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.     

Metallothioneins and lysosomes in metal toxicity and accumulation in marine mussels: the effect of cadmium in the presence and absence of phenanthrene

It has been confirmed that metallothioneins play an important role in the accumulation of cadmium (Cd) in the digestive gland cells of mussels (Mytilus galloprovincialis Lam.). The content of Cd in the tissue of mussels exposed for 9 d to the metal (estimated dosage of 180 g Cd mussel^-1 d^-1) was 66.2 ppm. This value is about the same as the metal content found in the digestive gland of Cd-exposed mussels kept in clean water for a recovery period of 28 d. At the end of the recovery period, however, the Cd bound to thionein had increased by approximately 250%. Our data demonstrate that the stability of lysosomes, a biological parameter adopted as a cellular stress index, is extremely low in mussels exposed to Cd for 9 d, but returns to control values in the digestive gland cells of mussels allowed to recover for 28 d in uncontaminated sea water. At this point most of the Cd present in the cytosol is bound to thionein. These data demonstrate the importance of metallothionein induction in the reduction of the cytotoxic effects exerted by high levels of Cd accumulation. The results of tests designed to clarify the reasons for the long biological half-life of Cd demonstrated that, in the digestive gland of mussels, the lysosomes are not able to eliminate Cd either bound to insoluble thionein polymers or to lipid peroxidation products such as lysosomal lipofuscin, both of which are apparently involved in the elimination of copper. The absence of these two mechanisms of metal sequestration and elimination via excretion of residual bodies (tertiary lysosomes) is in agreement with the persistence of cadmium in the digestive gland of mussels. Finally, the results also demonstrate that simultaneous exposure of mussels to Cd and phenanthrene, an established lysosomal membrane destabilizer, did not significantly alter the accumulation of Cd or the kinetics of the metal in mussels.     

Uptake and cellular distribution of cadmium in Mytilus edulis

Cadmium uptake has been studied in starved and fed Mytilus edulis L. It is suggested that fairly elevated cadmium contents in fed mussels are not due to contaminated food, but to increased pumping rate when food is available. Highest concentration and main body burden are found in the mid-gut gland. Transport via haemolymph, and selective discrimination at the basement lamina of the mid-gut gland tubuli are regarded as mainly responsible for accumulation. Mercury seems to be processed in a similar way as cadmium. In the tubuli, both metals are immobilized in membrane-bound vesicles, which are finally defaecated.This work was financially supported by the German Research Council (DFG) (Sto 75/4 and Th 158/13).     

Quantitative determination of metallothionein-like proteins in mussels. Methodological approach and field evaluation

Electrochemical quantitation of metallothionin-like proteins (MLP) in mussels was based on the determination of their constituent cysteinyl residues according to Brdika's catalytic reaction. Calibration was performed by an internal MLP standard isolated from the digestive gland of Mytilus galloprovincialis for which protein concentration had been estimated by Bradford's spectrophotometric method. For that purpose three metal-binding proteins [MLP-I, MLP-II and Cu-BP (binding protein)] were separated by DEAE-Sephadex A-25 chromatography from the digestive gland of mussels previously exposed to Cd. The most negatively changed MLP-II fraction was characterized by the fact that it contained the largest amount of both total metal and sulphydryl (-SH) content per mass of protein, although this was approximately two times lower than the-SH level of commercially available MT from rabbit liver. Exposure of mussels to a relatively low level of cadmium (0.2 g Cd l^-1) added into the seawater either by itself or as a mixture with other metals (2 g Cu l^-1 and 1.6 g Pb l^-1) resulted in a measurable level of MLP induction within 14 d in comparison to the control specimens. The effect of the metal mixture on MLP synthesis appears to be less than additive, suggesting a competitive interaction between metal ions for uptake and binding sites as well as differing potentials for MLP induction. Variations in the MLP content observed in the digestive gland of mussels seasonally collected from the same location are in the range 2.1±0.4 mg g^-1 on a wet weight basis. The methodological and conceptual aspects of the application of MLP induction in the Mytilus sp. as a biomarker in seawater trace metal monitoring are critically evaluated.     

