Effects of salinity and temperature on oxygen consumption in a freshwater population of Palaemonetes antennarius (Crustacea,decapoda)

• 1.1. After step-like increases in salinity the shrimps exhibit the smallest increase in oxygen consumption in the lower salinity range. At higher salinities the shrimps show longer recovery times and greater increases in the metabolic rate after salinity shock.
• 2.2. In steady-state experiments, the shrimps display the lowest oxygen consumption rates near the isosmotic point. The lowest metabolic rates occur at salinities of 3‰ and 10‰ At salinities of 20‰ and above the rate of metabolism increases by 20–30%.
• 3.3. The calculated osmoregulatory work for animals in fresh water amounts to only 2.7% of routine metabolism and drops to 1.1% for shrimps in 3‰ and 0.7% in 5‰ salinity.
• 4.4. Locomotory activity in the form of position change was not responsible for the increased oxygen consumption of the animals after salinity shocks. A “tentative swimming activity” by fast and frequent beating of the pleopods without position change may be an important factor in the increase of metabolic rates.
• 5.5. In its temperature response, the brackish water population has a higher metabolic rate than the freshwater one. Between 5 and 35°C Q ₁₀-values range from 4.01 to 1.37.

     

The effect of salinity on respiratory metabolism in selected ontogenetic stages of the freshwater shrimp Macrobrachium olfersii (Decapoda,palaemonidae)

• 1.1. The effect of acute salinity exposure (0, 7, 14, 21, 28 and 35%.S) on the respiratory metabolism of selected ontogenetic stages (zoeae, postlarvae and adults) of the freshwater shrimp Macrobrachium olfersiiwas examined.
• 2.2. Metabolic rates are salinity independent from 14 to 28%. S in zoeae 1–4, but tend to increase with increasing salinity in zoeae 5 and 8. Postlarvae exhibit maximal rates in midrange salinities while in adult shrimps, oxygen consumption rates decrease with salinity increase.
• 3.3. Salinity has little effect on the metabolism-weight relationship, regression analysis indicating that b varies from 0.69 in 0%. S to 0.62 in 35%. S.
• 4.4. Data are discussed as to whether larval responses reflect adaptation to the adult biotope and whether development of the larval neurosecretory system might affect metabolic response to salinity exposure.

     

The combined effects of temperature,salinity, and declining oxygen tension on oxygen consumption in the marine pulmonate Amphibola crenata (Gmelin, 1791)

Oxygen consumption of Amphibola crenata (Gmelin) was measured in various salinity-temperature combinations (< 0.1‰ to 41‰ salinity and 5 to 30°C) in air, and following exposure to declining oxygen tensions. In all experimental conditions, respiration varied with the 0.44 power of the body weight (sd = 0.14). The aquatic rate was consistently higher than the aerial rate of oxygen consumption, although at 30 °C the two rates were similar. Oxygen consumption increased with temperature up to 25 °C in all salinities; the lowest values were recorded at temperatures below 10 °C and at 30 °C in the most dilute medium. At all exposure temperatures, the oxygen consumption of Amphibola decreased regularly with salinity down to 0.1 ‰, and following exposure to concentrated sea water (41‰). Salinity had the least effect at 15 °C which was the acclimation temperature. In general, all of the temperature coefficients (Q₁₀ values) were low, < 1.65. However, Q₁₀ values above 2.8 were recorded at a salinity of 17.8‰ between 10 and 15 °C. Oxygen consumption of all size classes of Amphibola was more temperature dependent in air than in water and small individuals show a greater difference between their aerial and aquatic rates than larger snails. The rates of oxygen consumption in declining oxygen tensions were expressed as fractions of the rates in air saturated sea water at each experimental salinity-temperature combination. The quadratic coefficient B₂ becomes increasingly more negative with both decreasing salinity and temperatures up to 20 °C. At higher temperatures (25 and 30 °C) the response is reversed such that O₂ uptake in snails becomes increasingly independent of declining oxygen tensions at higher salinities. On exposure to a salinity of 4‰, Amphibola showed no systematic response to declining oxygen tension with respect to temperature. The ability of Amphibola to maintain its rate of oxygen consumption in a wide range of environmental conditions is discussed in relation to its potential for invading terrestrial habitats and its widespread distribution on New Zealand's intertidal mudflats.     

