The filtration rate of Mytilus edulis and its dependence on algal concentration,measured by a continuous automatic recording apparatus

A new apparatus for long-term, continuous automatic measurements of filtration rates in suspension-feeding organisms is described. As the concentration of algae in the experimental medium is diminished by the filter-feeding activity of the experimental animals, algal suspension is automatically added, thus keeping the algal concentration constant. In this way, accurate determinations of filtration rates in relation to particle concentration are made possible. For determination of filtration rates in the common mussel Mytilus edulis L., individuals of different body size (shell length 8.5 to 56.5 mm) were used. Within the range of 10x10⁶ to 40x10⁶ cells of Dunaliella marina/l, mussels of the same body size filter-out approximately the same amount of algae at high or low concentrations. A low algal concentration is counterbalanced by a corresponding higher filtration rate. Within the range of body size (W=dry weight of tissues) and algal concentrations used, the filtration rate (F) follows the general allometric equation F=a·W ^b, where a and b are constants at specific experimental conditions. At a temperature of 12 °C, the values obtained for a are 2410 at a concentration of 20x10⁶, and 1313 at a concentration of 40x10⁶ Dunaliella cells/l; correspondingly, the filtration rates of a mussel of 1 g dry-tissue weight are 2410 ml/h and 1313 ml/h. b, the slope of the regression line (0.73 to 0.74), is independent of algal concentration. However, examination of all known measurements reveals that, most probably, the general allometric equation is an oversimplification; in large individuals there is a more pronounced decrease in filtration rate. The relationship between filtration rate, body size of mussels, and algal concentrations used is discussed.This work was made possible through a research grant from the Deutsche Forschungsgemeinschaft in connection with the program Litoralforschung — Abwässer in Küstennähe.     

Energy budgest,growth and filtration rates in Mytilus edulis at different algal concentrations

Growth of Mytilus edulis L. was measured in aquaria with through-flowing sea water at different levels of constant algal concentrations. The amount of food and oxygen consumed by the mussels were measured over given periods as well as the changes in dry organic weight during the same periods. From these parameters it was possible to make simple energy budgets and to compare the estimated growth with actual growth, and, further, to determine growth efficiences at different food levels. Energy budgets were made for mussels grown at algal concentrations of 0, 1.6×10³, 3.0×10³ and 26.0×10³ Phaeodactylum tricornutum cells x ml^-1. The estimated growth was found to be close to actual growth at algal concentrations above maintenance level and the net growth efficiency was found to be between 18% (3.0×10³ cells x ml^-1) and 61% (26×10³ cells x ml^-1). It has been shown that the filtration rate is independent of algal concentrations between about 1.5×10³ to 30×10³ P. tricornutum cells x ml^-1. Outside this range a decrease in filtration rate was noticed.     

Growth of juvenile Mercenaria mercenaria and the effect of resuspended bottom sediments

The influence of silt on growth of juvenile hard clams Mercenaria mercenaria (L.) (9 mm in mean shell length) was investigated in the laboratory using mixed suspensions of algae (50x10⁶ Pseudoisochrysis paradoxa cells l^-1) and fine-grained bottom sediments (0 to 44 mg l^-1). Growth rates, expressed as percent increase in ash-free dry tissue weight, were not significantly affected by sediment concentrations up to 25 mg l^-1. Significant reduction in growth (by 16% relative to controls fed only algae), and condition of clams, occurred at 44 mg silt l^-1. The results of the 3-week growth experiment agree well with predictions made in an earlier study by integrating results of shortterm physiological measurements. Growth rates obtained with experimental algal-silt diets at 21°C (2.6 to 3.3% increase in dry tissue weight d^-1) were comparable to those determined at ambient concentrations of Great South Bay particulates at 20°C (0.9 to 4.0% d^-1). Levels of particulate inorganic matter in seawater from Great South Bay, New York, exhibited pronounced daily changes, and ranged from 6 to 126 mg dry weight l^-1. Growth enhancement by the addition of silt to an algal diet, reported in mussels, surf clams and oysters, was not found in M. mercenaria. It is suggested that these three species are better suited than hard clams for culturing efforts in inshore turbid waters above uncompacted, muddy bottoms.Contribution No. 452 from the Marine Sciences Research Center, State University of New York at Stony Brook, USA     

