Sodium regulation in the shore crab Carcinus maenas as related to ambient salinity

The activity of Na–K-ATPase was measured in crude homogenates prepared from various organs (leg muscle, pincer muscle, heart, testes, digestive gland, hypodermis, gills 1–9) of shore crabs, Carcinus maenas L., acclimated to salinities ranging between 10 and 50 S (in steps of 10 S). In all salinities tested, Na–K-ATPase activity was highest in posterior gills 7–9 (10–12 mol P_i mg protein^-1 h^-1), followed by anterior gills 1–6 (ca. 2.5 mol P_i mg protein^-1 h^-1) and the other organs (in most cases far below 2mol P_i mg protein^-1 h^-1). In gills only, Na–K-ATPase activity was salinity-dependent, with the highest values in the lowest salinities and vice versa. In gills 7–9, Na–K-ATPase activity was increased more than threefold following a reduction in salinity from 50 to 10 S. Na–K-ATPase activity, expressed as percentage of total ATPase activity, amounted to 60–80% in gills, about 60% in hypodermis and 20–40% in the other organs. Ouabain, a specific inhibitor of Na–K-ATPase activity, reduced serum osmolalities in crabs kept at 9–10 S only when injected into the hemolymph (1 and 5 · 10^-5 M), but had no effect when dissolved in ambient water (10^-4 M). The results obtained underline that crustacean gills are the main organs for ionic regulation, and confirm the hypothesis of the central role of the Na–K-ATPase in active Na uptake as the basic mechanism of hyperregulation in dilute media. Reduction of serum osmolalities following injection of ouabain into the hemolymph confirms previous reports on localization of the sodium pump in the basolateral parts of epithelial cells.     

Changes of plasma osmolality,chloride concentration and gill Na−K-ATPase activity in tilapia Oreochromis mossambicus during seawater acclimation

Changes of plasma osmolality, chloride concentration and gill Na–K-ATPase activity in tilapia Oreochromis mossambicus (obtained from Tainan Fish Culture Station of Taiwan Fisheries Research Institute, 1987) during seawater acclimation were examined. Three experiments were performed. (1) Freshwater (FW) to 30 salinity seawater (SW): plasma osmolality and chloride rose violently immediately post-transfer. At 6 h, gill Na–K-ATPase activity began to increase but most fish died from excessive plasma osmolality and Cl. (2) FW to 20 salinity SW: plasma osmolality and chloride increased immediately post-transfer, but more slowly than in (1), and began to decrease at 24 h. However it was not until 12 h post-transfer that gill Na–K-ATPase activity rose slowly. (3) FW to 20 salinity SW for 24 h, then to 30 salinity SW: after transfer to 30 salinity, plasma osmolality and chloride showed only a small increase initially then declined, while gill Na–K-ATPase activity started to rise rapidly within 3 h. The present results coincided with our previous morphological data concerning the ultrastructural responses of gill chloride cells. These are discussed to elucidate the osmoregulation mechanisms in tilapia during seawater acclimation.     

Effects of arsenic on osmoregulation in the tilapia Oreochromis mossambicus reared in seawater

The effects of arsenic (As₂O₃) on plasma osmolarity, Na and K concentrations, the activity of gill Na–K-ATPase, and on the ultrastructure of gill chloride cells were compared between seawater tilapia (Oreochromis mossambicus) and freshwater tilapia in the Institute of Zoology, Academia Sinica, between 1989 and 1991. Arsenic was found to be more lethal in seawater tilapia [96 h LC₅₀ (median lethal concentration): 26.5 ppm] than in freshwater ones (71.7 ppm). No significant effect was found on plasma ion concentrations and osmolarity, enzyme activity or the ultrastructure of chloride cells in freshwater tilapia after 96 h exposure to 70 ppm arsenic. In contrast, 96 h exposure to 15 ppm arsenic caused evident effects in seawater tilapia: an increase in plasma osmolarity and activity of gill Na–K-ATPase, as well as better development of the chloride cell tubular system. These data suggest that the lethal effect of arsenic may be partially attributed to a hydromineral disturbance in seawater tilapia, but in freshwater tilapia arsenic perhaps causes destruction in some physiological mechanisms other than osmoregulation. The activation of gill Na–K-ATPase and chloride cells in seawater tilapia appears to indicate an adaptation in the osmoregulatory mechanism to arsenic exposure, i.e., to enhance secreting ions or arsenic in the gills.     