Diversity of juvenile fish assemblages in the pelagic waters of Lebanon (eastern Mediterranean)

Oxygen consumption rates of nauplii of the brine shrimp Artemia franciscana Kellogg 1906 were determined over a range of salinities from 10 to 110 ppm, in temperatures from 0 to 30°C, using a multi-factorial design. The oxygen micro-sensors employed have a fast response time and are capable of accurately measuring oxygen concentrations at temperatures well below 0°C. Oxygen uptake rate ranged from 0.03 to 0.66 μmol O₂ mg⁻¹ h⁻¹ and was sensitive to changes in both salinity and temperature. Temperature was the dominant factor affecting oxygen consumption rates, which showed a significant increase with increasing temperature. A slight decrease was measured in oxygen consumption with increasing salinity related to differential solubility of oxygen in waters of different salinities. Thermal sensitivity of oxygen consumption determined from calculations of Q ₁₀, indicated physiological adaptation of Artemia nauplii to the ranges of temperatures tested. Handling editor: A. van Kerchove     

Antioxidant defenses and oxidative stress parameters in tissues of mud crab (Scylla serrata) with reference to changing salinity

The effects of salinity (10, 17 and 35 ppt) on O₂ consumption, CO₂ release and NH₃ excretion by crabs and oxidative stress parameters and antioxidant defenses of its tissues were reported. An increase in salinity caused a decrease in O₂ consumption and CO₂ release and an increase in ammonia excretion by crabs. Lipid peroxidation, protein carbonyl, H₂O₂ levels and total antioxidant capacity of the tissues elevated significantly at 35 ppt salinity except in abdominal muscle where H₂O₂ content was low. Ascorbic acid content of tissues was higher at 17 ppt salinity than at 10 and 35 ppt salinities. With increasing salinity, a gradual decrease in SOD, an increase in catalase, no change in GPx and a decrease followed by an increase in GR activities were recorded for abdominal muscle. While for hepatopancreas, an increase followed by a decrease in SOD and catalase, decrease in GPx and GR activities were noticed with increasing salinity. In the case of gills, a decrease followed by an increase in SOD, a decrease in catalase and GPx and an increase in GR activities were noted when the salinity increased from 10 ppt to 35 ppt. These results suggest that salinity modulation of oxidative stress and antioxidant defenses in Scylla serrata is tissue specific.     

Effect of temperature and salinity on the energetics of juvenile gray snapper (Lutjanus griseus): implications for nursery habitat value

Gray snapper (Lutjanus griseus) encounter a wide range of temperatures and salinities in nearshore and estuarine juvenile habitats. The energetic response of juvenile gray snapper to temperature and salinity was measured in laboratory experiments to determine the influence of these physicochemical factors on the potential value of different juvenile nurseries. Maximum consumption and growth rates of juvenile (25-50 mm SL) gray snapper were determined in 12-day trials at 20 temperature/salinity combinations representing conditions in juvenile habitats. Ad libitum feeding level of individual fish was measured daily. Maximum weight specific feeding rate increased significantly with temperature and salinity; however, the effect of salinity was much less than that of temperature. Linear growth rate and specific growth rate both increased with temperature, and salinity did not have a significant effect on either. Gross growth efficiency (K₁, growth×consumption⁻¹*100) increased with temperature and was significantly lower at high salinities, indicating increased energetic costs. The higher K₁ at lower salinities has several implications for juvenile gray snapper in low salinity habitats: (1) they would need less food to achieve the same somatic growth as juveniles in high salinity habitats; (2) they would have higher growth at limited ration levels as compared to high salinity habitats; and (3) they would have less impact on prey populations than higher salinity habitats assuming similar gray snapper densities.     

