Effects of cadmium on metallothionein and histology in gills of tilapia (Oreochromis niloticus) at different salinities

The objectives of this study were to evaluate the effects of sublethal cadmium concentrations on the levels of cadmium, metallothionein (MT) and histological changes in gills of East Java strain tilapia (Oreochromis niloticus) at different salinity levels. The levels of cadmium in control gills were not significantly different at 0, 5 and 10 practical salinity unit (PSU). The cadmium concentrations in gills of cadmium-exposed fish were significantly higher at 0 PSU than at 5, 10 and 15 PSU. The MT concentrations in control gills were not significantly different at 0, 5, and 10 PSU. The MT concentrations of cadmium-exposed fish were significantly higher than those in respective control groups at 0, 5 and 10 PSU. Significant gill damage occurred in fish exposed to cadmium at lower salinity. The epithelial lifting was noted at gills of fish exposed to 2.5 mg/L of cadmium at 0 PSU, and telangiectasis was observed at gills exposed to 5 mg/L of cadmium at 0 PSU. The level of gill damage decreased with increasing salinity of media. The increased MT and histological changes in gills of our findings could be a protective response of animals to toxic effect of cadmium.     

Effect of Cd on accumulation and loss of 210Po in the mussel Mytilus edulis

As a result of ²¹⁰Po's previously identified association with sulphur-rich proteins, metallothioneins could have a significant effect on the behaviour and fate of ²¹⁰Po in molluscs. Starved control and cadmium-exposed mussels, Mytilus edulis, were fed ²¹⁰Po-labelled algae (Isochrysis galbana) for 5 d and then allowed to depurate in clean sea water. Cadmium-exposed M. edulis accumulated less ²¹⁰Po in the digestive gland and the remainder of the tissue than control mussels, although this was due to a decrease in tissue weight. More than 40% of ²¹⁰Po was identified as being associated with high molecular weight and heat-treated cytosol proteins in M. edulis. Mussels in a starved state are known to recycle as much as 90% of their amino acids. It is proposed that ²¹⁰Po associated with these and other proteins is recycled, explaining why no significant loss of ²¹⁰Po was observed from the remainder of the tissue in either control or Cd-exposed mussels. Cadmium-induced metallothioneins had no effect on the distribution of ²¹⁰Po in M. edulis; <5% associated with the cytosolic fraction was considered to principally contain metallothioneins. It is suggested that ²¹⁰Po's apparent relationship with metallothioneins is coincidental rather than connected with its role in the regulation of metals. Received: 30 March 1998 / Accepted: 3 August 1998     

Trends in sediment metal concentrations in the River Avoca, South-East Ireland

Variation in sediment metal concentrations in the River Avoca, which is severely polluted by acid mine drainage (AMD) discharged from the abandoned sulphur and copper mines in Avoca, is reported. A survey of surface and subsurface sediments was repeated after seven years during exceptionally low flow conditions in 2001. The present study found that the reference (up-stream) site used in the original 1994 study was itself impacted by AMD, showing sediment metal enrichment by AMD to be greater than originally thought. The new reference site contained elevated Pb (570 µg g^–1) in the subsurface sediment due to abandoned Pb-Zn mines 25 km further upstream. Concentrations of Cu (43 µg g^–1), Zn (349 µg g^–1) and Fe (4.0%) were normal for uncontaminated rivers. All the downstream sites showed sediment metal enrichment arising from the AMD (Cu and Zn p < 0.001; Fe p < 0.01). Subsurface concentrations of metals immediately below the mixing zone were Cu 904 µg g–1 (sd 335), Zn 723 µg g–1 (sd 93), Fe 6.3% (sd 1.5) and Pb 463 µg g^–1 (sd 279). Monthly variation in metal concentrations at sites was not significantly different (p > 0.05). Although surface sediment metal concentrations were more variable, they followed similar trends to subsurface sediment. There were no significant differences in the subsurface sediment concentrations for either Cu or Zn over the period 1994 and 2001 immediately below the mines, although at the lowest site Zn had decreased by 35% over the period (p < 0.01). However there was a significant (p < 0.01) decrease over the period in the Fe concentration at all the impacted sites. This corresponds to a reduction in Fe concentration in the AMD and indicates that some remediation has occurred in the river since 1994.     

