.     

Control of the harmful alga Cochlodinium polykrikoides by the naked ciliate Strombidinopsis jeokjo in mesocosm enclosures

Red tides dominated by the harmful dinoflagellate Cochlodinium polykrikoides have caused annual losses of USD $5–60 million to the Korean aquaculture industry annually since 1995 and a loss of USD $3 million during a 1999 net-pen fish mortality event in Canada. In order to evaluate the potential to control C. polykrikoides red tides dominated by using mass-cultured heterotrophic protistan grazers, we monitored the abundance of Strombidinopsis jeokjo (a naked ciliate) and C. polykrikoides after mass-cultured S. jeokjo was introduced into mesocosms (ca. 60 l) deployed in situ and containing natural red tide waters dominated by C. polykrikoides. Water temperature, salinity, and pH, as well as the abundance of co-occurring other protists and metazooplankton were measured concurrently. To compare the growth and ingestion rates of S. jeokjo feeding on cultured versus natural populations of C. polykrikoides, we also monitored the abundance of cultured C. polykrikoides and S. jeokjo in bottles during laboratory grazing experiments. S. jeokjo introduced into the mesocosms grew well, effectively reducing natural populations of C. polykrikoides from approximately 1000 cells ml⁻¹ to below 10 cells ml⁻¹ within 2 days. The growth and ingestion rates of cultured S. jeokjo on natural populations of C. polykrikoides in the mesocosms for the first 30 h (0.72 day⁻¹ and 51 ng C grazer⁻¹ day⁻¹) were 84% and 44%, respectively, of those measured in the laboratory during bottle incubations with similar initial prey concentrations. The calculated grazing impact of S. jeokjo on natural populations of C. polykrikoides suggests that large-scale cultures of this ciliate could be used for controlling red tides by C. polykrikoides in small areas.     

Swimming behaviour of <Emphasis Type="Italic">Brachionus plicatilis</Emphasis> in relation to food concentration and feeding rates

We examined feeding rates and swimming speed in amictic females of Brachionus plicatilis over algal cell concentrations ranging from 15 × 10³ to 30 × 10⁶ cell ml⁻¹, to determine to what extent filtration rate is a consequence of a real modulation of swimming speed in response to food availability. Swimming rates were measured using an automated motion analysis system via video recording. The results showed that swimming speed changed as a function of food density. Swimming speed increased from the lowest tested concentration of algae to reach a maximum at 6 × 10⁶ cell ml⁻¹. Above this density, swimming speed declined slightly and then remained constant at a mean speed of 0.45 mm s⁻¹. Filtration and ingestion rates changed as cell concentration increased, following patterns consistent with those generally described for suspension feeders. However, the observed swimming pattern did not explain the recorded changes in clearance rate. These results suggest that filtration, and therefore ingestion, is mainly regulated by modifying particle retention efficiency. Guest editors: S. S. S. Sarma, R. D. Gulati, R. L. Wallace, S. Nandini, H. J. Dumont & R. Rico-Martínez Advances in Rotifer Research     

Temperature aspects of ecological bioenergetics in Brachionas angularis (Rotatoria)

The influence of temperature and food quality was studied on the following energy balance parameters of B. angularis: ingestion, production, growth and mortality. The ingestion rate rises to an optimum at 15 and 20 °C and decreases at 25 °C. The other rates increase continuously over the 5–25 °C range. The Q₁₀-values of production rate are higher than those of ingestion rate. Temperature also modifies the relationship between food concentration and bioenergetic rates. They react according to a Monod function (production at all temperatures, growth at 10 °C) or decrease at high concentrations (growth at 15° and 20 °C.)     