Transbranchial potentials and ion fluxes across isolated,perfused gills of Uca rapax

Transbranchial potentials (TP) and sodium or chloride fluxes were measured in an apparatus designed for the simultaneous perfusion of eight isolated gills of Uca rapax. In anterior gills perfused with U. rapax–saline (US) the TP varied almost linearly from-7.5 to +10 mV inside, and in posterior gills from +2 to-8.5 mV (inside), on exposure to salinities ranging from 8.7 through 52, i.e. 25 to 150% seawater (100%=34.6 S). Sodium influx and efflux in anterior gills exposed to US, 8.7 or 43.3 S (0.7 to 4.0 mmol h^–1 g^–1 dry wt) were always greater than in posterior gills (0.5 mmol h^–1). The chloride fluxes were slightly smaller than sodium fluxes in anterior gills, while in the posterior gills the chloride influx (2.8 to 4.6 mmol h^–1) was always larger than chloride efflux (0.6 to 1.1 mmol h^–1) or the sodium fluxes. At least three ion-transport mechanisms may be present in these gills: (1) an internal ( = basolateral), ouabain-sensitive Na⁺, K⁺ pump, restricted to anterior gills; (2) a furosemide-sensitive Na⁺, K⁺, 2Cl^– (plus water) transporter, apparently restricted to posterior gills, and (3) a Na⁺ exchanger (and possibly other as yet unidentified ion transporters, as suggested by large increases of the chloride influxes caused by amiloride), probably located on the apical membranes of the epithelial cells of both gill types. The differential selectivity of the gills of U. rapax for sodium or chloride may limit the transbranchial movements of either ion, without a reduction of the overall permeability of these crabs.Communicated by N.H. Marcus, Tallahassee     

Effects of salinity on respiration and nitrogen excretion in two species of echinoderms

The 30-d survival limit of Eupentacta quinquesemita and Strongylocentrotus droebachiensis is 12–13 S. The activity coefficient (1 000/righting time in seconds) of stepwise acclimated sea urchins declined from 16.3 at 30 S to 3.5 at 15 S. Oxygen consumption rates (QO₂) of both species held at 30 S and 13°C were highest in June and lowest in December. During the summer, when environmental salinity is most variable in southeastern Alaska, the QO₂ of both species held at 30, 20 and 15 S varied directly with salinity. Perivisceral fluid PO₂ varied directly with acclimation salinity in sea urchins, but not in sea cucumbers. Perivisceral fluid oxygen content of acclimated sea urchins was significantly lower at 15 and 20 S than at 30 S due to reduced PO₂ and extracellular fluid volume at the lower salinities. The QO₂ of both species varied directly with ambient salinity during a 30-10-30. semidiurnal pattern of fluctuating salinity. No change occurred in the average QO₂ of either species over a 15-30-15. semidiurnal pattern of fluctuating salinity. Sea urchin perivisceral fluid PO₂ declined as ambient salinity fluctuated away from the acclimation salinity in both cycles and increased as ambient salinity returned to the acclimation salinity. Total nitrogen excretion of stepwise acclimated sea cucumbers declined significantly from 30 to 15 S, but there was no salinity effect on total nitrogen excretion in sea urchins. Ammonia excretion varied directly with salinity in stepwise acclimated sea cucumbers (67–96% of total nitrogen excreted), but there was no salinity effect on ammonia excretion (89–95% of total nitrogen excreted) of sea urchins. Urea excretion did not vary with salinity in sea cucumbers (2–4% of total nitrogen excreted) or sea urchins (2–9% of total nitrogen excreted). Primary amines varied inversely with salinity in sea cucumbers (2–30% of total nitrogen excreted), but did not vary with salinity in sea urchins (2–4% of total nitrogen excreted). The oxygen: nitrogen ratio of both species indicated that carbohydrate and/or lipid form the primary catabolic substrate. The O:N ratio did not vary as a function of salinity. Both species are more tolerant to reduced salinity than previously reported, however, rates of oxygen consumption and/or nitrogen excretion are modified by salinity as well as season.     