Relationship between filtration activity and food availability in the Mediterranean mussel <Emphasis Type="Italic">Mytilus galloprovincialis</Emphasis>

The filtration activity of the Mediterranean mussel, Mytilus galloprovincialis, was assessed under different concentrations and compositions of seston by using a new automated image acquisition and analysis system. This approach allowed for frequent and simultaneous measurements of valve gape and exhalant siphon area. Filtration rates were measured through clearance measurements whereas pumping rates were measured using hot-film probes. The average filtration rate (17.5 l g h⁻¹ DW⁻¹ for a 0.36 g DW mussel) recorded during the present study was higher than those available for Mytilus edulis when standardized to flesh dry weight but almost equivalent (17.5 l h⁻¹ g DW⁻¹ for a 53 mm shell length mussel) to those rates when standardized to shell length. Immediately after the addition of algal cells (Isochrysis galbana; 4.5 μm in size), valve gape, exhalant siphon area and filtration rate increased quickly as mussels reached their maximum filtration activity. These three parameters then gradually decreased until complete closure of the shell. The algal cell concentration inducing this transition was close to 800 cells ml⁻¹ and 0.5 μg Chl a l⁻¹. When algal concentration was maintained above this threshold by successive algal additions, both valve gape and exhalant siphon area remained maximal. Temporal changes in the exhalant siphon area were continuous as opposed to those of valve gape. Therefore, despite the significant correlation between these two parameters, valves and siphon were sometimes dissociated due to a reduction of the area or even a closure of the exhalant siphon while the valves remained open. The velocity of exhaled water tended to be constant irrespective of exhalant siphon area and thus pumping rates were a linear function of exhalant siphon area. Consequently, reductions in exhalant siphon area and pumping rate were almost similar in M. galloprovincialis. Our results thus clearly support the hypothesis that exhalant siphon area constitutes a better proxy of pumping rate than valve gape as already suggested for Mytilus edulis. Finally, the high filtration rates measured during the present study together with the high concentrations of inorganic matter (> 40 mg DW l⁻¹) requested to alter those rates suggest that the studied mussels were well adapted to oligotrophic waters featuring strong hydrodynamism and frequent sediment resuspension events.     

Ingestion rate,assimilation efficiency and energy balance in Mytilus chilensis in relation to body size and different algal concentrations

Basing on a quantification of filtration, ingestion, assimilation, biodeposition, excretion and respiration rate, energy budgets were established in Mytilus chilensis Hupé in relation to body size and three different food concentrations of the unicellular green alga Dunaliella marina. The present quantifications revealed that in M. chilensis the ingestion rate only increases slightly with an increase in food concentration which, however, is counterbalanced by a significant decrease in assimilation efficiency in such a way that assimilation rate finally is nearly constant and independent of the food concentrations tested. The quantifications of these results are given by the a-values of the general allometric growth equation P=aW^b relating the energy disposable for growth and reproduction (P; cal d^-1 to body size (W; dry-tissue wt, g). The best energy budget was obtained at the lowest food concentration tested (0.8 mg algal dry wt l^-1; at 12°C and 30 S) with an a-value of 58.8, while the energy budget at the highest food concentration (2.14 mg l^-1) was only slightly lower with an a-value of 49.8; the b-values were 0.49 and 0.51, respectively. The net growth efficiencies (K₂) decreased with increasing body size (from 20 mg to 3 000 mg drytissue wt) from 76.7 to 47.9% at the lowest food level and from 72.6 to 44.0% at the highest food level tested. These relatively high net growth efficiencies seem to reflect optimal experimental conditions. Furthermore, by a comparison of estimated growth (calculated on the basis of the best energy budget) with growth actually quantified in culture raft mussels in the south of Chile during the highest production period of the year, it is obvious that the energy budgets established really reflect the conditions experienced by the mussels in their natural environment.This research was supported by grants S-80-3 and C-80-1 of the D.I.D.-UACH, by CONICYT, Found. Volkswagenwerk, Found. Fritz-Thyssen, by the GTZ, DFG and by the DAAD     