Allocation of45calcium to body components of starved and fed purple sea urchins (Strongylocentrotus purpuratus)

Several lines of evidence in the literature indicate that environmental stress such as starvation may initiate reallocation of sea urchin endoskeletal tissue. For example, Aristotle's lantern enlarges under conditions of starvation, and sea urchins tagged with tetracycline and then fed develop a distinct growth line, while starved individuals develop a diffuse pattern. We designed anin vivo system to examine stress-related changes in calcification in the purple sea urchinStrongylocentrotus purpuratus. SmallS. purpuratus (ca. 2 cm test diam) were collected from the Mission Bay jetty or Imperial Beach (San Diego, California, USA) in 1987.⁴⁵Ca was incorporated from seawater into all body fractions including the organic tissue/coelomic fluid. In an initial experiment, sea urchins were fed or starved for 4 wk and then post-incubated in isotope. Overall, starved individuals deposited new calcite more slowly than did fed individuals; however, allocation was very different and calcification of teeth of starved sea urchins was nearly as great as in fed individuals. In a second experiment,S. purpuratus were first pre-labeled with isotope and then treated by feeding or starving. More of the labeled calcium was mobilized from the soft tissues and coelomic fluid into calcite in fed than in starved individuals. Growth of the teeth in starved sea urchins was significantly greater than in those fed. We conclude that starvation changes the metabolism of calcium in order to preferentially build teeth. However, we also found no evidence that calcium was resorbed from old skeletal calcite in order to build new skeleton.     

Effects of feeding history on mobilisation and deposition of body constituents and on growth in juvenile Ambassis vachelli (Pisces: Chandidae)

Young Ambassis vachelli (Richardson) 40 to 50 d old, were used in a laboratory experiment to test the effects of starvation and subsequent re-feeding on body constituents and growth. Fish in three laboratory treatments (fed continuously; fed for 9 d and then starved for 15 d; starved for 9 d and fed for 15 d), were compared to fish from a local field population. Different body stores were mobilised at different times and rates during starvation. Carbohydrates were mobilised from the onset of starvation and were depleted after 3 d. Lipid and protein were mobilised at an increasing rate from the onset of starvation. The mortality in starved fish was relatively high (up to 70%) until re-feeding. Upon feeding, all body stores were restored rapidly in fish that were starved, with carbohydrate levels displaying an overshoot (carbohydrate level exceeding normal levels) in comparison to the levels in continuously fed fish. After 15 d of feeding, the starved fish had levels of constituents similar to those in continuously fed fish. Fish that were fed and subsequently starved were able to maintain themselves for at least 15 d prior to death, indicating a better degree of starvation resistance than fish without a history of feeding. This implies that feeding history in the early life of a fish is important in growth and survival but that young fish may have growth regimes flexible enough to survive relatively long periods of starvation.     

Bioenergetics and survival of the marine snail Thais lima during long-term oil exposure

The carnivorous snail Thais lima was fed Mytilus edulis during a 28-d exposure to the water soluble fraction (WSF) of Cook Inlet crude oil. The LC-50 of T. lima declined from >3000 ppb aromatic hydrocarbons on Day 7 to 818±118 ppb on Day 28. The LC-50 of M. edulis declined from >3 000 ppb aromatic hydrocarbons on Day 7 to 1 686±42 ppb on Day 28. Predation rate declined linearly with increasing aromatic hydrocarbon concentration up to 302 ppb; little predation occurred at 538 ppb and none at 1 160 or 1 761 ppb. Snail absorption efficiency averaged 93.5% and did not vary as a function of WSF dose. Total energy expenditure (R+U) increased at 44 ppb aromatics and declined at lethal WSF exposures. At sublethal WSF exposures, percentages of total energy expenditure were: respiration (87%), ammonia excretion (9%) and primary amine loss (4%). These percentages did not vary as a function of WSF dose or time. Oxygen:nitrogen ratios were not affected by WSF concentration or time and indicated that T. lima derived most of its energy from protein catabolism. The uptake of aromatic hydrocarbons into the soft tissues of snails and mussels was directly related to the WSF concentration. Naphthalenes accounted for 67 to 78% of the aromatic hydrocarbons in T. lima and 56 to 71% in M. edulis. The scope for growth was negative above 150 ppb WSF aromatic hydrocarbons and above 1 204 ppb soft-body aromatic hydrocarbons. These snails were physiologically stressed at an aromatic hydrocarbon concentration which was 19% of the 28-d WSF LC-50 (818±118 ppb) and/or 48% of the 28-d LC-50 of soft tissue aromatics (2 502 ppb).     

