Biochemical evaluation of naphthalene intoxication in the tropical acrid blood clam Anadara granosa

Exposure of the tropical arcid blood clam Anadara granosa L., collected from Bombay waters in 1986, to sublethal concentrations of naphthalene (Nap) (5, 10 and 15g Nap ml^-1), induced various changes in vital biochemical systems. The condition index (CI) remained largely within the control range, although tissue water content after 96h exposure increased significantly (p<0.001). Glycogen levels appreciably decreased, both in muscles (p<0.001) and digestive glands (p<0.01). AMP activity remained unaltered irrespective of the ambient Nap concentration. ADP levels decreased by more than 20% and ATP levels also decreased significantly (p0.001) by more than 60% with increases in ambient Nap levels from 5 to 15 g ml^-1. Lysosomal marker enzymes-arylsulphatase and acid phosphatase-showed various changes. Levels of the former were 10 to 17 times higher than the latter. Total and free arylsulphatase activity in hepatic cells decreased on exposure of clams to 5 and 10g Nap ml^-1, but not significantly. However, it was significantly inhibited (p<0.001) towards the upper limits of exposure concentration. The same was also true of acid phosphatase activity. Nicotinamide adenine dinucleotide (NADH₂) oxidation of lipochrome showed a dramatic decrease in activity in the range of 37 to 88% over controls with increasing Nap from 5 to 15 g ml^-1. Fatty acids also exhibited significant changes in composition with a decrease in polyunsaturated acids and an increase in certain saturated fatty acids. Protein and carbohydrate levels increased significantly (p<0.001) towards upper limits of exposure concentration. Pyruvic acid levels increased significantly by 2 to 6 times over controls on exposure to 5 to 15 g Nap ml^-1. Explanation of these changes is attempted in terms of the glycolysis pathway involving pyruvic acid oxidation and oxidative phosphorylation in the electron transport system.     

Uptake of cadmium in tropical marine lamellibranchs,and effects on physiological behaviour

The effect of cadmium introduced as inorganic salts (chloride, nitrate, sulfate, carbonate, acetate and iodide) or organic chelates (with EDTA, NTA and humic acid) on the physiological behaviour of six species of tropical lamellibranchs — arcid blood clamsAnadara granosa andA. rhombea, venerid clamsMeretrix casta andKatelysia opima, and mytilid musselsPerna viridis andP. indica, collected from various intertidal areas in southern India from 1986 to 1989 — was evaluated. Inorganic salts of Cd are reported to completely ionize upon introduction to full-strength sea water and form predominantly (97%) chloride complexes. Some inorganic Cd salts, therefore, would hardly affect physiological parameters. However, bioaccumulation of Cd was greatest upon exposure to Cd introduced as sulfate, followed by iodide, acetate, chloride, nitrate and carbonate; 96-h LC₅₀'s also varied, but in a different order, being highest for chloride (3.5µg ml^–1), followed by nitrate, acetate, iodide and sulfate (1.8µg ml^–1). Furthermore, Cd levels increased linearly with time of exposure and levels in medium, and were species-specific, being highest in the arcid clams, followed by the venerid clams and mytilid mussels. The presence of other metals such as Zn reduced bioaccumulation of Cd significantly (P < 0.001), but the reverse was not true. Upon exposure to Cd in the presence of Cu, on the other hand, accumulation of both metals was reduced by 15 to 20%. In the presence of organic chelators — EDTA, NTA and reduced glutathione (GSH) — Cd accumulation was significantly inhibited, by 1/2 to 1/3. Humic acid, on the other hand, had no effect. Cd levels in soft tissues were inversely related to ambient salinity in the range of 12 to 32. However, both Zn and Cu significantly inhibited Cd accumulation irrespective of salinity. Cd increased the rate of filtration inAnadara granosa over the first 24 h by 28%, but on prolonged exposure (96 h) that rate decreased significantly, by 50%. Zn alone and in the presence of Cd, on the contrary, initially reduced filtration activity, which subsequently increased to control levels upon continued exposure. Cu alone and in combination with Cd and Zn also significantly (P < 0.001) inhibited filtration relative to controls. This combination also progressively reduced respiratory activity with time, the maximum decrease being 80% after 96 h of exposure. Furthermore, impact of all three metals on both filtration rate and oxygen consumption was initially synergistic, but changed to antagonistic upon prolonged exposure up to 96 h.Deceased. Please send all correspondence and requests for reprints to Dr. S. Patel at the same address     

