Algal Cell Concentration Research Articles

Clearance rates in the Arctic bivalves Hiatella arctica and Mya sp.

Filtration was studied in two Arctic clams, Hiatella arctica and Mya sp., collected in Young Sound, Northeast Greenland. Clearance rates were determined as a function of ambient temperature and algal cell concentration, using the clearance method and feeding with a unicellular flagellate. For both species, clearance rates increased with increasing temperature from <−1 up to 4–8°C. At higher temperatures, filtration ceased and the clams closed their valves. Clearance rates were also determined in temperate specimens of H. arctica collected on the west coast of Sweden. For these specimens, clearance rates increased with increasing temperature from 0 to 18–20°C. When weight-specific clearance rates were compared between the two populations and between species, there were no differences at 1°C. Clearance rates in Arctic H. arctica were maximal at algal cell concentrations corresponding to 2.5–8 µg chlorophyll a l-1. Temperature compensation in Arctic bivalves is discussed and it is concluded that adaptations to constant low temperatures consist of a lower minimum temperature, for active filtration. Low clearance rates due to low temperatures did not seem to limit growth, under the prevailing conditions in Young Sound.

Zoobenthic biomass limited by phytoplankton abundance: evidence from parallel changes in two long-term data series in the Wadden Sea

We address the question of whether year-to-year variability in pelagic algal food supply can explain long-term variability in macrozoobenthic biomass in an estuarine area. Starting in the early 1970s, quantitative data were frequently collected in standardized ways in the western part of the Dutch Wadden Sea on (1) concentrations of phytoplankton species and chlorophyll (and rates of primary production) in the main tidal inlet (Marsdiep) and (2) numerical densities and biomass of macrozoobenthic animals (and growth rates in a few species) in a nearby extensive tidal-flat area (Balgzand). In both data series, the most distinctive feature was a sudden change that took place around 1980, viz. a rather sudden and persisting doubling of concentrations of chlorophyll and algal cells and of primary production rates, as well as of numerical densities and biomass of zoobenthos. From these parallel changes we hypothesise that algal food largely determines the abundance of zoobenthos in the Wadden Sea. The following observations substantiate this hypothesis: (1) the significant correlation between annual mean values of chlorophyll concentration and overall mean numerical density and biomass of zoobenthos (as estimated after an appropriate time lag), (2) the observed limitation of zoobenthic biomass doubling (after the doubling of food supply) to areas with already high biomass values (where food demand was high and food could therefore be in short supply), (3) the limitation of a strong response to changes in food supply to functional groups that are directly dependent on algal food, i.e. suspension and deposit feeders, as opposed to carnivores, (4) the significant correlation between annual growth rates in Macoma balthica and food supply in the growing season, particularly in areas close to the tidal inlet where food concentrations were monitored. Some other factors were identified that could decisively influence zoobenthic abundance locally and/or temporarily. Harsh environmental conditions will have limited zoobenthic biomass in extreme areas such as the upper part of the intertidal and areas exposed to strong currents and wave action. Severe winters temporarily reduced the abundance of several sensitive (southern) species, including most of the infaunal and epifaunal predators. Even stronger temporary and local reductions of zoobenthic biomass occurred as a consequence of fishery activities for such benthic species as cockles, mussels and lugworms. Recovery after temporary biomass reductions was generally rapid, but late-winter values of total-Balgzand zoobenthos biomass never exceeded an upper level of 45 g AFDW per m 2 probably set by maximal annual rates of primary production of between 400 and 500 g C per m 2.

