Acid-base status in the sea urchins Psammechinus miliaris and Echinus esculentus (Echinodermata: Echinoidea) during emersion

The acid-base status of two sea urchins, Psammechinus miliaris (Gmelin) and Echinus esculentus (L.) during experimental emersion has been investigated. Sea urchins were collected from the Firth of Clyde between August and September 1987. The carbon dioxide capacity of the coelomic fluid of P. miliaris was greater than that of E. esculentus, although both were low and only marginally greater than that of sea water. The pH of the coelonic fluid was also low (7.05 to 7.17) and was influenced mainly by the internal partial pressure of CO₂ (P_{CO 2}). Acid-base disturbance in the coelomic fluid of both species during emersion, although minimal, was more pronounced in E. esculentus than in P. miliaris and was due primarily to an increase in the internal P_{CO 2}, although there was an increase in the concentration of L-lactate in the coelomic fluid of E. esculentus. The coelomic fluid of both species was in a state of perfectly compensated respiratory acidosis. An increase in the concentration of divalent ions (Ca²⁺ and Mg²⁺) may be related to the dissolution of the test as a source of carbonate buffer.     

Anaerobic and aerobic energy metabolism in ovaries of the sea urchin Strongylocentrotus droebachiensis

The gonads of sea urchins undergo large changes in mass during their gametogenic cycle. In addition, they have relatively low aerobic capacities and are poorly perfused by the circulatory system and thus are continually hypoxic or anoxic. The present study of Strongylocentrotus droebachiensis investigates seasonal changes in the relationships among mass of the ovaries, pH and P_O2 of the perivisceral coelomic fluid which bathes the ovaries, and partitioning of ovary energy metabolism into its anaerobic and aerobic components. S. droebachiensis were collected at Blue Hill Falls, Maine, USA, from August 1982 to March 1984. We found that from 76 to 92% of the heat dissipated by isolated ovaries of the sea urchin S. droebachiensis derives from anaerobic energy metabolism at partial pressures of oxygen prevailing in vivo. Ovaries from S. droebachiensis have the capacity to produce large amounts of lactate under imposed anoxia, but lactate accounts for only 37% of the total anoxic heat dissipation, which suggests that other end products of anaerobiosis are present. Seasonal changes in pH and P_O2 of the perivisceral coelomic fluid can be explained by a complex relationship among changes in temperature, reproductive condition, and anaerobic and aerobic metabolism in the ovaries, gut and body wall. Seasonal changes in the buffering capacity of the perivisceral coelomic fluid must be determined before the effects of respiratory and metabolic acid production on the acid-base status of the coelomic fluid can be fully understood.     

Accumulation and release of petroleum-derived aromatic hydrocarbons by four species of marine animals

Survival of Ctenodiscus crispatus during exposure to hypoxia (P _{O 2}<3 mm Hg) at 5°C is greater than that of any echinoderm reported in the literature, the LT₅₀ being 248 h; this is reduced to 236 h in the presence of hydrogen sulfide. Unlike Asterias vulgaris and A. forbesi, both of which lose the tube foot response to tactile stimulation long before death from hypoxia occurs, C. crispatus remains responsive until death. The extension of the highly protrusible epiproctal cone, which occurs in 75% of the mud stars simultaneously exposed to hypoxia and H₂S, serves to maintain burrow contact with the overlying water. The rate of oxygen consumption remains constant down to an ambient oxygen partial pressure of 10 to 25 mm Hg, becoming more oxygen-dependent after prior exposure of the asteroids to hypoxia. C. crispatus exhibits a clear oxygen-debt phenomenon as well as a compensatory reduction in the residual P _{O 2} (oxygen partial pressure at which oxygen consumption ceases) from 2.4 to 0.2 mm Hg after hypoxic exposure.     