Accumulation and depuration of mercury in the American oyster Crassostrea virginica

To study the kinetics of mercury uptake in oysters, adult Crassostrea virginica (Gmelin) were held in seawater containing 10 g mercury/l (ppb) or 100 g mercury/l (ppb), added in the form of mercuric acetate, for 60 days. Mercury concentration in tissues was determined by analysis of individually homogenized oyster meats, using wet digestion and flameless absorption spectrophotometry. After 45 days, average mercury tissue concentration was 140,000 g mercury/kg tissue (ppb) and 28,000 g mercury/kg tissue (ppb) in the 100 ppb and 10 ppb experimental groups, respectively. After this time, concentrations dropped sharply, probably due to spawning. Clearance of mercury from tissue was studied by exposing treated adults to estuarine water (with no additions) for 30 days (100 ppb group) and 160 days (10 ppb group). Tissue concentrations in the 100 ppb mercury environment group declined from 115,000 to 65,000 ppb, and those of the 10 ppb group declined from 18,000 to 15,000 ppb, in 18 days; there-after, no further decline occurred in either group. Oysters accumulated mercury 1,400 times and 2,800 times above the environmental concentrations of 100 and 10 ppb mercury, respectively. Total self-purification was not achieved over a 6 month cleansing period.     

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     

Uptake and loss of radioactive cadmium by the sea-skater Halobates robustus (Heteroptera: Gerridae)

Sea-skaters, Halobates robustus Barber, caught around the Galápagos Islands, were exposed over a period of 3 days to radioactive cadmium dissolved in seawater. Although ^115mCd (metastable ¹¹⁵Cd) was accumulated by the insects, they did not concentrate it above the seawater level. The experiments clearly showed that cadmium is taken up into the body, not merely adsorbed onto surfaces. The uptake of Cd followed a biphasic time course. When sea-skaters labelled in this way were transferred back into unlabelled seawater, the rate of loss of Cd was likewise biphasic. During uptake and loss, the biological half-life times for the first compartments were almost identical (0.64 and 0.79 h), indicating that the same compartment might be involved. On the other hand, the biological half-life times for the second compartments were different (1.7 days during uptake, 19.5 days during loss), indicating that the site or chemical form of bound Cd in the sea-skater had changed. For an adult female, weighing about 8.5 mg wet weight, the drinking rate of seawater was estimated at 2.5 l day^-1, equivalent to 29% body weight.     

Effects of the polychlorinated biphenyl Aroclor® 1254 on the American oyster Crassostrea virginica