Normoxic and anoxic energy metabolism of the southern oyster drillThais haemastoma during salinity acclimation

The energetic cost associated with salinity acclimation was determined in the marine gastropodThais haemastoma by direct calorimetry under normoxic and anoxic conditions. Snails were collected from Caminada Pass near Grand Isle, Louisiana (Longitude 90°2W; Latitude 29°2N) in September 1987. Metabolic heat flux of snails acclimated to and measured at 10 or 30 S was similar at 15.06 or 16.39 J g^–1 dry wt h^–1, respectively, (corresponding to 0.76 or 0.83 ml O₂ g^–1 dry flesh wt h^–1) under normoxic conditions, and 2.39 or 2.53 J g^–1 dry wt h^–1 under anoxic conditions. Inter-individual variability was high, obscuring the effect of salinity gradient on heat flux. When standardized to the pre-transfer control level of each individual under anoxic conditions, a significant increase (55%) of energy expenditure was observed for snails transferred to hyperosmotic conditions. In contrast, heat flux varied insignificantly in individuals in the anoxic 30 to 10 S transfer. After transfer of individuals from 10 to 30 S under normoxic conditions, heat flux was depressed initially to 38% of the control rate, but recovered after 14 h to a higher metabolic rate (56%) than the pre-transfer control rate. After transfer of individuals from 30 to 10 S under normoxic conditions, the standardized heat flux decreased to 28% of the control rate, followed by a 20 h period of recovery to the control rate. The energy cost of intracellular hypoosmotic regulation was less than hyperosmotic regulation under anoxic conditions. The retraction of the foot ofT. haemastoma after normoxic salinity transfers did not generally correlate with the time course of metabolic heat flux.     

In vitro reproduction of the turbellarian<Emphasis Type="Italic"> Urastoma cyprinae</Emphasis> isolated from<Emphasis Type="Italic"> Mytilus galloprovincialis</Emphasis>

Urastoma cyprinae is a species infecting the gills of several marine bivalves. Although there is some literature on this turbellarian, its life cycle remains unknown. In our work we have demonstrated that reproduction of U. cyprinae can be completed out of its host. More than 50% of turbellarians isolated from mussels (Mytilus galloprovincialis) secreted and cemented a cocoon to the well bottom during the first 72 h of incubation in seawater (34 salinity) at 14°C. Oviposition started at days 1–18 (average 4.8 days) and occurred in most cases inside the protective cocoon. Each Urastoma laid an average of 2.9 egg capsules (range 1–10) and 3.9 embryos were developed inside each egg capsule (range 1–11). Hatching started at days 20–43 (average 24 days). An average of 12.8 juvenile forms (range 1–64) escaped from the cocoon after hatching. The free-swimming juveniles showed a positive phototactic response and survived about a month after hatching. On the basis of our results, we propose a life cycle for U. cyprinae involving a sexual maturation parasitic period in the bivalve gills and a reproduction period including cocoon secretion, egg laying, and hatching that is entirely completed in the external environment.Communicated by S.A. Poulet, Roscoff     

Na<Superscript>+</Superscript>/K<Superscript>+</Superscript>–ATPase activity and gill ultrastructure in the hyper-hypo-regulating crab<Emphasis Type="Italic"> Chasmagnathus granulatus</Emphasis> acclimated to dilute,normal, and concentrated seawater

