Effect of amino acids on the swimming activity of newly hatched turbot larvae (Scophthalmus maximus)

The swimming behaviour of newly hatched turbot (Scophthalmus maximus L.) larvae was observed in artificial seawater (ASW) and in solutions of 21 l-amino acids at a concentration of 10⁻⁵  M. The behaviour of 20 larvae was analysed in each solution. Each larva was observed for 1 min. Individual movements were recorded on video and analysed using a computer-assisted program. The larvae swam in convoluted, randomised three-dimensional paths, rested and started swimming again. There were large variations in the swimming behaviour of turbot larvae during ontogeny. In ASW the mean frequency of trajectories longer than a body length of 4 mm larva⁻¹ min⁻¹ increased from 1.2 at Day 1, to 10 at Day 4. Analysing the data (Dunnett's method) revealed that the frequency of swimming trajectories increased in the presence of glycine, histidine and glutamine, and decreased in the presence of proline. The total distance swum increased for glycine but decreased for proline. The threshold concentration for glycine detected by turbot larvae was 10⁻⁵  M. The straightness index did not change in the presence of the amino acids. The possible role of these changes in behaviour is discussed. Received: 12 June 1997 / Accepted: 13 January 1998     

Microsensor studies of photosynthesis and respiration in larger symbiotic foraminifera. I The physico-chemical microenvironment of Marginopora vertebralis, Amphistegina lobifera and Amphisorus hemprichii

 The physico-chemical microenvironment of larger benthic foraminifera was studied with microsensors for O₂, CO₂, pH, Ca²⁺ and scalar irradiance. Under saturating light conditions, the photosynthetic activity of the endosymbiotic algae increased the O₂ up to 183% air saturation and a pH of up to 8.6 was measured at the foraminiferal shell surface. The photosynthetic CO₂ fixation decreased the CO₂ at the shell down to 4.7 μM. In the dark, the respiration of host and symbionts decreased the O₂ level to 91% air saturation and the CO₂ concentration reached up to 12 μM. pH was lowered relative to the ambient seawater pH of 8.2. The endosymbionts responded immediately to changing light conditions, resulting in dynamic changes of O₂, CO₂ and pH at the foraminiferal shell surface during experimentally imposed light–dark cycles. The dynamic concentration changes demonstrated for the first time a fast exchange of metabolic gases through the perforate, hyaline shell of Amphistegina lobifera. A diffusive boundary layer (DBL) limited the solute exchange between the foraminifera and the surrounding water. The DBL reached a thickness of 400–700 μm in stagnant water and was reduced to 100–300 μm under flow conditions. Gross photosynthesis rates were significantly higher under flow conditions (4.7 nmol O₂ cm⁻³ s⁻¹) than in stagnant water (1.6 nmol O₂ cm ⁻³ s⁻¹), whereas net photosynthesis rates were unaffected by flow conditions. The Ca²⁺ microprofiles demonstrated a spatial variation in sites of calcium uptake over the foraminiferal shells. Ca²⁺ gradients at the shell surface showed total Ca²⁺ uptake rates of 0.6 to 4.2 nmol cm⁻² h⁻¹ in A. lobifera and 1.7 to 3.6 nmol cm⁻² h⁻¹ in Marginopora vertebralis. The scattering and reflection of the foraminiferal calcite shell increased the scalar irradiance at the surface up to 205% of the incident irradiance. Transmittance measurements across the calcite shell suggest that the symbionts are shielded from higher light levels, receiving approximately 30% of the incident light for photosynthesis. Received: 6 July 1999 / Accepted: 28 April 2000     

Photosynthetic utilisation of inorganic carbon by seagrasses from Zanzibar, East Africa

Photosynthetic rates of eight seagrass species from Zanzibar were limited by the inorganic carbon composition of natural seawater (2.1 mM, mostly in the form of HCO₃ ⁻), and they exhibited more than three time higher rates at inorganic carbon saturation (>6 mM). The intertidal species that grew most shallowly, Halophila ovalis, Halodule wrightii and Cymodocea rotundata, showed the highest affinity for inorganic carbon (K _1/2 = ca. 2.5 mM), followed by the subtidal species (K _1/2 > 5 mM). Photosynthesis of H. wrightii, C. rotundata, Cymodocea serrulata and Enhalus acoroides was >50% inhibited by acetazolamide, a membrane-impermeable inhibitor of carbonic anhydrase, indicating that extracellular HCO₃ ⁻ dehydration is an important part of their inorganic carbon uptake. Photosynthetic rates of H. wrightii, Thalassia hemprichii, Thalassodendron ciliatum, C. serrulata and E. acoroides were strongly reduced by changing the seawater pH from 8.2 to 8.6 in a closed system. In H. ovalis, C. rotundata and Syringodiumisoetifolium, photosynthesis at pH 8.6 was maintained at a higher level than could be caused by the ca. 30% CO₂ concentration which remained in the closed experimental systems at that pH, pointing toward HCO₃ ⁻ uptake in those species. It is suggested that the ability of H. ovalis and C. rotundata to grow in the high, frequently air-exposed, intertidal zone may be related to a capability to take up HCO₃ ⁻ directly, since this is a more efficient way of HCO₃ ⁻ utilisation than extracellular HCO₃ ⁻ dehydration under such conditions. The inability of all species to attain maximal photosynthetic rates under natural conditions of inorganic carbon supports the notion that seagrasses may respond favourably to any future increases in marine CO₂ levels. Received: 19 March 1997 / Accepted: 31 March 1997     