The persistence of chronically accumulated hydrocarbons in the hard shell clam Mercenaria mercenaria

Hard shell clams, Mercenaria mercenaria, from the chronically polluted environment of the Providence River, USA, were transferred to a clean laboratory system located in lower Narragansett Bay, Rhode Island. The hydrocarbon contents of these transplanted clams were monitored for 120 days after transfer. After this period only slight depuration had occurred. A 41.9 g g wet weight^-1 average initial hydrocarbon burden decreased to 29.3 g g^-1, a decrease that became statistically significant (P<0.1) only after 120 days. At most, only 30% of the clams' hydrocarbons were lost. These findings indicate that the duration of the exposure period and the chemical nature of the source hydrocarbons are both instrumental in determining the persistence of these compounds in filter-feeding bivalves. Chronically accumulated petroleum hydrocarbons are strongly retained by the organisms and are only very slowly depurated.     

Effects of environmental stressors on blood-glucose levels in sea hares,Aplysia dactylomela

Effects of natural stressors such as tidepool strandings, air exposure, and low salinity on blood-glucose levels were investigated in the sea hare Aplysia dactylomela from shallow areas of Discovery Bay, Jamaica. All treatments produced large and significant elevations in blood-glucose titre, 1.5-to 2.3-fold above baseline levels of 25 to 35 g glucose ml^-1. Response times were variable, with significant elevations being manifested within 30 to 120 min from initiation of the stressor. Recovery was swift, within an hour or two of restoration to pretreatment conditions, and often involved an undershoot to levels below control values. In two experiments involving tidepool strandings and associated high body-temperatures, excessively low blood-glucose titres were followed by death of all test individuals. When sea hares were exposed to 75 and 50% seawater (100%=33S) for 1 h, maximum elevation in blood-glucose concentrations occurred 1 to 2 h from onset of exposure, coincidental with maximum dilution of the body fluids of test individuals. The responsiveness of blood-glucose titres to relatively small temperature or salinity changes, or to short-duration air exposures, suggests that monitoring this physiological parameter may be a useful and sensitive means of diagnosing a wide variety of stressors in marine gastropods.     

Accumulation of cadmium from contaminated water and sediment by the shrimp Callianassa australiensis

The burrowing marine shrimp Callianassa australiensis (Dana) was collected from an uncontaminated area in Western Port, Victoria, Australia in 1977. The shrimp were exposed to cadmium-contaminated water and sediment for 8 wk. The concentrations ranged from 0.5 to 63 g Cd 1^-1 for water and 0.5 to 63 g Cd g^-1 for sediment. The shrimp accumulated cadmium from water at a rate commensurate with increases in the concentration of cadmium in water and the duration of the experiment. Although the cadmium concentration in the sediments was 10³ times higher than that in water, it hat no effect on cadmium uptake by the shrimp. The concentration factors decreased with increasing concentration of cadmium in water but increased as the duration of exposure increased. The shrimp dry weight decreased with increasing concentration of cadmium in water and duration of exposure. As was the case with cadmium uptake by the shrimp, these two factors acted interactively on the shrimp dry weight, but the third factor, concentration of cadmium in sediment, had no effect.     