Uptake and depuration of cesium in the green mussel Perna viridis

 The accumulation and depuration of Cs in the green mussels (Perna viridis) commonly found in the subtropical and tropical waters were studied under the laboratory conditions using radiotracer techniques. Following an initial rapid sorption onto the mussel's tissues, uptake of Cs exhibited linear patterns over a short exposure time (8 h) at different ambient Cs concentrations. The concentration factor was independent of ambient Cs concentration. The calculated uptake rate and initial sorption constant of Cs were directly proportional to the ambient Cs concentration. The calculated uptake rate constant from the dissolved phase in the mussels was as low as 0.026 l g⁻¹ d⁻¹. Uptake rates of Cs in the mussels were inversely related to the ambient salinity. Uptake increased about twofold when the salinity was reduced from 33 to 15 ppt. The effect of salinity on Cs uptake was primarily due to the change in ambient K⁺ concentration. The uptake rate decreased in a power function with increasing tissue dry weight of the mussels, although the initial sorption was not related to the mussel's body size. The efflux rate constant of Cs in the mussels was 0.15 to 0.18 d⁻¹, and was the highest recorded to date among different metals in marine bivalves. The efflux rate constant also decreased in a power function with increasing tissue dry weight of mussels. A simple kinetic model predicted that the bioconcentration factor of Cs in the green mussels was 145, which was higher than measurements taken in their temperate counterparts. The bioconcentration factor also decreased in a power function with increasing tissue dry weight of mussels. Received: 27 October 1999 / Accepted: 16 June 2000     

Effect of suspended bottom material on growth and energetics in Mytilus edulis

The influence of suspended, natural silt (0 to 20 mg l^-1) in addition to unicellular algal cells (Phaeodactylum tricornutum) (o to 20.000 cells ml^-1) on clearance, growth and energetics in Mytilus edulis has been studied. Clearance increased by 32 to 43% by the addition of 5 mg silt l^-1 as compared to clearance in a pure algal suspension. Ingestion and growth rate increased with algal concentration, and growth rate was further increased by 30 to 70% by the addition of 5 mg silt l^-1. A growth rate comparable to maximum natural growth rates was reached only at the highest algal concentration in the presence of 5 mg siltl^-1. Assimilation efficiency of P. tricornutum decreased from 77% at 5,000 cells ml^-1 to 52% at 20,000 cells ml^-1. In the experiments with silt added, some 20 to 30% of the assimilated organic matter originated from the suspended bottom material. Net growth efficiency increased with growth rate at a decelerating rate, approaching a maximum of about 70%. It is concluded that suspended bottom material, which is always present in M. edulis' natural habitats, serves as an additional food source, and that M. edulis depends on suspended bottom material to exploit fully its clearance potential, and to reach the maximum growth rates observed in nature.     

Influence of algal and suspended sediment concentrations on the feeding physiology of the hard clam Mercenaria mercenaria

