Metabolic characteristics of midwater zooplankton: Ammonia excretion,O:N rations,and the effect of starvation

The nature of protein catabolism in a wide range of species of midwater zooplankton was investigated. The weight-specific ammonia excretion rates (g NH₃–N g^–1 dry wt h^–1, y) decline exponentially with minimum depth of occurreece (MDO, x), y=163.4 x^{–0.479±0.212} (95%ci) (CI=confidence interval), when temperature is held constant. The change in ammonia excretion can be partially explained by the decrease in percent protein (%P) with MDO, %P=80.17 MDO^{–0.148±0.122 (95%ci)} The atomic O:N ratio of freshly caught zooplankters ranged from 9.1 to 91, with most measurements between 9 and 25. Detailed studies were carried out on the response of one of the species studied (Gnathophausia ingens) to starvation (28 d). After 14 d of starvation the average ammonia excretion rate declined by more than 75% to less than 1 g NH₃–N g^–1 wet wt h^–1, although the average oxygen consumption declined by only 13% within the first 7 d of starvation and then remained stable. This differential response of oxygen consumption and ammonia excretion to starvation resulted in an increase in the average O:N ratio of starved animals from an initial 33 to 165 after 21 d. The average O:N ratios of fed mysids remained below 38 during the experiment. G. ingens maintains a relatively uniform metabolic rate during starvation by relying more heavily on its large lipid stores than when being fed.     

Background levels of soil beryllium in several countries

Beryllium and aluminium contents in uncontaminated soils from six countries are reported. The means and ranges of beryllium in the surface soils were as follows: 1.43(0.20–5.50)g g^–1 in Thailand (n=28), 0.7 (0.31–1.03) g g^–1 in Indonesia (n=12), 0.99(0.82–1.32) g g^–1 in New Zealand (n=3), 0.58(0.08-1.68)g g^–1 in Brazil (n=16), 3.52(2.49–4.97)g g^–1 in the former Yugoslavia (n=10), and 1.56(1.01–2.73) g g^–1 in the former USSR (n=8). The mean and range of beryllium contents of the surface soils in Japan (1.17(0.27–1.95)g g^–1 n=27) are situated within the values of the soils from these countries except for the Yugoslav soils derived from limestones. The mean of the mean beryllium contents of the surface soils in all these countries is 1.42 g g^–1 which will be used as a tentative average content of beryllium in uncontaminated surface soils, except for the soils derived from parent materials high in beryllium content. The beryllium contents of the subsoils were higher than those of the surface soils in New Zealand and Yugoslavia as is the case with Japan. The correlation coefficient between the contents of beryllium and aluminium in all the soil samples (n=113) including surface soils and subsoils was 0.505 (p < 0.001).     

Seasonal and depth related variation in the photosynthesis–irradiance response of<Emphasis Type="Italic"> Ecklonia radiata</Emphasis> (Phaeophyta,Laminariales) at West Island,South Australia

The photosynthesis–irradiance response of Ecklonia radiata (C. Agardh) J. Agardh, a common kelp in the temperate southern hemisphere, was investigated in situ throughout the year and across a depth profile at West Island, South Australia. Temperature and irradiance environment altered throughout the year, varying at 3 m between 14–20°C and 279–705 mol photons m^–2 s^–1. Photosynthetic capacity (P_m) varied throughout the year between 177–278 mol O₂ g^–1 dry wt h^–1 at 3 m and 133–348 mol O₂ g^–1 dry wt h^–1 at 10 m. The irradiance required for sub-saturation of photosynthesis (E_k) varied between 97–152 and 81–142 mol photons m^–2 s^–1 for 3 m and 10 m respectively, and the respiration rate varied between 15–36 and 13–20 mol O₂ g^–1 dry wt h^–1 for 3 m and 10 m. A clear seasonal change in photokinetic parameters was detected and provided strong evidence for a seasonal acclimation response. During winter an increase in the efficiency of light utilisation at low irradiance () was accompanied by a decrease in both E_k and that required for photosynthetic compensation. P_m also increased during the winter and autumn months and respiratory requirements decreased. These changes enable E. radiata to display an optimal photosynthetic performance throughout the year despite significant changes in the surrounding environment.Communicated by P.W. Sammarco, Chauvin     