Physiological energetics of the zebra musselDreissena polymorpha in lakes II. Food uptake and gross growth efficiency

Food uptake ofDreissena polymorpha from two shallow water sites and one site at a 9 m depth in lakes was monitored over the course of 1 1/2 years. Feeding was characterized by the filtration capacity and ingestion capacity (i.e. the unrestricted maximum rates) at ambient temperature. The available food was estimated as seston dry weight, as seston ash free dry weight and as seston volume (sum of the volumes of the particles in the water column). The filtration capacity and ingestion capacity varied strongly during the course of the year by more than 1:10, with maximum values during late spring and early summer. The filtration capacity was correlated with water temperature, the ingestion capacity with temperature and seston concentration. However, at identical water temperatures both capacities were higher in spring than in autumn. At the 9 m site, filtration and ingestion capacity was also significantly influenced by lack of oxygen caused by stratification during summer. In the allometric equations by which both capacities (C) were related to body weightW (C=a W ^b ), an exponent b of 0.89±0.14 (mean±95% confidence interval) was calculated for the filtration capacity and 1.00±0.18 for the ingestion capacity. Both exponents did not vary significantly during the course of the year. The seasonal trend of the incipient limiting concentration (i.e. the seston concentration at which the intestine is filled to its capacity when the animal filters at maximum rate) was less pronounced. It showed a significantly positive correlation with seston concentration and a negative correlation with temperature. Except during the spring bloom, the incipient limiting concentration was in the range of the seston volume registered at the sites. Gross growth efficiencies were highly variable. An annual average between 5 and 20% was calculated. Growth efficiencies were lower at the shallow water sites with the highest seston concentrations.     

Grazing and growth responses of a marine oligotrichous ciliate fed with two nanoplankton: does food quality matter for micrograzers?

To investigate whether predator growth and grazing would depend on prey properties besides size, we studied the numerical and functional responses of a marine oligotrichous ciliate isolated in Hong Kong coastal waters, Strobilidium sp., on two nanoplanktonic preys of similar size. The growth and ingestion rates of Strobilidium sp. could be fit with prey concentrations by hyperbolic curves. Strobilidium sp. exhibited higher maximal growth rates and gross growth efficiencies, and lower maximal clearance rates on Nannochloropsis sp. than on Isochrysis galbana. Our results demonstrate that prey properties presumably food quality can have a considerable effect on predator growth and grazing and implications on phytoplankton community structure and biogeochemical cycling.     

Predator–prey interactions between a planktonic ciliate Strombidium sp. (Ciliophora, Oligotrichida) and the dinoflagellate Pfiesteria piscicida (Dinamoebiales, Pyrrophyta)

The functional response of a planktonic ciliate, Strombidium sp. feeding on the dinoflagellate Pfiesteria piscicida non-toxic zoospores (NTZ) was experimentally studied with four different prey concentrations (43–3153 cells ml⁻¹). Data from direct observations (NTZ inside individual Strombidium sp.) was used to calculate predator–prey specific ingestion and clearance rates. The ingestion rates varied between 0.68 and 14.26 NTZ ind⁻¹ h⁻¹, and with the predator–prey specific handling time of 2.83 min the U_max was 21.18 NTZ ind⁻¹ h⁻¹. The increase in the prey concentration between approximately 700 and 3000 NTZ ml⁻¹ did not increase the uptake of prey, and at the lowest Pfiesteria NTZ concentrations the feeding efficiency of Strombidium sp. was lowered, possibly indicating a situation of threshold feeding. When data from direct observations of ingested Pfiesteria NTZ were compared with values of total NTZ loss from the experimental water during the experiment, ingestion was found to represent only a fraction of the total NTZ loss in the presence of ciliates. This discrepancy was concluded to be due to other grazer related factors than actual ciliate grazing. The control of the initial growth of Pfiesteria community, in a pre-bloom situation, would require only a small ciliate abundance (less than 5 ml⁻¹), but when the Pfiesteria NTZ are scarce, relatively more ciliates are needed to limit the population growth of the dinoflagellate community because of the apparent feeding threshold. It is concluded that the formation of non-toxic P. piscicida blooms require periods of low grazing pressure or a means to escape grazing.     

