Growth,mortality and shell morphology of cultivated mussel (Mytilus edulis) stocks cross-planted between two Scottish sea lochs

One-year-old rope-grown blue mussels (Mytilus edulis L.) were held in experimental lantern nets and cross-transplanted between two sea lochs (Lochs Etive and Leven) on the west coast of Scotland. Growth and mortality were monitored from May 1991 to May 1992, as well as shell morphology in native and transplanted mussels. There were highly significant differences (P0.001) in growth rates between lochs; both native and transplanted mussels performed better in all shell and tissue growth-parameters in Loch Etive than in Loch Leven. Stock also had a significant (P0.05) influence on shell length and live weight, but its contribution to total variance was considerable only in the latter case. Wet and ash-free dry meat weights were governed mainly by site and to some extent by site x stock interaction. Mortality rates were quite low (6 to 7% yr^-1) and did not show any significant variation either between sites or stocks. There were significant morphological differences (ratios of shell length, height and width) between the Loch Etive and Loch Leven populations (P0.001) which persisted for one year after transfer. Stock appeared to be the main factor affecting shell morphology, as opposed to site. Linear regressions of shell height and width on length were significantly different between the native stocks, but became indistinguishable from those of the recipient populations one year after reciprocal transfer. This did not, however, conceal the effect of stock origin on dimensional ratios. It is concluded that site differences related to environmental factors, notably chlorophyll a levels and currents, and also possible stress caused by high levels of Zn and Cu, are major determinants of growth, which are of main interest to aquaculture, while morphological differences most probably result from genotypic variation.     

Sedimentation of organic detritus in Lochs Etive and Creran,Argyll, Scotland

The rates of sedimentation of organic detritus were measured at 3 stations in two Scottish sea lochs, Loch Etive and Loch Creran, using sedimentation jars exposed at various depths. Details are given of the seasonal and depth distribution of sedimenting material, and its composition for a 1-year period. Differences in the pattern of sedimenting material collected at different depths and in the seasonal patterns of sedimentation at the different stations suggested that, in each case there were differences in the relative importance of detritus from various sources. At all stations, phytoplankton production made a relatively small contribution to the total detritus collected, either directly as dead cells, or indirectly as the faeces of zooplankton organisms. Near the head of Loch Etive there were contributions by filamentous algae and Enteromorpha sp., but a major source of detritus was terrestrial debris, mainly carried into the loch in the waters of the River Etive. In the lower basin of Loch Etive, terrestrial detritus also contributed to the total sedimenting near the surface, but at greater depths much of the material collected in the sedimentation jars probably resulted from short-term resuspension and re-deposition of bottom material, reflecting a net transport of fine sediment from the shallower to the deeper areas of the loch. Secondarily resuspended material was also a major source of material collected in the jars exposed in Loch Creran.     

Responses of Mytilus edulis on exposure to the water-accommodated fraction of North Sea oil

Individuals of Mytilus edulis L., collected from the Erme estuary (S.W. England) in 1978, were exposed to low concentrations (7 to 68 g l^-1) of the water-accommodated fraction (WAF) of North Sea crude oil. The pattern of accumulation of petroleum hydrocarbons in the body tissues was affected by the presence of algal food cells, the period of exposure, the hydrocarbon concentration in seawater, the type of body tissue and the nature of the hydrocarbon. Many physiological responses (e.g. rates of oxygen consumption, feeding, excretion, and scope for growth), cellular responses (e.g. lysosomal latency and digestive cell size) and biochemical responses (e.g. specific activities of several enzymes) were significantly altered by short-term (4 wk) and/or long-term (5 mo) exposure to WAF. Stress indices such as scope for growth and lysosomal latency were negatively correlated with tissue aromatic hydrocarbons.     