Environmental Se–Mo–B Deficiency and its Possible Effects in Jiantou Keshan Disease Area in Shaanxi Province, China

Keshan disease (KD) occurs in a wide geographic belt stretching from the Heilongjiang Province in northeastern China to Yunnan Province in southwestern China, including Huangling County, Shaanxi Province. In order to research relationships between eco-environmental geochemistry and KD pertaining to Se, Mo, B, Zn, Mn, and Cu, this investigation was conducted in the Jiantou KD area in Huangling County, one of the areas in China where the incidence of KD is highest. Environmental samples (rock, soil, plant and childrens hair) were collected from the area. Se in plants is low, ranging from 0.03 to 0.06 µg Se g^–1 in corn, potato and soybean. Se contents in childrens hair are normal or reach the limitation of dangerous level. This study reports 0.18 µg Se g^–1, B <40 µg g^–1, and Mo <1.0 µg g^–1 in aeolian soil, 0.14–0.38 µg Mo g^–1 and 3–8 µg B g^–1 in corn and potato (daily staple food for local human beings in the area). The Jiantou KD area is one where the elements Se, Mo and B are deficient. It is proposed that the deficiency of elements Se, Mo and B may be involved in the pathogenicity of KD with respect to the eco-environmental system because Se, Mo and B are essential micronutrients for plants and human beings. It seems that there is no significant relationship between the Zn–Mn–K–Pb–Ba associations and KD.     

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

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

Respiration rates of<Emphasis Type="Italic"> Beroe ovata</Emphasis> in the Black Sea

Metabolic rates of the ctenophore Beroe ovata within the length range from 0.4 mm (newly hatched larvae) to 60 mm were investigated. At 20° the respiration rates (Q, µg O₂ ind.^–1 h^–1) of individuals with wet weights (W, mg) less than or greater than 100 mg changed according to the equations Q=0.093W^0.62 and Q=0.016W^0.99, respectively. The weight-specific respiration rate of the juvenile ctenophores with wet body weights of 0.021–100 mg diminished approximately 20-fold (from 0.35 to 0.017 µg O₂ mg^–1 h^–1, respectively), but did not change within the range from 100 to 30,000 mg. The difference in the slope of the regression lines seems to be attributable to the ontogenetic changes in B. ovata metabolism. For the tested temperature range of 10–28°, the mean Q₁₀ coefficient was equal to 2.17±0.5. The basal metabolism of B. ovata narcotised by chloral hydrate was 4.5±0.9 times lower than total metabolism. Such a metabolic range is considered to be characteristic of aquatic invertebrates with high levels of locomotory activity.Communicated by O. Kinne, Oldendorf/Luhe     

Some properties of calcium-activated adenosine triphosphatase from the hermatypic coralGalaxea fascicularis

Samples of the hermatypic coralGalaxea fascicularis were collected between April 1987 and April 1990 from coral reefs off Singapore (103 °45E; 1 °13N). Ca²⁺-activated adenosine triphosphatase (ATPase) activity was detected in the plasma-membrane-enriched heavy microsomal fraction ofG. fascicularis. The high affinity component hadKm andVmax values of 0.0021 mM and 0.050 µmol Pi mg^–1 protein min^–1, respectively; corresponding values for the low affinity component were 0.15 mM and 0.85 µmol mg^–1 protein min^–1. The activity of the high affinity component was inhibited 80 and 50%, respectively, by the anticalmodulin drugs calmidazolium and chlorpromazine. The low affinity component of the Ca²⁺-ATPase may represent activities of alkaline phosphatase, Ca²⁺-ATPase from membranes of mitochondria and endoplasmic reticulum, or calmodulin-dissociated plasma membrane Ca²⁺-ATPase resulting from the removal of Ca²⁺ by EDTA during the isolation process. The high affinity Ca²⁺-ATPase is probably the enzyme responsible for Ca²⁺ extrusion from the cells ofG. fascicularis. The high and low affinity components of this Ca²⁺-ATPase could use ATP and ADP as substrates. Maximum activities of both components were registered at pH 7 and at 45°C. Ruthenium red, a specific inhibitor of Ca²⁺-ATPase, inhibited the activities of the high and low affinity Ca²⁺-ATPase by 100 and 60%, respectively. Inhibition of the activities of both components was also observed with sulphydryl reagents (PCMB and mersalyl). However, DCMU, diamox, dinitrophenol, iodoacetate, fluoride, cyanide, ouabain, oligomycin B and L-phenylalanine had no effect on the enzyme activities.     