Interactive accumulation of mercury and selenium in the sea starAsterias rubens

Interactions between mercury and selenium accumulation and subcellular binding inAsterias rubens (L.), collected in 1987 from Lille Bælt at Middelfart, Funen, Denmark, were investigated in laboratory experiments. Sea stars exposed to 10µg Hg l^–1 for 30 d accumulated mercury in body wall, tube feet and stomach linearly with time at 1.2, 1.2 and 0.5µg Hg g^–1 dry wt d^–1, respectively. Mercury was accumulated in pyloric caeca and coelomic fluid initially at 1.4µg Hg g^–1 dry wt d^–1 and 9.4 ng Hg ml^–1 d^–1, respectively; after 10 d uptake rates decreased. Sea stars exposed to 75µg Se-SeO ₃ ^{- -} l^–1 accumulated selenium linearly with time over 30 d in the stomach, pyloric caeca, tube feet and body wall at 2.0, 1.2, 1.2 and 0.6µg Se g^–1 dry wt d^–1. Sea stars exposed to 75µg Se-SeO ₄ ^{- -} l^–1 maintained selenium levels in the coelomic fluid at 75µg Se l^–1 over 30 d. Exposure to selenate did not alter the selenium concentrations in the tissues. Sea stars exposed concurrently to 75µg Se-SeO ₃ ^{- -} and 10µg Hg l^–1 accumulated more mercury and selenium in tube feet and body wall than did sea stars exposed to the two elements alone. In pyloric caeca and stomach concurrent exposure reduced accumulation of both elements. Mercury was bound predominantly in the insoluble fraction of the tissues, and soluble mercury was bound in proteins of high (> 70 kilodaltons) or very low (< 6000 daltons) molecular weight. Ca. half of the selenium recovered was bound in the insoluble fraction, and soluble selenium was bound in proteins of high (> 70 kilodaltons) or very low (< 6000 daltons) molecular weight. Interaction between the two elements was exerted predominantly in the insoluble fraction of the tissues.     

Accumulation of cadmium and bioenergetics in the mussel Mytilus edulis

Accumulation rates of cadmium, the amount of food ingested and assimilated, the amount of oxygen consumed and changes in dry flesh weight have been measured in Mytilus edulis L. exposed to 0, 10 and 100 ppb cadmium for 17 d in aquaria with seawater flowing continously and at constant algal concentration. The accumulation rates were linear at 10 and 100 ppb, amounting to 0.58 and 8.89 ppm d^-1, respectively. Body loads up to 150 ppm caused no effects on either clearance, ingestion, assimilation, respiration, or growth. High net growth efficiencies between 55–59% were obtained, indicating near optimal experimental conditions. It is suggested that the setup and experimental procedure provide an excellent tool in the study of accumulation and sublethal effects of environmental pollutants in suspension feeding bivalves.     

Relationship between cadmium concentrations in seawater and those in the mussel Mytilus edulis

Various forms of regression analysis are presented which show that there is a significant equilibrium relationship between total recoverable cadmium in seawater and its concentration in the mussel Mytilus edulis (P<0.001). The calculations show that the concentration of cadmium in seawater should not exceed 0.20 g l^-1 if the mussel is not to reach a cadmium concentration of 2 mg kg^-1 wet weight: a value frequently used as a food standard for human consumption. Further, when a cadmium value of 2 mg kg^-1 wet weight is reached, the concentration factor by mussels for cadmium from seawater is 9 950.     

