Survival of the intertidal pulmonate Onchidium tumidium during short term and long term anoxic stress

Onchidium tumidium showed a triphasic response to anoxia. Twelve hours of anoxic exposure had no effect on the glycogen content in O. tumidium. However, there were significant increases in the alanine, lactate and succinate contents in the anoxic individuals. These were accompanied by a significant decrease in the ATP content. These results suggest that O. tumidium survived the first 12 h of anoxic exposure without increasing the glycolytic flux to compensate for the lower efficiency of ATP production through anaerobic pathways. Indeed, the fructose-2,6-bisphosphate (F-2,6-P₂) content and the percentage of phosphofruc-tokinase (PFK) associated with the subcellular particles remain unchanged in O. tumidium exposed to 12 h of anoxia. Hence, a reduction in the metabolic rate of these individuals might have occurred during such a period of anoxia. In contrast, in between 12 and 24 h of anoxic exposure, the glycogen content O. tumidium decreased significantly, and levelled off thereafter. A significant increase in the percentage of PFK associated with the subcellular particles was observed in individuals exposed to 24 h of anoxia. In addition, the F-2,6-P₂ content of these anoxic individuals increased significantly. Taken together, these two mechanisms could activate PFK and lead to a greater glycolytic flux. Beyond 24 h of anoxic exposure, survival of O. tumidium must have required considerable suppression of metabolism as accumulation of end products and depletions of glycogen and ATP had reached constant levels.     

Lactate formation in Callianassa californiensis and Upogebia pugettensis (Crustacea: Thalassinidea)

The ability to accumulate lactate as a result of laboratory exposure to anoxia was examined in 2 species of mud-dwelling shrimp, the ghost shrimp Callianassa californiensis and the mud shrimp Upogebia pugettensis. Hemolymph lactate accumulated to a much greater degree in the mud shrimp, even though the overall levels of lactate dehydrogenase activity were similar in tissues of the two species. Carbohydrate reserves, estimated as glycogen, were not significantly depleted in muscle or midgut gland of either species as a result of anoxic stress. The results are discussed in relation to possible metabolic strategies employed to cope with the hypoxic environment of these crustaceans.     

Effects of anoxia on the activities of pyruvate kinase and phosphoenolpyruvate carboxykinase,and the production of lactate and succinate in the intertidal pulmonate Onchidium tumidium

Onchidium tumidium, an intertidal pulmonate, has evolved to depend mainly on the formation of succinate, rather than lactate and opines, to survive in anoxia. For our study O. tumidum were collected from the mud flats of the mangrove swamp at Mandai, Singapore between 1988 and 1991. After 24 h of anoxic exposure, the lactate and succinate contents of the anoxic individuals were approximately 10 and 150 times, respectively, the corresponding values of the normoxic individuals. Alanine and acetate accumulations also occurred during anoxia, though to a much lesser extent. No propionate or octopine was detected. The depletion in aspartate content in O. tumidium could not account for the amount of succinate accumulated during anoxia. The succinate formed might have originated from glycogen involving the flow of carbon through the phosphoenolpyruvate (PEP) branch point of glycolysis. In support of such a hypothesis, results indicate that there was a decrease in the affinity of pyruvate kinase from O. tumidium exposed to 24h of anoxia to PEP to facilitate succinate formation through phosphoenolpyruvate carboxykinase (PEPCK). In comparison, the affinity of PEPCK from O. tumidium exposed to anoxia to PEP was apparently unaltered.     