Respiratory and osmoregulatory responses of the hermit crab, Clibanarius vittatus (Bosc), to salinity changes

Intertidal hermit crabs were stepwise acclimated to 10, 20, and 30‰ salinity (S) and 21 ± 1 °C. Hemolymph osmolality, sodium, chloride, and magnesium were isosmotic (isoionic) to ambient sea water at 30‰ and hyperosmotic (hyperionic) at 20 and 10‰ S, while hemolymph potassium was significantly hyperionic in all acclimation salinities. Total body water did not differ significantly at any acclimation salinity. Oxygen uptake rates were higher in summer-than winter-adapted crabs. No salinity effect on oxygen consumption occurred in winter-adapted individuals. Summer-adapted, 30‰ acclimated crabs had a significantly lower oxygen consumption rate than those acclimated 10 and 20‰ S. Crabs exposed to 30 10 30‰ and 10 30 10‰ semidiurnal (12 h) and diurnal (24.8 h) fluctuating salinity regimes showed variable osmoregulatory and respiratory responses. Hemolymph osmolality followed the osmolality of the fluctuating ambient sea water in all cases, but was regulated hyperosmotically. Hemolymph sodium, chloride, and magnesium concentrations were similar to hemolymph osmolality changes. Sodium levels fluctuated the least. Hemolymph potassium was regulated hyperionically during all fluctuation patters, but corresponded to sea water potassium only under diurnal conditions. The osmoregulatory ability of Clibanarius vittatus (Bosc) resembles that reported for several euryhaline brachyuran species. The time course of normalized oxygen consumption rate changed inversely with salinity under semidiurnal and diurnal 10 30 10‰ S fluctuations. Patterns of 30 10 30‰ S cycles had no effect on oxygen consumption rate time course changes. The average hourly oxygen consumption rates during both semidiurnal fluctuations were significantly lower than respective control rates, but no statistical difference was observed under diurnal conditions.     

Metabolic response of juvenile gray snapper (Lutjanus griseus) to temperature and salinity: Physiological cost of different environments

Juvenile gray snapper (Lutjanus griseus) occupy a wide range of estuarine and nearshore habitats that differ in physico-chemical properties. To quantify the energetic cost of inhabiting these different habitats, routine metabolism of individual gray snapper was measured in the laboratory at 20 combinations of temperature (18, 23, 28, and 33 °C) and salinity (5, 15, 25, 35, and 45 psu). An open, flow-through respirometer was used, enabling trials to be run for long periods (∼16 h), while maintaining water quality (dissolved O₂>70% saturation), and providing fish sufficient time to habituate to the chambers undisturbed. Video recordings of fish in the respirometer chambers were analyzed to quantify the spontaneous activity rate of individuals. Analysis of covariance, using fish weight and mean activity rate as covariates, indicated significant temperature and salinity effects on oxygen consumption. Oxygen consumption was significantly higher at high salinities, and the salinity effect was temperature dependent. A polynomial equation describing oxygen consumption as a function of temperature and salinity indicated the increase due to salinity from 5 to 45 psu at high temperatures (30-33 °C) was equivalent to a 3 °C increase in temperature. At intermediate temperatures (24-26 °C), the increase due to salinity from 5 to 45 psu was less dramatic, equivalent to a 2 °C increase in temperature. At the lowest temperatures (18 °C), salinity did not have a significant effect on oxygen consumption. The increased metabolic costs in high salinities (∼7% at the high temperature) represent a significant energy cost for juveniles, that would need to be balanced by lower predation risk or greater food availability to result in similar juvenile production compared to lower salinity environments.     

Iodine contributes to osmotic acclimatisation in the kelp Laminaria digitata (Phaeophyceae)