Influence of sex and age on the feeding habits of the common soleSolea solea

The lethal concentration of cadmium was determined for the mysidLeptomysis lingvura G.O. Sars, a Mediterranean species from surface coastal waters, and the effect of sublethal doses on respiration, ammonia excretion, and feeding efficiency at different temperatures, and on activities of 19 hydrolases was tested. Experiments were carried out on individuals collected in spring 1987 near Marseille. At 18°C, respiration rate was significantly affected only by concentrations >0.05 mg Cd l^–1. At 0.1 mg Cd l^–1, respiration rate was more significantly depressed at 20°C than at 10°C. There was a concomitant decrease in the Q₁₀ rate (by 23 to 59%, according to the particular experiment), indicating a strong synergistic effect of temperature. Ammonia excretion was likewise affected by cadmium, also with a concomitant decrease in the Q₁₀ rate (by 34%). Daily faecal pellet production was maximum at 18°C; it was inhibited by cadmium at temperatures between 14 and 20°C, and enhanced at extreme temperatures (10 and 22°C). The assimilation efficiency of contaminated individuals was reduced by 9%. These decreases in faecal pellet production and assimilation efficiency reflect a significant decrease in energy (by about 43%) which could rapidly lead to an unbalanced energy budget with a consecutive lowering of the reproductive potential. Generally, hydrolase activities usually increased initially in the presence of 0.2 mg Cd l^–1, but after 48 h they declined, reaching very low values at 72 h. Most physiological processes are therefore affected by exposure to cadmium and the unbalanced energy budget arises from the inability to utilize environmental food. These results are consistent with the literature data on cadmium contamination in marine organisms. Physiological and biochemical changes appear to be very informative in studies of in vitro sublethal effects of micropollutants and in situ environmental modifications.     

Effect of the neurotransmitters dopamine,serotonin and norepinephrine on the ciliary activity of mussel (Mytilus edulis) larvae

The acute and long-term effects of neurotransmitters dopamine (DA), serotonin (SE) and norepinephrine (NE) on the feeding rates of Mytilus edulis veliger larvae were investigated through concentration-response curves. Increasing DA concentrations increasingly inhibited food uptake. Acute exposure to high levels of DA caused long-term inhibitory effects on feeding rates (10^–5 MDA) and growth rates (3x10^–4 MDA). Feeding activity was also inversely related to NE concentration. SE concentrations between 10^–8–3x10^–7 M supported enhanced feeding rates. Neither NE nor SE showed long-term inhibitory effects on feeding at concentrations <10^–4 M. These results were consistent with the observed effects of the different neurotransmitters on the swimming pattern of the larvae. The experimental evidence supports the model of ciliary control in adult mussels, involving dual innervation of the ciliated cells of the velum, with excitatory serotonergic and inhibitory dopaminergic fibers.     

Isolation of novel metal-binding proteins distinct from metallothionein from spotted seatrout (Cynoscion nebulosus) and Atlantic croaker (Micropogonias undulatus) ovaries

Metal-binding proteins were isolated from ovaries of the spotted seatroutCynoscion nebulosus and the Atlantic croakerMicropogonias undulatus collected in 1988 near Port Aransas, Texas, USA. Gel-filtration analysis of spotted seatrout trout ovarian cytosolic fraction on Sephadex G-75 revealed the presence of three zincbinding protein fractions. A major zinc/calcium-binding protein fraction had a low molecular weight (M _r)(6 000 to 10 000), similar to mammalian hepatic metallothionein (MT). All the metals were displaced from this fraction following saturation with exogenous cadmium. After exposure of Atlantic croaker to 2 mg cadmium l^–1 seawater for 2 mo, the majority of the cadmium in the ovarian cytosolic fraction was associated with a similar low molecular weight protein fraction. These proteins were further purified by heat treatment and sequential acetone precipitation. Three isoforms were isolated by reversephase high-performance liquid chromatography. All the isoforms were found to be distinct from mammalian MT, based on amino acid composition. The major isoform contained low amounts of cysteine (approximately 5 residues per molecule) and aromatic amino acids, compared to high amounts of cysteine (typically 17 to 20 residues/molecule) and a lack of aromatic amino acids for mammalian MT. All the ovarian protein isoforms contained more glutamate than mammalian MT. The spotted seatrout and Atlantic croaker ovarian isoforms showed a high degree of homology with metal-binding proteins isolated from mammalian gonadal tissues. The results suggest a physiological role for these metal-binding proteins in developing vertebrate ovaries as well as an involvement in the sequestration of cadmium following environmental exposure.     