Community structure of the benthos in Scottish sea-lochs. I. Introduction and species diversity

The diversity of the macrobenthos was measured, using the rarefaction method of Sanders (1968), from bottom samples from Loch Etive, Loch Creran and the Firth of Lorne (Scottish west coast). Each sample (representing 1.6 m² of bottom area) was accumulated as a series of separate hauls taken consecutively in a systematic pattern with a van Veen grab. Two habitats were considered: soft mud and muddy sand. Within-habitat comparison of species diversity clearly indicates that diversity is lower in Loch Etive than in Loch Creran or the Firth of Lorne. The reasons for this are probably connected with the relatively high freshwater runoff into Loch Etive, possibly limiting the survival of planktonic larval stages of the benthos. The values of species diversity measured for the soft-mud areas in Loch Creran and the Firth of Lorne are thought to be representative for this habitat along the west coast of the British Isles. They agree well with the diversity predicted by Sanders for such a boreal inshore area, where a maritime climate prevails, on the basis of his time-stability hypothesis and the results of his sampling elsewhere.     

Effects of salinity gradients on the tolerance and bioenergetics of juvenile blue crabs (Callinectes sapidus) from waters of different environmental salinities

Juvenile Callinectes sapidus Rathbun were collected from brackish and hypersaline coastal environments in August 1986 and July 1987, respectively. The brackish collection site was a salt-marsh near Grand Isle, Louisiana (USA), and the hypersaline site was in the barrier island system on the north end of the Laguna Madre near Corpus Christi, Texas (USA). On the dates of collection, salinities fluctuated daily between 20 and 30 S and between 30 and 45 S at the brackish and hypersaline collection sites, respectively. The high-salinity 21 d LC₅₀ (50% mortality) was 56.0 for brackish-water individuals and 66.5 S for hypersaline individuals. The brackish-water individuals survived 0 S. The lowsalinity 21 d LC₅₀ was 0.5 S for the hypersaline individuals. Respiration and excretion comprised a small portion of the energy budget and did not vary with salinity for individuals from brackish water. However, both respiration and excretion increased with decreasing salinity in individuals from the hypersaline environment. Respiration accounted for more energy than excretion. As energetic expenditure (due to respiration and excretion) was relatively small, scope for growth usually paralleled energy absorption. Scope for growth responses to salinity differed significantly between crabs from the two environments. Peaks in scope for growth for both the brackish-water and hypersaline individuals corresponded to salinities normally encountered by these crabs in their natural habitats. Individuals from the brackish-water population had maximal energy absorption and scope for growth at 10 and 25 S. Individuals from the hypersaline population displayed maximal energy absorption at 35 S and maximal scope for growth at 35 and 50 S.     

Comparison of the scope for growth with the growth performance of Ostrea edulis seed reared at different food concentrations in an open-flow system

Oyster (Ostrea edulis L.) seed was reared on five rations of Isochrysis galbana Parke: 10, 30, 100, 200 and 300 cells l^-1, in an open-flow system. Physiological parameters such as clearance, ingestion, absorption and respiration rates were measured, and the scope for growth (SFG) calculated from these parameters was compared with actual growth over 20 d. Actual growth was negligible at 10 cells l^-1 (daily maintenance ration=2.5% organic wt) and maximum (growth rate=13.64 d^-1) at 200 cells l^-1 (daily ration=43% organic wt), which also supported the maximum gross and net growth efficiencies (K ₁=50%, K ₂=85%). Ingestion rate was directly correlated to cell concentration up to maximum of 100 cells l^-1, but further increases failed to support higher ingestions. Absorption efficiency decreased with increasing algal concentration from 95% down to 60%. Due to the costs of growth, respiration rate significantly increased when food was added above maintenance levels; however, metabolic costs associated with feeding activity were undetectable. The scope for growth calculated from these physiological parameters agreed with the long-term growth performance, validating the physiological energetics method as a valuable tool for predicting long-term growth performance under constant environmental conditions.     