Energy metabolism in the foot of the marine gastropod Nassa mutabilis during environmental and functional anaerobiosis

This study concerns the effects of oxygen deprivation due to incubation in oxygen free sea water (environmental anoxia) or exercise (functional anoxia) and of exposure to air on the mode of energy production in the foot of the whelk Nassa mutabilis. Additionally, energy metabolism of the foot muscle was investigated during exercise after different anoxia periods and during the subsequent recovery period. During environmental anoxia, phosphoarginine, glycogen and aspartate are broken down as substrates and alanine and succinate are formed as products. There was no production of D-lactate or octopine. The energy charge value fell after 24-h anoxia. Exposure to air resulted in only small changes in phosphoarginine and alanine levels, suggesting that oxygen uptake was impaired in the first phase of air exposure but that, later, aerial respiration kept pace with the energy demand. Exercise caused a dramatic decrease of phosphoarginine concentration, coupled with glycolytic ATP production via octopine formation. In the recovery period (after exercise), the level of phosphoarginine was rapidly restored. An anaerobic component was evident during recovery as shown by the accumulation of D-lactate. Thus, both terminal dehydrogenases, octopine- and lactate dehydrogenase, are active in the muscle, but under different physiological conditions. Octopine formation also took place when the whelks were subjected to exercise after 4 or 24 h of anoxia. In this case, glycolysis provided between 70 and 90% of the energy required since the phosphagen store had already been depleted during the anoxic period. When the work load was increased (greater number of leaps), it became evident that the action of arginine kinase and octopine dehydrogenase are not closely linked. First there was an increase of arginine and then later a condensation of arginine with pyruvate to form octopine.     

Anaerobic metabolism in the shrimp Crangon crangon exposed to hypoxia,anoxia and hydrogen sulfide

The brown shrimp Crangon crangon was collected in the Penzé estuary, Bretagne, in April 1994 and exposed to hypoxia, anoxia and combinations of hypoxia and sulfide. Exposure to sulfide induced total anaerobic metabolism even at an oxygen saturation which would otherwise permit totally aerobic metabolism. In addition to preventing aerobic metabolism there was a direct toxic effect of sulfide. Haemocyanin oxygen affinity (p₅₀) values from non-stressed C. crangon were relatively low. The p₅₀ values all exceed those where environmentally induced lactate accumulation occurs. It seems unlikely that lactate is an affinity modulating factor under environmental hypoxia.     

Metabolic responses of the prawns Palaemon elegans and P. serratus (Crustacea: Decapoda) to acute hypoxia and anoxia

Using prawns, Palaemon elegans (Rathke) from intertidal pools on the Isle of Cumbrae, Scotland, and P. serratus (Pennant) from the subtidal at Plymouth, England, some metabolic responses to hypoxia and anoxia have been studied. P. elegans was found to have a greater tolerance of severe hypoxia than P. serratus. Tolerance of totally anoxic conditions, however, was limited to only 4 h in P. elegans and to approximately 1 h in P. serratus. exposure to moderate hypoxia (30 torr) resulted in little change in the concentration of L-lactate in the blood or in the tissues of either P. elegans or P. serratus. When exposed to extreme hypoxia (10 or 5 torr for P. elegans), however, there was a progressive increase in the concentration of L-lactate in the blood and in the tissues of both species. After normoxic conditions had been restored, the concentration of L-lactate in the blood and in the tissues returned to normal resting levels more rapidly in P. elegans than in P. serratus. Under hypoxic conditions, both P. elegans and P. serratus showed an increase in the concentration of blood glucose and a slight reduction in the glycogen content of the tissues. The concentrations of blood glucose and of tissue glycogen returned to normal levels within 6 h of the prawns being returned to normoxic conditions. The results of an in situ study in April and August 1986 to examine the metabolic responses of P. elegans to the hypoxic conditions normally experienced in high-shore rock pools are also presented. The ecological significance of the differing abilities of these species to survive hypoxic exposure is discussed.     