Microsensor studies of photosynthesis and respiration in the symbiotic foraminifer Orbulina universa

Oxygen and pH microelectrodes were used to investigate the microenvironment of the planktonic foraminifer Orbulina universa and its dinoflagellate endosymbionts. A diffusive boundary layer surrounds the foraminiferal shell and limits the O₂ and proton transport from the shell to the ambient seawater and vice versa. Due to symbiont photosynthesis, high O₂ concentrations of up to 206% air saturation and a pH of up to 8.8, i.e. 0.5 pH units above ambient seawater, were measured at the shell surface of the foraminifer at saturating irradiances. The respiration of the host–symbiont system in darkness decreased the O₂ concentration at the shell surface to <70% of the oxygen content in the surrounding air-saturated water. The pH at the shell surface dropped to 7.9 in darkness. We measured a mean gross photosynthetic rate of 8.5 ± 4.0 nmol O₂ h⁻¹ foraminifer⁻¹. The net photosynthesis averaged 5.3 ± 2.7 nmol O₂ h⁻¹. In the light, the calculated respiration rates reached 3.9 ± 1.9 nmol O₂h⁻¹, whereas the dark respiration rates were significantly lower (1.7 ± 0.7 nmol O₂ h⁻¹). Experimental light–dark cycles demonstrated a very dynamic response of the symbionts to changing light conditions. Gross photosynthesis versus scalar irradiance curves (P vs E _o curves) showed light saturation irradiances (E _k) of 75 and 137 μmol photons m⁻² s⁻¹ in two O. universa specimens, respectively. No inhibition of photosynthesis was observed at irradiance levels up to 700 μmol photons m⁻² s⁻¹. The light compensation point of the symbiotic association was 50 μmol photons m⁻² s⁻¹. Radial profile measurements of scalar irradiance (E _o) inside the foraminifera showed a slight increase at the shell surface up to 105% of the incident irradiance (E _d). Received: 26 January 1998 / Accepted: 11 April 1998     

Low molecular-weight factor from Plesiastrea versipora (Scleractinia) that modifies release and glycerol metabolism of isolated symbiotic algae

When symbiotic dinoflagellate algae (Symbiodinium sp., isolated from the coral Plesiastrea versipora) were incubated with NaH¹⁴CO₃ in the light in seawater, they released 22.69±9.16 nmol carbon/10⁶ algae. Release of photosynthetically fixed carbon was stimulated more than six-fold for algae incubated in host-tissue homogenate (148.54±97.03 nmol C/10⁶ algae) and more than four-fold (102.00±49.16 nmol C/10⁶ algae) for algae incubated in a low molecular weight fraction (≤1 000 M _r ) prepared from host homogenate. Soluble released ¹⁴C-labelled products, as determined by chromatography and autoradiography, were the same when algae were incubated in either host homogenate or the low molecular weight fraction. After 4 h incubation in the light (300 mol photons m⁻² s⁻¹),␣intracellular␣glycerol increased in algae incubated with the low molecular weight fraction (an increase of 0.39 to␣0.67 nmol glycerol/10⁶ algae) compared with little or no increase in algae incubated in seawater (0 to 0.12 nmol glycerol/10⁶ algae). Partial inhibition of triglyceride synthesis (up to 51%) was also observed when algae were incubated in the low molecular weight fraction. All these effects are the same as those observed when algae were incubated in host homogenate. These data indicate that the “host release-factor” activity of P.␣versipora is a compound of low molecular weight. Received: 13 February 1997 / Accepted: 24 October 1997     

Inhibition of Na+/K+-ATPase and of active ion-transport functions in the gills of the shore crab Carcinus maenas induced by cadmium