Filtration rate in seven Scandinavian ascidians: implications of the morphology of the gill sac

The ascidian branchial basket is functionally responsible for pumping water through the animal. Within Ascidiacea the branchial basket and the stigmata are morphologically variable and these features are important taxonomical characters. However, the functional significance of this morphological variation has not been studied in great detail. Here, we have measured filtration rates in seven ascidians: Clavelina lepadiformis (Order Aplousobranchiata); Ciona intestinalis, Corella parallelogramma, Ascidia virginea (Order Phlebobranchiata); Boltenia echinata, Molgula manhattensis, Pyura tessellata (Order Stolidobranchiata) and compared these rates with the morphological characteristics of the branchial basket and the stigmata. Filtration rates were measured in the laboratory and determined from an exponential reduction in algal cell (Rhodomonas sp.) concentration as a function of time. The branchial baskets of the experimental ascidians were dissected free and photographs were taken of the entire basket and of the stigmata. It was found that filtration rates in the investigated ascidians are determined primarily by the area of the branchial basket and the length of the ciliary band lining the stigmatal openings, and that the form of the stigmatal opening has no impact on filtration rates.

An automatic device for in vivo absorption spectra acquisition and chlorophyll estimation in phytoplankton cultures

In order to aid the study of photoacclimation, a new programmable device is described which provides automatic on-line acquisition of in vivo cell absorption in phytoplankton cultures. The system was used for a long-term study of Rhodomonas salina grown at constant photon flux density in a nitrate-limited continuous culture with different dilution rates. Particulate absorption measured at the red chlorophyll a (Chl a) maximum was not a good proxy of biomass, because of the large variability of cellular chlorophyll induced by nitrogen limitation. However, the device is well suited to automatic assessment of Chl a and phycoerythrin (PE) concentrations in phytoplankton cultures, if algal cell size and concentration are measured in parallel to correct the packaging effect. The effects of nitrogen limitation on Chl a and PE contents and particle absorbance are discussed.

Feeding activity, retention efficiency, and effects of temperature and particle concentration on clearance rate in the marine bryozoan Electra crustulenta

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 215:133-141 (2001) - doi:10.3354/meps215133 Feeding activity, retention efficiency, and effects of temperature and particle concentration on clearance rate in the marine bryozoan Electra crustulenta Dennis Lisbjerg, Jens Kjerulf Petersen* National Environmental Research Institute, PO Box 358, Frederiksborgvej 399, 4000 Roskilde, Denmark *Corresponding author. E-mail: jkp@dmu.dk ABSTRACT: Various factors influencing clearance rate were elucidated on the bryozoan Electra crustulenta (Pallas). Measurements of clearance rates were performed using the algae Rhodomonas sp. (6 µm in diameter). Clearance rates were related to the area of the active zooids within the colonies in order to obtain area-specific clearance rates. Specific area was 42% of the total colony area. Several replicates were performed with each colony to obtain maximum clearance rate (Fmax). Fmax increased with temperature from 90 ml h-1 cm-2 at 6°C to 229 ml h-1 cm-2 at 22°C. Clearance rate decreased at increasing algal cell concentration from 1600 to 19000 cells ml-1. The decrease in clearance corresponded to a maximum ingestion rate at particle concentrations >8500 Rhodomonas sp. cells ml-1. E. crustulenta zooids are capable of retaining and ingesting particles in the range from ca 5 to ca 30 µm in diameter. Smaller particles are less efficiently retained due to the structure of the feeding apparatus, the lophophore and larger particles due to the size of the mouth (30 µm in diameter). Feeding activity was observed on single zooids and it was found that zooids have periodical retraction of the lophophore. At low particle concentrations (ca 1500 cells of Rhodomonas sp. ml-1) the lophophore is retracted 5 x h-1 for periods of 38 s. Zooidal activity measured as the time of protruded lophophore thus leads to an activity of 95% of the total time. At high algae concentrations, zooidal feeding activity decreased to 70% as the lophophore was retracted more frequently (10 x h-1) and for longer periods of time (107 s). Despite the decreased activity at high algae concentration, this could only account for 50% of the decrease in clearance rate. Thus, regulatory mechanisms of the clearance rate other than retraction of the lophophore must be considered in bryozoans. KEY WORDS: Clearance rate · Feeding activity · Filtration · Functional response · Ingestion rate · Particle spectrum · Regulation of filtration rate · Retention efficiency Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 215. Online publication date: May 31, 2001 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2001 Inter-Research.