Iodide (I^?) retained by the brown macroalga Laminaria digitata at millimolar levels, possesses antioxidant activities, but the wider physiological significance of its accumulation remains poorly understood. In its natural habitat in the lower intertidal, L. digitata experiences salinity changes and osmotic homeostasis is achieved by regulating the organic osmolyte mannitol. However, I^? may also holds an osmotic function. Here, impacts of hypo- and hypersaline conditions on I^? release from, and accumulation by, L. digitata were assessed. Additionally, mannitol accumulation was determined at high salinities, and physiological responses to externally elevated iodine concentrations and salinities were characterised by chl a fluorometry. Net I^? release rates increased with decreasing salinity. I^? was accumulated at normal (35 S _A) and high salinities (50 S _A); this coincided with enhanced rETR_max and q_P causing pronounced photoprotection capabilities via NPQ. At 50 S _A elevated tissue iodine levels impeded the well-established response of mannitol accumulation and prevented photoinhibition. Contrarily, low tissue iodine levels limited photoprotection capabilities and resulted in photoinhibition at 50 S _A, even though mannitol was accumulated. The results indicate a, so far, undescribed osmotic function of I^? in L. digitata and, thus, multifunctional principles of this halogen in kelps. The osmotic function of mannitol may have been substituted by that of I^? under hypersaline conditions, suggesting a complementary role of inorganic and organic solutes under salinity stress. This study also provides first evidence that iodine accumulation in L. digitata positively affects photo-physiology.     

Impacts of varying durations of passive oxygen exposure on freshwater denitrifier community structure and function

Fertilizer use has dramatically increased the availability of nitrate (NO₃ ^?) in aquatic systems. Microbe-mediated denitrification is one of the predominant means of NO₃ ^? removal from freshwaters, yet oxygenation (O₂)-induced disruptions—e.g., extreme precipitation events—can occur, resulting in a disproportional increase in nitrous oxide (N₂O) production and efflux as facultative anaerobic bacterial populations use of O₂ as a terminal electron acceptor increases. We examined the effects of 12- and 24-h passive O₂ exposure on previously anaerobic bacterial communities focusing on denitrification enzyme activity (DEA), N₂O production, and bacterial community 16S rRNA and nitrous oxide reductase gene (nosZ) profiles after 12, 24, and 48 h of anaerobic recovery. Treatments experiencing 24-h O₂ exposure had significantly higher DEA 12 h into anaerobic recovery than treatments undergoing 12-h O₂ exposure. Initial N₂O emissions were significantly lower in the 24-h O₂ exposure treatments although by 24 h a dramatic spike (tenfold relative to the 12-h O₂ exposure treatments) in N₂O concentrations was observed. However, within 6 h (30-h anaerobic recovery) these differences were gone. Community nosZ profiles experiencing 24-h O₂ exposure exhibited reduced diversity after 24-h recovery, which corresponded with an increase in N₂O emissions. However, after 48 h of anaerobic recovery, nosZ diversity had recovered. These observations highlight the effects of short-term aerobic disruption on denitrification, as well as the effects on the denitrifier community profile. Together, these data suggest that recovery to ambient N cycling is exacerbated by disturbance length due to increased lag time and subsequent loss of denitrifier community diversity.     

Physiological impact of salinity increase at organism and red blood cell levels in the European flounder (Platichthys flesus)

Blood respiratory, acid-base, and ionic changes in response to hyperosmotic shock were studied in vivo and in vitro in the European flounder. One primary aim was to evaluate regulatory changes in red blood cell (RBC) volume and its interrelationship with blood O₂ transporting properties. An acute increase in the ambient salinity from 10 to 30 ppt caused small but significant increases in extracellular osmolality (<20 mosM kg⁻¹), [Na⁺], and [Cl⁻], which were corrected within 48 h. RBC volume was not significantly changed 3 h after the in vivo exposure to elevated salinity. A small metabolic acidosis was fully developed within 3 h, and this acidosis seemed responsible for a modest decrease in blood O₂ affinity (i.e., increased P₅₀-O₂ tension at 50% O₂ saturation). RBC organic phosphates were unchanged. In vitro elevation of whole blood extracellular osmolality by 60 mosM kg⁻¹ caused immediate RBC shrinkage. The subsequent regulatory volume increase (RVI) showed a graded dependency on blood O₂ saturation (S_O2). At S_O2 values of 0% and 20%, there were full RBC volume recoveries within 120 min, RVI was partial at S_O2 values of 45% and 55%, and RVI was absent at a S_O2 of 100%. S_O2 and P₅₀ did not change significantly during RBC shrinkage and RVI. Thus, the up-concentration of cellular haemoglobin and organic phosphates in hyperosmotically shrunken RBCs had minimal influence on blood O₂ transporting properties. The degree of cell shrinkage and time needed for RVI were positively correlated with the magnitude of the rise in extracellular osmolality. The RVI proceeded via elevation of cellular [Na⁺], [Cl⁻], and to some extent also [K⁺]. Cell volume regulatory mechanisms are only needed to correct minor volume disturbances in vivo, because changes in extracellular osmolality were limited by an efficient osmotic regulation at the epithelial interface between extracellular compartment and environment.     