L-Lactate dehydrogenase in the longitudinal muscle of the sea cucumber Sclerodactyla briareus (Echinodermata: Holothuroidea)

The infaunal holothurian Sclerodactyla briareus (Thyone briareus) is able to tolerate exposure to hypoxic conditions for over 2 days. Since the in vitro anaerobic degradation of glucose-U-C¹⁴ by longitudinal muscle preparations leads to an accumulation of labeled lactic acid, it is apparent that lactate dehydrogenase plays a key role during anoxia. Disc electrophoresis resolved one major band of lactate dehydrogenase (LDH) activity in longitudinal muscle extracts. Muscle extracts of s. briareus oxidized L-lactate only, as is the case with most other echinoderms. The apparent Michaelis constants for lactate oxidation and pyruvate reduction are dissimilar from values reported for other marine invertebrates. The LDH activity in this holothurian is higher than the activities reported for other marine invertebrates with the exception of some active, large arthropods. Substrate inhibition of LDH maximal activity occurs at substrate concentrations (pyruvate) exceeding 10 mM, and then to only a minor extent. The characteristics of lactate dehydrogenase from the longitudinal muscle of S. briareus support the hypothesis that it functions to maintain glycolytic flux during prolonged periods of exposure to anoxic or hypoxic conditions.     

Regulation of glycolytic enzymes in the marine invertebrateHalicryptus spinulosus (Priapulida) during environmental anoxia and exposure to hydrogen sulfide

A particularly strong reduction of metabolic activity is a precondition for long-term survival ofHalicryptus spinulosus von Siebold under anoxic habitat conditions because of its relatively low fuel reserves (mainly glycogen). The present study analyses the mechanism of this metabolic slow-down. For this purpose the effects of environmental anoxia and exposure to hydrogen sulfide on the activity and selected kinetic properties of glycolytic enzymes [glycogen phosphorylase (GP), pyruvate kinase (PK)] and the concentrations of fructose-2,6-bisphosphate in the body wall ofH. spinulosus were analysed. Anoxia and hydrogen sulfide exposure stimulated modifications of the properties of the enzymes, in both cases due to probable covalent modification of the enzyme proteins. Under both conditions phosphorylase activity was depressed by about 1/3, the result of changes in the percentage of enzyme in the activea-form as well as the total amount of enzyme activity expressed (a +b). Effects of anoxia on the properties of pyruvate kinase included reducedV _max , decreasedS _0.5 for phospho-enolpyruvate, changes inK _a for fructose-1,6-bisphosphate (an initial decrease was followed by a later increase). TheI ₅₀ forL-alanine of PK was extremely reduced under anoxia and showed an even greater sensitivity to the presence of hydrogen sulfide. Anoxia stimulated a slight reduction in the content of fructose-2,6-bisphosphate, whereas exposure to hydrogen sulfide caused a dramatic decrease of this allosteric activator of phos-phofructokinase. The study gives evidence that mechanisms of glycolytic rate depression are conserved within a wide variety of vertebrate and invertebrate phyla. With two exceptions (fructose-2,6-bisphosphate levels and alanine inhibition of PK) the responses to hydrogen sulfide were the same as those to anoxia, suggesting that at a metabolic level, the consequences of each stress on energy metabolism are similar.     

Effects of anaerobiosis on root metabolism of Zostera marina (eelgrass): implications for survival in reducing sediments

The temperate seagrass Zostera marina L. typically grows in highly reducing sediments. Photosynthesis-mediated O₂ supplied to below-ground tissues sustains aerobic respiration during photosynthetic periods. Roots, however, experience daily periods of anoxia and/or hypoxia at night and under conditions that reduce photosynthesis. Rhizosphere cores of Z. marina were collected in August 1984 from Great Harbor, Massachusetts, USA. We examined short-term anaerobic metabolism of [U-¹⁴C]sucrose in excised roots and roots of intact plants. Under anaerobic conditions roots showed appreciable labeling of CO₂, ethanol and lactate, and slight labeling of alanine and other metabolites. Over 95% of the ¹⁴C-ethanol was recovered in the root exudate. Release of other metabolites from the roots was minimal. Ethanol was also released from hypoxic/anoxic roots of intact plants and none of this ethanol was transported to the shoot under any experimental conditions. Loss of ethanol from roots prevented tissue levels of this phytotoxin from increasing during anaerobiosis despite increased synthesis of ethanol. Anaerobic metabolism of [U-¹⁴C]glutamate in excised roots led to appreciable labelling of -aminobutyrate, which was known to accumulate in eelgrass roots. Roots recovered to fully aerobic metabolism within 4 h after re-establishment of aerobic conditions. The contributions of these root metabolic responses to the ability of Z. marina to grow in reducing marine sediments are related to light-regulated interactions of shoots and roots that likely dictate depth penetration, distribution and ecological success of eelgrass.     