A comparative approach to study inhibition of grazing and lipid composition of a toxic and non-toxic clone of Chrysochromulina polylepis (Prymnesiophyceae)

Since the massive bloom in 1988 in the North Sea, the prymnesiophyte flagellate Chrysochromulina polylepis Manton et Parke has been known for its ichtyotoxicity. Laboratory experiments using two different clones of C. polylepis were conducted in a comparative approach. Both clones were nearly similar in size and shape, but differed in their toxicity, as demonstrated by the Artemia bioassay. In order to study the effects of toxic C. polylepis on protozooplankton grazers, grazing experiments were performed with the heterotrophic dinoflagellate Oxyrrhis marina Dujardin as grazer. A first experiment was carried out in order to follow batch culture growth and initial grazing of O. marina when fed toxic or non-toxic clones of C. polylepis. Ingestion of the toxic clone was 27% of ingestion when fed with the non-toxic clone. When O. marina was fed with the toxic clone, vacuoles within O. marina contained fewer food particles per cell and the cells attained slower division rate (58% of the division rate estimated for the non-toxic clone). A second experiment was conducted to determine the grazing and growth response of O. marina as a function of algal food concentration. Profound differences in ingestion, clearance, division and gross growth efficiency of O. marina when fed the two clones of C. polylepis again were apparent. However, even at algal concentrations of 400×10³ ml⁻¹, O. marina is not killed by the presence or by the ingestion of toxic C. polylepis, indicating that the toxin deters grazers. In addition to grazing experiments, lipid classes and fatty acids of both algal clones were analysed and compared in order to follow the hypothesis that toxicity of C. polylepis is caused by liposaccharides, lipids, or fatty acids. However, the chemical composition with respect to lipid classes and fatty acids of both clones were quite similar, making an involvement of these substances in the toxicity towards Artemia and O. marina unlikely.     

Clearance Rates of Crustacean Macrofiltrators: The Nature of in situ Rate Depressions in a Fertilized Oligotrophic Lake in the Kuokkel Area,Northern Sweden

Lake seston labelled by ¹⁴CO₂, ¹⁴C-acetate and ³²-PO₄ in parallel was used in zooplankton feeding experiments and checked for size distribution of the labelled particulates. The in situ experiments were made to find out if depressed Eudiaptomus and Holopedium clearance rates, in an artificially fertilized lake where seston was dominated by μ-algae, were due to low retention of such algae. Addition of a labelled reference alga (Chlamydomonas sp.) was used to find out if high food concentrations (above the Incipient Limiting Concentration) or toxins caused the depressions. Clearance rates mostly ranked highest for CO₂-labelled seston followed by ³²P and ¹⁴C-acetate labelled seston, reflecting approximately the size distributions of the labelled food. Clearance rates for the added reference alga were high and similar in the fertilized lake and in an oligotrophic reference lake. It was concluded that the detected “rate depression” could be explained purely by poor retention of small particles (passive size selection) by the crustaceans studied, but that active food selection offers optional explanations to the experimental results.     

Development of In Vivo Sponge Cultures: Particle Feeding by the Tropical Sponge Pseudosuberites aff. andrewsi

The rate of food particle uptake of the tropical sponge Pseudosuberites aff. andrewsi was studied in relation to particle concentrations and particle size. A range of different concentrations of either the marine microalga Dunaliella tertiolecta (∼5–8 μm) or the marine cyanobacterium Synechococcus sp. (∼1 μm) was supplied to the sponges. D. tertiolecta had a pronounced effect on the filtration activity of the sponges: at concentrations higher than approximately 4 × 10⁵ cells/cm³, the filtration rates dropped dramatically. Such a clear effect was not found for Synechococcus sp. The results further showed that the maximal amount of food (when expressed in organic carbon) that can be taken up per cubic centimeter of sponge volume per unit of time should in principle be sufficient to enable growth (irrespective of the food particle type). At the maximal food particle concentration that did not affect the filtration rates, the uptake of organic carbon is already highly in excess of the amount of organic carbon that the sponges need to cope with their respiratory demand. Based on these findings, a series of growth experiments was carried out in which the sponges were subjected to a constant concentration of different types of food particles (Synechococcus sp. and the microalgae Chlorella sorokiniana and Nannochloropsis sp). Although initial growth was sometimes observed, continuous growth at a constant rate could not be obtained. It is concluded that qualitative aspects of feeding rather than quantitative aspects are the key to successful in vivo sponge culture. Received December 20, 2000; accepted March 26, 2001     