Inhibition of Na⁺/K⁺-ATPase from gill plasma membranes of the shore crab Carcinus maenas by cadmium was investigated and compared with inhibitory effects by known antagonists (ouabain and Ca²⁺). For comparative considerations the Cd²⁺-inhibition of the enzyme from dog kidney was also tested. Na⁺/K⁺-ATPase from dog kidney and from crab gill differed greatly in sensitivity against ouabain. The inhibition constant K _i of the dog enzyme amounted to 9.1 × 10⁻⁷ mol l⁻¹, i.e. more than 300-fold smaller than the K _i of 2.9 × 10⁻⁴ mol l⁻¹ determined for the crab enzyme. Ca²⁺ inhibited the activity of Na⁺/K⁺-ATPase from crab gill plasma membranes with a K _i of 4.3 × 10⁻⁴ mol l⁻¹. The Na⁺/K⁺-ATPase from crab gill was inhibited by Cd²⁺ with a K _i of 9.1 × 10⁻⁵ mol l⁻¹. Cd²⁺ inhibited the Na⁺/K⁺-ATPase from dog kidney with a K _i (6.4 × 10⁻⁵ mol l⁻¹) comparable to that observed in the crab gill enzyme. Under experimental conditions Cd²⁺-inhibition of Na⁺/K⁺-ATPase was irreversible. Repeated washing, centrifugation and homogenization of the plasma membranes (four times) with Cd²⁺-free buffer did not restore any activity lost in the presence of 1 × 10⁻³ mol l⁻¹ Cd²⁺. Since ouabain-insensitive (nonspecific) ATPases in the plasma membrane fraction of crab gills were inhibited by Cd²⁺ in the same way as Na⁺/K⁺-ATPase, the heavy metal is considered as an unspecific ATPase inhibitor. Comparing these results with literature data on Cd²⁺-binding to electrophoretically separated proteins suggests that Na⁺/K⁺-ATPase is a Cd²⁺-binding enzyme. The results obtained on Na⁺/K⁺-ATPase were reflected by Cd²⁺-inhibition of the branchial ion-transport functions depending on this enzyme. The transepithelial short-circuit current of isolated gill half lamellae, a direct measure of area-specific active ion uptake, and the transepithelial potential difference of isolated, perfused whole gills, also indicative of active ion uptake, were inhibited by the heavy metal in a time- and dose-dependent mode. Remarkably these inhibitions were also irreversible. These findings are ecologically and biomedically significant: even when the actual environmental or tissue concentrations measured are low, biological microstructures such as Na⁺/K⁺-ATPase may accumulate the heavy metal by tight binding over prolonged periods until the first inhibitory effects occur. Received: 25 June 1997 / Accepted: 25 August 1997     

Effect of an organophosphorus insecticide, fenitrothion, on survival and osmoregulation of various developmental stages of the shrimp Penaeus japonicus (Crustacea: Decapoda)

The toxicity of fenitrothion was determined in larvae (nauplii, Zoeae 1 to 3, Mysis 1 to 3), postlarvae (PL stages) and juvenile shrimp (Penaeus japonicus Bate), in two media, seawater (SW) and diluted seawater (DSW) (1100 and 550 mosM kg⁻¹, ≃ 37 and 19‰ S). The effects of fenitrothion on the osmoregulatory capacities (OC) of juveniles were recorded. A gill and epipodite histopathological study was also conducted. For larvae in seawater, 24 and 48 h LC₅₀s ranged from 32.9 μg l⁻¹ (Zoeae 2) to 10.7 μg l⁻¹ (Mysis 3), and from 3.9 μg l⁻¹ (Zoeae 3) to 2.0 μg l⁻¹ (Mysis 3), respectively; 48 and 96 h  LC₅₀s in postlarvae (PL) at the same salinity ranged from 1.8 μg l⁻¹ (PL1) to 0.6 μg l⁻¹ (PL5), and from 0.3 μg l⁻¹ (PL7) to 0.4 μg l⁻¹ (PL15). In juveniles, 96 h LC₅₀s were 0.8 μg l⁻¹ in seawater and 1.5 μg l⁻¹ in diluted seawater. From hatching to juvenile stages, the overall trend was a rapid decrease (from nauplii to PL5–PL7) followed by a slight increase (from PL7 to PL15 and juveniles) in the shrimp's ability to tolerate the insecticide. In juveniles kept in seawater and in diluted seawater, fenitrothion decreased the osmoregulatory capacity (OC = difference between the hemolymph osmotic pressure and the osmotic pressure of the medium) at both lethal and sublethal concentrations. This effect was time- and dose-dependent. In SW, the decrease in hypo-OC was ˜ 25% at sublethal concentrations and ˜ 35% at the 96 h LC₅₀. In DSW, the decrease in hyper-OC was ˜ 10 to 15% at sublethal concentrations. In SW, shrimp were able to recover their OC in less than 48 h when transferred to water free of pesticide. In DSW, recovery at 48 h was only possible after exposure to the lowest tested sublethal concentration. Haemocytic congestions (thrombosis) of the gills, lamellae necrosis and other alterations of gills and epipodites (breakage of the cuticle, reduction of the hemolymph lacunae) were noted in juveniles exposed to lethal and sublethal concentrations of fenitrothion. Received: 7 October 1996 / Accepted: 13 November 1996     