Physiological ecology of a mussel with methanotrophic endosymbionts at three hydrocarbon seep sites in the Gulf of Mexico

In situ growth rates were determined, using two, 1-yr mark/recapture experiments, conducted between September 1991 and July 1993, for an undescribed mytilid, Seep Mytilid Ia, at three hydrocarbon seep sites in the Gulf of Mexico. The sites are located at depths of 540 to 730m, approximately 27°45N; 91°30W, and are separated by distances of 6 to 18 miles. These seep mytilids harbor methanotrophic endosymbionts and use methane as both a carbon and energy source. The mussel habitats were chemically characterized by analysis of water samples taken from precisely located microenvironments over, among and below the mussels, using small-volume, interstitial water samplers and the Johnson Sea Link submersible. Substantial differences were found in habital conditions, growth rates, and population structure for the mussels at the three sites examined. The growth rate of these seep mytilids reflects the methane concentration in their immediate habitat. Mussels at sites with abundant methane had growth rates that were comparable to shallow water mytilids at similar temperatures (5 to 8°C) with increases in shell length up to 17 mm yr^–1 documented for smaller mussels (<40 mm shell length). In conjunction with measurements of growth rates, three condition indices (glycogen content, tissue water content, and the ratio of ash-free dry weight to shell volume) were used to determine the relationship between the condition of the mussels, their growth rates, and their habitat chemistry. The three condition indices were correlated with growth rate and were often significantly different between mussels in different samples.     

The influence of fresh weight and water temperature on metabolic rates and the energy budget of Meretrix meretrix Linnaeus

Meretrix meretrix L. was held in the laboratory under simulated natural conditions to measure specific physiological parameters of its energy budget. O₂ consumption rate, NH₃ excretion rate (NR), ingestion rate, faeces excretion rate and scope for growth (SFG) were negatively related in an exponential manner to the fresh weight of the clams at all water temperatures, while almost all metabolic rates of the clams were positively related in an exponential or e-exponential manner with water temperature. However, the co-relationship between metabolic rates and water temperature was not as close as that between metabolic rates and fresh weight of the clam. The combined effect of fresh weight and water temperature was observed on all metabolic rates except for NR and SFG. At all culture temperatures and for all fresh weights of clams used, respiration took the largest percentage of ingested energy (41.5–51.2%), faeces excretion was second (31.0–42.3%), growth third (12.1–15.5%) and urine production last (2.1–5.6%).     

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.     

Brood size and chemical composition of Pareuchaeta norvegica (Crustacea: Copepoda) in Loch Etive,Scotland

Brood size and chemical composition (carbon, nitrogen, and ash) of Pareuchaeta norvegica in Loch Etive, Scotland have been determined. From 23 to 37 eggs were found in each egg mass (mean=30 eggs). The eggs are oval; the mean size of the longer axis is 438 m. Variation in egg mass (as dry weight) is related to increase in dry weight of the maternal body. an increase of 1 mg in maternal body dry weight produces an increase of 0.03 mg dry weight in the egg mass. Carbon content increases with increasing body dry weight both in pre-spawning and spent females, but nitrogen content decreases with increasing body weight. Thus, the carbon:nitrogen ratio increases with increasing body dry weight. The carbon content of an egg mass ranges from 61.4 to 65.3%, and nitrogen content from 9.6 to 13.2% of the total dry weight. Some examples of partitioning of chemical components of the maternal body into the egg mass are also described.     

An integrative response by Mytilus chilensis to the toxic dinoflagellate Alexandrium catenella

Physiological responses of Mytilus chilensis exposed to the toxic dinoflagellate Alexandrium catenella were measured over 21 days in the laboratory and were compared with control mussels not exposed to the dinoflagellate. Mussels were collected from culturing ropes at Yaldad Bay, southern Chile (43o08′S 73o44′W), in August 2004 and acclimated to laboratory conditions for one week prior to the experiment. After 8 days, the paralytic shellfish poisoning (PSP) toxins (i.e. saxitoxin) in the tissues of exposed mussels exceeded safe levels for human consumption. Clearance rates, ingestion of organic matter, and absorption efficiency of exposed mussels were significantly lower than those of controls on day 0, but this was followed by an increase on day 3. The exposed mussels also increased their excretion rate over time, and this increase was significantly correlated with the accumulation of PSP toxins in their tissues. Oxygen consumption was not affected by the PSP toxins. The scope for growth (SFG) on day 0 was negative in exposed mussels, but it increased during the experiment. Although feeding activity and absorption efficiency were adversely affected during the first few days of exposure to PSP toxins from A. catenella in the laboratory, the M. chilensis cultured in Yaldad Bay may have evolved mechanisms that allow them to exploit the toxic dinoflagellate as a food source.     