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.     

Biochemical composition of Nyctiphanes australis and its possible use as an aquaculture feed source: Lipids,pigments and fluoride content

Nyctiphanes australis contained, on a dry weight basis, an average of 52% crude protein and 5.0 to 9.5% lipid. The fatty acid profile of N. australis was markedly unsaturated, with a mean total 3 fatty acid content of 48.6±2.4% of total fatty acids. N. australis contained high levels of the essential long-chain polyunsaturated fatty acids eicosapentaenoic (EPA, 20:53) and docosahexaencic (DHA, 22:63), ranging from 16.6 to 36.5% and 11.1 to 24.8%, respectively. The concentration of total carotenoids ranged from 137 to 302 g g^–1 dry wt, with no significant differences in concentrations found with season or life stage. The carotenoids were comprised of 79.5% astaxanthin and 20.5% canthaxanthin. The lipid and pigment compositions of N. australis suggest that the species could serve as a suitable feed source for cultured salmonids. Like other euphausiids, N. australis contained high levels of fluoride, with a seasonal range between 277 and 3507 g g^–1 dry wt. The high fluoride levels found in N. australis would not detract from its potential as a feed source for salmonids because ingested fluoride is largely absorbed by the skeleton.     

Feeding habits of a pelagic amphipod,Themisto japonica

Vertical distribution, chlorophylla (chla) and phaeopigment concentrations in the gut, and natural nitrogen isotope ratio ( ¹⁵N) were investigated for pelagic amphipodsThemisto japonica (Bovallius) collected from the Sea of Japan in July 1987. Differences in diel vertical migration behavior were clearly observed between small and largeT. japonica. Many small (<5 mm body length) amphipods appeared in the phytoplankton-rich shallow layers. Their gut pigment concentrations were higher (mean 0.52 ± 0.15µg chla g^–1 amphipod) than those of large amphipods (mean 0.33±0.14µg g^–1); this implies that the amphipods fed on a large amount of phytoplankton during the early stage of life. The ¹⁵N values of small amphipods were lower (5.7 to 6.3) than those of large amphipods (6.8 to 11.7), reflecting the lower trophic level of small amphipods compared to large ones. The ¹⁵N values for small amphipods were similar to those of herbivorous zooplankton. The amphipods' feeding behavior thus changes from herbivorous to carnivorous as they grow.     

Daily energy requirements and trophic positioning of the sand shrimp<Emphasis Type="Italic"> Crangon septemspinosa</Emphasis>

Sand shrimp, Crangon septemspinosa Say, are important to the trophic dynamics of coastal systems in the northwestern Atlantic. To evaluate predatory impacts of sand shrimp, daily energy requirements (J ind.^–1 day^–1) were calculated for this species from laboratory estimates of energy losses due to routine (R_R), active (R_A), and feeding (R_SDA) oxygen consumption rates (J ind.^–1 h^–1), coupled with measurements of diel motile activity. Shrimp used in this study were collected biweekly from the Niantic River, Connecticut (41°33N; 72°19W) during late spring and summer of 2000 and 2001. The rates of shrimp energy loss due to R_R and R_A increased exponentially with increasing temperature, with the magnitude of increase greater between 6°C and 10°C (Q₁₀=3.01) than between 10°C and 14°C (Q₁₀=2.85). Rates of R_R doubled with a twofold increase in shrimp mass, and R_SDA was 0.130 J h^–1+R_R, irrespective of shrimp body size. Shrimp motile activity was significantly greater during dark periods relative to light periods, indicating nocturnal behavior. Nocturnal activity also increased significantly at higher temperatures, and at 20°C shifted from a unimodal to a bimodal pattern. Laboratory estimates of daily metabolic expenditures (1.7–307.4 J ind.^–1 day^–1 for 0.05 and 1.5 g wet weight shrimp, respectively, between 0°C and 20°C) were combined with results from previous investigations to construct a bioenergetic model and make inferences regarding the trophic positioning of C. septemspinosa. Bioenergetic model estimates indicated that juvenile and adult shrimp could meet daily energy demands via opportunistic omnivory, selectively preying upon items of high energy content (e.g. invertebrate and fish tissue) and compensating for limited prey availability by ingesting readily accessible lower energy food (e.g. detritus and plant material).Electronic Supplementary Material Supplementary material is available in the online version of this article at Communicated by J.P. Grassle, New Brunswick     