The use of growth and ingestion rates of Capitella sp. I as the bioassay approaches to determine the sediment quality of coastal wetlands of Taiwan

Food is a limiting factor for the deposit feeders. The availability of sediment nutrients thus has a tight relationship with the growth, survival and development of the animal. There are two purposes of this study: (1) to determine if the ingestion and growth rates can be used as a bioassay approach to assess the sediment nutrients; and (2) use the combination of bioassay approaches and chemical analyses to determine which chemical parameter is the better predicator of the sediment nutrients to the animals. In the preliminary study, the optimal growth length and average ingestion rate of Capitella sp. I were obtained from the laboratory. The standardized relationships of the growth and ingestion rates in response to different nutrients were prepared. Then, the sediments collected from different coastal wetlands in Western Taiwan were used in the feeding, growth experiments and chemical analyses. The comparisons were made between the field and laboratory experiments to determine the sediment nutrients in the wetland of Taiwan. In the growth rate standardized relationship, Capitella sp. I increased its growth rate with the total organic nitrogen (TON) concentration between 0 to 2.8 mgN·g sediment⁻¹, total organic carbon (TOC) concentration between 0 and 22.4 mgC·g sediment⁻¹, and enzymatically hydrolyzable amino acid (EHAA) concentration between 0 and 4.48 mg protein·g sediment⁻¹. After the nutrient concentrations exceed these values, the growth rates decreased gradually. In the ingestion rate standardized relationship, the animal increased its ingestion rate with the total organic nitrogen (TON) concentration between 0 and 2 mgN·g sediment⁻¹, total organic carbon (TOC) concentration between 0 and 14.1 mgC·g sediment⁻¹, and EHAA concentration between 0 and 3.2 mg protein·g sediment⁻¹. After the nutrient concentrations exceed these values, the ingestion rates also decreased. To determine which nutrient parameter is the best predictor for the sediment nutrient in the field, we first analyzed whether the data obtained from the laboratory fell within 99% confidence interval of the regression obtained from the field data. Then, to determine which parameter had the shortest perpendicular distance between the field and the laboratory regression curves. Both the growth and ingestion rates comparisons showed that the EHAA is the best candidate of the sediment nutrient of deposit feeders in the field. The results of this study proved tentatively that the growth and ingestion rates of Capitella sp. I can be used as the bioassay approaches to estimate the sediment nutrients. The combination of the bioassay approaches and the relevant chemical analyses allows us to determine the bioavailability fraction of sediment to the deposit feeders.     

Grazing, Growth, and Ammonium Excretion Rates of a Heterotrophic Microflagellate Fed with Four Species of Bacteria

We studied aspects of the population growth of a microflagellate, Monas sp., isolated from Lake Kinneret, Israel. The protozoan growth rates, rates of ingestion of bacteria, and final population yields generally increased with increasing bacterial concentrations, although the exact relationship varied depending on the species of bacteria used as food. Grazing rates decreased hyperbolically with increasing food density. Gross growth efficiencies and ammonia excretion rates were similar over a range of food densities among the four species of bacteria. Population doubling times and ammonia excretion rates were lowest, and growth efficiencies were highest, at temperatures between 18 and 24°C. Under optimum conditions, the microflagellates had average population doubling times of 5.0 to 7.8 h, average growth efficiencies of 23.7 to 48.7%, and average ammonia excretion rates of 0.76 to 1.23 μmol of NH₄⁺ per mg (dry wt) per h.     