Metabolic and blood characteristics of the hydrothermal vent tube-worm Riftia pachyptila

Specimens of the hydrothermal vent pogonophoran Riftia pachyptila Jones were collected by submersible at a depth of 2 600 m at the 21°N hydrothermal vent site on the East Pacific Rise (20°50N, 109°06W) in April and May of 1982. The worms were maintained in pressurized aquaria for up to 45 d for metabolic studies. Consumption of O₂ was regulated down to low P_{O 2} (oxygen partial pressure) values; O₂ consumption rates were 0.63 and 1.12 mol g^-1 wet wt h^-1 at 2.5° and 8°C, respectively; such rates were comparable to those previously measured for other pogonophorans. Intact specimens of R. pachyptila (including bacterial symbionts) did not consume significant amounts of CH₄ from the environment. The respiratory quotients, in the absence of added sulfide, indicated that metabolism was mainly heterotrophic. High rates of uptake of dissolved amino acids were recorded for one specimen. The total [CO₂] in the vascular blood and the Hb-containing coelomic fluid were high. Under anaerobic conditions, there were equilibrium distributions of pH, total [CO₂] and sulfide concentrations between the vascular blood and the coelomic fluid, apparently because these metabolites were readily exchanged between the two compartments. The vascular blood bound neither CH₄ nor H₂. However, sulfide was reversibly bound by both the vascular blood and coelomic fluid; because this binding depended strongly on pH (with a maximum at about 7.5), HS^- was probably the molecular species bound. Under anaerobic, but not aerobic conditions, the trophosome bound substantial amount of sulfide; thus, the high concentrations of sulfide in the trophosome may have resulted mainly from sulfide bound to sulfide oxidases under anaerobic conditions. The coelomic fluid had a relatively low buffering capacity (2.2 mmol CO₂pH^-1).     

Effects of hypoxia on the respiratory and circulatory regulation of Nephrops norvegicus

The burrowing decapod Nephrops norvegicus (L.) was kept under various degrees of hypoxia in order to measure respiration, heart rate, scaphognathite rate, haemolymph oxygen content and pH. An emergence reaction to hypoxia occurred only in dim light (<10^-2 m-c) or darkness, but after 10 d of moderate hypoxia the decapods showed no emergence response at all. The weight specific respiration of quiescent individuals was relatively low and increased only slightly in hypoxia (P_wO₂=40 torr). Heart rate, about 50 beats min^-1, changed little during hypoxia, down to P_wO₂=40 torr, whereas scaphognathite rates rose from about 60 beats min^-1 at normoxia to peak at 120 beats min^-1 at P_wO₂=40 torr. The oxygen extraction efficiency (E) remained at 20 to 30% during the first hour of hypoxia then rose gradually to maximum values of 30 to 40%. A small respiratory alkalosis of the blood became evident only after 4h of hypoxia (P_wO₂=50 torr). Normoxic postbranchial O₂ tensions (P_aO₂) were low (25–30 torr) and showed only a small decline during hypoxia. Over 10 to 13 d in moderate hypoxia an effective biosynthesis of 0.024 mM haemocyanin individual^-1 d^-1 occurred in fed decapods, whereas controls (normoxic) showed no significant change in pigment levels. A linear relationship between oxygen carrying capacity and haemocyanin concentration was found. It is contended that N. norvegicus is better able to cope with periodic exposure to hypoxia when food of sufficient quantity and quality is available.     

The hypoxia avoidance behaviour of juvenile Atlantic cod (<Emphasis Type="Italic">Gadus morhua</Emphasis> L.) depends on the provision and pressure level of an O<Subscript>2</Subscript> refuge