Nitrogen regeneration by the surf zone penaeid prawn Macropetasma africanus

Nitrogen excretion of individual Macropetasma africanus (Balss) from an exposed beach/surf zone in Algoa Bay, South Africa was monitored under laboratory and field conditions in relation to body mass, temperature and feeding during 1985. Excretion rate experiments were performed on starved prawns at 15°, 18°, 20° and 25°C, as well as on individuals fed on four different diets (mussel, fish, shrimp and natural diet) at 15° and 20°C. The ratios of the excreted compounds to total nitrogen excreted were similar for the four diets despite differences in their nitrogen content and in the amount of food consumed. At 15° and 20°C, ammonia excretion rates of fed individuals were four to seven times higher than in starved prawns. the excretion rates were not correlated with nitrogen content of diets. M. africanus recycles 1 557 g NH₄–N per metre strip per year or 1 832 g total nitrogen m^-1 yr^-1, which constitute 12 and 14%, respectively, of total phytoplankton requirements of the surf zone. This study indicates that large motile crustaceans, when abundant, can play an important role in nutrient recycling in turbulent marine environments.     

Relationship of daily and circatidal activity rhythms of the fiddler crab,<Emphasis Type="Italic"> Uca princeps</Emphasis>, to the harmonic structure of semidiurnal and mixed tides

Intertidal organisms may employ circatidal rhythms to track the tidal cycle, but tidal patterns may vary within a species range and necessitate adaptation to the local tides. Circatidal rhythms were examined in populations of the eastern Pacific fiddler crab Uca princeps (Smith) from four sites with differing tidal characteristics, La Paz (24°10N; 110°21W), San Blas (21°33N; 105°18W) and Manzanillo (19°6N; 104°24W), Mexico (lower amplitude, mixed semidiurnal tides) and Mata de Limon, Costa Rica (9°55N; 84°43W) (high-amplitude, semidiurnal tides). Local tides were characterized by harmonic constants of M₂, S₂, K₁, and O₁, partial tides that largely determine their semidiurnal and diurnal features. Rhythmic structure in continuously recorded locomotor activity of individual crabs held under laboratory conditions was described by cosinor and periodogram methods of time-series analysis. Both daily and circatidal rhythms were found in crabs studied in light–dark cycles set to local conditions at the time of collection. Crabs at all four sites shared a tendency toward bimodality, with a mid-morning activity peak and varying degrees of nocturnal activity. Circatidal rhythms closely matching the period of the 12.42-h M₂ partial tide were consistently present at all sites except Manzanillo. At Mata de Limon, the circatidal rhythm clearly dominated locomotor activity, but was strongly modulated by a daily rhythm in a repeating pattern at a semilunar interval. In contrast, the amplitude of the daily rhythm was higher than that of the circatidal rhythm in crabs from the three mixed tide sites on the Mexican coast, where the tidal pattern is dominated by a diurnal inequality arising from the diurnal K₁ and O₁ partial tides. These results suggest that populations of U. princeps use both daily and circatidal timing systems to track local forms of the tide generated by their M₂, S₂, K₁, and O₁ geophysical counterparts.Communicated by J.P. Grassle, New Brunswick     

Predicting the risk of cobalt deprivation in grazing livestock from soil composition data