Salinity-dependent modulation by protein kinases and the FXYD2 peptide of gill (Na+, K+)-ATPase activity in the freshwater shrimp Macrobrachium amazonicum (Decapoda,Palaemonidae)

The geographical distribution of aquatic crustaceans is determined by ambient factors like salinity that modulate their biochemistry, physiology, behavior, reproduction, development and growth. We investigated the effects of exogenous pig FXYD2 peptide and endogenous protein kinases A and C on gill (Na⁺, K⁺)-ATPase activity, and characterized enzyme kinetic properties in a freshwater population of Macrobrachium amazonicum in fresh water (<0.5 ‰ salinity) or acclimated to 21 ‰S. Stimulation by FXYD2 peptide and inhibition by endogenous kinase phosphorylation are salinity-dependent. While without effect in shrimps in fresh water, the FXYD2 peptide stimulated activity in salinity-acclimated shrimps by ≈50 %. PKA-mediated phosphorylation inhibited gill (Na⁺, K⁺)-ATPase activity by 85 % in acclimated shrimps while PKC phosphorylation markedly inhibited enzyme activity in freshwater- and salinity-acclimated shrimps. The (Na⁺, K⁺)-ATPase in salinity-acclimated shrimp gills hydrolyzed ATP at a V_max of 54.9 ± 1.8 nmol min^?1 mg^?1 protein, corresponding to ≈60 % that of freshwater shrimps. Mg²⁺ affinity increased with salinity acclimation while K⁺ affinity decreased. (Ca²⁺, Mg²⁺)-ATPase activity increased while V(H⁺)- and Na⁺- or K⁺-stimulated activities decreased on salinity acclimation. The 120-kDa immunoreactive band expressed in salinity-acclimated shrimps suggests nonspecific α-subunit phosphorylation by PKA and/or PKC. These alterations in (Na⁺, K⁺)-ATPase kinetics in salinity-acclimated M. amazonicum may result from regulatory mechanisms mediated by phosphorylation via protein kinases A and C and the FXYD2 peptide rather than through the expression of a different α-subunit isoform. This is the first demonstration of gill (Na⁺, K⁺)-ATPase regulation by protein kinases in freshwater shrimps during salinity challenge.     

Effects of temperature and salinity on the standard metabolic rate (SMR) of the caridean shrimp Palaemon peringueyi

The standard metabolic rate (SMR) of the caridean shrimp Palaemon peringueyi to changes in temperature (15-30 °C), salinity (0-45‰) and a combination thereof was investigated. The rate of oxygen consumption of the shrimp was determined using a YSI oxygen meter. At a constant salinity of 35‰ the respiration rate of P. peringueyi increased with an increase in temperature and ranged between 0.260 and 0.982 μl O₂ mg wwt^− 1 h^− 1. The Q₁₀ value over the temperature range 15-25 °C was estimated at 3.13. At a constant temperature of 15 °C the respiration rate of P. peringueyi also increased with an increase in salinity and ranged between 0.231 and 0.860 μl O₂ mg wwt^− 1 h^− 1. For combination experiments the absence of any significant difference in the respiration rate of P. peringueyi at the four temperatures over the salinity range 15-35‰ suggests that the shrimp is well adapted to inhabiting environments characterised by variations in salinity and temperature such as those encountered within the middle and lower reaches of permanently open estuaries with substantial freshwater inflow. On the other hand, the total mortality of the shrimp recorded at salinities < 5‰ at all four temperatures suggests that the upper distribution of the shrimp may reflect physiological constraints. Similarly, the increase in the respiration rate of the shrimp at the four temperatures at salinities > 35‰ suggests that the shrimp may experience osmotic stress in freshwater deprived permanently open and intermittently open estuaries where hypersaline conditions may develop.     