We studied Na⁺/K⁺ –ATPase activity and ultrastructure in gills of the hyper-hypo-regulating crab Chasmagnathus granulatus Dana, 1851 acclimated to different salinities: 10, 30 and 45, known to be hypo-, iso-, and hyper-osmotic to the hemolymph, respectively. After centrifugation of homogenates at 11,000 g, Na⁺/K⁺–ATPase activity was almost entirely found in the pellets from the posterior (6–8) and anterior (3–5) gills, whereas very little was detected in the supernatant liquid. Specific activity of gill 6 was 41.3, 30.2, and 28.2 µmol Pi h^–1 mg prot^–1 for crabs acclimated to 10, 30, and 45, respectively, the result for 10 being significantly higher than those at 30 and 45. Although the concentration of sodium at which the reaction rate is half-maximal (K _M) was similar in the three acclimation salinities, only the enzyme from crabs acclimated to 10 was inhibited by high sodium concentration. Specific activity of gill 5 increased with the increment in external salinity (10.1, 15, and 18.1 µmol Pi h^–1 mg prot^–1 for 10, 30, and 45, respectively), the only significant difference being that between the extreme salinities. The epithelium thickness of the dorsal portion of gill 6 showed a variation among salinities: 21.7, 15.8 and 17.2 µm for 10, 30 and 45, respectively. There were significant differences in epithelium thickness between the 10 and the other salinities. In all three salinities, the ultrastructure of gill 6 epithelium showed a high density of mitochondria, estimated by their volume fraction (Vv _m=0.307–0.355). These mitochondria were packed between extensive basolateral membrane interdigitations in ionocytes and pillar cells. Gill 5 showed three cell types: pillars which possess mitochondria packed between membrane folds only in their interdigitations with neighbouring cells; type-I cells 8.0 µm thick with low density of mitochondria (Vv _m=0.088), and type-II cells, 9.9 µm thick and rich in mitochondria (Vv _m=0.423), but lacking basolateral interdigitations. Vv _m of type-I cells of gill 5 was significantly lower than those of type-II cells of the same gill and the ionocytes of gill 6. No significant difference in Vv _m was detected between the latter cell types.Communicated by P.W. Sammarco, Chauvin     

Conductive sodium entry in gill cells of the shore crab,Carcinus maenas

Isolated posterior gills of shore crabs, Carcinus maenas, collected from the Baltic Sea, were perfused and bathed with sea water and solutions of alkali chlorides. The preparation was used to measure fluxes of sodium from the external medium across the gills into the hemolymph and to determine transepithelial potential differences (PDs). Internally negative active transport PDs resulted from perfusion and bathing the gills symmetrically with the same medium (50% sea water). Passive (asymmetry) PDs following employment of 100% sea water as internal and 50% sea water as external medium were — in contrast to symmetry PDs — insensitive to cyanide and ouabain. This result indicates that the gill recognized the desired hyperosmotic state and responded by switching off the active transport component observed under symmetry conditions. Diffusional potential differences and fluxes of Na⁺ were inhibited by the externally applied diuretic amiloride. Gradients of pure alkali chlorides between medium and blood were accompanied by cation specific PDs. These PDs and their amiloride sensitivity were inversely related to the diameter of the unhydrated cation and allowed the calculation of the permeability sequence P: Li⁺>Na⁺>K⁺>Rb⁺>Cs⁺>Cl^-. The results obtained show that the permeability of the gills to cations greatly exceeds that to anions. In addition, these findings indicate that the initial amiloride-sensitive step in Na⁺ transport across the gill is not represented by an electroneutral sodium/proton exchange but by a conductive mechanism.     

Kinetics of osmoregulation in the crab Carcinus maenas

When shore crabs Carcinus maenas are transferred from 11 to 38 S at 11°C, new constant levels of hemolymph freezing points and of concentrations of Na, K, Ca, and Mg in the hemolymph are accomplished within 24h. From a decrease in serum protein and in serum free amino acids and an increase in the relative amounts of individual essential free amino acids in the body fluids of whole crabs, a participation of proteolytic activities and a transport of amino acids from hemolymph to cell is deduced; the stationary concentration of total intracellular free amino acids increases up to a nearly two-fold value, compared with the concentration in crabs remaining in diluted sea water. Also, the low molecular neutral sugars increase in whole crabs after high salinity stress, reaching values of more than two-fold initial concentrations within a period of 10 days. This increase is fully accounted for by a 6.7-fold increase in trehalose levels. The processes of increasing the concentrations of low molecular organic material seem to be slower than those of establishing new osmotic pressures in the hemolymph. The oxygen consumption decreases by 30 to 45% to new constant values within 8 to 12 h after the salinity change from 11 to 38, reflecting similar kinetics as the establishment of new osmotic pressures in the hemolymph.     