Respiration and excretion rates of Calanus glacialis in arctic waters of the Barents Sea

The respiration and excretion rates of Calanus glacialis (Jaschnov) Copepodite Stages III, IV, V, and adult females from the drift-ice area east of Svalbard (Barents Sea) were measured in shipboard experiments during the period from 27 May to 13 June, 1983. The phytoplankton biomass and abundance varied considerably between localities, but these variations were not generally reflected in the respiration and excretion rates of the copepod. The respiration and excretion rates of C. glacialis at the ambient temperature of-1.8°C (average respiration rates of 0.95, 0.73, 0.57, and 0.60 l O₂ mg^-1 dry wt h^-1 for Copepodite Stage III, IV, V, and adult females, respectively) were similar to those previously reported for other large-sized copepods from cold or temperate areas. Average respiration and excretion rates tended to decrease with incubation time or time after capture. Measurements on ten occasions within a period of 27 h after capture revealed excretion rates of ammonium ranging between 2.9 and 16.8 for C III, 3.7 and 21.1 for C IV, 1.3 and 28.4 for C V, and 1.6 and 18.7 for adult females, all expressed as nmol mg^-1 dry wt h^-1. In all experiments, excretion rates of inorganic phosphate varied between 0.7 and 1.5 (C III), 0.5 and 1.1 (C IV), 0.2 and 0.8 (C V), and 0.3 and 1.0 (adult females) nmol mg^-1 dry wt h^-1. Ratios of O:N, O:P, and N:P indicated that much of the metabolic energy was derived from catabolism of proteins. Comparison of the turnover rate of carbon and nitrogen showed, however, that nitrogen turnover was between 2.6 and 8.9 times higher than that of carbon. This may indicate that the copepods deaminate ingested protein, with the carbon skeleton of the amino acids subsequently being used in the synthesis of lipid compounds, possibly wax esters.     

Community structure of the benthos in Scottish sea-lochs. III. Further studies on patchiness

Large-scale patchiness in the distribution of the benthic fauna was investigated in Loch Etive (Scottish west coast) by two series of van Veen grab hauls. Each series was taken along a traverse across the width of the loch, with sampling points about 100 m apart. One sample series was taken on sandy mud and the other, at a greater depth, on soft mud. Two approaches in data processing were applied: (1) The variance: mean ratio and the Morisita I tests for significant aggregation were applied to the species abundances in the sample series; (2) 3 measures of sample homogeneity, each involving the calculation of an index of faunal similarity, were applied to the separate samples. The results, however, could not show significant differences between the two series of samples. These findings were compared to results obtained from (a) a previous study, where differences in patchiness between areas were shown for a smaller scale of sampling design in Loch Etive and neighbouring areas, and to which the I method is also applied here; and (b) the results of applying the variance: mean ratio and I tests to data published by Holme (1953). The present results indicate greater aggregation at the present scale of sampling than for the previous, smaller scale of sampling, or for the comparable scale of Holme's sampling. The degree of concordance shown by the values of I for the circular-design sampling to the values of the 3 measures of patchiness applied previously, and to the means of the species abundances, was measured by Spearman's rank correlation coefficient. The results clearly demonstrated the I values, unlike the others measured, to be almost completely independent of the mean. It was concluded that, for comparing the pattern from benthic samples using standard-size bottom samplers, where the mean may vary widely between each set of samples, the I method is probably most useful.     

Acclimatization to intertidal conditions modifies the physiological response to prolonged air exposure inMytilus edulis