Temperature and salinity effects on the respiratory metabolism of the first zoeal stage of Macrobrachium holthuisi Genofre & Lobão (decapoda: Palaemonidae)

Oxygen consumption rates of stage I Macrobrachium holthuisi Genofre & Lobão zoeae were measured in 24 different temperature and salinity combinations using Cartesian diver microrespirometers. Metabolic rates varied little with salinity at 15°C while at 20°C a marked elevation occurred in 0 and 35‰ At 25°C, a slight elevation occurred in 0‰; rates remained constant, however, in the other salinities. At 30°C, respiratory rates were similar to those recorded at 25°C except for decreases at 0 and 28‰ salinity. Q₁₀ values in the different salinities were usually highest between 15 and 20°C. Statistical analyses showed that while both temperature, salinity and their interaction significantly influenced larval respiratory rates, temperature had the more pronouced effect. Larval metabolism is salinity independent over the salinity range encountered in the larval biotope (7–21‰) at temperatures of 15–30°C.     

Effects of salinity on photosynthesis and respiration of the seagrass Zostera japonica: A comparison of two established populations in North America

Photosynthetic responses were quantified for two Zostera japonica Aschers. and Graebn. populations from the northern and southern limits of distribution exposed to a range of salinities along the Pacific Coast of North America. Plants were collected from Padilla Bay, Washington (northern) and Coos Bay, Oregon, USA (southern) and cultured together in experimental tanks at 3 salinities (5, 20 and 35) under saturating irradiance for 3 weeks. Subsequently, photosynthesis–irradiance (P vs. E curves) relationships for leaf segments from the two populations were assessed using an oxygen electrode system. We found no evidence for diel rhythms in either light saturated photosynthesis (P_max) or dark respiration (R_d). For the Padilla Bay population, P_max ranged from 192 to 390 μmol O₂ g DW⁻¹ h⁻¹; for the Coos Bay population P_max ranged from 226 to 774 μmol O₂ g DW⁻¹ h⁻¹. Photosynthetic maxima of the Coos Bay plants occurred at a salinity of 20, whereas salinity had no effect on the photosynthetic maxima of the Padilla Bay plants. There were significant differences in leaf tissue R_d among salinity treatments but the two populations responded similarly to salinity. North American populations of Z. japonica are best adapted to intermediate salinities, displaying minimum R_d rates, lower compensation irradiance, higher saturation irradiance, and greater P_max rates at a salinity of 20. Additionally, the southern population may be better adapted to southward expansion along the Pacific Coast and changes associated with global climate change.     

Coordination chemistry of the heterotopic 1,2-phenylenebis(thio)diacetic acid ligand: Rhodium(I), palladium(II) and nickel(II) complexes

Starting from the heterotopic multidentate ligand 1,2-phenylenebis(thio)diacetic acid (1), cis-rac-[PdCl₂{1,2-(HOOCCH₂S)₂C₆H₄-κ²S,S′}] (2), cis-rac-[Rh{1,2-(HOOCCH₂S)₂C₆H₄-κ²S,S′}(cod)]BF₄ (3) and cis-rac-[Ni{1,2-(OOCCH₂S)₂C₆H₄-κ⁴O,O′S,S′}{cis-(C₃H₄N₂)}₂] (4) were prepared and characterised by X-ray diffraction and conventional spectroscopic techniques. Compounds 1-4 show extensive hydrogen-bonded networks (XH?O, X = O, N) in the solid state.     

Effect of SO(2) and O(3) on Production of Antioxidants in Conifers

Production of antioxidants was investigated in needles of fir (Abies alba Mill.) and spruce (Picea abies (L.) Karst) after exposure to low concentrations of SO₂, O₃, and a combination of both pollutants. Glutathione reacted most sensitively to pollutants followed by vitamin E and vitamin C. In spruce needles, the overall increase of antioxidants after exposure to air pollutants was lower than in needles of fir. SO₂ was more potent than O₃. Maximum increase of antioxidants was found in needles after exposure of trees to SO₂ + O₃.     