Autecology and clonal variability of the marine centric diatom Thalassiosira rotula (Bacillariophyceae) in response to light,temperature and salinity

The influence of 49 combinations of salinity (10–40 S, at 5 S intervals) and temperature (0°–30°C, at 5C° intervals) on the maximum daily division rate (K) and 18 combinations of light intensity (six levels) and temperature (5°, 15°, and 25°C) on photosynthesis, cell division, and chlorophyll a was examined using two clones of Thalassiosira rotula Meunier isolated from the upwelling area of Baja California (clone C8) and from Narragansett Bay, Rhode Islands (clone A8). Physiological differences appear to characterize these to clones with regard to their temperature tolerance (C8 5°–30°C, A8 0°–25°C), maximum growth rate (C8 K=2.9, A8 K=2.4), chlorophyll a content, and in the rates of growth and photosynthesis in response to light intensity and temperature. Optimum salinity for both clones (25–30 S) was generally independent of temperature, while chlorophyll a content decreased with temperature. T. rotula is a cosmopolitan paractic species; experimental studies indicate that it is eurythermal and moderately euryhaline. Comparison of five additional Narragansett Bay isolates of T. rotula reveal minimal spacial or temporal variability in genetically determined physiological characteristics within this local population.     

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

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

Mechanisms of copper toxicity in the shore crab,Carcinus maenas

The influence of copper(II)chloride on selected key enzymes and metabolites in intermediary metabolism and the energy charge potential of the hyperregulating shore crab, Carcinus maenas (L.) were investigated. Crabs, collected in Odense Fjord, Denmark between September 1989 and May 1990, were exposed to 10 ppm copper(II)chloride, in 10 ppt salinity seawater at 15°C for up to 1 wk. Hexokinase activity was 77% lower in the posterior gills and 60% lower in the midgut gland than in control crabs. Phosphofructokinase activity was reduced in the midgut gland by 82% but was unaffected in the gills. Pyruvate kinase activity was undetectable in the gills of exposed crabs and reduced by 47% in the midgut gland. Citrate synthase activity was depressed by 30% in the posterior gills and unaffected in other tissues. Copper exposure had no apparent effect on tissue cytochrome c oxidase activity. Chela muscle was the only tissue in which copper exposure did not bring about reductions in the enzyme activities tested. As a result of 1 wk of copper exposure the average lactate level increased by 3.5-fold in haemolymph, 9.3-fold in posterior gills and 6.5-fold in midgut gland. The average glucose level was raised by a factor of 6 in the haemolymph, 3.4 in the posterior gills and 1.2 in the midgut gland. Energy charge potential was at a very high level (ca. 0.9) and was unaffected by copper exposure.     

Na-K-ATPase generates an active transport potential in the gills of the hyperregulating shore crab Carcinus maenas

Perfusing and bathing isolated gills of shore crabs Carcinus maenas with artificial saline or sea (brackish) water enabled us to determine potential differences (PDs) between ambient bathing medium and perfusion solution. Establishment of diffusional PDs was avoided by employment of the same solution on the internal and external side. The PDs measured were therefore of an active nature. We compared the properties of the PDs with the well-known properties of the Na-K-ATPase: dependence on biological energy (ATP), on salinity and sodium concentration, susceptibility of PD to depletion of internal K and to the addition of 5 mM internal ouabain. Considering also the magnitude of the PDs measured, the results obtained indicate that it is the Na-K-ATPase that generates an active transport potential for Na in the gills of shore crabs. This PD represents the driving force for the active uptake of Na in crabs that hyperregulate their body fluids when they inhabit environments of reduced salinity regimes or fluctuating salinities in tidal estuaries. This process counteracts diffusional losses of Na in crabs exposed to dilute media.     

Comparison of osmoregulation between Adriatic and North Sea Carcinus

In two spatially isolated species — North Sea Carcinus maenas L. and Adriatic Carcinus mediterraneus Czerniavsky —osmoconcentration in hemolymph and Na-transport were investigated. The experiments were performed on crabs which had been long-term acclimated to sea water (1190 mOsmol/l) and to 50% sea water, and on individuals immediately after transfer from sea water to 50% sea water, until new steadystate conditions had been reached. About 10 to 12 h after transfer, a new steady state of total osmoconcentration as well as of the concentrations of the most representative cations Na, K, Ca, and Mg was attained. The hemolymph contents of Na and total osmotically active substances of the North and Adriatic Sea populations are significantly different when they are long-term acclimated to sea water and to 50% sea water. Total sodium fluxes, as calculated from influx and outflux experiments, are in the range 12.1 to 15.2 M Na/g/h in both species when acclimated to sea water. In 50% sea water, sodium fluxes are retarded, especially in C. maenas (6.6 M Na/g/h). This value is significantly lower than the corresponding value in C. mediterraneus (11.4 M Na/g/h). Differences are discussed on the basis of adaptation of the populations to their different environments.     