The frequency of low O₂ (hypoxia) has increased in coastal marine areas but how fish avoid deleterious water masses is not yet clear. To assess whether the presence and oxygen pressure (PO₂) level of an O₂ refuge affects the hypoxia avoidance behaviour of fish, individual Atlantic cod (Gadus morhua L.) were exposed to a range of O₂ choices in a 2-way choice chamber at 11.4°C over two different experiments. Cod in the first experiment were allowed access to a fixed O₂ refuge (fully air-saturated seawater) whilst oxygen pressure (PO₂) on the other side was reduced in steps to a critically low level, i.e. 4.3 kPa—a point where cod can no longer regulate O₂ consumption. Under these conditions, cod did not avoid any level of hypoxia and fish swimming speed also remained unchanged. In contrast, strong avoidance reactions were exhibited in a second experiment when fish were again exposed to 4.3 kPa but the safety, i.e. PO₂, of the refuge was reduced. Fish not only spent less time at 4.3 kPa as a result of fewer sampling visits but they also swam at considerably slower speeds. The presence of an avoidance response was thus strongly related to refuge PO₂ and it is unlikely that cod, and possibly other fish species, would enter low O₂ to feed in the wild if a sufficiently safe O₂ refuge was not available. It is therefore hypothesized that the feeding range of fish may be heavily compressed if hypoxia expands and intensifies in future years.     

Respiratory impairment by water-borne copper and zinc in the edible crab cancer pagurus (L.) (Crustacea: Decapoda) during hypoxic exposure

Specimens of the edible crab Cancer pagurus (L.) collected in the Skagerrak, Denmark, between June and August 1990 were examined in the laboratory. Impairment of respiratory function after pre-exposure (7 d) to sub-lethal concentrations of Cu and Zn (0.4 mg l^-1) was only detectable during hypoxic exposure [PO₂ (partial pressure of oxygen) =60 torr]. This was indicated by a decrease in the transfer factor (TO₂), due principally to an increase in the PO₂ differential across the gills. Cu and Zn exposure did not cause significant changes in ventilation or perfusion although there was some indication that cardiac output may increase in respiratory-impaired individuals. After 28 d exposure no difference was noted in the respiratory responses to hypoxia of treated and untreated crabs. It is concluded that respiratory impairment was due to an increase in the diffusion barrier thickness at the gills and that this was reversible even during continued exposure to trace metal contamination.     

Oxygen dependent sulfide detoxification in the lugwormArenicola marina

The lugwormArenicola marina L. oxidizes entering sulfide to thiosulfate. After 8 h of normoxic incubations with sulfide concentrations of 0.2 to 1.0 mmoll^-1 thiosulfate in the coelomic fluid amounted up to about 4 mmoll^-1 whereas sulfite concentrations were 100-fold lower and no accumulation of sulfate in the coelomic fluid was found. The sulfide oxidation was highly oxygen dependent. An increase of oxygen partial pressure ( ) in the medium was followed by enhanced thiosulfate production and by a decrease of sulfide concentration in the coelomic fluid. Under normoxia, the sulfide oxidation rate was sufficient to compensate the influx of sulfide into the coelomic fluid when the sulfide concentration in the medium was below 0.33 mmoll^-1. When external sulfide was raised beyond this level, sulfide up to 5 moll^-1 in the coelomic fluid appeared. Succinate in the body wall tissue was low as long as no sulfide appeared in the coelomic fluid, indicating the maintenance of an aerobic metabolism. The oxidation of sulfide to thiosulfate was localized in the mitochondria of the body wall tissue. The oxygen consumption of mitochondria was stimulated by the addition of sulfide. The mitochondrial sulfide oxidation rate depended on the amount of mitochondrial protein and followed a Michaelis-Menten kinetic. An apparentK _m of 0.68±0.29 moll^-1 and aV _max of 41.9±22.3 nmol min^-1 mg^-1 protein was calculated. Sulfide was stoichiometrically oxidized to thiosulfate with 1 mol sulfide consuming 1 mol oxygen. Sulfide oxidation was not inhibited by sulfide concentrations as high as 100 moll^-1. At low concentrations of cyanide or azide, when respiration without sulfide was already inhibited, sulfide oxidation could still be stimulated, tentatively indicating the existence of an alternative terminal oxidase. Specimens examined in the present study were collected near St. Pol de Leon, France, from 1989 to 1992.     