Young oysters (Crassostrea virginica) were continuously exposed to Aroclor^® 1254, a polychlorinated biphenyl (PCB), in flowing, unfiltered seawater. Growth rate (height and in-water weight) was significantly reduced (=0.05) in oysters exposed to 5 g/l (ppb) for 24 weeks. Growth rate was not affected in oysters exposed to 1 ppb for 30 weeks. Mortality was not significant in exposed and control groups. In oysters exposed to 5 ppb, greatest PCB residue (whole body) was 425 mg/kg (ppm), 85,000x the concentration in the water, and less than 0.3 ppm was retained after 28 weeks depuration in PCB-free water. In oysters exposed to 1 ppb, greatest residue was 101 ppm, 101,000x the concentration in the water, and less than 0.2 ppm was retained after 12 weeks depuration. Examination of oysters exposed to 5 ppb of this PCB for pathogenesis revealed atrophy of digestive diverticular epithelium and degeneration of vesicular connective tissues concomitant with leukocytic infiltration, but tissue recovery seemed excellent after 12 weeks depuration.Registered trademark, Monsanto Company, St. Louis, Missouri, USA. Mention of commercial products or trade names does not constitute endorsement by the Environmental Protection Agency.Contribution No. 146, Gulf Breeze Laboratory.     

Effect of feeding regime and irradiance on the photophysiology of the symbiotic sea anemone Aiptasia pulchella

To determine how the animal and algal components of the symbiotic sea anemone Aiptasia pulchella respond to changes in food availability and culture irradiance, sea anemones from a single clone were maintained at four irradiance levels (320, 185, 115, and 45 E m^-2 s^-1) and either starved or fed for 5 wk. Changes in protein biomass of sea anemones maintained under these conditions were not related to the productivity of zooxanthellae, since the protein biomass of fed A. pulchella decreased with increase in irradiance and there was no difference in protein biomass among starved sea anemones at the four irradiance levels. Except for the starved high-light sea anemones, the density of symbiotic zooxanthellae was independent of culture irradiance within both starved and fed. A. pulchella. Starved sea anemones contained over twice the density of zooxanthellae as fed sea anemones. Within both starved and fed individuals, chlorophyll per zooxanthella increased with decreasing culture irradiance while algal size remained constant (in fed sea anemones) at about 8.80 m diameter. Chlorophyll a: c ₂ ratios of zooxanthellae increased with decreasing culture irradiance in zooxanthellae from starved sea anemones but remained constant in zooxanthellae from fed sea anemones. As estimated from mitotic index data, the in situ growth rates of zooxanthellae averaged 0.007 d^-1 and did not vary with irradiance or feeding regime. Photosynthesis-irradiance (P-I) responses of fed A. pulchella indicated an increase in photosynthetic efficiency with decreasing culture irradiance. But there was no consistent pattern in photosynthetic capacity with culture irradiance. Respiration rates of fed sea anemones also did not vary in relation to culture irradiance. The parameter I _k , defined as the irradiance at which light-saturated rates of photosynthesis are first attained, was the only parameter from the P-I curves which increased linearly with increasing culture irradiance. The daily ratio of net photosynthesis to respiration for A. pulchella ranged from 1.6 to 2.8 for sea anemones maintained at the three higher irradiances, but was negative for those maintained at 45 E m^-2 s^-1. Since the final protein biomass was greatest for sea anemones maintained at the lowest irradiance, these results indicate that sea anemone growth cannot be directly related to productivity of zooxanthellae in this symbiotic association.     

Effects of feeding frequency and symbiosis with zooxanthellae on nitrogen metabolism and respiration of the coral Astrangia danae

Colonies of the temperate coral Astrangia danae occur naturally with and without zooxanthellae. Basal nitrogen excretion rates of nonsymbiotic colonies increased with increasing feeding frequency [average excretion rate was 635 ng-at N (mg-at tissue-N)^-1 h^-1]. Reduced excretion rates of symbiotic colonies were attributed to N uptake by the zooxanthellae. Nitrogen uptake rates of the zooxanthellae averaged 8 ng-at N (10⁶ cells)^-1 h^-1 in the dark and 21 ng-at N (10⁶ cells)^-1 h^-1 at 200 Ein m^-2 s^-1. At these rates the zooxanthellae could provide 54% of the daily basal N requirement of the coral if all of the recycled N was translocated. Basal respiration rates were 172 nmol O₂ cm^-2 h^-1 for starved colonies and 447 nmol O₂ cm^-2 h^-1 for colonies fed three times per week. There were no significant differences between respiration rates of symbiotic and nonsymbiotic colonies. N excretion and respiration rates of fed (symbiotic and nonsymbiotic) colonies increased greatly soon after feeding. N absorption efficiencies decreased with increasing feeding frequency. A N mass balance, constructed for hypothetical situations of nonsymbiotic and symbiotic (3×10⁶ zooxanthellae cm^-2) colonies, starved and fed 15 g-at N cm^-2wk^-1, showed that the presence of symbionts could double the N growth rate of feeding colonies, and reduce the turnover-time of starved ones, but could not provide all of the N requirements of starved colonies. Rates of secondary production, estimated from rates of photosynthesis and respiration were similar to those estimated for reef corals.     