Planktonic rotifers and temperature

The influence of temperature (t) upon rotifer embryonic development rate (D_e) has been analysed using data from the literature, and the author's own results from experimental and natural populations. For Keratella cochlearis (Gosse), within the temperature range of 1–28°C, this relationship is best expressed by the equation: 1/D_e = 0.002 + 0.00025t + 0.000065t².For Brachionus calyciflorus Pallas, between 8°C and 35°C, the best relationship is given by the equation: 1/D_e = 0.005 + 0.00013t + 0.00013t².Increasing the incubation temperature to 37–40°C resulted in a decrease in development rate and a sharp reduction in life length.Analysis of the relationship between respiration rate and temperature in experimental and natural populations of Brachionus calyciflorus and Hexarthra mira (Hudson) showed that the maximum rate of oxygen consumption occurred at 32–33°C.The effects of temperature upon the ingestion rates of rotifers is greatly influenced by food concentration. Consequently, this factor also influences the secondary production of experimental populations at different temperatures.     

Observations on the existence of lower threshold and upper critical food concentrations for the copepod Acartia tons a Dana

Acartia tonsa Dana represents a genus of temperate-tropical inshore copepods which, by virtue of its high biomass and rapid generation times, may be assumed to be an important planktonic primary consumer in terms of total production world-wide; its grazing response to different food concentrations is little known. Using wide ranges of concentrations of phytoplankton cultures, we have found that A. tonsa has a maximum grazing rate of ≈ 10.0 μg chl $\text{a}\text{1}$, decreasing to zero below 1.0 μg chl $\text{a}\text{1}$. This was confirmed using the more limited range of naturally-occurring particulate material. Although grazing rate became progressively reduced above 10 μg chl $\text{a}\text{1}$, ingestion rates continued to increase over the next order of magnitude of food concentration. It appears that A. tonsa is rarely exposed to food concentrations in its natural environment (as measured by conventional techniques) high enough to stimulate the maximum grazing effort. On the other hand, it is suggested that the continued increase of ingestion rates in the laboratory at much higher concentrations may indicate an adaptive mechanism associated with the encountering of ephemeral micro-patches of such concentrations, which would permit rapid filling of an empty gut in an energy-efficient manner. Fecal pellet production was also measured and shown to be a good indicator of ingestion rate.     

Filtration and ingestion rates of Salpa fusiformis Cuvier (Tunicata : Thaliacea): Effects of size,individual weight and algal concentration

Filtration and ingestion rates of Salpa fusiformis Cuvier were determined while fed Phaeodactylumtricomutum Bohlin at concentrations of 2?64 × 10³ cells·ml^?1. Filtration and ingestion rates increase exponentially with increasing length and body protein. The relations between protein content and body length, and between filtration rate and weight are similar for blastozooids and oozooids. A capture efficiency of the order of 6–32% is calculated: Salpa fusiformis seems to have a low retention efficiency, but its very high filtration rate gives it pride of place amongst filter-feeders. Specific filtration rates are independent of weight; specific ingestion rates are independent of weight for blastozooids, but for oozooids they seem to diminish with increasing weight. The mean daily ration (μg C ingested · μg body C^?1) is 107% for a blastozooid and 117% for an oozooid. Specific filtration rates decrease exponentially as particle concentration rises, as for many other filter-feeders, and the specific ingestion rate follows an Ivlev relation.     

Results Regarding the Food of the Planktic Crustaceans Daphnia hyalina and Eudiaptomus gracilis

The graph of maximum filtering and grazing rates versus particle size shows that Daphnia hyalina is a microfiltrator and Eudiaptomus gracilis is a macrofiltrator. In contrast to Eudiaptomus gracilis, Daphnia hyalina is also able to utilize larger bacteria (c. 1 μm³) as a food source.