UV-absorbing substances in the tunic of a colonial ascidian protect its symbiont, Prochloron sp., from damage by UV-B radiation

The infaunal bivalve Ruditapes decussatus L. was collected from Ria Formosa, Faro, southern Portugal, and subjected to a range of hypoxic conditions and anoxia. Physiological measurements, clearance rates, respiration rates and absorption efficiency were undertaken at slightly different oxygen partial pressures (11, 6, 3 and 1.2 kPa for clearance rates and absorption efficiency and 12, 7, 5, 1.9 and 0.9 kPa for respiration rates). Metabolic rates under hypoxia were measured as oxygen consumption and anoxic metabolism was measured using direct calorimetry. Increasing hypoxia resulted in lower clearance rates, leading to lower ingestion rates and reduced faeces production. Clearance and ingestion rates declined below ˜6 kPa, reflecting decreasing ventilation and feeding activity, although complete cessation was not observed even at 1.2 kPa. Under extreme hypoxia (< 2 kPa) clams showed an irregular behaviour, with valves either closed or only slightly open, and siphons compressed or retracted. Clearance rate was 12% and respiration rate was 35% of normoxic rates. R. decussatus responded to increasing hypoxia by lowering its metabolic rate. Regulation of respiration was absent through moderate hypoxia (˜␣7␣kPa), but was observed in the lower hypoxia range (7 to 0.9 kPa). Under anoxia, rates of heat dissipation were 3.6% of normoxic rates. The low anoxic metabolic rate is indicative of a reduced energy expenditure, and this energy-saving mechanism is common in bivalves. Scope for growth was always pos itive, and even at low oxygen levels clams did not have to utilize their energy reserves. The ability to reduce metabolic costs but still meet the maintenance costs by aerobic catabolism enables R. decussatus to tolerate hypoxia. Such conditions can occur, particularly in the summer, in southern Portugal. Received: 19 July 1996 / Accepted: 17 September 1996     

Metabolic disposition of lactate in the horseshoe crab Limulus polyphemus and the stone crab Menippe mercenaria

The metabolism of ¹⁴C-labelled lactate was investigated in the horseshoe crab Limulus polyphemus and the stone crab Menippe mercenaria. When a bolus of (¹⁴C-U)-D-lactate was injected into L. polyphemus, there was substantial release pf ¹⁴CO₂ into the medium. In the case of M. mercenaria, ¹⁴CO₂ release was also observed after injection of (¹⁴C-U)-L-lactate into experimental individuals. Analysis of the distribution of radioactivity in whole body extracts of both species revealed easily detectable amounts of radioactivity in the glycogen fraction, although the bulk of the radioactivity was in the cation, anion/neutral and CO₂ fractions. To investigate the metabolism of lactate further, ¹⁴C-labelled lactate was injected into large individuals of L. polyphemus and M. mercenaria, and the distribution of radioactivity was determined in the hemolymph, muscle and hepatopancreas. Utilization of (¹⁴C-U)-D-lactate by L. polyphemus resulted in the accumulation of significant amounts of labelled glucose in all three body compartments as well as the production of labelled glycogen in the telson levator muscle and hepatopancreas. Utilization of (¹⁴C-U)-L-lactate resulted in a similar pattern of glucose and glycogen labelling in the hemolymph, cheliped muscle and hepatopancreas of M. mercenaria. These studies demonstrate that both L. polyphemus and M. mercenaria have the capacity for glyco- and gluconeogenesis using lactate as the substrate.     