Blood oxygen-binding characteristics of bigeye tuna (Thunnus obesus), a high-energy-demand teleost that is tolerant of low ambient oxygen

 We found blood from bigeye tuna (Thunnus obesus) to have a significantly higher O₂ affinity than blood from other tunas. Its P₅₀ (partial pressure of oxygen, P_O2 required to reach 50% saturation) was 1.6 to 2.0 kPa (12 to 15 mmHg) when equilibrated with 0.5% CO₂. Previous studies employing similar methodologies found blood from yellowfin tuna (T. albacares), skipjack tuna (Katsuwonus pelamis), and kawakawa (Euthynnus affinis) to have a P₅₀ of 2.8 to 3.1 kPa (21 to 23 mmHg). These observations suggest that bigeye tuna are more tolerant of low ambient oxygen than other tuna species, and support similar conclusions derived from laboratory whole-animal studies, depth-of-capture data, and directly-recorded vertical movements of fish in the open ocean. We also found the O₂ affinity of bigeye tuna blood to be essentially unaffected by a 10 C° open-system temperature change (as is the blood of all tuna species studied to date). The O₂ affinity of bigeye tuna blood was, however, more affected by a 10 C° closed-system temperature change than the blood of any tuna species yet examined. In other words, bigeye tuna blood displayed a significantly enhanced Bohr effect (change in log P₅₀ per unit change in plasma pH at P₅₀) when subjected to the inevitable changes in partial pressure of carbon dioxide (P_CO2) and plasma pH that accompany closed-system temperature shifts, than when subjected to changes in plasma pH accomplished by changing P_CO2 alone. In vivo, the resultant large decrease in O₂ affinity (i.e. the increase in P₅₀) that occurs as the blood of bigeye tuna is warmed during its passage through the vascular counter-current heat exchangers ensures adequate rates of O₂ off-loading in the swimming muscles of this high-energy-demand teleost. Received: 12 March 1999 / Accepted: 18 December 1999     

Essential fatty acids influence metabolic rate and tolerance of hypoxia in Dover sole (Solea solea) larvae and juveniles

Dover sole (Solea solea, Linneaus 1758) were raised from first feeding on brine shrimp (Artemia sp.) with different contents and compositions of the essential fatty acids (EFA) arachidonic acid (ARA, 20:4n − 6); eicosapentaenoic acid (EPA, 20:5n − 3), and docosahexaenoic acid (DHA, 22:6n − 3), and their metabolic rate and tolerance to hypoxia measured prior to and following metamorphosis and settlement. Four dietary Artemia preparations were compared: (1) un-enriched; (2) enriched with a commercial EFA mixture (Easy DHA SELCO Emulsion); (3) enriched with a marine fish oil combination (VEVODAR and Incromega DHA) to provide a high ratio of ARA to DHA, and (4) enriched with these fish oils to provide a low ratio of ARA to DHA. Sole fed un-enriched Artemia were significantly less tolerant to hypoxia than the other dietary groups. Larvae from this group had significantly higher routine metabolic rate (RMR) in normoxia, and significantly higher O₂ partial pressure (PO₂) thresholds in progressive hypoxia for their regulation of RMR (P _crit) and for the onset of agitation, respiratory distress and loss of equilibrium. Metamorphosis was associated with an overall decline in RMR and increase in P _crit, but juveniles fed on un-enriched Artemia still exhibited higher P _crit and agitation thresholds than the other groups. Sole fed un-enriched Artemia had significantly lower contents of EFA in their tissues, both before and after settlement. Thus, enriching live feeds with EFA has significant effects on the respiratory physiology of sole early life stages and improves their in vivo tolerance to hypoxia. We found no evidence, however, for any effect of the ratio of ARA to DHA.     