The objective was to derive predictive equations for acetic acid-extractable cobalt (A-ECo) in soils so that extensive national databases for total (T) Co in soils and stream sediments could be converted to plant available concentrations for the purpose of predicting risk of Co deficiency in grazing livestock. Data on the chemical and physical properties of 103 soils from 15 different parent materials and 54 soil series in England and Wales were used. Ranges for the mean values for parent materials were: TCo, 5.0–20.4 and A-ECo, 0.20–1.30 mg kg^–1; percentage (P) A-ECo, 3.4–13.5; soil manganese (Mn) 268–1174 mg kgDM^–1; pH, 3.7–8.0. There were significant effects of parent material on all parameters with Chalks, Old and New Red Sandstones particularly low in A-ECo. Multiple linear regression yielded the following equation for predicting A-ECo, which accounted for 56% of the variance with 12 outliers, including the lowest pH values, omitted:A-ECo(mg kg^-1) = 1.4 - 0.0619TCo (mg kg^-1) - 0.432TMn(g kg^-1) - 0.171pHPrediction of PA-ECo was less precise:PA-ECo(%) = 21.1 - 4.5TMn(g kg^-1) - 1.77pH(r ² = 44.8%; 88 d.f.REML was used on the complete, unbalanced, log-transformed data set to fit a Generalised Mixed Model with parent material as random effect and soil Mn and pH as fixed effects; the effect of parent material was no longer significant. It was concluded that A-ECo can be satisfactorily predicted for most soils in England and Wales from TCo, TMn and soil pH.     

Seasonal variations of organic-carbon and nutrient transport through a tropical estuary (Tsengwen) in southwestern Taiwan

This paper reports the fluvial fluxes and estuarine transport of organic carbon and nutrients from a tropical river (Tsengwen River), southwestern Taiwan. Riverine fluxes of organic carbon and nutrients were highly variable temporally, due primarily to temporal variations in river discharge and suspended load. The sediment yield of the drainage basin during the study period (1995–1996, 616 tonne km^–2 year^–1) was ca. 15 times lower than that of the long-term (1960–1998) average (9379 tonne km² year^–1), resulting mainly from the damming effect and historically low record of river water discharge (5.02 m³ s^–1) in 1995. The flushing time of river water in the estuary varied from 5 months in the dry season to >4.5 days in the wet season and about 1 day in the flood period. Consequently, distributions of nutrients, dissolved organic carbon (DOC) and particulate organic carbon (POC) were of highly seasonal variability in the estuary. Nutrients and POC behaved nonconservatively but DOC behaved conservatively in the estuary. DOC fluxes were generally greater than POC fluxes with the exception that POC fluxes considerably exceeded DOC fluxes during the flood period. Degradation of DOC and POC within the span of flushing time was insignificant and may contribute little amount of CO₂ to the estuary during the wet season and flood period. Net estuarine fluxes of nutrients were determined by riverine fluxes and estuarine removals (or additions) of nutrients. The magnitude of estuarine removal or addition for a nutrient was also seasonally variable, and these processes must be considered for net flux estimates from the river to the sea. As a result, nonconservative fluxes of dissolved inorganic phosphorus (DIP) from the estuary are –0.002, –0.09 and –0.59 mmol m^–2 day^–1, respectively, for dry season, wet season and flood period, indicating internal sinks of DIP during all seasons. Due to high turbidity and short flushing time of estuarine water, DIP in the flood period may be derived largely from geochemical processes rather than biological removal, and this DIP should not be included in an annual estimate of carbon budget. The internal sink of phosphorus corresponds to a net organic carbon production (photosynthesis–respiration, p–r) during dry (0.21 mmol m^–2 day^–1) and wet (9.5 mmol m^–2 day^–1) seasons. The magnitude of net production (p–r) is 1.5 mol m^–2 year^–1, indicating that the estuary is autotrophic in 1995. However, there is a net nitrogen loss (nitrogen fixation–denitrification < 0) in 1995, but the magnitude is small (–0.17 mol m^–2 year^–1).     

Annual reproductive cycle of the captive female Japanese sardineSardinops melanostictus: Relationship to ovarian development and serum levels of gonadal steroid hormones

Gonad and blood samples were taken from the captive female Japanese sardineSardinops melanostictus between 1988 and 1989, and changes in serum levels of gonadal steroids were correlated with the annual gonadal cycle. Under captive conditions, female fish did not mature and spawn spontaneously, although oocytes developed up to the end of vitellogenic growth. Based on evidence from ovarian histology, the annual gonadal cycle of the Japanese sardine was divisible into four periods, i.e., immature (June to October), vitellogenesis (November to December), spawning (January to March), and post-spawning (April to May). The pattern of seasonal change in the gonadosomatic index (GSI) showed an inverse correlation to change in water temperature and reflected the degree of ovarian maturity. The serum estradiol-17 level increased from its lowest concentration (0.12 ng ml^–1) in September to a peak (1.14 ng ml^–1) in March. Serum 17,20-dihydroxy-4-pregnen-3-one (17,20-P) was detectable at low levels (<0.3 ng ml^–1) between October and February, but was below the assay detection limit (0.06 ng ml^–1) at all other times. Testosterone was not detectable (<0.06 ng ml^–1) in the serum of any fish throughout the year. The effects of several steroids on the maturation of follicle-enclosed oocytes of sardine were examined in vitro, and 17,20-P was found to be the most potent inducer of maturation. This suggests that post-vitellogenic oocytes of the Japanese sardine in captivity have an ability to respond to an appropriate hormonal effector and subsequently to resume meiotic maturation.     