Metabolic constraints on burst-swimming in the Antarctic teleost Notothenia neglecta

Immediate-energy-supply pathways were analysed during burst-swimming in white muscle of the Antarctic fish Notothenia neglecta, (collected during Austral summer 1984 near Signy Island, South Orkneys). Selected enzyme activities were determined, and tissue metabolites were measured, before and after 3 min of burst-work. The activity of glycolytic enzymes is very low compared to that in other fish, while the activities of creatine phosphokinase, adenylate kinase and AMPdeaminase are relatively high. Concentrations of metabolites associated with cellular energy status declined with exercise. At the same time, there was no change in the concentrations of most of the glycolytic metabolites measured (including glycogen, glucose and lactate), while [creatine phosphate] declined and [inosine monophosphate] increased. These observations were used to propose that the potential for ATP generation via creatine-phosphate hydrolysis is enhanced in N. neglecta, while glycolytic capacity is relatively reduced. This is an unusual pattern of ATP production and places severe constraints upon the behavior of the fish. While the capacity for very short-term, high-power-output swimming is increased, the capacity for medium-duration swimming is reduced. Ecological repercussions are discussed.     

Relation of habitat to glycogen concentration and glycogen synthetase in polychaetes

The glycogen content of whole body or muscle of 14 species of polychaetes was determined, and the activity, co-factor requirements, and substrate affinity of glycogen synthetase from muscles of 4 of the species were measured. Species average glycogen concentrations were positively correlated with the risk of anoxia each species faced in the field. Total activity of glycogen synthetase was not correlated with glycogen concentration in muscle, but polychaetes most likely to experience anoxia had the highest proportion of the enzyme in the active (co-factor independent = I) form; moreover, in such species, the glycogen synthetase had the highest affinity for substrate. It was concluded that evolutionary adaptation to oxygen-poor habitats occurs through qualitative changes in enzyme properties rather than through quantitative changes in enzyme production.     

Ammonia production and kinetic properties of glutamate dehydrogenase in the sipinculid Phascolosoma arcuatum exposed to anoxia

The amounts of total NH ₄ ⁺ detected in the external media in which Phascolosoma arcuatum had been exposed to various periods of anoxia were significantly greater than those in which the worms were exposed to normoxia for a similar period. The increased NH ₄ ⁺ production by P. arcuatum during anoxic exposure was unlikely to be due to an increased catabolism of adenine nucleotides or urea. In contrast, there were significant decreases in the concentrations of several free amino acids in the coelomic plasma and body tissues of individuals during the 48 h of anoxic exposure. The amount of NH ₄ ⁺ produced by the anoxic P. arcuatum could be accounted for by the decreases in the concentrations of aspartate or glycine. Increases in the catabolism of free amino acids (FAA), leading to the increased production of NH ₄ ⁺ , in P. arcuatum during anoxia were supported by the detection of significant changes in the kinetic properties of glutamate dehydrogenase (GDH), in the deaminating direction, from worms exposed to anoxia for 48 h. The apparent increase in the affinity of GDH from the anoxic worm to glutamate would bring about a greater deaminating activity at physiological concentrations of ths substrate. P. arcuatum used in these experiments were collected from the mangrove swamp at Mandai, Singapore between 1990 and 1993.     