Localisation of biogenic amines in larvae of Bugula neritina (Bryozoa: Cheilostomatida) and their effects on settlement

Distributions of serotonin and catecholamines in larvae of the marine bryozoan Bugula neritina (Bryozoa: Cheilostomatida) were investigated using immunohistochemistry with anti-serotonin antiserum and glyoxylic acid–induced fluorescence histochemistry. Anti-serotonin immunoreactive substances and glyoxylic acid–induced fluorescent substances had similar distributions in the equatorial neuromuscular ring, the neural plexus, the paired axial neuromuscular cords, and tracts connecting the neural plexus to ciliated cells bordering the pyriform organ. The effects of dopamine, noradrenaline, adrenaline, tyramine, octopamine, synephrine and serotonin, at 10⁻⁴, 10⁻⁵ and 10⁻⁶  M, on settlement were analysed. In filtered seawater, 98% of larvae settled in 3 h, but only 11%, 3% and 6% total settlement was observed after 8 h in 10⁻⁴  M dopamine, 10⁻⁴  M serotonin and 10⁻⁵  M serotonin, respectively. Total settlement was 70% in 10⁻⁴  M noradrenaline, 80% in 10⁻⁴  M adrenaline and 60% in 10⁻⁴  M tyramine. Less than 60% settlement was observed in 10⁻⁴ and 10⁻⁵  M octopamine and synephrine. Serotonin's inhibitory effect on settlement was mimicked by a range of serotonin receptor agonists and antagonists, among which 5-carboxamidotryptamine was the most potent. Received: 19 March 1999 / Accepted: 11 October 1999     

Symbiotic anemones can grow when starved: nitrogen budget for Anemonia viridis in ammonium-supplemented seawater

The ability of endosymbioses between anthozoans and dinoflagellate algae (zooxanthellae) to retain excretory nitrogen and take up ammonium from seawater has been well documented. However, the quantitative importance of these processes to the nitrogen budget of such symbioses is poorly understood. When starved symbiotic Anemonia viridis were incubated in a flow-through system in seawater supplemented with 20 μM ammonium for 91 d under a light regime of 12 h light at 150 μmol photons m⁻² s⁻¹ and 12 h darkness, they showed a mean net growth of 0.197% of their initial weight per day. Control anemones in unsupplemented seawater with an ammonium concentration of <1 μM lost weight by a mean of 0.263% of their initial weight per day. Attempts to construct a nitrogen budget showed that, over a 14 d period, ≃40% of the ammonium taken up could be accounted for by growth of zooxanthellae. It was assumed that the remainder was translocated from zooxanthellae to host. However, since the budget does not balance, only 60% of the growth of host tissue was accounted for by this translocation. The value for host excretory nitrogen which was recycled to the symbionts equalled that taken in by ammonium uptake from the supplemented seawater, indicating the importance of nitrogen retention to the symbiotic association. Received: 23 December 1997 / Accepted: 12 September 1998     

Extra- and intracellular acid-base balance and ionic regulation in cod (Gadus morhua ) during combined and isolated exposures to hypercapnia and copper

Cod (Gadus morhua) were exposed to hypercapnia (water Pco₂ = 7.5 mmHg), elevated copper level (0.4 ppm) or a combination of both in order to study extra- and intracellular acid-base regulation and the influence hereupon of copper. During pure hypercapnia, the extracellular respiratory acidosis was completely compensated within 12 to 24 h via a chloride-mediated increase in extracellular [HCO₃ ⁻]. Exposure to copper in normocapnic seawater caused a large and progressive increase in plasma [Na⁺] and [Cl⁻] and a metabolic acidosis. Exposure to copper in hypercapnic seawater was associated with smaller elevations of plasma [Na⁺] and [Cl⁻] than in normocapnic seawater, showing that hypercapnia had a protective effect on the copper-induced osmoregulatory disturbances. The compensation of the hypercapnic acidosis was, however, slow and incomplete in fish exposed to both copper and hypercapnia. Extracellular pH remained depressed by 0.3 pH units after 72 h. The data reveal that acid-base regulation was immediately and persistently inhibited by copper. The limited acid-base regulation during combined copper and hypercapnia exposure was chloride-mediated as during hypercapnia alone. Intracellular pH recovery was complete and very rapid in ventricular and skeletal muscle tissues during environmental hypercapnia, whereas acid-base compensation in liver tissue was slower, the kinetics being similar to that in the extracellular compartment. Intracellular pH compensation was significantly slowed down by copper. Copper concentration increased drastically in gill tissue already at 3 h, while copper concentrations in liver, muscle and plasma were significantly elevated only after 48 h, with liver showing the largest elevation. Received: 15 November 1996 / Accepted: 2 December 1996     

Irradiance and temperature regulation of oxygenic photosynthesis and O2 consumption in a hypersaline cyanobacterial mat (Solar Lake, Egypt)