Effects of cadmium on Pontoporeia affinis (Crustacea: Amphipoda) in laboratory soft-bottom microcosms

Laboratory soft bottom microcosms, containing sediment with natural populations of meio-and microfauna and the amphipod Pontoporeia affinis Lindström, were used to investigate chronic effects of cadmium on a typical Baltic Sea benthic community. Temperature, salinity, organic content of the sediment and the life cycles of the amphipods in laboratory control microcosms were in good agreement with conditions in the Baltic Sea. In Experiment 1, P. affinis was exposed to four assayed cadmium concentrations, 0 (control), 6.3, 41 and 127 g Cd·1^-1, for 265 d. At the lowest cadmium concentration (6.3 g Cd·1^-1), the sediment contained about 700 times, and P. affinis about 1 700 times, the water concentration at the end of the experiments. In microcosms without P. affinis, the sediments accumulated less cadmium. Effects on P. affinis embryogenesis were detected after 105 d of exposure in all tested cadmium concentrations. Mortality of juveniles was significantly increased after 265 d of exposure in mean assayed concentrations of 41 and 127 g Cd·1^-1. In Experiment 2, P. affinis was exposed to cadmium in assayed concentrations, 0, 6.5 and 46 g Cd·1^-1 for 460 d. At the lowest water concentration (6.5 g Cd·1^-1), the prolonged exposure did not increase the sediment concentration, which indicates a steady state, while concentrations in P. affinis reached about 3 500 times the lowest water concentration after 460 d. Juvenile P. affinis matured sexually and reproduced normally in all microcosms, but their offspring died in all microcosms with added Cd. This occurred at water concentrations not uncommon in polluted marine areas. The effects are serious in comparison to those found in conventional short-term laboratory experiments with the same concentrations and demonstrate the importance of long-term experiments in ecotoxicology.     

Sublethal effects of chronic oil exposure on the intertidal clam Macoma balthica

When exposed to Prudhoe Bay crude oil in flowing seawater for 180 days, the small intertidal clam Macoma balthica showed behavioral, physical, physiological and biochemical changes. At a high concentration of oil in seawater (3.0 mg l^-1) burrowing rate decreased, respiration rate increased, growth was inhibited, and very high mortalities resulted. The lowest concentration of oil in seawater (0.03 mg l^-1) inhibited growth and caused reabsorption of gametes. One group of adverse oil effects which was related to sluggishness and disorientation of the clams appeared after a week of exposure to oil; another group related to a negative energy balance was not observed until 60 days. We conclude that chronic exposure of M. balthica to oil-in-seawater concentrations even as low as 0.03 mg l^-1 will, in time, lead to population decreases.Please address requests for reprints to Dr. D. G. Shaw at the Institute of Marine Science     

Accumulation of 14C-1-naphthalene by an oceanic and an estuarine copepod during long-term exposure to low-level concentrations

Accumulation of the bi-cyclic aromatic hydrocarbon ¹⁴C-1-naphthalene in adult female Calanus helgolandicus Claus and adult female Eurytemora affinis Poppe in sea water concentrations of hydrocarbon ranging from 0.2 to 992 g/l was studied during exposure periods of up to 15 days as part of an investigation of the possible effects on marine zooplankton of persistent exposure to low levels of petroleum hydrocarbons. With both species the body levels of radioactivity increased rapidly during the first few days of the exposure period, but after exposure for 7 to 8 days to sea water containing 50 g hydrocarbon/l an equilibrium condition was approached; in some experiments where E. affinis was exposed to 1.0 and 10 g hydrocarbon/l for 15 days there was no further increase in body levels of radioactivity after 7 to 8 days. Using a low concentration of hydrocarbon (1 g/l), the quantity of radioactivity accumulated after 10 days was found to be nearly fifty times greater in the smaller species, E. affinis, than in C. helgolandicus, when expressed in terms of body weight. After they had been exposed to the hydrocarbon for several days the copepods contained a considerable proportion of radioactivity that was no longer identifiable as naphthalene and was presumably present as metabolites. Radioactivity accumulated in the copepods after several days was rapidly lost after they were transferred to uncontaminated sea water: e.g. C. helgolandicus lost nearly 90% of its body level of radioactivity in 24 h. Thereafter the rate of loss was greatly reduced, and 5% of the original body level of radioactivity still remained in the copepods at the end of 11 days. Experiments on the breakdown of naphthalene added at low concentrations to sea water samples containing natural microbial populations indicated degradation rates of 0.1 to 0.2 g/l/24 h in oceanic water, and 2.6 g/l/24 h in inshore water samples. The results are discussed in terms of the possible transfer of hydrocarbon to a higher trophic level in areas subjected to constant low-level inputs of petroleum hydrocarbons.     