Both the tolerance of air exposure and the metabolic means by which mussles,Mytilus edulis, face air exposure can be modified by intertidal acclimatization. Short-term intertidal acclimatization enhanced the tolerance of air exposure most in early summer. Prevention of air breathing increased the mortality of wild and non-acclimatized cultured (i.e., control) mussels, but only slightly enhanced that of intertidally acclimatized mussels, suggesting their increased dependence upon anaerobic metabolism. In June, anaerobic end products accumulated in the adductor muscle of cultured but not of wild mussels. Intertidal acclimatization shifted the pattern and rates of metabolite accumulation. Control mussels accumulated succinate and alanine in the adductor muscle while intertidally acclimatized mussels accumulated strombine + alanopine, albeit at far lower levels. Pyruvate kinase (PK) from adductor muscle of intertidally acclimatized mussels was gradually activated during prolonged air exposure, while that of control and wild mussels was more inhibited. In July and August, during prolonged air exposure, the PK from the most viable mussles generally was the most inhibited. Prevention of air breathing did not markedly change the time course of PK inhibition during air exposure. Cultured mussels used in the present study were obtained from growers in Québec, and wild mussels were collected from the Baie des Chaleurs (Québec, PQ) in 1988.     

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.     

Physiological energetics of the intertidal sea anemone Anthopleura elegantissima

Energy budgets were calculated for individuals of the sea anemone Anthopleura elegantissima (Brandt), collected in 1981 and 1982 from Bodega Harbor, California, USA. Rates of ammonium excretion were measured in high-and low-intertidal, symbiotic and aposymbiotic sea anemones within 24 h of collection. Among symbiotic and aposymbiotic individuals, no differences in excretion rate were found on the basis of intertidal height. However, rates of ammonium excretion in aposymbiotic anemones (2.14 mol NH ₊ ⁴ g^-1 h^-1) were significantly higher than in symbiotic ones (0.288 mol NH ₊ ⁴ g^-1 h^-1). Rates of excretion were used with estimated rates of oxygen uptake to calculate nitrogen quotients (NQ). NQ and RQ values from the literature were used to calculate an oxyenthalpic equivalent [501 kJ (mol O₂)^-1 for R+U], and mass proportions of protein (54%), carbohydrate (44%) and lipid (2%) catabolized during routine metabolism in this species 24 h after feeding. Integrated energy budgets of these experimental anemones were calculated from data on ingestion, absorption and growth, and estimates of translocated energy from the symbiotic algae. Contribution of zooxanthellae to animal respiration based on translocation=90% and RQ=0.97 are 41 and 79% in high-and low-intertidal anemones, respectively. Calculated scope for growth is greater than directly measured growth in both high-and low-intertidal individuals. The deficit, estimated as 30% of assimilated energy in high-intertidal anemones, is attributed to unmeasured costs (specific dynamic effect) or production (mucus). Low-intertidal anemones lost mass during the experiment, implying that the magnitude of the deficit was greater in these anemones than in upper intertidal individuals. Anemones from both shore levels lost zooxanthellae during the experiment, which contributed to energy loss since the contribution of the zooxanthellae is greater in low-intertidal anemones. Scope for growth is preserved in high-intertidal anemones (29% of assimilated energy) because metabolic demands are lower due to aerial exposure, and prey capture rate is higher compared to lowshore anemones. Although possibly underestimated, lower scope for growth in low-shore anemones may result from continuous feeding and digestion processes that are less efficient than those of periodically feeding high-intertidal anemones.     

Photoadaptation of photosynthesis in Gonyaulax polyedra

Gonyaulax polyedra Stein exhibited a combination of photoadaptive strategies of photosynthesis when only a single environmental variable, the light intensity during growth, was altered. Which of several biochemical/physiological adjustments to the light environment were employed depended on the level of growth irradiance. The photoadaptive strategies employed over any small range of light levels appeared to be those best suited for optimizing photosynthetic performance and not photosynthetic capacity. (Photosynthetic performance, P _i, is defined as the rate of photosynthesis occurring at the level of growth irradiance.) Among all photosynthetic parameters examined, only photosynthetic performance showed a consistent correspondence to growth rates of G. polyedra. Above 3500 to 4000 W cm^-2, where photosynthetic performance was equal to photosynthetic capacity, cells were not considered light-limited in either photosynthesis or growth. At these higher light levels, photosynthetic perfomance, cell volume, growth rates and respiration rates remained maximal; photosynthetic pigment content varied only slightly, while the photosynthetic capacity of the cells declined. At intermediate light levels (3000 to 1500 W cm^-2), photosynthesis, not growth, was light-limited, and photoadaptive strategies were induced which enhance absorption capabilities and energy transfer efficiencies of chlorophyll a to the reaction centers of G. polyedra. Photosynthetic capacity remained constant at about 280 mol O₂ cm^-3 h^-1, while photosynthetic performance ranged from 100 to 130 mol O₂ cm^-3 h^-1. Major increases in photosynthetic pigments, especially peridinin-chlorophyll a-proteins and an unidentified chlorophyll c component, accompanied photoadaptation to low irradiances. Maximal growth rates of 0.3 divisions day^-1 were maintained, as were respiration rates of about-80 mol O₂ cm^-3 h^-1 and cell volumes of about 5.4×10^-8 cm^-3 cell^-1. Below about 1250 W cm^-2, photosynthesis in G. polyedra was so light-limited that photosynthetic performance was unable to support maximal growth rates. Under these conditions, G. polyedra displayed photostress responses rather than photoadaptive strategies. Photostress was manifested as reduced cell volumes, slower growth, and drastic reductions in pigmentation, photosynthetic capacity, and rates of dark respiration.     