Beat frequency of cilia in the branchial basket of the ascidian Ciona intestinalis in relation to temperature and algal cell concentration

To elucidate the effects of temperature and algal cell concentration on pumping of water in the ascidian Ciona intestinalis a number of different experiments were performed. Beat frequency of the lateral cilia in the openings of the branchial sac was measured in intact specimens using a microprojection objective and a monochrome CCD video camera. At constant low algal cell concentration, beat frequencies increased linearly with temperature from 4.0 Hz (±0.5) at 7.4 °C to 13.6 Hz (±1.6) at 20.1 °C. At a constant temperature of 15 °C, beat frequency decreased with increasing algal cell concentration from approximately 3000 to >10 000 Rhodomonas sp. cells ml−1. The decrease was observed both in experiments where the ascidians had been acclimated to a fixed algal cell concentration and in experiments with changing concentrations. Effect of algal cell concentration on squirting/siphon closure and flow velocity in the exhalent siphon was measured using a thermistor. At low algal cell concentrations, flow velocity in the exhalent siphon was stable, apart from a few short squirts. At very high algal cell concentrations, the flow velocity was reduced and much less stable, with prolonged squirting. The effect of gut content on filtration was studied in experiments with specimens acclimated to high algal cell concentrations. Results showed a close relation between gut clearance and filtration rate. From the experimental results and a qualitative analysis of the Ciona-pump it was concluded that the ciliary beat frequency is proportional to the water flow through the sea squirt and that changes in pumping caused by temperature or algal cell concentration are under nervous control or governed by enzyme kinetics, rather than being a result of physico-mechanical properties, i.e. pump efficiency versus flow resistance, of the ascidian pump.

On-line determination of respiration rates of aquatic organisms in a mono-phase oxystat at steady-state dissolved oxygen tensions

On-line determination of respiration rates at steady-state dissolved oxygen tensions was performed in a thermostatted measuring chamber equipped with a galvanic oxygen electrode. The measuring chamber is designed to completely exclude gas bubbles from the liquid phase and is named a mono-phase oxystat. Additions of oxygenated water to maintain steady-state dissolved oxygen tensions are controlled by a computer, and the respiration rate is determined from the rate of these additions. An external loop with a flow cell in a spectrophotometer makes it possible to determine and control the concentration of algal cells in the mono-phase oxystat and allowed simultaneous determination of respiration and filtration rates of filter-feeding invertebrates. Because the system maintains steady-state conditions the experiments do not suffer from time limitations. The response time of the system is negligible compared to the response time of other open systems.

Minimal scaling of the lophophore filter-pump in ectoprocts (Bryozoa) excludes physiological regulation of filtration rate to nutritional needs. Test of hypothesis

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 156:109-120 (1997) - doi:10.3354/meps156109 Minimal scaling of the lophophore filter-pump in ectoprocts (Bryozoa) excludes physiological regulation of filtration rate to nutritional needs. Test of hypothesis Hans Ulrik Riisgård1, Andrew Goldson2 1Institute of Biology, Odense University, Campusvej 55, DK-5230 Odense M, Denmark 2School of Biological Sciences, University of Wales, Bangor, Gwynedd LL57 2UW, United Kingdom None Feeding activity and growth in different ectoprocts (Electra pilosa, E. crustulenta, Celleporella hyalina) were related to naturally occurring algal concentrations in order to reveal if physiological regulation of the lophophore filter-pump to nutritional needs takes place. It was found that filter-feeding activity in E. pilosa and E. crustulenta is influenced by the concentration of algal cells in the surrounding water. When the algal concentration becomes very low (corresponding to a few hundred Rhinomonas algal cells ml-1) the clearance rate of the ectoprocts is reduced due to a gradual shutting down of the number of actively feeding zooids. The zooids are inactive during starvation periods, but feeding is quickly resumed after a new addition of algal cells. Nearly 100% of the zooids are filter-feeding within a certain range of algal concentrations, corresponding to roughly 400 to 4000 Rhinomonas reticulata cells ml-1. The maximum individual zooidal clearance rate in E. pilosa was measured to be 0.28 ml h-1 zooid-1 (18°C). Simultaneous clearance of 2 different sized algal cells in E. crustulenta showed that R. reticulata (6 um) and Tetraselmis sp. (14 um) are cleared from the water at approximately the same rate, whereas the removal of 4 um diameter Isochrysis galbana cells is approximately half this rate. The growth in colony size of C. hyalina and E. pilosa was exponential. The specific growth rate plotted as a function of algal concentration showed that the growth potential (about 10 to 12% d-1) may be fully utilized at about 4000 Rhinomonas cells ml-1, corresponding to 5 ug chlorophyll a l-1. This implies that ectoprocts in nature, as a rule, always utilize their clearance capacity and hence have no requirement for physiological regulation of the filter-pump. Filtration · Clearance rate · Regulation of filter-pump · Retention efficiency · Food satiation · Specific growth rate · Doubling time Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 156. Publication date: September 25, 1997 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1997 Inter-Research.