Shell growth response of mussels (Mytilus edulis) exposed to toxic microalgae

Mussels (Mytilus edulis) were exposed to the algaeAlexandrium ostenfeldii, Chrysochromulina polylepis, Gyrodinium aureolum, Gymnodinium galatheanum andHeterosigma akashiwo for 24 h; significant reductions in growth rate, as compared to the control, were observed after exposure toA. ostenfeldii, C. polylepis, G. aureolum andG. galatheanum at initial concentrations of 4.5 × 10⁶, 110 × 10⁶, 9 × 10⁶ and 120 × 10⁶ cells l^–1, respectively. Exposure to high initial concentrations of the non-toxic algaeTetraselmis suecica (174 × 10⁶ cells l^–1) andIsochrysis galbana (610 × 10⁶ cells l^–1) showed no adverse effect on growth rate. When mussels with reduced growth were transferred to clean seawater, they recovered to > 90% of control growth within 2 to 4 d. Exposure to algal filtrates of the toxic algal cultures produced no reduction in growth rate.     

Growth and herbivory by heterotrophic dinoflagellates in the Southern Ocean,studied by microcosm experiments

Growth and herbivory of heterotrophic dinoflagellates (Gymnodinium sp.) from the Weddell Sea and the Weddell/Scotia Confluence were studied in 1988 in 100-liter microcosms. The microcosms were screened through 200-µm or 20-µm mesh nets and incubated for 12 d at 1 °C under artificial light. Mean cell volume of dinoflagellates was 1 000 to 1 500µm³, and that of their phytoplankton prey 360 to 430µm³. Dinoflagellate growth rate followed a Holling type II functional response, with a maximum growth rate of 0.3 d^–1 and half-saturation food concentrations of 1.0µg chlorophylla l^–1, 50µg C l^–1, or 1 500 cells ml^–1. Carbon budgets based on¹⁴CO₂ assimilation and biomasses of phytoplankton and heterotrophic dinoflagellates suggested a balance between phytoplankton grazing loss and dinoflagellate consumption, assuming a dinoflagellate carbon conversion efficiency of 40%. Applying this to the functional response yielded estimates of maximum ingestion rate (0.8µg Cµg^–1 C d^–1, or 6 pg C dinoflagellate^–1 h^–1) and maximum clearance (0.8 to 1.2 × 10⁵ body volumes h^–1, or 80 to 120 nl ind.^–1 h^–1). The microcosm experiments suggested that heterotrophic dinoflagellates may contribute significantly to maintenance of low phytoplankton biomass in the Southern Ocean.     

Environmental Se-Mo-B deficiency and its possible effects on crops and Keshan-Beck disease (KBD) in the Chousang area,Yao County,Shaanxi Province,China

Causes of Keshan–Beck disease (KBD) are still being probed and monitored in China. Relationships between trace elements from eco-environmental systems and KBD are poorly understood although relationships between environmental Se and human health have received extensive attention. In order to investigate relationships between eco-environmental geochemistry and KBD, we selected the Chousang KBD area in Yao County, Shaanxi Province, China, as an example of a prevailing KBD area applying I–Se-rich salts instead of utilizing Se-rich fertilisers on food crops to prevent local residents from developing KBD before 1995. Environmentally geochemical samples (rocks, soils, plants and children's hair) were collected from the Chousang KBD area. Soils in the study area contain 0.11±0.02 µg Se g^–1, 0.75±0.11 µg Mo g^–1, and 34.5±1.5 µg B g^–1 on average, indicating that the study area is a deficient-Se–Mo–B area. Se (0.07±0.007 µg g^–1), Mo (0.35±0.09 µg g^–1) and B (3±0 µg g^–1) contents are low in wheat and corn used as a daily main food staple of local inhabitants. It is indicated that the study area is deficient in environmental Se–Mo–B for the local residents. Se contents of children's hair from the Yangyuan Elementary School in the study area range from 0.09 to 0.26 µg Se g^–1 with an average of 0.165±0.05 µg Se g^–1 (n=10) in this KBD endemic area. Due to the low levels of Se, Mo and B available in soils and rocks, crops including wheat and corn are deficient in these elements, accordingly, the deficiency of Se, Mo and B in this area may be linked to the daily consumption of wheat and corn deficient in Se, Mo and B. Therefore, local inhabitants should be encouraged to fertilise mixtures of Se, Mo and B on crop plants in order to avoid development of KBD and guarantee a good harvest of crops.     