Uptake of cadmium and zinc by the mussel Mytilus edulis and inhibition by calcium channel and metabolic blockers

The mussel Mytilus edulis is extensively used to monitor metal contamination of estuarine and marine systems. Nonetheless, the mechanisms of metal uptake are poorly understood. To characterise the systems involved in cadmium and zinc uptake, the interaction between the two metals and the effects of different calcium channel blockers (diltiazem, nifedipine, verapamil) and inhibitors of active transport and metabolism (ouabain, sodium cyanide, 2,4 dinitrophenol) on the uptake of calcium, cadmium and zinc in Mytilus edulis have been studied. To separate direct from indirect effects of the inhibitors on metal uptake, their influence on the physiological condition of the mussels was also investigated. This was done by measuring clearance, respiration and excretion rates under the different exposure regimes and determining the scope for growth as an integrative index for physiological condition. The study has shown that the uptake of cadmium and zinc by Mytilus edulis can be modulated by calcium channel blockers and other inhibitors. The inhibitors also influenced physiological condition, but a significant correlation with the effects on metal uptake did not exist in most cases. Cadmium and zinc also inhibit each other's uptake, but the type of inhibition is not yet clear. The effects of the inhibitors on cadmium and zinc uptake are very different from the effects on calcium uptake, indicating that cadmium and zinc are preferentially taken up through other gateways. Overall, a significant degree of linear association is found between the effects of the inhibitors on the uptake of cadmium and zinc, suggesting common uptake routes. In addition, the effects of the calcium channel antagonist on the uptake of the metal ions are organ dependent, indicating that other types of channels are involved in the uptake of the metal ions in the gills and digestive system. Received: 16 February 1999 / Accepted: 23 September 1999     

Metabolism of epipelagic tropical ctenophores

Measurements of respiration and excretion at 25°C were made for five species of ctenophores collected during five cruises to the Bahamas (1982–1984). The mean element-specific respiration and ammonium excretion rates of freshly collected specimens of all species ranged from 4 to 16% d^-1, the mean atomic O:N ratios were 10 to 16, and ammonium averaged 60 to 90% of the total dissolved nitrogen excreted. For adult ctenophores, the carbon content ranged from 0.6% carbon (as percent of dry weight) for Bolinopsis vitrea to 3.7% carbon for Beroë ovata. There was a marked increase in the organic content (% carbon of dry weight) of small Bolinopsis vitrea with tentacles compared to fully lobate adults. B. vitrea had increasingly higher metabolic rates when held at food concentrations up to 100 copepods 1^-1 (about 250 g C 1^-1). The overall range between starved and well-fed B. vitrea was about two times for respiration and a factor of three for ammonium excretion. B. vitrea decreased from well-fed to a starved metabolic rate in about a day after removal from food. The metabolic rate of Eurhamphaea vexilligera was not measurably affected by short-term starvation or feeding (maximum 25 copepods 1^-1). In feeding experiments, E. vexilligera of 20 to 56 mm length fed at rates equivalent to clearance rates of 250 to 1 800 ml h^-1.     

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.