Uptake and incorporation of mercury into mercury-binding proteins of gills of Mytilus edulis as a function of time

Individuals of Mytilus edulis (collected from Sequim Bay, Washington, in April and August, 1980) were exposed to 5 g l^-1 mercury as HgCl₂ for 28 d. Gill mercury accumulation, mercury incorporation into the soluble fraction and low molecular weight, mercury-binding proteins of gills, and induction of these mercury-binding proteins were determined as a function of time. Short-term mercury uptake rates of excised gills were also determined for mussels sampled at intervals during exposure. Gill mercury accumulation occurred in three phases, represented by net uptake phases initially (up to Day 4) and toward the end of the exposure (Days 15 to 28), and an intermediate stable phase (Days 4 to 15). The stable phase was associated with induction of the predominant mercury-binding proteins and mercury incorporation into the proteins. After Day 15, the mercury-binding proteins were saturated and spillover of mercury into high molecular weight proteins had occurred. This was associated with saturation of the soluble fraction, increases of mercury on particulate fractions, and a loss of the ability of gills to maintain stable mercury concentrations. Mercury uptake rates of gills were not affected by the 28 d exposure of the whole organism.     

Kinetics of uranium uptake by the crab Pachygrapsus laevimanus and the zebra winkle Austrocochlea constricta

The crab Pachygrapsus laevimanus and the zebra winkle Austrocochlea constricta were exposed for 40 d to uranium (1.5 to 10 mg l^-1) in continuous-flow sea water in separate starved and fed treatments, and the kinetics of uranium bioaccumulation were estimated from an exponential model. Starved and fed crabs took up U at a similar rate, which suggests that sea water was the major source of U to the crab; the fed crabs excreted U more rapidly than the starved crabs and this led to a lower net uptake of U by fed crabs. Fed and starved winkles took up U at similar rates and excreted it at similar rates, so the sea water was also the major source of U to winkles. Crabs took up more U than winkles; the concentration factors were 7 to 18 and 4, respectively. Uranium turnover was quite slow for both species (11 to 36 d) as it was also for winkle shells (6 d); this suggests that the rate-limiting processes which control turnover are biological (e.g. growth or tissue replacement) or physical (e.g. diffusion into the shell) rather than chemical (e.g. precipitation, adsorption or exchange). There was no effect of increasing U concentration in water on the U kinetic parameters.     

Microprofiles of oxygen in epiphyte communities on submerged macrophytes

Mussels (Mytilus edulis) transferred in net bags from clean to chronically mercury polluted water readily accumulated mercury during an exposure period of three months. Growth of the transplanted mussels had a diluting effect on the mercury concentration, but the absolute weight of mercury uptake increased throughout the entire period, though there was a tendency for decreased efficiency of the removal of mercury per liter of water filtered by the mussels. Mussels were also translocated from polluted to clean (laboratory) water to depurate mercury. The biological half-lives of mercury was 293 d for M. edulis from the chronically polluted area in contrast to only 53 d for mussels from a temporary massive mercury polluted area near a chemical deposit. In both cases about 75% of the total mercury in the mussels was inorganic, and it is suggested that both inorganic and organic mercury species were immobilized in mussels from the long-term mercury polluted area, whereas the immobilization capacity was exceeded in the short-term mercury exposed mussels near the chemical deposit. Very slow elimination of mercury was observed in the deposit-feeding bivalve Macoma balthica from the chronically polluted area, and about 6% of the total mercury was methyl-+phenyl-mercury. This is more than three times lower than found in M. edulis from the same collecting site. A pronounced difference in the mercury speciation (i.e., total mercury, total organic mercury, methyl-mercury and phenyl-mercury) in M. edulis from the two mercury polluted areas is thought to reflect the different character of the mercury pollution in the two areas.     