The influence of algal concentration and body size on filtration and ingestion rates of the clam Tapes decussatus (L.) (Mollusca: Bivalvia)

The filtration and ingestion rates of Tapes decussatus (L.) (12.5-32.5 mm in size), collected from Timsah Lake, Suez Canal, Egypt in 1993, were determined in relation to food concentration and clam dry tissue weight. Suspensions of the unicellular green alga Dunaliella marina, in concentrations ranging from 103 to 105 cells ml-1, were provided as food. The filtration rate (F, ml h-1 clam -1) and the weight-specific filtration rate (F“, ml h-1 mg-1 dry tissue weight) generally decreased with increased algal concentration following the allometric equations F= 2736.8 W-0,183 and F’= 12.6 W-0.182 The amount of water filtered free of particles by a clam of 210 mg dry tissue weight was in the ratio 1:1.4:2.3 with decreasing algal concentrations at 105, 104 and 103 cells ml-1, respectively. In contrast, the ingestion rate (I, cells h-1 clam-1) and weight-specific ingestion rate (I“, cells h-1 mg-1 dry tissue weight), generally increased with increased algal cell concentration following the allometric equations I= 0.01 W0.87 and I= 0.005 W0.88, where W is the algal cell concentration per ml. When the clams were fed on 105 cells ml-1, F and I increased with increased body size following the equations F = 7.5 W0.74 and I“= 8.89 W0.63. Otherwise, F“ and I“ decreased with increased body size following the equations F“ 7.5 W-0.25 and I“ 698.6 W-0.36, where W is the dry tissue weight in mg.

Growth and energetics in the ascidian Ciona intestinalis

Rates of growth, filtration and respiration of the ascidian Ciona intestinalis (L.) were measured in the laboratory in the presence of food (flagellate Rhodomonas sp.) concentrations ranging from 0 to 12000 cells ml-' (0 to 500 pg C I-'). Weight-specific growth rate (dry weight of body parts not including the tunic) increased sigrnoidally with increasing algal cell concentration to 7.7 % d-' Maximum specific growth rate was related to age rather than size. A condition index (C1 = DWw@Wrotal) reflected level of growth. Specdic filtration rate decreased logarithmically with increased algal cell concentration. Weight-specific respiration rate showed a relation to algal cell concentration similar to that shown by weight-specific growth rate. All rates were transformed into units of carbon, and a carbon budget was established for 2 size groups. Assimilation efficiency (AE) was approximately 50% but decreased at the highest carbon concentrations. The amount of carbon assimilated per body unit that was needed to maintain body (not including the tunic) or total (including the tunic) carbon was independent of initial size and amounted to 10 or 16 pg C mg C' d' , respectively. Gross growth efficiency (GGE) and net growth efficiency (NGE) varied with food concentration and approached a level of 0.23 or 0.78, respectively, in terms of body carbon. In terms of total carbon, GGE was found to be 0.27 to 0.28 and NGE to be 0.79. Costs of maintenance were greater in the largest ascidians, while costs of body growth were equal in the 2 size groups (0.21 to 0.23).