Effect of salinity on hypoxia tolerance of resting green crabs, Carcinus maenas, after feeding

Mechanisms that can influence the tolerance of hypoxia in brackish waters were studied in resting and fed crabs, Carcinus maenas, at 15?°C. Mortality, blood oxygenation, acid-base status and lactate concentration were analysed in fed crabs held in full-strength normoxic seawater (32.5‰?S) and then transferred for 24?h to a partial pressure of oxygen (P_o2) of 3?kPa (1.4?mg?l^?1) and various salinities (17, 12.5, 10, 8‰?S). At salinity levels >10‰, fed crabs tolerated P_o2 values as low as 3?kPa in the ambient water and 0.5?kPa in their arterial blood for 24?h without switching to anaerobic metabolism. Only below 10‰?S did their blood-lactate content rise, leading to their death despite the fact that their blood O₂-content was twice the control value measured in full-strength normoxic seawater and their blood P_o2 did not decrease below values recorded at higher salinity levels. Addition of CO₂ to 8‰?S water (CO₂ partial pressure increasing from 0.1 to 0.3?kPa) decreased blood-lactate production and mortality, suggesting that at 10‰?S impairment of the O₂ supply is limited by an excessive blood O₂-affinity. The results are discussed in terms of the distribution (?10‰?S) of C. maenas along salinity gradients in estuaries and bays.     

The burrows and physiological adaptations to a burrowing lifestyle of Natatolana borealis (Isopoda: Cirolanidae)

The isopod Natatolana borealis Lilljeborg constructs U-shaped burrows in soft mud, the bore of which closely approximates the width of the occupant. Within artificial burrows, the isopods are largely quiescent and often adopt a position close to one of the burrow openings. Conditions within burrows constructed in the laboratory are moderately hypoxic [11.7 to 14.9 kPa (88 to 112 torr)], with isopods showing discontinuous irrigation behaviour (pleopod beating). Rates of oxygen consumption (measured at 10°C) are maintained approximately constant over a wide range of oxygen partial pressure (P_{O 2}) due, in part, to a pronounced increase in pleopod beat rate. Values for the critical partial pressure of oxygen (P_c), the P_{O 2} at which can no longer be maintained independent of P_{O 2}, were 2.0 to 3.3 kPa (15 to 25 torr). N. borealis can survive lengthy periods (65 h at 5°C) of anoxia, during which there is a significant reduction in the carbohydrate concentration and an increase in the l-lactate concentration of the tissues. The oxygencarrying capacity of the haemolymph of N. borealis was low. The haemocyanin showed a relatively high oxygen affinity [P₅₀=0.39 kPa (2.99 torr) at 10°C at the in vivo pH of 7.80] and a pronounced Bohr effect (-1.22). These characteristics may be advantageous to a burrowing mode of life and also for the conditions likely to be encountered in fish carcasses into which they burrow en masse to feed.     

Physiological and behavioral aspects of Calanus euxinus females (Copepoda: Calanoida) during vertical migration across temperature and oxygen gradients

 In the Black Sea, during summer stratification, Calanus euxinus (Hulsemann) undertakes diel vertical migrations with an amplitude of about 117 m from oxygenated, warm (18 °C) surface layers to hypoxic (∼0.8 mg O₂ l⁻¹) zones with lower temperature (7.9 °C). When such changes in temperature and oxygen concentration are reproduced in the laboratory, total metabolism, basal metabolism and scope of activity of copepods decrease 7.2, 7.8 and 6.7 times, respectively, while the frequency of locomotory acts and mechanical power decline 3.4- and 9.5-fold, respectively. These changes allowed the copepods to conserve a significant portion of food consumed near the surface for transformation to lipid reserves. Diel respiratory oxygen consumption of migrating individuals, calculated so as to include actual duration of residence in layers with different temperature and oxygen concentrations, is estimated at 17.87 μg O₂ ind⁻¹. The net energy cost of vertical migration made up only 11.6% of the total. Copepods expend 78.6% of diel energy losses during approximately 10 h in the surface layers, while about 5.4% is required during about 9 h at depth. Hypoxia is shown to have a significant metabolic advantage during diel vertical migrations of C. euxinus in the Black Sea. Received: 1 October 1999 / Accepted: 11 July 2000     