Nephtys hombergii, a free-living predator in marine sediments: energy production under environmental stress

Nephtys hombergii is a free-living, burrowing predator in marine sediments. The worm is, therefore, exposed to various environmental conditions which tube-dwelling polychaetes of the same habitat most likely do not encounter. The worms have to survive periods of severe hypoxia and sulphide exposure, while at the same time, they have to maintain agility in order to feed on other invertebrates. N. hombergii is adapted to these conditions by utilising several strategies. The species has a remarkably high content of phosphagen (phosphoglycocyamine), which is the primary energy source during periods of environmental stress. With increasing hypoxia, energy is also provided via anaerobic glycolysis (pO₂<7 kPa), with strombine as the main end-product. Energy production via the succinate pathway becomes important only under severe hypoxia (<2 kPa), suggesting a biphasic response to low oxygen conditions which probably is related to the worm's mode of life. The presence of sulphide resulted in a higher anaerobic energy flux and a more pronounced energy production via glycolysis than in anoxia alone. Nevertheless, after sulphide exposure under anaerobic conditions of <24 h, N. hombergii is able to recover completely. Although N. hombergii appears to be well adapted to a habitat with short-term fluctuations in oxygen and appearance of hydrogen sulphide, its high energy demand as a predator renders it likely to limit its survival in an environment with longer lasting anoxia and concomitant sulphide exposure. Received: 28 May 1997 / Accepted: 21 June 1997     

Carbohydrate metabolism during anoxia and post-anoxia recovery in Chasmagnathus granulata crabs maintained on high-protein or carbohydrate-rich diets

We assessed the effects of anoxia exposure and recovery on glycogen synthesis and mobilization, glucose uptake, and on the enzymes that control carbohydrate metabolism in the hepatopancreas of Chasmagnathus granulata crabs receiving either a carbohydrate-rich (HC) or a high-protein diet (HP). In both dietary groups, anoxia led to a reduction in glucose uptake and in glycogen synthesis, and to an increase in hepatopancreas glycogen mobilization and in hemolymph glucose concentration. During the first 4 h of exposure to anoxia, total glycogen phosphorylase (GPT) and a form activity increased in HP and HC crabs, leading to a decrease in hepatopancreas glycogen concentration. During recovery, HP and HC crabs rapidly restored the hemolymph glucose levels to pre-anoxia concentrations. In HC crabs, incorporation of ¹⁴C from glucose into glycogen increased gradually after 12 h in normoxia, leading to restoration of glycogen concentration. Also during recovery, the ratio of glycogen synthase I (GSI) to glycogen phosphorylase a (GPa) increased in the HC group. In turn, recovering HP crabs had two peaks of glycogen synthesis, related with two peaks in the ratio of GSI to GPa. Consequently, no mobilization of ¹⁴C-glycogen occurred in recovering HP animals. Anoxia in C. granulata induces a marked decrease in the synthesis of carbohydrate reserves that is accompanied by an increase in glycogen mobilization and in circulating glucose levels. During the recovery period, there is an activation of endergonic processes which cause a decrease in hemolymph glucose levels. In C. granulata, glycogen metabolism seems to be controlled by the ratio of the GSI form to the GPa form. In field conditions, theses changes in the metabolic pattern may result from environmental PO₂ availability. In the winter, C. granulata stays in its holes, where environmental PO₂ falls to zero. The carbohydrate or protein content of the diets administrated to the crabs seem to induce different metabolic adjustments during anoxia and recovery.     

Biologie du chinchard de la Mer Noire (Trachurus mediterraneus ponticus)

The carbohydrate and oxidative metabolism of the lateral musculature and of the liver was investigated in two Black Sea fishes. In Trachurus mediterraneus ponticus, muscular work leads to an intensification of glycolysis in the white muscle, and of oxidation in the red muscle as well as in the liver. Extirpation of the lateral red muscle provokes strong disturbances of muscle performance (without affecting the double character of contraction); the glycogen content of the white muscle decreases, while the lactate content of the liver increases. Hypoxic conditions lead, within a short time, to disturbances of the oxidative capacity in the red muscle and in the liver. In Gobius melanostomus, the effects of hypoxy or of muscular work are less pronounced. In isolated mixed muscle strips of Trachurus, contractions lead to a decrease of glycogen content in the red portion only. In isolated red muscle strips, the glycogen content rises during the incubation. These results are interpreted as supporting the hypothesis of a metabolic role of the lateral red muscle in fishes as energy source for the white muscle and as oxidative site for the catabolites of the latter.     