Lead and cadmium in urban allotment and garden soils and vegetables in the United Kingdom

In order to assess the intake of lead and cadmium by consumers of home grown vegetables in urban areas, replicated experimental plots of uniform size, comprising summer and winter crops, were established in 94 gardens and allotments in nine towns and cities in England.The geometric mean lead and cadmium concentrations for the soils (n = 94) were 217 g g^–1 (ranging from 27 to 1,676 g g^–1) and 0.53 g g^–1 (<0.2–5.9 g g^–1), respectively. Compared with agricultural soils, the garden and allotment soils contained elevated levels of lead but not cadmium.Lead concentrations in the vegetables ranged from <0.25 g g^–1 to 16.7 g g^–1 dry weight and cadmium concentrations ranged from <0.025 g g^–1 to 10.4 g g^–1 dry weight. Lead concentrations were higher than reported background levels, although <1% exceeded the statutory limit for saleable food in the UK (1 g g^–1 fresh weight). Cadmium concentrations were generally similar to background levels.     

Growth and size structure in a baltic Mytilus edulis population

Since Mytilus edulis L. has very few predators and competitors for space, it has become a biomass dominant in the Baltic proper covering hard substrates from the water surface to more than 30 m depth. In order to investigate the factors controlling size and production in a Baltic M. edulis population, growth was studied by the analysis of annual growth rings, measurements of caged individuals and the analysis of size classes in the population, and on settlement ropes. The total number of mussels in a representative mussel bed at 4 m depth varied between 36 000 and 158 000 ind · m^-2 during the year, mainly due to variations in very small mussels (<2 mm), whereas the abundance of mussels 2mm was rather constant between about 17 000 and 28 000 ind · m^-2. Maximum numbes of mussels < 2 mm, amounting to 132 000 ind · m^-2, were found after settlement in summer, but still half a year later in spring, 65 000 ind · m^-2 < 2 mm were registered, due to very strong intraspecific competition for food and space leading to the competitive suppression of small individuals and large variations in growth rates. Due to the special size-structure of the population only the analysis of annual growth rings could be used to estimate natural shell growth. From being very low in the smallest mussels, growth was linear between about 2–10 yr of age, corresponding to about 3–20 mm length, after which it decreased with a L=32 mm. Over the linear interval, growth in the populations from 3–6 m and 10–15m depth was 3.1 and 2.2 mm · yr^-1, respectively. Meat growth showed strong annual variations mainly due to gonad production. Starving mussels could, however, while utilizing energy reserves, survive losses of up to 78% of their meat biomass. This ability of M. edulis to respire away its own biomass and its apparent tolerance of weight loss has important implication. It will drastically reduce the energy flow to destruents from mussels dying naturally, which is of special significance in the Baltic, where predators and scavengers are scarce. It enables the mussels to endure bad food conditions and buffer strong seasonal variations in food abundance, maintaining the strongly food-and space-limited Baltic M. edulis population at the carrying capacity of the area.     