 Short-term effects of temperature and irradiance on oxygenic photosynthesis and O₂ consumption in a hypersaline cyanobacterial mat were investigated with O₂ microsensors in a laboratory. The effect of temperature on O₂ fluxes across the mat–water interface was studied in the dark and at a saturating high surface irradiance (2162 μmol photons m⁻² s⁻¹) in the temperature range from 15 to 45 °C. Areal rates of dark O₂ consumption increased almost linearly with temperature. The apparent activation energy of 18 kJ mol⁻¹ and the corresponding Q ₁₀ value (25 to 35 °C) of 1.3 indicated a relative low temperature dependence of dark O₂ consumption due to mass transfer limitations imposed by the diffusive boundary layer at all temperatures. Areal rates of net photosynthesis increased with temperature up to 40 °C and exhibited a Q ₁₀ value (20 to 30 °C) of 2.8. Both O₂ dynamics and rates of gross photosynthesis at the mat surface increased with temperature up to 40 °C, with the most pronounced increase of gross photosynthesis at the mat surface between 25 and 35 °C (Q ₁₀ of 3.1). In another mat sample, measurements at increasing surface irradiances (0 to 2319 μmol photons m⁻² s⁻¹) were performed at 25, 33 (the in situ temperature) and 40 °C. At all temperatures, areal rates of gross photosynthesis saturated with no significant reduction due to photoinhibition at high irradiances. The initial slope and the onset of saturation (E _k = 148 to 185 μmol photons m⁻² s⁻¹) estimated from P versus E _d curves showed no clear trend with temperature, while maximal photosynthesis increased with temperature. Gross photosynthesis was stimulated by temperature at each irradiance except at the lowest irradiance of 54 μmol photons m⁻² s⁻¹, where oxygenic gross photosynthesis and also the thickness of the photic zone was significantly reduced at 40 °C. The compensation irradiance increased with temperature, from 32 μmol photons m⁻² s⁻¹ at 25 °C to 77 μmol photons m⁻² s⁻¹ at 40 °C, due to increased rates of O₂ consumption relative to gross photosynthesis. Areal rates of O₂ consumption in the illuminated mat were higher than dark O₂ consumption at corresponding temperatures, due to an increasing O₂ consumption in the photic zone with increasing irradiance. Both light and temperature enhanced the internal O₂ cycling within hypersaline cyanobacterial mats. Received: 30 November 1999 / Accepted: 11 April 2000     

Uptake of dissolved organic matter by larval stage of the crown-of-thorns starfish Acanthaster planci

The life-history of the crown-of thorns starfish (Acanthaster planci) includes a planktotrophic larva that is capable of feeding on particulate food. It has been proposed, however, that particulate food (e.g. microalgae) is scarce in tropical water columns relative to the nutritional requirements of the larvae of A. planci, and that periodic shortages of food play an important role in the biology of this species. It has also been proposed that non-particulate sources of nutrition (e.g. dissolved organic matter, DOM) may fuel part of the nutritional requirements of the larval development of A. planci as well. The present study addresses the ability of A. planci larvae to take up several DOM species and compares rates of DOM uptake to the energy requirements of the larvae. Substrates transported in this study have been previously reported to be transported by larval asteroids from temperate and antarctic waters. Transport rates (per larval A. planci) increased steadily during larval development and some substrates had among the highest mass-specific transport rates ever reported for invertebrate larvae. Maximum transport rates (J _max ⁱⁿ) for alanine increased from 15.5 pmol larva^–1 h^–1 (13.2 pmol g^–1 h^–1) for gastrulas (J _max ⁱⁿ=38.7 pmol larva^–1 h^–1 or 47.4 pmol g^–1 h^–1) to 35.0 pmol larva^–1 h^–1 (13.1 pmol g^–1 h^–1) for early brachiolaria (J _max ⁱⁿ just prior to settlement=350.0 pmol larva^–1 h^–1 or 161.1 pmol g^–1 h^–1) at 1 M substrate concentrations. The instantaneous metabolic demand for substrates by gastrula, bipinnaria and brachiolaria stage larvae could be completely satisfied by alanine concentrations of 11, 1.6 and 0.8 M, respectively. Similar rates were measured in this study for the essential amino acid leucine, with rates increasing from 11.0 pmol larva^–1 h^–1 (or 9.4 pmol g^–1 h^–1) for gastrulas (J _max ⁱⁿ=110.5 pmol larva^–1 h^–1 or 94.4 pmol g^–1 h^–1) to 34.0 pmol larva^–1 h^–1 (or 13.0 pmol g^–1 h^–1) for late brachiolaria (J _max ⁱⁿ=288.9 pmol larva^–1 h^–1 or 110.3 pmol g^–1 h^–1) at 1 M substrate concentrations. The essential amino acid histidine was transported at lower rates (1.6 pmol g^–1 h^–1 at 1 M for late brachiolaria). Calculation of the energy contribution of the transported species revealed that larvae of A. planci can potentially satisfy 0.6, 18.7, 29.9 and 3.3% of their total energy requirements (instantaneous energy demand plus energy added to larvae as biomass) during embryonic and larval development from external concentrations of 1 M of glucose, alanine, leucine and histidine, respectively. These data demonstrate that a relatively minor component of the DOM pool in seawater (dissolved free amino acids, DFAA) can potentially provide significant amounts of energy for the growth and development of A. planci during larval development.     