Sulfide tolerance and detoxification in shallow-water marine fishes

Hydrogen sulfide is a potent inhibitor of aerobic respiration. Sulfide is produced in sediments, and many species of fish live in association with the bottom. Tolerance tests, enzyme assays, and chromatography of sulfur compounds in thirteen species of shallow-water marine fishes (collected in San Diego, California, USA in 1987–1988) indicate adaptations to sulfide that vary with habitat and lifestyle. Tidal-marsh inhabitants, like Gillichthys mirabilis and Fundulus parvipinnis, have higher tolerance to sulfide (96 h LC₅₀ at 525 to 700 M) relative to outer-bay and open-coast inhabitants (surviving <12 h at much lower concentrations). The cytochrome c oxidase of all species shows high activity and susceptibility to sulfide poisoning, with 50% inhibition at 30 to 500 nM in various tissues. The two marsh species are able to survive at sulfide concentrations already inhibitory to their cytochrome c oxidase and fatal to other species. All species detoxify sulfide by oxidizing it to thiosulfate. All have sulfide-oxidizing activity in the blood, spleen, kidney, liver and gills, which correlates significantly with heme content. Thiosulfate appears in the tissues of sulfide-exposed fish and builds up to high concentrations (up to 2 mM) with stronger and longer exposure. Unexposed fish contain little or no thiosulfate. Sulfide is barely detectable in the tissues, even in high-sulfide exposure tests. We suggest that fish blood, in having high sulfide-oxidizing activity and no cytochrome c oxidase, can act as a short-term first line of defense against sulfide, and thus minimize the amount that reaches the vital organs. The results of this study indicate that sulfide is a significant environmental factor influencing the ecological distribution of marine fishes.     

Über den Einfluß der Adaptationstemperatur und des Salzgehaltes auf die Hitze-und Gefrierresistenz von Enchytraeus albidus (Oligochaeta)

This paper investigates the combined effects of temperature and salinity on resistance-adaptation to temperature in the oligochaete Enchytraeus albidus Henle. This worm shows reasonable resistance-adaptation to both cold (-13.2°C) and heat (35.8 °C). Acclimation to high salinity increases the degree of resistance to temperature extremes. The effect of salinity on heat-resistance, and especially on cold-resistance, decreases with rising adaptation-temperature. While a general effect of cations (Na, K, Ca, Mg) on temperature resistance does not exist, the influence of special ions depends upon ion concentration and adaptation-temperature; addition of Na, K, Ca and Mg reduces cold-resistance in cold-acclimated (5 °C) individuals, while, in warm-acclimated (23 °C) specimens, cold tolerance increases after addition of K and Ca. Heat-resistance decreases in warm-acclimated worms after addition of Mg and Ca. Higher proportions of cations reduce thermal resistance in all cases. Over the salinity range which allows homeo-osmotic conditions (2 to 15‰), E. albidus does not exhibit a constant resistance level (at least not to heat). The cryoprotective agent dimethylsulphoxide is highly effective both in cold and warm acclimated worms.     