Effects of salinity on the respiration and heart rate of the common mussel, Mytilus edulis L., and the black chiton, Katherina tunicata (Wood)

The rate of oxygen consumption of stepwise acclimated Mytilus edulis L. increased linearly from 30 to 10‰ salinity (S) while that of Katherina tunicata (Wood) was not significantly different between 10 and 30‰ S. Heart rate was 21–22 and 17–18 beats m^?1 in Mytilus edulis and Katherina tunicata, respectively, and no difference was found in the heart rate of either species acclimated stepwise to 10, 20 or 30‰ S. The average oxygen consumption rate of Mytilus edulis exposed to 12 h, 30-10-30 and 10-30-10‰ S cycles of fluctuating salinity was significantly lower than the respective control rate: there was a similar response during the 30-10-30‰ S cycle in Katherina tunicata. The respiration rate of Mytilus edulis and Katherina tunicata declined as salinity deviated from the control salinity and increased as salinity returned to the control salinity. The rate of oxygen consumption by K. tunicata varied directly with the ambient salinity during the 10-30-10‰ S cycle. The average heart rate of Mytilus edulis was significantly lower during cyclic changes in salinity than at the respective control salinities; a similar relationship existed for Katherina tunicata during the 10-30-10‰ S cycle. Heart rate of Mytilus edulis varied in a parallel manner with oxygen consumption during both cycles. Katherina tunicata heart rate was relatively constant and could not be fitted to a regression line during the 10-30-10‰ S cycle. The normalized heart rate increased to 113% of control at 10‰ S of the 30-10-30‰ S cycle and returned to the control rate by 12 h. The oxygen consumption and heart rate of these two species are not directly coupled to regulation of water volume because different responses are observed with respect to salinity although there is poor water volume regulation in both species.     

The relationship between osmoregulation and nitrogen metabolism in the intertidal prawn,Palaemon elegans (Rathke)

• 1.1. The relationship between nitrogen metabolism and osmoregulation has been studied in the prawn Palaemon elegans (Rathke) following sudden exposure to hyper- and hyposaline conditions.
• 2.2. Animals acclimated to a salinity of 30‰ showed a pronounced increase in the rates of ammonia excretion during the first 2 hr after transfer to lower salinities. These gradually declined during the next 6 hr to rates that were significantly higher than that of control animals (30‰) and were maintained throughout the rest of the experiment.
• 3.3. Rates of ammonia excretion in animals transferred to hypersaline conditions (40‰) fluctuated considerably during the experiment. It was consistently observed, however, that there were two periods during the experiments when ammonia excretion rates had negative values indicating that NH⁺₄ ions were being taken up by the prawns.
• 4.4. Experiments in which small quantities of (NH₄)₂SO₄ containing the stable isotope ¹⁵N were added to the sea-water confirmed that P. elegans was able to take NH⁺₄ ions from the sea-water.
• 5.5. Changes in the Na⁺ ion concentration in the blood and the changes in free amino acid concentration in the blood and in the muscle after exposure to differing salinities were also determined. Their significance and relationship to the observed changes in the rates of ammonia excretion are discussed.

     

The effect of salinity and ion composition on oxygen consumption and nitrogen excretion of Macrobrachium rosenbergii (de man)

• 1.1. Oxygen consumption and nitrogen excretion rates of Macrobrachium rosenbergii were recorded in media of varying salinities and ion compositions (Mevo Hamma, Yahel, Elat—continental water; and 15 and 24%. seawater dilutions).
• 2.2. Oxygen consumption rates were not significantly different (P > 0.05) with the exclusion of Yahel having a metabolic rate of 0.258ml O₂/gfw/hr which was significantly different from the other experimental media at the P ≲- 0.05 level.
• 3.3. Nitrogen excretion rates were lowest in prawns adapted to Yahel water, 0.0188mg NH₄-N/gfw/hr and increased with salinity to 0.0494mg NH₄-N/gfw/hr in 24%.
• 4.4. The O: N ratios ranged from 12.24 to 22.65 indicating that in dilute media (Mevo Hamma and Yahel) relative to saline media (15%, Elat and 24%) more lipids and carbohydrates are utilized as an energy substrate while the latter group increased protein catabolism.