Cyclic AMP-dependent protein kinase: role in anoxia and freezing tolerance of the marine periwinkle Littorina littorea

A key regulatory mechanism underlying the switch between aerobic and anaerobic metabolism amongst anoxia-tolerant marine molluscs is reversible protein phosphorylation. To assess the role of cAMP-dependent protein kinase (PKA) in aerobic–anaerobic transitions, the effects of anoxia on the activity and subcellular distribution of PKA were assessed in foot and hepatopancreas of the marine periwinkle, Littorina littorea. Exposure to N₂ gas at 5 °C caused a rapid decline in the percentage of total enzyme present as the free catalytic subunit (PKAc) in both tissues; the percentage of PKAc fell from ∼30% in controls to 3% after 1 h anoxia and remained low over 72 h. Total PKA also fell by 30% after 72 h anoxia in hepatopancreas but rebounded during aerobic recovery. Freezing at −8 °C elicited parallel results for both percentage of PKAc and total PKA, suggesting that PKA responses to freezing were stimulated by the ischemia that develops when hemolymph freezes. Anoxia also led to a shift in PKA subcellular distribution in hepatopancreas (but not in foot), the percentage of total PKA activity associated with the nuclear fraction dropping from 25% in controls to 8% in 12 h anoxic snails with opposite changes in the cytosolic fraction. The catalytic subunit (PKAc) of foot PKA was purified to a final specific activity of 63.5 nmol phosphate transferred per minute per milligram protein. Enzyme properties included a molecular weight of 33 to 35 kDa, an activation energy from Arrhenius plots of 65.1 ± 4.8 kJ mol⁻¹, and substrate affinity constants of 151 ± 6 μM for the phosphate acceptor, Kemptide, and 72 ± 9 μM for Mg.ATP. Activity was strongly reduced by mammalian PKA inhibitors (H-89, PKA-I), by neutral chloride salts (I₅₀ values 165 to 210 mM) and by NaF (I₅₀ 62 mM). Reduced PKA activity under anoxic or freezing conditions would facilitate the observed suppression of the activities of numerous enzymes that are typically PKA-activated and thereby contribute to the overall anoxia-induced metabolic rate depression. Received: 19 November 1997 / Accepted: 30 September 1998     

Variability in larval development of the tropical reef fish Pomacentrus amboinensis (Pomacentridae): the parental legacy

The effects of food availability, female size, and social interactions on the quality of Pomacentrus amboinensis larvae at hatching were examined using two field-based experiments. In Experiment 1, food availability and female size significantly influenced size, eye diameter and levels of yolk reserves of larvae at hatching. Small females (47 to 52 mm standard length, SL) whose diets were not supplemented, produced the longest larvae (3.0 ± 0.01 mm total length, TL) with the least yolk reserves (50.1 ± 1.04 μm²). Irrespective of female size, those that received additional food produced larvae with the largest yolk-sacs (large females: 87.60 ± 1.53 μm²; small females: 80.14 ± 1.24 μm²). In Experiment 2, interactions with conspecifics had a greater affect on the somatic development of larvae at hatching than food availability. Increased social interactions resulted in larvae that were ⋍3% longer, with 2% greater head depth, than larvae from females that spawned in isolation on the experimental reefs. Fed females produced larvae with ⋍20% more yolk than larvae from females whose diets were not supplemented. All three factors (food availability, female size, and intensity of social interactions) tested within these experiments vary spatially and temporally among reefs. There is the potential, therefore, for larvae at the onset of the planktonic stage to vary in quality, level of development, and probability of survival. Received: 12 August 1996 / Accepted: 26 August 1996     

Interactions between NH+4 and NO−3 uptake and assimilation: comparison of diatoms and dinoflagellates at several growth temperatures