Experimental Study of Gas-Liquid Interfacial Properties in a Stepped Cascade Flow

Gas-liquid interface measurements were conducted in a strongly turbulent free-surface flow (i.e., stepped cascade). Local void fractions, bubble count rates, bubble size distributions and gas-liquid interface areas were measured simultaneously in the air-water flow region using resistivity probes. The results highlight the air-water mass transfer potential of a stepped cascade with measured specific interface area over 650 m^–1 and depth-average specific area up to 310 m^–1. A comparison between single-tip and double-tip resistivity probes suggests that simple robust single-tip probes may provide accurate, although conservative, gas-liquid interfacial properties. The latter device may be used in the field and in prototype plants. Notation a = specific interface area (m^–1); a _mean = depth-average specific interface area (m^–1): a _mean=frac1Y ₉₀limits sup> Y ₉₀ sup ₀(1–C)dy; C = local void fraction; C _gas = dissolved gas concentration (kg m^–3); C _mean = depth-average mean air concentration defined as: C _mean=1–d/Y ₉₀; C _s = saturation concentration (kg m^–3); D = dimensionless air bubble diffusivity (defined by [1]); d = equivalent clear-water flow depth (m): d=limits sup> Y ₉₀ sup ₀(1–C) dy; d_ab = air bubble diameter (m); d_c = critical flow depth (m); for a rectangular channel: d _c=sqrt[3]q _w ²/g; F = air bubble count rate (Hz); F _max = maximum bubble count rate (Hz), often observed for C=50%; g = gravity acceleration (m s^–2); h = step height (m); K _L = liquid film coefficient (m s^–1); K = integration constant defined as: K=tanh ^–1 sqrt0.1)+(2D)^–1 [1]; L = chute length (m); N = velocity distribution exponent; ———– ^*Corresponding author, E-mail: h.chanson@mailbox.uq.edu.au Q _w = water discharge (m³ s^–1); q _w = water discharge per unit width m² s^–1); t = time (s); V = local velocity (m s^–1); V _c = critical flow velocity (m s^–1); for a rectangular channel: V _c=sqrt[3]q _w g V _max = maximum air-water velocity (m s^–1); V ₉₀ = characteristic air-water velocity (m s^–1) where C = 90%; W = channel width (m); x = longitudinal distance (m) measured along the flow direction (i.e., parallel to the pseudo-bottom formed by the step edges); y = distance (m) normal to the pseudo-bottom formed by the step edges; Y₉₀ = characteristic distance (m) where C=0.90; Y ₉₈ = characteristic distance (m) where C=0.98; = slope of pseudo-bottom by the step edges; = diameter (m).     

Feeding selectivities of the marine cladocerans<Emphasis Type="Italic"> Penilia avirostris</Emphasis>,<Emphasis Type="Italic"> Podon intermedius</Emphasis> and<Emphasis Type="Italic"> Evadne nordmanni</Emphasis>