Short-term laboratory feeding experiments were conducted to determine the response of the hard clam Mercenaria mercenaria (L.) (32 mm in mean shell length) to increasing sediment concentrations. Clams were fed mixed suspensions of Pseudoisochrysis paradoxa (50 and 150 cells l^-1) and bottom sediments (0 to 44 mg l^-1). Algal ingestion rate deelined with increasing sediment loads. This resulted primarily from a reduction in clearance rate, which declined by 0.08 l h^-1 g^-1 (1.3%) for every 1 mg l^-1 increase in sediment load. This reduction was of similar magnitude for juvenile (13 mm) clams. At the algal concentrations tested, pseudofaeces production was intermittent and inconspicuous below about 10 mg silt l^-1. Loss of algae in pseudofaeces increased with increasing sediment loads; however, even at the highest silt and algal concentrations, clams lost a maximum of only 18% of the algae cleared from suspension. Thus, pseudofaeces production is not expected to cause significant loss of algal food at the sediment concentrations normally encountered in the natural environment ( ca 40 mg silt l^-1). Absorption rate of total organic matter remained constant, at least up to silt concentrations of 20 mg l^-1. Experiments using dual ⁵¹Cr:¹⁴C-formaldehyde-labelled sediment indicated that clams were able to counteract the dilution of algae by absorbing a considerable fraction (21 to 22%) of detrital sedimentary organics. Absorption efficiency of pure P. paradoxa ranged from 82% at 50 cells l^-1 to 58% at 150 cells l^-1. Integration of physiological rate measurements suggests that at moderate to high algal concentrations (300 g Cl^-1), growth improvement by the addition of silt, documented in mussels, surf clams and oysters, is unlikely to occur in M. mercenaria. It is suggested that a suspension-feeding bivalve's success in maximizing its energy gain in a turbid environment depends on the combination of two features: a high selection efficiency and a high rate of pseudofaeces production. It is proposed that species which regulate ingestion primarily by producing pseudofaeces are better adapted to cope with high suspended sediment loads than species such as M. mercenaria, which control ingestion mainly by reducing clearance rate.Contribution No. 451 from the Marine Sciences Research Center, State University of New York at Stony Brook, USA     

Some relationships between size,food availability and energy balance in the ribbed musselAulacomya ater

The effects of body size and suspension density on filtration rates, assimilation efficiencies and respiration rates in the ribbed musselAulacomya ater (Molina) have been determined by means of short-term laboratory experiments. Filtration rates accelerate rapidly in response to increasing algal concentration up to approximately 10×10⁶ cellsDunaliella primolecta l^-1, beyond which a plateau is approached. Percentage increments are greatest in small individuals. Assimilation efficiencies are independent of body size, but decline rapidly with increasing ration to approach zero above 32×10⁶ cells l^-1. Increases in respiration rate accompany increments in filtration rate in all but the smallest size class tested. Filtration, assimilation efficiency and respiration measurements are used to calculate ingestion rations, assimilation rations and scope for growth for mussels of different sizes over a range of algal concentrations. Scope for growth, expressed as percentage change in body energy per day, is a declining function of body size, but larger individuals achieve their maximum growth rates at lower ration levels than smaller ones. Growth efficiency is independent of body size, and is maximal at 5×10⁶ cells l^-1, where 29 to 43% of ingested ration is converted into body energy. The applicability of these experimental results to natural ecosystems is discussed.     

Lead uptake from sea water and food,and lead loss in the common mussel Mytilus edulis

Common mussels, Mytilus edulis (shell length 19 to 21 mm, average dry weight 30 mg) were maintained for 6 weeks in sea water containing different concentrations of lead (0.005 to 5 mg · l^-1). The lead concentration in the mussels' whole soft parts was analysed at different times during the experiment. A constant rate of lead uptake, linearly dependent on the lead concentration of the medium, was observed. Thus, the temporal change of the concentration factor is also linear (regression coefficient 149.9 daily). Rate of lead loss, measured after transferring the mussels into natural sea water, is linearly dependent on the original lead concentration in the soft parts. Rates of uptake and loss in large mussels (shell length 45 to 55 mm, average dry weight 750 mg) are less than those in small mussels (shell length 19 to 21 mm, average dry weight 30 mg). During a much more extended experimental period, adjustment to a steady state is expected to occur; rates of lead uptake and loss are then non-linear. Lead uptake by individual organs (kidney, gills, adductor muscle, digestive gland, foot, mantle with gonads) of large M. edulis (shell length 45 to 55 mm, average dry weight 750 mg) was analysed in 2 test series. In the test series medium, the mussels were kept in a seawater medium containing 0.01 mg. Pb.l^-1. In the test series food, the mussels were kept in natural sea water but fed with the green algae Dunaliella marina containing lead (approximately 600 g.g^-1 dry weight). The lead quantity given per mussel per day was about 2 g in both test series. Within 35 days, the mussels of test series medium took up 29% of the total amount of lead given, those of test series food took up 23.5%. In all organs, lead concentration increased, but rates of uptake differed; the kidney displayed by far the highest rate of uptake. With these physiological properties M. edulis is an ideal indicator organism for lead pollution in the marine environment. A biologic calibration curve, the relationship between lead concentration in the mussels' whole soft parts at equilibrium and lead concentration in sea water, is presented.This paper forms part of a doctoral thesis in biology at Hamburg University     