Ammonium concentrations of ∼1 M are commonly cited as being the threshold for inhibition of NO₃ ⁻ uptake, but the applicability of this threshold to phytoplankton from different taxonomic classes has rarely been examined. Additionally, little is known about the influence of environmental variables (e.g. growth temperature) on the interaction between ambient NH₄ ⁺ and NO₃ ⁻ uptake. Four species of estuarine phytoplankton, two diatom [Chaetoceros sp., and Thalassiosira weissflogii (Grunow) Fryxell et Hasle] and two dinoflagellate [Prorocentrum minimum (Pavillard) Schiller, and Gyrodinium uncatenum Hulburt], were grown on NO₃ ⁻ at several different temperatures (4, 10, 15, or 20 °C), and the impact of NH₄ ⁺ additions on NO₃ ⁻ uptake/assimilation (non-TCA-extracted) and assimilation (TCA-extracted) was assessed. For all species at all temperatures, NO₃ ⁻ uptake/assimilation and assimilation rates decreased in a roughly exponential manner with increasing NH₄ ⁺ concentrations but were not completely inhibited even at elevated NH₄ ⁺ concentrations of 200 μM. Estimated half-inhibition concentrations (K _i) were significantly greater in the diatom species (mean ± SE; 2.70 ± 0.67 μM) than in the dinoflagellate species (1.26 ± 0.55 μM). Half-inhibition constants were positively related to temperature-limited relative growth rate although not significantly. The observed inhibition of NO₃ ⁻ uptake and assimilation, as a percentage of NO₃ ⁻ uptake in the absence of NH₄ ⁺, averaged about 80% and ranged from 49 to 100%. For all species, a significant (P < 0.001) positive correlation was found between percent inhibition of NO₃ ⁻ assimilation and temperature-limited relative growth rate. Two experiments on Chesapeake Bay phytoplankton during an April 1998 diatom bloom showed that in short-term (∼1 h) temperature manipulation experiments, percent inhibition of NO₃ ⁻ uptake/assimilation was also positively related (P = 0.05) to experimental temperature. The observed relationships between temperature-limited relative growth rate and percent inhibition of NO₃ ⁻ assimilation rates for the species tested suggest that at the enzyme level, the inhibitory mechanism of NO₃ ⁻ assimilation is similar among species, but at the whole cell level may be regulated by species-specific differences in the accumulation of internal metabolites. These findings add not only to our understanding of species-specific variability and the role of growth temperature, but also provide additional data with which to evaluate current models of NH₄ ⁺ and NO₃ ⁻ interactions. Received: 31 August 1998 / Accepted: 7 December 1998     

Growth and productivity of the high Antarctic Bryozoan Melicerita obliqua

We analysed growth of the Antarctic bryozoan Melicerita obliqua (Thornely, 1924) by x-ray photography and stable isotope analysis. M. obliqua colonies form one segment per year, thus attaining maximum length of about 200 mm within 50 years. In the Weddell and Lazarev Seas, annual production/biomass ratio of M. obliqua is 0.1 yr⁻¹, which is in the range of other Antarctic benthic invertebrate populations. Production amounts to 3.34 mg C_orgm⁻² yr⁻¹ and 90.6 mg ash m⁻² yr⁻¹ on the shelf (100 to 600 m water depth), and to 0.13 mg C_orgm⁻² yr⁻¹ and 36.8 mg ash m⁻² yr⁻¹ on the slope (600 to 1250 m water depth). Received: 27 February 1998 / Accepted: 8 May 1998     

Carbon- and oxygen-isotope composition of the cuttlebone of Sepia officinalis: a tool for predicting ecological information?

Analysis of the isotope composition of calcareous structures of marine organisms has proved useful in providing biological data. The present study constitutes the first detailed work undertaken on the isotope composition of coleoid cephalopods. We analysed the carbon- and oxygen-isotope composition [δ¹³C (CO²⁻ ₃) and δ¹⁸O (CO²⁻ ₃), respectively] of the cuttlebone aragonite of wild and cultivated specimens of Sepia officinalis Linnaeus, 1758. δ¹³C (CO²⁻ ₃) ranged from −2.94 to 1.00‰, δ¹⁸O (CO²⁻ ₃) from −0.18 to 2.08‰. The carbon-isotope composition is not in equilibrium with the carbon species of the ambient seawater, and does not reflect the deposition of CaCO₃ in seawater. The potential influence of environmental factors and biological processes on the carbon-isotope composition of the cuttlebone is discussed. In contrast to δ¹³C, the oxygen-isotope composition of cuttlebone aragonite appears to be in isotopic equilibrium with the ambient seawater. Seasonal changes in isotopic temperature revealed by our analyses agreed with changes in the temperature of the ambient seawater. CaCO₃ was deposited all year round. A maximum life span of 2 yr, a year-round spawning season, and variable growth rates among and within individuals have been inferred from the isotopic temperatures. Received: 14 April 1998 / Accepted: 26 November 1998     

Rates of energy consumption and acquisition by lecithotrophic larvae of Bugula neritina (Bryozoa: Cheilostomata)