Relative Importance of Nutrient Availability and Food Chain for Size and Community Composition in Phytoplankton

In a field experiment, algal community structure and size distribution were assessed at different grazing pressure and nutrient supply. Our aim was to study the interactive effects of food web composition and nutrients on algal community structure. High grazing reduced algal biomass and cell numbers, but had no consistent effect on algal size, except at extremely high Daphnia abundance, which promoted large, filamentous, algal forms. At high fish predation, the grazer assemblage altered towards small, less efficient grazers (copepods, Bosmina), but no trend in algal size was recorded. In enclosures with low grazing and low nutrient supply, algal cell concentration, but not chlorophyll, was as high as in corresponding enclosures with nutrient supply, indicating the importance of food web structure. Algal size was reduced by nutrient supply, which promoted dominance by small, fast growing, algal forms.

Copper Dynamics and the Mechanism of Ecosystem Level Recovery in a Standardized Aquatic Microcosm.

The Standardized Aquatic Microcosm (SAM) was used to assess the effects and behavior of copper at the ecosystem level. The concentration of algal cells and Daphnia magna, pH, dissolved organic carbon (DOC), and dissolved and ionic copper concentration were measured for 489 d and used to explain the recovery sequence of a community of organisms. The results indicate that a resistant algal species was crucial for initiating the recovery sequence in these microcosms and that the timing of D. magna blooms was variable but highly correlated with decreasing ionic copper. In order to explain copper toxicity and the success of the recovery phase, a stepwise analysis of the functional role of the resistant algal species Oocystis pusilla, and the tolerance of D. magna was undertaken. These process studies determined that O. pusilla was a suitable food for D. magna, and that this algal species could also act as a major ligand for copper, although sorption was probably important only for a limited time during the bloom. These studies also concluded that copper bioavailability controlled toxicity because it was shown that D. magna from the microcosms exhibited no resistance to copper toxicity, even though the dissolved copper concentration was 5 times the LC50 value (concentration lethal to 50% of the population). DOC and pH, which were controlled by algal metabolism, were probably important for decreasing ionic copper, which allowed the recovery sequence to begin. Additional studies showed that the microcosm-derived DOC was able to complex copper at low pH and that DOC was highly correlated with reduced concentrations of ionic copper.

Crystallographic structure of sea ice along a salinity gradient and environmental control of microalgae in the brine cells

Duplicate ice cores were taken in southeastern Hudson Bay (Canadian Arctic), at 8 stations along a transect, from the mouth of the Great Whale River to saline waters 25 km offshore. One core from each station was cut into 10-cm sections, which were melted at room temperature for determinations of salinity, nutrients, algal pigments and taxonomic composition of the microalgal assemblages. On the second core, thin sections were cut every 2 cm to optically determine the ratio of brine/gas pockets to the total sections. Relative volumes of brine in melted samples were computed from the observed ratios and calculated values, and used to convert per unit brine volume the concentrations of pigments, nutrients and algal cells, initially measured per unit volume of melted sample. Salinity of the melted samples indicate the presence of freshwater beneath the sea ice close to shore throughout the growth season, and the vertical salinity profiles suggest intermittent intrusions of freshwater. Nutrient concentrations in the brine were high, suggesting that microalgae in the brine cells were generally not nutrient limited. Concentrations of ice algae in the brine cells reached relatively high values, that are often of the same order as those reported for eutrophic marine waters. Statistical analyses identified the rate of ice growth as the most important factor controlling the vertical and horizontal distributions of algal biomass and taxonomic composition in the sea ice, along the salinity gradient. Higher biomasses were generally associated with slower ice growth and also possibly lower grazing activity. In addition, the rate of ice growth influenced the distribution of microalgal assemblages, with nitrogen limitation potentially playing a secondary role in some instances.

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&lt;2 μm) reduced the algal ingestion rate of Daphnia ambigua by 29–87%, but fine suspended clay (&lt;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.