Effects of suspended sediments on egg production of the calanoid copepod Acartia tonsa

The estuarine copepod Acartia tonsa was collected on several occasions between 4 April and 14 August 1985 from Terrebonne Bay, Louisiana (29°08N; 90°36W) and the effects in its diet of suspended sediments, collected from the same area, were measured at five different concentrations of sediment (100 to 1 000 ppm) and six phytoplankton concentrations (500 to 13 000 cells ml^-1 Thalassiosira weissflogii). Egg production rate was used as an index of diet quality. At low phytoplankton concentrations (500 cells ml^-1), and at intermediate phytoplankton concentrations (2 000 cells ml^-1) for previously starved copepods, egg production was reduced by up to 40% at a sediment concentration of 250 ppm and further reduced at higher sediment concentrations. At higher food concentrations (4 000 to 13 000 cells ml^-1), suspended sediment had no effect on egg production rates at sediment concentrations up to 500 ppm. Rates were reduced only at the highest sediment concentration of 1 000 ppm. Under most natural conditions, suspended sediment would not significantly affect egg production rates in A. tonsa.     

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     

The effect of low concentrations of phenol and ammonia on egg production rates,fecal pellet production and egg viability of the calanoid copepod Acartia clausi

Estimates of daily fecundity, hatching success and fecal pellet production are reported for Acartia clausi females exposed for 10 d to low levels of phenol and ammonia. Copepods were collected in 1991 and 1992 from a southern coastal area of the Mar Grande of Taranto (southern Italy). A reduction in egg numbers and fecal pellet production was observed for females after 8 d of exposure to 500 g l^-1 phenol concentration. Ammonia (120 g l^-1) produced a significant increment in egg production, but hatching success was reduced by about 50% after nine exposure days. A. clausi was more sensitive to ammonia than phenol at high concentrations (24-h LC₅₀ phenol-32.26 mg l^-1; 24-h LC₅₀ ammonia=0.91 mg l^-1). At low concentrations, only long-term exposure to phenol determined a reduction in fecundity.     

Reductions in photosynthetic carbon uptake in epiphytic diatoms by water-soluble extracts of leaves of Zostera marina

A water-soluble fraction of green leaves of Zostera marina L. decreased carbon uptake rates in diatoms found as epiphytes at Roberts Bank (Lat 49°2N; Long. 123°8W) on the west coast of Canada. Extract concentrations of 11 to 1 g dry leaf ml^-1, added immediately before ¹⁴C-uptake was measured over a 3-h period, reduced uptake to 36 to 80% of controls, respectively. A lower concentration (0.6 g dry leaf ml^-1) reduced uptake significantly in only one of four cultures. Addition of the whole extract 3 d before carbon uptake was measured or in one-third doses, 0, 1, and 2 d before, resulted in inhibition similar to that observed when the whole extract was added immediately before the ¹⁴C.     

Symbiont photosynthesis increases both respiration and photosynthesis in the symbiotic sea anemone Anemonia viridis