Calorimetric studies on the energy metabolism of an infaunal bivalve,Abra tenuis,under normoxia,hypoxia and anoxia

Direct calorimetry was employed to measure the energy metabolism of infaunal bivalves, Abra tenuis, collected from a tidal lagoon in the Fleet, southern England, in June 1989, at various oxygen partial pressures. A significant anaerobic component (i.e., 20% of total metabolic rate) was detected under normoxia, presumably brought about by the intermittent ventilatory activity of this bivalve under these conditions. Under hypoxia (2.3 to 10 kPa, or 11 to 48% of full air saturation), however, the energy metabolism was maintained fully aerobic; the measured heat equivalent of oxygen uptake was not significantly different from the theoretical ranges for fully aerobic catabolism. Under anoxia, the rate of heat dissipation was reduced to 5–6% of the normoxic rate of heat dissipation. This conserves energy expenditure and would thus increase resistance of A. tenuis to anoxia or emersion. Physiological compensation by A. tenuis under conditions of declining oxygen tension involved a marked increase in ventilation rate. Comparison between fed and starved individuals indicated that costly physiological processes, such as digestion, absorption and growth declined at 10 and 5 kPa and were arrested at P_{O 2} (oxygen partial pressure) levels below 2.3 kPa. The present study provides evidence that there are no major differences between the metabolic responses of epifaunal suspension-feeding (eg. Mytilus edulis) and infaunal deposit-feeding (eg. A. tenuis) bivalves when exposed to environmental hypoxic stress.     

Does oxygen deficiency modify the functional response of Saduria entomon (Isopoda) to Bathyporeia pilosa (Amphipoda)?

The functional response of the predatory isopod Saduria entomon to the prey amphipod Bathyporeia pilosa was measured in normoxia (95% O₂ saturation), moderate hypoxia (45% O₂ saturation) and hypoxia (35% O₂ saturation) in aquarium experiments. The prey densities tested ranged from 400 to 8000 ind m⁻². Prey density influenced consumption rates of S. entomon in normoxia and 45% O₂ saturation, but there was no difference between consumption rates at these two oxygen levels. Nevertheless the form of functional response differed. In normoxia S. entomon showed a positively density-dependent functional response to B. pilosa, indicating a potentially stabilizing effect on the prey population. In moderate hypoxia the variance in consumption increased, decreasing the statistical power to distinguish between response models. The functional response of S. entomon in moderate hypoxia was best described with a density-independent response, characterized as destabilizing for the prey population. In hypoxia (35% O₂) predation by S. entomon did not respond to increasing prey density, as almost no amphipods were eaten at this oxygen level. The results are discussed in terms of the usability of theoretical models to examine predator–prey relationships in stressful environments. Received: 26 April 1997 / Accepted: 20 May 1997     

Some effects of hypoxia and medium ammonia enrichment on efflux rates and circulating levels of ammonia inNephrops norvegicus