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     

The effect of chelating agents on the uptake and accumulation of cadmium by Mytilus edulis

The uptake, storage and excretion of cadmium by the common mussel Mytilus edulis (L.) has been studied at sub-lethal concentrations using the radioactive isotope ^115mCd as a marker. After an initial lag period, the uptake at low concentrations in sea water is linear with time and directly proportional to the sea water concentration, with a maximum concentration factor of 165 at 0.7 g Cd/ml sea water. A decrease occurs at higher concentrations indicating saturation of the available binding capacity. Prior complexation of the cadmium with either EDTA, humic and alginic acids or pectin doubles both the rate of accumulation and the final tissue concentrations (order: kidneyviscera>gillsmantle>muscle) and eliminates the lag period, suggesting that ionic cadmium must first be complexed before uptake can occur. A mechanism for this effect, which may involve thionein, is described. The rate of excretion of cadmium is 18 times slower than that of uptake, with the major route via the kidney but not via the byssal threads as with particulate iron. The need to detoxify and store cadmium by an immobilization mechanism is a consequence of this slower rate of elimination.     

Interactive effects of salinity,temperature and polycyclic aromatic hydrocarbons on the survival and development rate of larvae of the mud crabRhithropanopeus harrisii

Zoeae of the mud crabRhithropanopeus harrisii (Gould) were exposed continuously throughout larval development to factorial combinations of salinity, temperature and specific aromatic hydrocarbon concentrations. Salinities and temperatures were 5, 15, or 25 and 20°, 25°, or 30°C, respectively. Either phenanthrene or naphthalene was tested separately at respective concentrations of 0, 100, 150 or 200 ppb and 0, 125, 250 or 500 ppb. Phenanthrene was much more toxic than naphthalene. Naphthalene was not acutely toxic at any physical factor combination-naphthalene concentration tested. Both compounds caused the highest mortality at low salinities. The time course of mortality due to phenanthrene exposure showed that ecdysis between the first and second zoeal stage was the most sensitive period for the larvae exposed to aqueous hydrocarbons. Phenanthrene-exposed larvae had a decreased development rate, but the naphthalene-exposed larvae developed faster than the controls.     

Effect of light on the total lipid content and storage lipids of the symbiotic sea anemoneAnemonia viridis

In order to examine the effect of light level on the storage lipids of the symbiotic sea anemoneAnemonia virudis (Forskäl), anemones were exposed to three experimental light regimes of 10, 100 and 300 E m^-2s^-1. Anemones were fed once a week. After 30 d there were no significant differences in the total lipid levels between anemones at any of the light intensities. However, after 60 d lipids had increased in proportion to light level in both the animal-tissue and zooxanthellae compartments. The higher levels of total lipid were in part due to increases in storage lipid (wax esters and triglycerides). Wax ester levels increased in the animal tissues but remained constant in the zooxanthellae, whereas triglycerides increased in both compartments. In contrast to fed anemones, starved anemones which were maintained at 300 E m^-2s^-1 for 30 or 60 d did not show a statistically significant change in lipid levels at 60 d, although a slight increase in the lipid level was observed. However, there was a significant increase in the storage lipids, which suggested that the non-storage phospholipids and structural lipids had declined as a result of cellular catabolism. The composition of the wax esters and triglycerides of both fed and starved anemones was analysed and compositional changes were observed at higher light intensities.