Influence of environmental factors on burrow irrigation and oxygen consumption in the mudflat invertebrate Urechis caupo

We examined burrow irrigation activity by the mudflat worm Urechis caupo in response to suspended food, ambient hypoxia (down to 3.3 kPa PO₂), hydrogen sulfide exposure (up to 100 µmol l^-1), and short-term temperature change (range 10-22°C). In normoxic, nutrient-free water at 14°C, O₂ consumption ( [(M)\dot]O₂ ) \left( {\dot M{\rm O}_2 } \right) was 45 nmol min^-1 g^-1, water flow rate ( [(V)\dot]_W ) \left( {\dot V_{\rm W} } \right) was 27 ml min^-1 (0.66 ml min^-1 g^-1), frequency of peristaltic waves (F_P) was 2.6 contractions min^-1, stroke volume (SV) was 11 ml, and O₂ extraction coefficient (EO₂) was 0.27. Adding suspended food to the burrow water occasionally elicited stereotypical feeding behavior but had no effect on any measured variables during nonfeeding periods. Hypoxia greatly decreased [(M)\dot]O₂ \dot M{\rm O}_2 (75% reduction at 3.3 kPa PO₂) but did not affect [(V)\dot]_W \dot V_{\rm W} , F_P, SV, or EO₂. Sulfide at 50 µmol l^-1 or less had no effect on burrow irrigation activity, whereas 100 µmol l^-1 sulfide decreased [(V)\dot]_W \dot V_{\rm W} by 58% and F_P by 50% but had no effect on SV. Temperature strongly affected [(V)\dot]_W \dot V_{\rm W} (Q₁₀ of 1.9 from 10°C to 22°C). We propose that U. caupo's ability to live in the hypoxic, sulfidic mud of productive mudflat environments, combined with its very efficient mucous net, allows it to process much less water for feeding than other suspension-feeding invertebrates. This, in turn, necessitates an efficient O₂ extraction mechanism, which is provided by the water lung activity of U. caupo's unique hindgut.     

Short-term effect of microencapsulated hydrocarbons on shell growth of Mytilus edulis

Two North Sea crude oils, weathered crude oil, n-alkanes, medical liquid paraffin and a fish oil were microencapsulated and added to seawater. This gave a medium containing both water soluble fractions (WSF) and oil particles, and thus simulated the conditions in natural seawater contaminated with oil. The microencapsulated oils were fed to Mytilus edulis L. in different concentrations, and the growth in terms of shell length of the mussels was measured in intervals of 24 to 48 h for 4 to 12d. With the crude oilss A and B, weathered crude oil and n-alkanes at concentrations1 mg l^-1, shell growth rate decreased rapidly compared to controls. With liquid paraffin at levels of 1 to 12 mg l^-1, a small but significant negative effect on shell growth occurred after 5 d of exposure. Exposure to fish oil at 1 and 4 mg l^-1 gave no significant reduction in growth rate. The toxicity of the different hydrocarbons was not related to their content of aromatic fractions. Crude oil B was tested at concentrations ranging from 0.12 to 12 mg l^-1. At 0.12 mg l^-1 shell growth was not significantly different from the control, while at 0.25 and 0.50 mg l^-1 a temporary and significant stimulation of growth was observed. The product concentration (C)xresponse (R) shows a linear regression on exposure time (t). The regression model CxR=75-0.18t is used to estimate EC-values (effect of a given concentration) for given response levels. The model gives a very good fit to observed data.     