Dark respiration of the symbiotic sea anemone Anemonia viridis (Forskäl) was observed to increase by 34% when anemones were exposed to hyperoxic sea water (150% oxygen saturation) overnight, and by 39% after exposure to 6 h in the light at a saturating irradiance of 300 E m^-2 s^-1 at normoxia (100% oxygen saturation). No increase due to light stimulation was observed in aposymbiotic control anemones. In darkness, the oxygen concentration of the coelenteric fluid was hypoxic. However, within 10 min of anemones being illuminated, coelenteric fluid was hyperoxic, and it remained elevated throughout a 12 h light period. When measured over a 24 h period (12 h light: 12 h dark), the dark respiration rate increased gradually over the first 6 h of the light period until it was 35% above the dark night-time resting rate. It remained elevated throughout the remaining light period and for 2 h into the following dark period, after which it fell back to the resting rate. Gross photosynthesis (P ^gross) increased significantly when anemones were exposed to either hyperoxia (150% oxygen saturation) or 300 E m^-2 s^-1 at normoxia. This increase was not observed when symbiotic anemones were illuminated at a low-light intensity of 100 E m^-2 s^-1. The results of this study suggest that respiration in the dark is limited by oxygen diffusion and that normal respiration is restored in the daytime by utilisation of the oxygen released by photosynthesis. Furthermore, it appears that the increased respiration following exposure to high-light intensities provides a CO₂-rich intracellular environment which further enhances the photosynthetic rate of the zooxanthellae.     

Phosphate acquisition in the giant clam-zooxanthellae symbiosis

The effect of phosphate on the giant clam Tridacna gigas and on its symbiotic dinoflagellate Symbiodinium sp. was compared with that on cultured Symbiodinium sp. originally isolated from the same clarn species. Incubation of whole clams in elevated phosphate (10 M) reduced their capacity for phosphate uptake, but the uptake capacity of the clam's zooxanthellae population was not influenced. In addition, there was no change in the zooxanthellae density and the N:P ratio, of these algae., On the other hand, cultured zooxanthellae were influenced by the phosphate regimen of their culture medium. Compared with controls (0 M P), addition of 10 M phosphate to the culture medium caused an increase of 100% in cell density and decreases of 50% in the N:P ratio, and 80% in the phosphate-uptake capacity of the zooxanthellae. Zooxanthellae freshly isolated from the clams exhibited properties similar to those of zooxanthellae cultured in the absence of phosphate. These results demonstrate that the zooxanthellae population of T. gigas have limited access to the inorganic phosphate in sea water and the phosphate reserves within the animal host.     

Uptake of cadmium by the eelgrassZostera marina

The uptake of cadmium by the shoots ofZostera marina L. (eelgrass) was examined in the laboratory. Experiments were carried out in experimental chambers which allowed the separation of the leaves from the root-rhizome portions of intact shoots. Cadmium uptake by the root-rhizome portions over 24 h was directly related to substrate cadmium concentration (1.0, 5.0 and 10.0 g Cd ml^-1) and varied from 6.5 to 30.0 g Cd g^-1. Cadmium uptake by the root-rhizomes and the leaves in a substrate concentration of 1 g Cd ml^-1 was also related to exposure times (24, 48 and 72 h). Maximum uptake by the root-rhizomes and the leaves was observed after 72 h at a substrate concentration of 1 g Cd ml^-1 and was equivalent to 48 and 94 g Cd g^-1, respectively. Translocation of cadmium from the leaves to the root-rhizomes was observed after 24 h, and at the end of 72 h was equivalent to 27% of the total leaf uptake. No cadmium movement from the root-rhizomes to the leaves was detected.     

Growth response of Chaetoceros calcitrans (Bacillariophyceae) in batch culture to a range of initial silica concentrations

Batch cultures of the marine unicellular centric diatom Chaetoceros calcitrans (Paulsen) Takano were maintained by serial subculturing every 4 d into nutrient-enriched natural sea-water medium supplemented with 350, 950 and 1 400 g-at Si l^-1. The diatom cultures removed initial silica concentrations of 350 and 950 g-at l^-1 from the medium within 2 and 3 d, respectively. About 30 g-at l^-1 of the highest initial concentration remained in the medium after 4 d. The mean final cell density with an enrichment of 350 g-at Si l^-1 was 3.43±0.26×10⁴ cells l^-1 (median cell volume = 77.5±5.0 m³); with 950 g-at Si l^-1, 8.55±0.55×10⁴ cells l^-1 (50.0±4.5 m³); and with 1 400 g-at Si l^-1, 9.72±0.48×10⁴ cells l^-1 (37.3±5.0 m³). There was no significant difference in the final total organic weight of cells produced, which was in the range of 170 to 190 mg per 250 ml culture. This consisted of proportionately more lipid and carbohydrate and less protein from the treatment with 350 g-at Si l^-1 than from the 1 400 g-at Si l^-1 treatment.     