Cadmium kinetics in oysters — a comparative study of Crassostrea gigas and Ostrea edulis

The accumulation of cadmium was investigated in two species of oysters [Crassostrea gigas (L.) and Ostrea edulis (L.)] from the same environment and in oysters of the same species (O. edulis) from two different environments (contaminated and uncontaminated), under controlled laboratory conditions (33‰ salinity, 10°C, 100 μg Cd l^-1) for up to 111 d in 1982. C. gigas accumulated cadmium twice as fast as O. edulis (1.07 vs 0.52 μg Cd g^-1 wet wt d^-1). Furthermore, O. edulis from an uncontaminated environment accumulated cadmium faster than O. edulis from a metal-contaminated environment (0.52 vs 0.34 μg Cd g^-1 wet wt d^-1). There was no effect of cadmium exposure on total soft-tissue copper and zinc concentrations. Investigation of cytosolic metal-binding using Sephadex G-75 gel-permeation chromatography indicated that binding to very low molecular weight ligands (MW<1000) accounted for>70% of the cytosolic zinc in all oysters and>40% of the cytosolic cadmium in all oysters except O. edulis from Conwy at 83 d. In copper-contaminated oysters, excess copper was also associated with very low molecular weight ligands. Intermediate molecular weight cadmium/copper-binding proteins (similar to metallothionein in molecular weight) were observed in the cytosol and were shown to differ between species in terms of their behavior on Sephadex G-75. Finally, the distribution of accumulated cytosolic cadmium in O. edulis from the contaminated environment was shown to have a unique distribution, i.e., there was no cadmium associated with high molecular weight cytosolic macromolecules. The data indicate that both genetic and environmental factors influence cadmium accumulation in oysters.     

Primary production of phytoplankton at a frontal zone located at the northern slope of the Dogger Bank (North Sea)

In July 1988 a survey was made in the Dogger Bank area of the North Sea. As a result of wind stress the area was found to be frequently well mixed. At the northerly slope a transition zone was observed between the stratified central North Sea and the well-mixed Dogger Bank area. Low nutrient concentrations were observed in surface waters; especially for nitrate (<0,1µM). High concentrations of phosphate (>0,5µM), nitrate (>1µM), ammonium (>2µM) and silicate (>2µM) only prevailed below the thermocline. Chlorophylla values were below 1µg l^–1 near the surface. Enhanced values (up to 4µg l^–1) were observed in the deeper layer at the transition zone and just below the thermocline at well-stratified locations. At the transition zone high specific C-fixation rates (up to 100 mg C mg^–1 chla d^–1) at the surface indicated the presence of enhanced productivity. The compensation depth for primary production was found to coincide with a specific C-fixation rate of 5 mg C mg^–1 chla d^–1. At greater depths, phytoplankton was only found where tidally induced vertical mixing allowed a regular exposure to higher light intensities. Storms resulted in a rapid redistribution of chlorophylla and enhancement of the C-fixation rate in the upper layer of the water column.Publication No. 10 of the project Applied Scientific Research Netherlands Institute for Sea Research (BEWON)     

Formation of metallothioneins in relation to accumulation of cadmium in the common mussel Mytilus edulis

Accumulation rates of Cd have been studied in the common mussel Mytilus edulis L. under different laboratory conditions. Semi-static and through-flow experiments were carried out at Cd concentrations of 200 ppb and 50/100 ppb in the water, respectively. A linear uptake of Cd throughout the experimental periods of 36 or 124 d was found in all experiments. The accumulation rate was 3.10 ppm d^-1 at 50 ppb in the through-flow water experiment, 4.1 ppm d^-1 in starved and 6.6 ppm d^-1 in fed mussels in the semi-static experiments with 200 ppb Cd in the water. The Cd-accumulation rate in various fractions of soft parts decreased in the order: body>mantle>muscles. Elution patterns obtained from gel-filtrations showed an increasing amount of Cd-binding proteins (metallothioneins) when the body burden of Cd increased. The Cd content in the body fraction of mussels transferred to clean water for 42 d after first being exposed to Cd during 124 d decreased from 564 ppm on a dry weight basis to 417 ppm while the fraction of Cd bound to metallothioneins rose from 22 to 78% during the same period.     