Filter-feeding ethology of benthic invertebrates (ascidians). V. Influence of temperature on pumping,filtration and digestion rates and rhythms in Phallusia mamillata

The influence of temperature has been studied simultaneously on the pumping, filtration, and digestion rates of Phallusia mammillata (Cuvier, 1815). Eighteen experiments were made between 7° and 25°C on 5 individuals. The average velocities of the water current varied between 3.37 and 9.65 cm sec^-1 (maximum 34.90 cm sec^-1). No recognizable rhythm emerged; pumping was continuous except at 7°C, where it soon ceased. Above 20°C, the curves were irregular and reflected the high sensitivity of the ascidian. The pumping rate was highest at 15°C (mean=5,788 ml h^-1 g^-1 dry weight of organs). At 10°C, the mean was 3,560; at 20°C, 2,629 ml h^-1 g^-1 dry weight of organs. At 20°C, the coefficients of variation displayed higher values, indicating a more irregular pumping at this temperature. Although there was no filtration rhythm, the variability of the results was higher at 20°C and above. As for pumping, maximum values were observed at 15°C (mean=4,286 ml h^-1 g^-1 dry weight of organs) decreasing with lower and higher temperatures, such decreases being more marked at the higher temperatures. Means were 352 ml h^-1 g^-1 dry weight of organs at 7°C; 2,935 at 10°C; 1,995 at 20°C; 973 at 25°C. The mean temperature coefficients for the filtration rates were: Q₁₀ for 7° to 15°C=11.86, Q₁₀ for 10° to 20°C=0,66, Q₁₀ for 15° to 25°C=0.22. The filtering efficiency was fairly constant throughout an experiment; the pumping and filtration curves were in fact almost parallel. The filtering efficiency of the branchial sac was high (75 to 85%), with constant values at 10° and 15°C; it became smaller (59%) at 20°C, with a higher coefficient of variation. The digestion rate also displayed maximum values at 15°C (mean=5.47 mg of albumin equivalent 24 h^-1 g^-1 dry weight of organs). It was lower at 10°C (mean=3.60 mg) and reached its minimum at 20°C (mean=1.71 mg). The higher temperature affected the percentage of food utilization, which showed smaller values at 20°C (59%) than at 10°C (89%) and 15°C (87%).     

Sediment-induced reduction in the pumping rate of the tropical sponge Verongia lacunosa

The pumping rate of Verongia lacunosa (Lamarck), a tropical marine sponge, varied between 1 and 6 l h^-1 in clear seawater for sponges with a volume of about 500 ml. Sponges were exposed to seawater containing suspensions of clay maintained at a constant level for 4 h; concentrations of 11 mg l^-1 or greater significantly reduced the pumping rate, while concentrations of 3 mg l^-1 did not. Other sponges were exposed to suspensions of clay for 4 days; a concentration of 95 mg l^-1 caused a continuing decline in the pumping rate. These sponges were more sensitive to sediment than some other suspension-feeding organisms. Such sensitivity may limit the distribution of V. lacunosa and other sponge species.Please address requests for reprints to A.O. Flechsig at the address shown above.     

Application of Laser Doppler Spectroscopy (LDS) in determining swimming velocities of motile phytoplankton

Pumping rates in Mytilus edulis L. were measured by means of a constant-level-tank method, in which hydrostatic pressure differences between inhalant and exhalant water levels were recorded by means of a laser beam reflected from a tethered mirror floating on the water surface. Hydrostatic pressure gradients were determined to ±0.05 mm H₂O or better. The developed technique of directly measuring pumping rates in mussels is not subject to the artefacts of other methods. The pumping rates measured in M. edulis were substantially higher than those previously determined by means of direct techniques, but similar to the maximum filtration rates, as obtained by means of two indirect techniques, i.e. about 50 ml min^-1 for a 0.15 g dry weight mussel. Positive hydrostatic pressures drastically affected water pumping. The pumping rate decreased linearly with increasing hydrostatic pressures towards a maximum pump pressure between 3 and 5 mm H₂O. Negative pressures only affected the pumping rate slightly or insignificantly, except when the mussels were exposed to rapidly increasing negative pressures. Under this condition a shunt was presumably established between the inner demibranchs, allowing water to bypass the gills.     