Eutrophication has been reported for autumn months in regions of the Kattegat/Skagerrak, causing stress to bottom-living organisms. The present studies, undertaken in April (1989), investigated the effects of hypoxia and high ammonia levels in the burrowing decapodNephrops norvegicus (L.). The net ammonia efflux rates and circulating ammonia levels at 6 and 12°C, at normoxia [partial pressure of O₂ in the water (torr),P _wO₂ = 155 torr)] and hypoxiaP _wO₂ = 24 torr) in normal seawater and ammonia-enriched (300µmol ammonia l^–1) seawater were examined. The hourly weight-specific efflux rates were very variable and in all groups included some individuals which showed periods of no net efflux, or even a net uptake of ammonia. At each temperature, net efflux-rate differences due to treatments were not significant (P>0.05; ANOVA, in all cases) and only the differences between the net efflux rates of the normoxic groups were significantly affected by temperature (P<0.05; ANOVA). Circulating ammonia levels were also variable, and at 6°C the ammonia-enriched groups had significantly higher weight-specific blood ammonia content values than the normoxic group (P<0.05 in both cases). A net uptake of ammonia occurred in ammoniaenriched conditions — probably along a reversed NH ₄ ⁺ gradient, as downhill pNH₃ gradients were maintained in all groups — and may represent the only means by which some branchial efflux of ammonia could proceed.     

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.     

Respiration as a function of oxygen concentration in intertidal barnacles

Respiration as a function of oxygen concentration was studied in two species of intertidal barnacles: Balanus amphitrite amphitrite ¹ (Darwin) and B. tintinnabulum tintinnabulum (L.). A critical oxygen tension was observed in both species below which the respiratory regulation broke down. In B. amphitrite amphitrite the critical oxygen tension was 2.5 ml O₂/l, and in B. tintinnabulum tintinnabulum 3.5 ml O₂/l. Species differences and habitat relations were observed in both species in their respiratory adaptation to oxygen concentration. B. amphitrite amphitrite which inhabits oxygen-deficient areas was able to regulate to much lower concentrations than B. tintinnabulum tintinnabulum which inhabits oxygen-rich open intertidal regions.     

Zonation,vesicle pressure and gas composition in Fucus vesiculosus and Ascophyllum nodosum at Kristineberg (West Coast of Sweden)

Features of fucoid zonation (Fucus spiralis, F. vesiculosus, Ascophyllum and F. serratus) in a vertical range of 60 cm at Kristineberg (Gullmar Fjord, W. Coast of Sweden) are described. In contrast to identical species occupying areas with wider tidal ranges, these plants are smaller in size and inhabit narrow, overlapping zones. Investigation into the magnitude of pressure and gas composition in vesicles of F. vesiculosus and Ascophyllum nodosum revealed an average positive pressure equivalent to 1.7 and 7 cm of water for the 2 plants in succession. These small values compare favourably with the pressure head to which such vesicles are subjected at Kristineberg. O₂-percentage amounts to 28.5% and 32.7% in vesicles of both plants in succession. O₂-values increase in daytime and decrease at night or when plants are maintained in the dark. CO₂-content in the two plants fluctuates between 0 to 2.6% and bears no correlation to the oxygen values. It is suggested that the pressure produced in the vesicles is due mainly to oxygen. Comparison of these results with those by other authors are made whenever possible.     

Respiration of Sepia officinalis during embryonic and early juvenile life

Adult Sepia officinalis L. were caught in June 1984, in the coastal waters of Wimereux (France). Deposition of the eggs took place in the seawater aquaria of the Station Marine. The oxygen consumption of S. officinalis was measured during embryonic and juvenile development. Aerobic metabolism occurs as soon as the early embryonic Stage 21. Oxygen diffuses through the initially thick egg shell; the oxygen level in the perivitelline liquid reaches a maximal value just before hatching (116.7±6.9 mm Hg). Hatchings display only a slight increase in oxygen consumption compared to embryos in the last stage of development. Respiration experiments with 40 d old juveniles showed that oxygen consumption increases with temperature, but is not affected by photoperiod. Experiments under increasing hypoxia revealed that S. officinalis juveniles are good regulators and maintain a constant oxygen consumption in the range of 4 to 7 mg O₂l^-1. Juveniles successfully recover from an hypoxic stress of 2 mg O₂l^-1 maintained for 1 h. This suggests that the respiratory pigments (pre-hemocyanins) of 40 d-old juveniles have a high oxygen affinity and/or that these juveniles have the ability to adapt to anaerobic conditions.