Effects of salinity fluctuations on the respiration rate of the southern oyster drill Thais haemastoma and the blue crab Callinectes sapidus

Respiration rates of Thais haemastoma and Callinectes sapidus were determined as a function of salinity with a flow-through respirometer at 20°C. Respiration rates were measured at 10, 20 and 30 S for acclimated animals. The effects of 10-5-10, 20-10-20, 30-10-30 and 10-30-10 S semidiurnal cycles (12 h) of fluctuating salinity on the rate of respiration of the oyster drill were studied. During each cycle, salinity was changed from the acclimation salinity over a 4 h interval, held at that salinity for 2 h, returned to the acclimation salinity over 4 h and held at that salinity for 2 h. The effects of diurnal (24.8 h) salinity cycles on respiration in the oyster drill and blue crab were also studied. Salinity was changed from the acclimation salinity over a 10.4 h interval, held at that salinity for 2 h, then returned to the acclimation salinity over 10.4 h and held at that salinity for 2 h. The respiration rate of 30 S acclimated oyster drills (679 l O₂ g dry weight^–1 h^–1) was significantly higher than for individuals acclimated to 10 S (534 l O₂ g dry weight^–1 h^–1). Blue crab respiration was 170 l O₂ g dry weight^–1 h^–1 at 30 S, and was significantly higher at 10 and 20 S than at 30 S. With the exception of the 20-10-20 S semidiurnal cycle, the respiration rate of oyster drills declined as salinity fluctuated in either direction from the acclimation salinity and increased as ambient salinity returned to the acclimation salinity. Semidiurnal cycles (12 h) of fluctuating salinity produced greater changes in the respiration rate of snails than analogous diurnal cycles (24.8 h). A 10-30-10 S pattern of fluctuation caused a greater percentage reduction in the steady state respiration rate of oyster drills than the 30-10-30 S pattern. The respiration rate of blue crabs varied inversely with fluctuating salinity. Relatively minor changes occurred in blue crab respiration rate with fluctuating salinity. Blue crab respiration rate characteristically dropped during the initial phase of declining salinity at a rate directly proportional to the rate of salinity decrease, perhaps representing a metabolic adjustment period by the blue crabs. The respiratory response of T. haemastoma to salinity is consistent with its incomplete volume regulation, while the response of C. sapidus is compatible with its ability to regulate extracellular fluid osmotic and ionic composition.     

Changes in the excretory patterns of the fresh-water field crab Paratelphusa hydrodromous upon adaptation to higher salinities

Changes in the exeretory patterns of the fresh-water field crab Paratelphusa hydrodromous were studied in relation to salinity adaptation. Fifty percent sea-water medium was found to be the threshold of a change from ammonotelism to ureotelism in the crabs. Adaptation for 11 days in the 100% (=34 S) sea water brought about this change. Sea-water-adapted crabs excreted more urea, uric acid, and trimethylamine than controls, irrespective of starvation. Starvation reduced the quantitative excretion. Blood aspartic and glutamic acid levels increased on adaptation to sea water, in contrast to the levels of asparagine and glutamine. The activities of asparaginase and glutaminase in the tissues decreased on salinity adaptation. The reduction in amidase activity in 100% sea-water-adapted crabs is discussed with reference to acid-base homeostasis in the crabs.Dedicated to the memory of the late Professor K. Pampapathi Rao, who died on 23 June, 1973.     

Assessment of Groundwater Quality and Contamination from Uranium-Bearing Black Shale in Goesan–Boeun Areas, Korea

This study was initiated to identify the impact of metals and uranium enriched soil and black shale in groundwater quality and contamination. From a Piper diagram, groundwater was classified into four types as (Ca+Mg)–HCO₃ type, (Ca+Mg)–SO₄ type, the mixed type of these two and Na–HCO₃ type, reflecting the complicated nature of geology of the study area. Silicate weathering appeared to be the major water–rock interaction. In groundwater, metals including Cr, Pb, Cu and V, previously identified as being enriched in soils and black shale, were much lower in concentrations than Korean and US EPA drinking water guidelines. Instead, Fe and Mn caused major water-quality problems. In the artesian groundwater from an abandoned uranium mine, the uranium concentration was 21.3 µg L^–1, slightly higher than EPA guidelines of 20 µg L^–1. Heavy metals in groundwater appeared to be controlled mostly by sorptions on to Fe- and Mn-oxyhydroxides. They could be remobilised in groundwater with changes of pH and Eh conditions due to acid mine drainage from black shale or the recharge of fresh water. Uranium would be associated with carbonate and sulphate complexes in groundwater. Because of the remaining water-quality problems in the study area, we suggested containment of identified mine wastes, considering remedial measures for local problems with Fe and Mn, continuous monitoring of groundwater and developing groundwater from deep aquifers.