Filter-feeding ethology of benthic invertebrates (ascidians). IV. Pumping rate,filtration rate,filtration efficiency

A combination of a direct and an indirect method has been used for the first time in the study of filter-feeding in benthic invertebrates. Experiments over 12 h periods under constant temperature, pH, light and feeding conditions have been carried out with 3 species of ascidians: Ciona intestinalis (Linné, 1767); Phallusia mammillata (Cuvier, 1815) and Styela plicata (Lesueur, 1823). In C. intestinalis and P. mammillata, no pumping rhythm has been found; the water flow was constant for 12 h, except for some brief accidental interruptions. In S. plicata, the particular rhythm of spontaneous periodical contractions recorded during the experiment were related to gamete emission. The speed of water flow, which was fairly constant during recording, varied considerably during the 12 h period; these variations were generally related to modifications in the diameter of the cloacal siphon. The average speeds, in cm sec^-1, lay between 5.7 and 9.5 for C. intestinalis, 5.2 and 19.4 for P. mammillata, and between 5.3 and 10.7 for S. plicata. Variations in the pumping-rate were small, oscillating around a mean value. In ml h^-1 g^-1 dry weight of organs these were 5,829 to 5,982 (mean=5,906) for C. intestinalis, 6,142 to 6,592 (mean=6,312) for P. mammillata, 1,0508 to 1,1505 (mean=1,0708) for S. plicata. Filtration was continuous without any particular rhythm; filtration rates in ml h^-1 g^-1 dry weight of organs varied between 4,244 and 4,418 (mean=4,331) for C. intestinalis, 4,620 and 4,960 (mean=4,779) for P. mammillata, 8,482 and 9,078 (mean=8,760) for S. plicata. The curves representing pumping and filtration were clearly parallel, indicating that filtration efficiency did not vary greatly during the course of an experiment; the rates obtained were 65 to 87% (mean=74%) for C. intestinalis, 66 to 88% (mean 76%) for P. mammillata, and 73 to 90% (mean=80%) for S. plicata. The slightly higher mean value in S. plicata is probably related to the higher complexity of the branchial apparatus of this species.     

Relationship between lead concentrations in seawater and in the mussel Mytilus edulis: a water-quality criterion

Regression analysis on data collected from Port Phillip Bay and Western Port, Australia in 1979 shows that there is a significant equilibrium relationship between total recoverable lead in seawater and its concentrations in the mussel Mytilus edulis (P<0.001). The concentration of lead in seawater should not exceed 1.27 g l^-1 if the mussel is not to reach a lead concentration of 2.5 mg kg^-1 wet weight, a value frequently used as a food standard for human consumption. When a lead value of 2.5 mg kg^-1 wet weight is reached, the concentration factor by mussels for lead from seawater is 1969. The critical value of 1.27 g l^-1 could be used as a marine water-quality criterion for lead in waters where mussels are harvested.     

Zooplankton responses to hypoxia: behavioral patterns and survival of three species of calanoid copepods