Explanation of Size Diversity Among Artemia Cohorts: A Model of Food Uptake Kinetics

AbstractModels describing the food uptake kinetics of a growing Artemia culture and the hatching rate of Artemia cysts are combined to yield equations capable of predicting the effects of variable algal cell concentration upon the growth rates of brine shrimp cohorts. The model illustrates that the feeding ability of the brine shrimp can be viewed as one becoming increasingly more efficient as the animals mature. This increasing efficiency in a population of variable age animals (from a single hatch) results in accelerated growth of first hatched animals relative to later hatched animals, especially at algal cell concentrations below certain threshold values. Growth rates of variable age groups of brine shrimp are mathematically manipulated to predict variable size brine shrimp at low algal cell concentration and uniformly sized brine shrimp at high algal cell concentration. This predicted result is confirmed with data from Artemia growth trials at high and low algal cell concentrations. It is suggested that similar variations in population attributes of other species may be explained as an animal‐food interaction in which minor initial variations in individual animal maturity (weight, size, etc.) are magnified as a consequence of continuous competition for a common pool of food.

Cascading trophic interactions: Uncoupling at the zooplanktonphytoplankton link

Four limnocorrals (8 m dia. by 15 m deep) located at Lake St. George, Ontario, Canada; were used to examine the interactions between planktivorous fish, crustacean zooplankton (notably Daphnia galeata mendotae), and phytoplankton. During the spring, in all of the limnocorrals, high Daphnia biomasses were correlated with increased water transparency and a spring ‘clear-water’ phase. However, as the summer progressed, the relationship between Daphnia biomass and phytoplankton abundance became more complex and less predictable. Investigation of these interactions suggested four conclusions. (1) During late July and throughout August and September, water transparency decreased and algal cell counts increased. In 3 of 4 limnocorrals, deterioration in water quality occurred 3–5 weeks before zooplankton (and Daphnia populations) declined. In all cases decreased transparency was associated with increased concentrations of algal cells (Gloeococcus) that were poor food sources for Daphnia. These results suggested that decreased water transparency was not ‘caused by’ decreases in Daphnia biomass. (2) Taken together, data from all of the limnocorrals showed no correlation between the magnitude of July Daphnia biomasses and the percentage of ‘poor food source’ algae that were observed in August. This suggested that grazer effects were not necessary for the onset of summer ‘poor food source’ algal blooms. (3) In two limnocorrals, there was a positive correlation between increased Daphnia mortality and the onset of ‘poor food source’ blooms. In the other two limnocorrals there was no correlation. In all limnocorrals there was no correlation between decreased Daphnia reproductive capacity and ‘poor food source’ blooms. These data suggested that blooms of ‘poor food source’ algae were not necessary for the collapse of Daphnia populations. (4) In all 4 limnocorrals there was a strong correlation between the time that 0+ yellow perch planktivores reached biomasses of 30–50 kg ha−1 and the collapse of Daphnia populations Species and size selection was also observed. These results suggested that for this set of limnocorral experiments, fish biomasses in the 30–50 kg ha−1 were responsible for the collapse of Daphnia populations in the summer.

The adsorption of fenvalerate to laboratory glassware and the alga Chlamydomonas reinhardii, and its effect on uptake of the pesticide by Daphnia galeata mendotae

Fenvalerate is a synthetic pyrethroid known to be lipophilic and of potential hazard to aquatic ecosystems. Several studies were conducted to measure the adsorption of [ 14C]fenvalerate to laboratory glassware and to the alga, Chlamydomonas reinhardii, and to determine the effects of absorptions on accumulation of the pesticide by Daphnia galeata mendotae. In the absence of algae, 23–33% of [ 14C]fenvalerate at concentrations of 5.170, 0.515, and 0.109 μg/l, was adsorbed to the walls of glass beakers (100 ml) over 48 h. In the presence of increasing concentrations of algal cells (100–2,000,000 cells/ml), the fraction of fenvalerate adsorbed to the cells increased from 0–93%. The amount of [ 14C]fenvalerate adsorbed to the glass at concentrations of 5,000–100,000 algal cells/ml decreased as the number of algal cells increased. This indicates that an increase in organic matter increases the number of sites for adsorption of fenvalerate thus decreasing the amount of pesticide adsorbing to the glassware. D. galeata mendotae exposed to 0.515 and 0.109 μg fenvalerate/l in the absence of algae showed an increase in pesticide accumulation with an increase in time of exposure (48 h) but not with an increase in concentration of pesticide. The concentration in the animals ranged from 1.46–2.66 μg fenvalerate/g wet weight and this may represent maximum uptake and/or equilibrium over 48 h. The presence of algae (5,000–100,000 cells/ml) did not significantly affect the accumulation of the pesticide by D. galeata mendotae and concentrations of fenvalerate in the animals ranged from 0.51–1.08 μg/g wet weight after exposure to 0.420 and 0.084 μg fenvalerate/l. Contamination of food (algae) with fenvalerate does not, therefore, contribute to an increase in bioaccumulation. However, reduced rates of filtration due to toxicity could also account for a reduced intake of fenvalerate adsorbed to algae.