Glycogen storage in relation to the moult cycle in the two crustaceansEmerita asiatica andLigia exotica

InEmerita asiatica, the quantitative fluctuations in the glycogen content of the hepatopancreas were markedly related to the moult cycle. The glycogen content of the hepatopancreas was maximum during premoult stages. It has been suggested that reserve glycogen, in addition to meeting general metabolic needs, may be especially involved in the genesis of the sugar precursors of chitin. The marked fall in the hepatopancreas glycogen values following moulting is probably due to its utilization in chitin synthesis during and immediately following moulting. InE. asiatica, the storage of glycogen was found to be meagre in muscles, and muscle glycogen had no bearing on chitin synthesis during moulting. InLigia exotica, glycogen is stored to a lesser extent than inE. asiatica, and was found in connective tissue and muscles. Significant fluctuations were noted in glycogen values correlated with the phases in the moult cycle when chitin synthesis took place. InL. exotica, the hepatopancreas does not serve as a storage depot for glycogen related to chitin synthesis.     

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.     

Effect of dissolved oxygen level on respiratory metabolism, nutritional physiology, and immune condition of southern king crab Lithodes santolla (Molina, 1782) (Decapoda, Lithodidae)

Episodes of hypoxia are common in the marine environment, and their ecological effects depend, in part, on their severity and duration. Many species of decapod crustaceans reside in areas with fluctuating oxygen regimens. Physiological mechanisms enhance the ability of these crustaceans to cope with acute episodes of hypoxia. Southern king crab, Lithodes santolla, fishery is important in the south of South America, and some data describe fishing zones with low dissolved oxygen (DO) levels (3.5 mgO₂ l⁻¹, i.e., 8.3 kPa). Our main objective was to evaluate the effect of dissolved oxygen level on respiratory metabolism, nutritional physiology, and immunological condition of L. santolla juveniles. Individual animals were exposed for 10 days to different oxygen tensions (2.1, 4.2, 8.5, 12.7, and 21.1 kPa) to quantify the oxygen consumption rate; thereafter, blood oxyhemocyanin (Hc), protein concentration, as well as hemocytes, were sampled. Freeze-dried animals were dissected, and digestive gland metabolites (glycogen, protein, glucose, cholesterol, acylglycerol, and lactate) and digestive enzyme activity (general protease, trypsin, and chymotrypsin), as well as gill lactate dehydrogenase (LDH) activity, were quantified. In the present study, Lithodes santolla showed a critical oxygen tension between 4 and 9 kPa, indicating that this crab species is more sensitive to DO than other crustacean species. Protein and Hc concentrations followed a similar pattern to that of oxygen consumption. Digestive gland glycogen and protein concentration did not change after 10 days at different oxygen exposures, but glucose, cholesterol, and acylglycerol concentrations decreased linearly and proportionally to the available oxygen in the water. As in other decapods, chymotrypsin showed over 90% of the total quantified proteases activity. Chymotrypsin activity together with total proteases and trypsin was not affected by the environmental oxygen tension. Gill LDH and digestive gland lactate followed a similar increase at lower environmental oxygen tension but dropped sharply at the lowest tension (2.1 kPa). Dissolved oxygen affected also the immune system through reduction of hemocytes. This could provide a critical window for opportunistic pathogens to become established when crabs are exposed to hypoxic conditions. L. santolla juveniles show a moderate tolerance to low oxygen availability by modifying the concentration of hemolymph proteins, mainly OxyHc, some digestive gland metabolites, and by activating the anaerobic metabolism. This allows L. santolla juveniles to inhabit temporarily low oxygen zones in the deep ocean and suggests an advantage for culture conditions.