Seasonally recurrent and persistent hypoxic events in semi-enclosed coastal waters are characterized by bottom-water dissolved oxygen (d.o.) concentrations of < 2.0 ml l⁻¹. Shifts in the distribution patterns of zooplankters in association with these events have been documented, but the mechanisms responsible for these shifts have not been investigated. This study assessed interspecific differences in responses to hypoxia by several species of calanoid copepods common off Turkey Point, Florida, USA: Labidocera aestiva (Wheeler) (a summer/fall species), Acartia tonsa (Dana) (a ubiquitous year-round species), and Centropages hamatus (Lilljeborg) (a winter/spring species). Under conditions of moderate to severe hypoxia 24-h survival experiments were conducted for adults and nauplii of these species from August 1994 to October 1995. Experiments on adults used a flow-through system to maintain constant d.o. concentrations. Adults of A. tonsa showed no decline in survival with d.o. as low as 1.0 ml l⁻¹, sharp declines in survival at d.o. = 0.9 to 0.6 ml l⁻¹, and 100% mortality with d.o. = 0.5 ml l⁻¹. Adults of L. aestiva and C. hamatus were more sensitive to oxygen depletion: both species experienced significant decreases in survival for d.o. = 1.0 ml l⁻¹. Nauplii of L. aestiva and A. tonsa showed no significant mortality with d.o. = 1.1 to 1.5 ml␣l⁻¹ and d.o. = 0.24 to 0.5 ml l⁻¹, respectively. In addition, experiments investigating behavioral avoidance of moderate to severe hypoxia were carried out for adults of all three species. None of the three species effectively avoided either severely hypoxic (d.o. < 0.5 ml l⁻¹) or moderately hypoxic (d.o. ≈ 1.0 ml l⁻¹) bottom layers in stratified columns. These results suggest that in␣nearshore areas where development of zones of d.o. < 1.0 ml l⁻¹ may be sudden, widespread, or unpredictable, patterns of reduced copepod abundance in bottom waters may be due primarily to mortality rather than avoidance. Received: 31 August 1996 / Accepted: 24 September 1996     

Effects of pressure,temperature and oxygen on the oxygen consumption rate of the Midwater copepod Gaussia princeps

In this study we assessed the amount of lead accumulated in the body of a grazing mollusc by transfer from its algal food in laboratory experiments, and compared these results with the amounts found in naturally occurring molluscs and seaweed. Near La Jolla, California (USA), where the concentration of lead in seawater is probably less than 0.08 g l^-1, most of the naturally occurring Egregia laevigata contains less than 0.4 g Pb g^-1 wet weight. The total body masses, without shells, of juvenile Haliotis rufescens fed on this seaweed for 3 to 6 months showed similar concentrations. When, however, E. laevigata is placed for 1 to 6 days in seawater to which lead has been added (0.1 or 1.0 mg l^-1) both the seaweed and the abalone subsequently fed with it accumulate proportionally larger amounts of lead. After 6 months, young abalone fed on E. laevigata pretreated with 1.0 mg Pb l^-1 accumulated up to 21 g Pb g^-1 wet weight. This amount of lead had no apparent consequences on the growth or activity of the molluscs. Analyses of 6 different organs from adult abalone showed that the lead was selectively concentrated in the digestive gland. In the foot (muscle tissue), which is the part normally consumed by humans, only negligible amounts were found.     

Deep-sea caging of the mussel Mytilus galloprovincialis: Potential application in ecotoxicological studies

We experimented with caging the Mediterranean mussel (Mytilus galloprovincialis) at various depths for 69 d to measure basic physiological parameters, histological response and bio-accumulation of contaminants in a deep-sea contaminated area. In preliminary experiments, we demonstrated, under artificial pressure conditions, the ability of mussels Mytilus galloprovincialis to tolerate rapid immersion (at a speed of up to 120 m min^?1). In situ experiments were performed using submerged lines enabling mussels to be maintained at depths ranging of 40–1550 m with survival rates ranging from 80 to 38%, respectively. No significant differences in condition indexes were observed between treated and control specimens. However, histological observations demonstrated a clear reduction in thickness of the digestive epithelium with increasing depth exposure. By determining the contaminants in caged mussels, we found the following values for chromium accumulation: 27.4 μg g^?1 dry weight at 580 m depth and 9.8 μg g^?1 dry weight at 1550 m. Selected stations were located downstream of an industrial effluent at 420 m. The biological and environmental consequences of deep-sea contamination demonstrate the suitability of caged mussels for monitoring contaminant accumulation.