Stratigraphic Evidence of Eutrophication in an Estuary

Vertical changes in chlorophyll degradation products preserved in sediments deposited in an urban estuary show a significant increase in algal productivity with the introduction of sewage effluent into the river. By comparison, algal production during intensive agriculture of the watershed, including heavy applications of fertilizers, was less by an order of magnitude where there was no sewage discharge from a point source. Concentrations of orthophosphorus correspond with concentrations of algal cells and chlorophyll in the water column and are greater by an order of magnitude where sewage is discharged into an estuary draining an urban‐agricultural watershed than where there is no sewage. The response of the estuary to short‐ and long‐term changes in the amount of sewage discharged is reflected by similar changes in chlorophyll production. However, chlorophyll production does not correspond with increases in the amount of fertilizers used in recent years over the amount used in the middle to late nineteenth century.

Growth in length of Mytilus edulis L. fed on different algal diets

Mytilus edulis L. was fed on different algal diets and the increase in shell length was measured every 12–24 h. The mussels respond within 12 h to major changes in the diet. When pre-starved mussels were fed every 24 h with monocultures of Tetraselmis suecica (Kylin) Butch, there was a pronounced lag period followed by a linear increase in shell growth rate. When both pre-starved and pre-fed mussels were fed on equal rations of T. suecica with concentrations ranging from 2.5 to 10.0 × 10 7 cells · 1 −1, the growth rate levelled off at about the same rate. Within the same range of concentrations there was a linear correlation between final growth rates and algal cell concentration. Feeding with monocultures of Isochrysis galbana (Parke) or Thalassiosira pseudonana Hasle et Heimdal (Hustedt) gave approximately the same shell growth as with Tetraselmis suecica alone, while combinations of these three algal species produced significant synergistic effects. When filtrate only from T. suecica cultures was supplied to the mussels there was a rapid initial stimulation of the shell growth. Centrifugated cells of T. suecica which were resuspended in filtered sea water, homogenized and sonicated to rupture the cells, gave 13% less growth than with untreated cells ( P < 0.05). The use of the accurate laser diffraction method for length growth measurements may greatly reduce the time and effort involved in growth experiments.

PUMPING RATES AND PARTICLE RETENTION EFFICIENCIES OF THE LARVAL LAMPREY, AN UNUSUAL SUSPENSION FEEDER

The suspension feeding larvae of lampreys (ammocoetes) inhabit fine-grained sediments where particulate organic matter is concentrated, but whose low permeability limits the rate at which ammocoetes can pump water (flow rate). This study determined: 1) flow rates through the pharynges of ammocoetes, both within and out of the sediment, and 2) the ability of ammocoetes to filter particles from suspension (retention efficiency) over a wide range of algal cell concentrations (Chlorella pyrenoidosa, 1-75 mg/l).For most suspension feeders, flow rate and retention efficiency must be measured indirectly (clearance method). Direct measurement was possible here, as ammocoetes remain apparently undisturbed in glass tubes that allow the separation of inhalent from exhalent ventilatory currents. Problems arise in attempting to use clearance methods to determine flow rates in burrowed suspension feeders, and these problems are discussed.Ammocoete flow rates are exceptionally low compared to the rates of other suspensi...