We conducted grazing experiments with the three marine cladoceran genera Penilia, Podon and Evadne, with Penilia avirostris feeding on plankton communities from Blanes Bay (NW Mediterranean, Spain), covering a wide range of food concentrations (0.02–8.8 mm³ l^–1, plankton assemblages grown in mesocosms at different nutrient levels), and with Podon intermedius and Evadne nordmanni feeding on the plankton community found in summer in Hopavågen Fjord (NE Atlantic, Norway, 0.4 mm³ l^–1). P. avirostris and P. intermedius showed bell-shaped grazing spectra. Both species reached highest grazing coefficients at similar food sizes, i.e. when the food organisms ranged between 15 and 70 µm and between 7.5 and 70 µm at their longest linear extensions, respectively. E. nordmanni preferred organisms of around 125 µm, but also showed high grazing coefficients for particles of around 10 µm, while grazing coefficients for intermediate food sizes were low. Lower size limits were >2.5 µm, for all cladocerans. P. avirostris showed upper food size limits of 100 µm length (longest linear extension) and of 37.5 µm particle width. Upper size limits for P. intermedius were 135 µm long and 60 µm wide; those for E. nordmanni were 210 µm long and 60 µm wide. Effective food concentration (EFC) followed a domed curve with increasing nutrient enrichment for P. avirostris; maximum values were at intermediate enrichment levels. The EFC was significantly higher for P. intermedius than for E. nordmanni. With increasing food concentrations, the clearance rates of P. avirostris showed a curvilinear response, with a narrow modal range; ingestion rates indicated a rectilinear functional response. Mean clearance rates of P. avirostris, P. intermedius and E. nordmanni were 25.5, 18.0 and 19.3 ml ind.^–1 day^–1, respectively. Ingestion rates at similar food concentrations (0.4 mm³ l^–1) were 0.6, 0.8 and 0.9 g C ind.^–1 day^–1.Communicated by O. Kinne, Oldendorf/Luhe     

Ingestion and assimilation of nitrogen from benthic sediments by three species of coral

We quantified the nitrogen and enzyme hydrolyzable amino acid (EHAA) concentrations of sediments prior to and after corals sloughed, ingested, and egested sediments layered onto their surfaces, for the three coral species Siderastrea siderea, Agaricia agaricites, and Porites astreoides in Jamaica. The percent nitrogen of the sediments egested by all three species was lower than in the sediments available to the corals. Additionally, the sediments sloughed (not ingested) by A. agaricites and P. astreoides were lower in percent nitrogen, while the sediments sloughed by S. siderea had the same percent nitrogen as that of the available sediments. The percent nitrogen of the sediments sloughed and egested by P. astreoides showed significant negative and positive relationships, respectively, to increasing sediment loads, while the percent nitrogen of the sediments sloughed and egested by both S. siderea and A. agaricites showed no relationship to sediment load. EHAA concentrations were not significantly different between the sloughed and available sediments but were significantly lower in the sediments egested by S. siderea and A. agaricites (EHAA concentrations were not measured for P. astreodies sediment fractions). Comparisons of the nitrogen and EHAA concentrations in the sloughed and egested sediments to what was available prior to coral processing show that maximum ingestion was between 0.1 and 0.2 µg N µg^–1 coral N cm^–2 and between 0.5 and 0.6 µg EHAA·cm^–2. Maximum assimilation efficiencies were estimated to be 30–60% of the available nitrogen. The data show that corals ingest and alter the nitrogen concentration of particles that land on their surfaces. The corals abilities to process these sediments, and the sediments possible contributions to coral nutrition, are discussed based on these results.Communicated by O. Kinne, Oldendorf/Luhe     

Life in a warm deep sea: routine activity and burst swimming performance of the shrimp<Emphasis Type="Italic"> Acanthephyra eximia</Emphasis> in the abyssal Mediterranean

Measurements of routine swimming speed, tail-flip escape responses, and oxygen consumptions were made of the deep-sea shrimp Acanthephyra eximia using autonomous landers in the Rhodos Basin at depths of up to 4,400 m and temperatures of 13–14.5°C. Routine swimming speeds at 4,200 m averaged 0.18 m s^–1 or 3.09 body lengths s^–1, approximately double those of functionally similar oceanic scavengers. During escape responses peak accelerations of 23 m s^–2 or 630.6 body lengths s^–2 were recorded, with animals reaching speeds of 1.61 m s^–1 or 34.8 body lengths s^–2. When compared to shallow-water decapods at similar temperatures these values are low for a lightly calcified shrimp such as A. eximia despite a maximum muscle mass specific power output of 90.0 W kg^–1. A preliminary oxygen consumption measurement indicated similar rates to those of oceanic crustacean scavengers and shallower-living Mediterranean crustaceans once size and temperature had been taken into account. These animals appear to have high routine swimming speeds but low burst muscle performances. This suite of traits can be accounted for by high competition for limited resources in the eastern Mediterranean, but low selective pressure for burst swimming due to reductions in predator pressure.Communicated by J.P. Thorpe, Port Erin