Sublethal effects of zinc and municipal effluents on larvae of the red abalone Haliotis rufescens

Experiments were conducted to develop a sensitive sublethal toxicity test protocol to determine the toxicity of municipal wastewater effluents to larvae of the red abalone Haliotis rufescens. In multiple tests, fertilized abalone embryos were exposed for 48 h to dilutions of a reference toxicant, zinc sulfate, and to dilutions of primary-and secondary-treated effluents. The resulting veliger larvae were examined microscopically for larval shell abnormalities. In a longer flowthrough experiment, abalone were exposed for the entire larval phase, from the two-cell stage through metamorphosis, to compare zinc effects on metamorphosis with zinc effects on short-term larval shell development. Dissolved oxygen, pH, salinity and temperature were measured daily in test solutions, and zinc concentrations were verified by chemical analysis. No observed effect concentrations (NOECs) for zinc were 39±2.1 g l^-1 in three 48 h exposures, and 19 g l^-1 for the 9 d exposure through metamorphosis. Median effect concentrations (EC₅₀s) were 68±6.9 g l^-1 in 48 h tests and 50 g l^-1 in the 9 d test. Abalone larvae were affected at lower concentrations of primary than of secondary effluent.     

Effects of copper on the latency of lysosomal hexosaminidase in the digestive cells of Mytilus edulis

Mytilus edulis collected from Tomales Bay, California, USA, during mid-winter 1979 were exposed to increased concentrations of dissolved copper under controlled laboratory conditions. A dose-dependent reduction in the latency of lysosomal hexosaminidase activity in digestive cells was induced after a 30 d exposure to copper. The half-time of the hexosaminidase staining reaction in sections of digestive gland from control mussels was 15.5 min; for mussels exposed to 25, 50, and 75 g Cu l^-1 it was 11.8, 8.5 and 5.5 min, respectively. In addition, the dyecoupled reaction product was seen earlier in sections from individuals exposed to 50 and 75 g Cu l^-1 (after 30 s) and 25 g Cu l^-1 (1 min) than in sections from control individuals (2.5 min). Copper accumulations were demonstrated histochemically to have the same distribution as the hexosaminidase reaction product, indicating that copper is sequestered in lysosomes. Copper concentrations in digestive gland tissue, were related to the concentrations of copper in the water to which the mussels were exposed.     

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.     

Nutrient enrichment and the ultrastructure of zooxanthellae from the giant clam Tridacna maxima

The separate and combined effects of ammonium (10M) and phosphate (2M) on the ultrastructure of zooxanthellae (Symbiodinium sp.) from giant clams, Tridacna maxima, were examined in the field. Nitrogen addition significantly changed the ultrastructure of the zooxanthellae inhabiting the clams. After 9 mo exposure, the cross-sectional area of zooxanthellae from N-treated clams was significantly lower than that from other treatments [N=39.3 m²; C=47.9 m²; P=43.2m²; N+P=44.5 m²; (P=0.001)]. There was also a significant decrease in the size of starch bodies, especially around the pyrenoid of the zooxanthellae from N and N+P treatments [N=1.2 m²; C=2.0 m²; P=1.8 m²; N+P=1.2 m²; (P=2.08E-11)]. This presumably occurs as a result of the mobilization of organic carbon stores in response to stimulated amino acid synthesis under enriched nutrient conditions. These data strongly suggest that the symbiotic zooxanthellae of clams are limited to some extent by the availability of inorganic nitrogen, and that relatively minor changes to the nutrient loading of the water column can have substantial effects on the biochemistry of symbioses such as that which exists between clams and zooxanthellae.