Lecithotrophic larvae of the cheilostome bryozoan, Bugula neritina (L.), lose metamorphic competence 12 to 24 h after release from the maternal zooid. The high respiration rate of newly released larvae (mean=306.3 pmol O₂ larva^-1 h^-1, range=149.3 to 466.6, n=18 trials, 22.5°C) from adults collected at Link Port, Fort Pierce, Florida during the winter/spring of 1990–1991 reflects their active swimming behavior. The average energy content per larva was 15.24 mJ (range: 13.35 to 20.17 mJ ind^-1, n=5 groups). If all cells have an identical energy content and metabolic rate, then 2 and 20% of the total energy content would be consumed by the onset (2 h post-release) and the loss (24 h post-release) of metamorphic competence. Larvae of B. neritina are a composite of both larval and juvenile tissues and the loss of metamorphic competence may be due to regional depletion of labile energy stores in transitory larval cells, particularly the ciliated cells that comprise the locomotory organ, the corona. Although nonfeeding, B. neritina larvae can acquire nutrients from the environment in the form of dissolved organic materials (DOM) in seawater. Both the amino acid alanine and the fatty acid palmitic acid can be transported from seawater ([S]=1 M, 22.5°C). The rates of alanine influx (appearance of label in tissue) averaged 0.366 pmol larva^-1 h^-1 and, based on comparisons between rates of solute transport and metabolism, would contribute little (<1% of required energy) to offset the metabolic demand. The average rate of palmitic acid influx was 4.668 pmol larva^-1 h^-1 and assuming that the measured influx equals the net solute flux, could account for 21 to 72% of energy requirements. These data suggest that the duration of planktonic life of B. neritina larvae is principally regulated by the amount of endogenous energy stores, but may be modulated by available DOM in seawater.     

Contrasting life histories and secondary production of populations of Munnopsurus atlanticus (Isopoda: Asellota) from two bathyal areas of the NE Atlantic and the NW Mediterranean

The isopod Munnopsurus atlanticus occupies bathyal depths in both the Bay of Biscay (NE Atlantic; between 383 and 1022 m) and in the Catalan Sea (Northwestern Mediterranean; between 389 and 1859 m). The species was dominant in both assemblages, reaching bathymetric peaks of abundance on the upper part of the continental slope (400 m depth) in the Bay of Biscay and at ˜600 m in the Catalan Sea. Both the Atlantic and the Mediterranean populations are bivoltines. Demographic analysis of the Bay of Biscay population revealed the production of two generations per year with different potential longevity (5 mo for G₁ and 11 mo for G₂). The mean cohort-production interval (CPI) was estimated at 8 mo, and results of the demographic analysis were also used to estimate production for the Catalan Sea populations. Mean annual density (D) and biomass (B) were higher in the Bay of Biscay (D = 356.7 individuals 100 m⁻²; B = 0.803 mg dry wt m⁻² yr⁻¹) than in the Mediterranean (D = 16.3 individuals 100 m⁻²; B = 0.078 mg dry wt m⁻² yr⁻¹). Also, mean annual production was an order of magnitude higher in the Atlantic (between 4.063 and 4.812 mg dry wt 100 m⁻² yr⁻¹ depending on the method used) than in the Catalan Sea (between 0.346 and 0.519 mg dry wt 100 m⁻² yr⁻¹). M. atlanticus feeds on a wide variety of benthic and pelagic food sources. In both study areas, phytodetritus was not important in the diet of M. atlanticus. In contrast, gut-content data suggested an indirect coupling with phytoplankton production in both areas via foraminiferans. The life history and the recorded production are considered in respect to both the dynamics and levels of primary production and the total mass flux in the respective study areas. Differences in the secondary production of both populations seemed to be more consistently explained by differences in total mass flux than by differences in the primary production levels; this is also consistent with the variety of food sources exploited by M. atlanticus. Received: 22 February 1999 / Accepted: 3 February 2000     

Neuroprotective potential of N -acetylcysteine in carbofuran neurotoxicity: A biochemical and histopathological study

The present study was undertaken to evaluate biochemical markers of chronic carbofuran exposure to rats in terms of lipid peroxide and intrasynaptosomal calcium levels and to correlate them with the histopathological changes in brain regions. A significant increase in lipid peroxidation (LPO) in terms of thiobarbituric acid reactive substances (TBARS) was observed in the cerebral cortex (65%) and brain stem (33%) after carbofuran exposure. This was accompanied by a significant increase (87%) in the intracellular free-Ca²⁺ [Ca²⁺]_i levels. N-acetylcysteine (NAC) administration, on the other hand, reversed the carbofuran-induced increase in LPO and [Ca²⁺]_i. Histopathological studies of carbofuran-exposed brain revealed high frequency of pyknotic neurons in the cerebral cortex and microhaemorrhages in the brain stem. NAC supplementation to carbofuran-treated animals resulted in normalisation of the brain architecture as seen by a reduction in the number of pyknotic nuclei in the cerebral cortex. These findings indicate that increased LPO and elevated [Ca²⁺]_i levels are involved in the development of carbofuran neurotoxicity and are eventually responsible for the pathological alterations. The study also demonstrates potential neuroprotective effect of NAC treatment in carbofuran neurotoxicity.