An improved automatic recording apparatus for determining the filtration rate of Mytilus edulis as a function of size and algal concentration

An automatic recording apparatus for measuring the filtration rate in suspension-feeding bivalves is described. The concentration of algae in the experimental medium is kept constant throughout each experiment by addition of Phaeodactylum tricornutum from a chemostat. Within the range of body size 5.7 to 283 mg (W=dry weight of tissues), the filtration rate (F=ml min^-1) at 15°C in Mytilus edulis L. follows the allometric equation F=0.85 W ^0.72. Within the concentrations 0.18 to 0.70 mg algal dry weight l^-1, the filtration rate in mussels of 132 mg dry flesh weight ranges from 33.1 to 41.0 ml min^-1. At 0.18 mg algal dry weight l^-1 the mussels filter continuously for 20 h, with a high constant rate that presumably represents the water transport capacity under optimal laboratory conditions.     

Respiration rate and cost of swimming for Antarctic krill,<Emphasis Type="Italic"> Euphausia superba</Emphasis>, in large groups in the laboratory

Constructing realistic energy budgets for Antarctic krill, Euphausia superba, is hampered by the lack of data on the metabolic costs associated with swimming. In this study respiration rates and pleopod beating rates were measured at six current speeds. Pleopod beating rates increased linearly with current speed, reaching a maximum of 6 beats s^–1 at 17 cm s^–1. There was a concomitant linear increase in respiration rate, from 1.8 mg O₂ g_D^–1 h^–1 at 3 cm s^–1 to 8.0 mg O₂ g_D^–1 h^–1 at 17 cm s^–1. The size of the group tested (50, 100 and 300 krill) did not have a significant effect on pleopod beating rates or oxygen consumption (ANCOVA, F=0.264; P>0.05). The cost of transport reached a maximum of 75 J g^–1 km^–1 at 5 cm s^–1, and then decreased with increasing current speed to 29 J g^–1 km^–1. When considered in light of energy budgets for E. superba, these data indicate that the cost of swimming could account for up to 73% of total daily metabolic expenditure during early summer.Communicated by G.F. Humphrey, Sydney     

Acute toxicities of eleven metals to early life-history stages of the yellow crab Cancer anthonyi

We report findings from the first laboratory experiments to assess toxicities of metals found in drilling muds to embryos and prezoeae of a brachyuran crab. Embryos of Cancer anthonyi are brooded externally on the abdomen of female crabs; thus, embryos may be continuously exposed to pollutants contained in sediments of contaminated benthic habitats. Lethal concentrations of metals to embryos after 7 d exposures were: iron and barium (sulfate), 1 000 mg l^–1; barium (chloride), 100 mg l^–1; aluminum and nickel, 10 mg l^–1; copper and lead, l mg l^–1; cadmium, chromium VI and manganese, 0.01 mg l^–1; mercury, 0.001 mg l^–1. All metals effectively retarded embryos from hatching at concentrations equal or lower to those causing mortality, except for cadmium. Particularly impressive was iron, which suppressed hatching at l to 10 mg l^–1, concentrations previously found non-deleterious to marine organisms and 100 times more dilute than concentrations causing significant embryo mortality. The effects of metals on embryos increased as a function of exposure duration. Embryo mortality was delayed for at least 120 h at concentrations 1.0 mg l^–1, with the exception of mercury. Lethal concentrations established at 96 h were meaningless for crab embryos, because acute toxic thresholds were not attained by that time. Larval survivorship to chromium VI, copper, and zinc increased following exposure of embryos to these metals at low concentrations (1.0 mg l^–1), suggesting induction of biochemical pathways for products which bind or metabolize metals. Identical exposures of embryos to lead failed to enhance subsequent larval survivorship, showing that inductions may be metal-specific. We suggest that exposures of brachyuran embryos at field sites and the success of their subsequent hatching in the laboratory may be a means of assessing environmental contamination otherwise difficult to monitor.