Distribution and species-specific egg production of Pseudocalanus in the Gulf of Alaska

Pseudocalanus species are important contributors to the secondaryproduction of the northern hemisphere mid- to high-latitudeoceans. In the coastal Gulf of Alaska, Pseudocalanus are presentyear round and are represented by three species. In 2001, Pseudocalanusmimus was the dominant Pseudocalanus species on the shelf duringspring and summer, comprising 30–100% of the total, whilePseudocalanus newmani dominated in Prince William Sound (10–90%).Pseudocalanus minutus were only abundant in Prince William Soundduring early spring. Egg production (by number and volume) wasa function of female prosome length and decreased from springto summer; however, significant variability was attributableto regional influences that were independent of size. For thesame sized female, P. newmani produced more eggs per clutchthan P. mimus. Pseudocalanus mimus, however, tended to havea larger mean egg size than P. newmani. Consequently, clutchvolumes of the two species were indistinguishable. Pseudocalanusegg production rates (EPRs) (eggs female^–1 day^–1)were lower in July and August (ca. 2–4) than April andMay (ca. 1–9), but total egg production by the population(eggs day^–1) was nearly equivalent for the two time periodsdue to higher female concentrations in summer.     

Photosynthetic pigments in the ciliate Laboea strobila from Long Island Sound, USA

Laboea sirobila Lohmann, a marine oligotrich ciliate, was presentin Long Island Sound, USA, from March through June 1984. Peakabundance occurred in mid-June, when it was estimated that 10.2x 10⁶ individuals m^–2 were present in the 37-m deep watercolumn. When preserved specimens were examined with epifluorescencemicroscopy, the photosynthetic pigments chlorophyll and phycoerythrinwere observed within chloroplasts inside the ciliate. Thesepigments were also present in Myrionecta (formerly Mesodinium)rubrum Jankowski, a photosynthetic ciliate which co-occurredwith L. strobila during the present study. Vertical profilesshowed both ciliates to be most abundant in the upper few metersof the water column, especially during periods of strong thermalstratification.     

Characterization of phycoerythrin-containing Synechococcus spp. populations by immunofluorescence

Using an immunofluorescence assay developed to identify serogroups(i.e. clusters of strains labelled by one antiserum), the compositionof natural populations of phycoerythrin-containing Synechococcusspp. was examined. The 7803 (open ocean clone)-serogroup wasfound in most oceanic regions, but was most prevalent (up to85%) in tropical and subtropical waters during spring and summer.At coastal Long Island stations it was most abundant (up to65%) when water temperatures were >22°C. The seasonaland geographic distribution of the 7803-serogroup appeared tobe limited by water temperature. No consistent pattern was observedin the per cent composition with depth in the Sargasso Sea orat coastal to offshore stations in the North-west Atlantic Oceanor eastern tropical North Pacific Ocean. The 8016 (coastal clone)-serogroupwas abundant at coastal and estuarine stations off Long Island(up to 95 %) and its appearance was also correlated with warmwater temperature (> 15°C). However, this serogroup remaineda constant proportion of the population at the Long Island Soundstation during early winter months (through January) when abundanceof the 7803-serogroup was negligible. Owing to limited data,the oceanic distribution of the 8016-serogroup is not yet discernible.Lastly, antisera to the phycocyanin-dominant Synechococcus spp.clones failed to label any cells in samples collected from severaloceanic stations. Thus, these strains appear to be limited tocoastal and estuarine regions, which is consistent with predictionsfrom experiments comparing the photosynthetic performance ofthe phycoerythrin-dominant and phycocyanin-dominant clones. ¹Present address: Department of Oceanography, University ofHawaii, Honolulu, HI 96822, USA     

Resting egg production and oviducal cycling in two sympatric species of alpine diaptomids (Copepoda: Calanoida) in relation to temperature and food availability

Resting egg production and oviducal cycling were investigatedfor the calanoid copepods Arctodiaptomus alpinus and Acanthodiaptomusdenticornis both in the laboratory and in a small karstic alpinelake by making a census of the number of eggs produced and theproportion of females in each of four morphologically distinguishedreproductive conditions each day in the laboratory or duringa 2–3 week period in lake enclosures. In the laboratory,individuals were maintained on a mixed diet of natural phytoplanktonat constant temperatures of 4, 10, 15 and 20C, respectively.Both species differed considerably in their temperature requirementsfor reproduction. Lifetime fecundity was highest at 10C in A.alpinusand at 20C in A.denticornis, with up to 327 eggs ^–1 spawnedin the former and up to 582 eggs ^–1 in the latter species.Unfavorable temperatures were further reflected in an increasein egg mortality and the allocation of time spent in a post-reproductivephase, as well as in a decrease of longevity. Increasing temperaturesenhanced egg production rates due to decreasing clutch productionperiods, although clutch size was negatively correlated withtemperature. Maximum rates reached 5.88 and 7.98 eggs ^–1day^–1 in the laboratory, and 0.73 and 0.55 eggs ^–1day^–1 in enclosures in A.alpinus and A.denticornis, respectively.Egg production rates and clutch size were clearly governed bynutritional conditions in the lake, but were less affected byfood supply in the laboratory. Here, rates of egg productionwere adapted to improving food supply by increasing the frequencyof spawning events, rather than the number of eggs per clutch.No correlation was found between female body size and reproductiveparameters in the laboratory. A very low proportion of totalclutch production resulted in clutches composed of subitaneouseggs, i.e. 0.14% in A.denticornis and 1.20% in A.alpinus. Oviducalphase duration allocations indicate that there exists a temperatureoptimum for gamete maturation.     

SPAWNING SEASON AND EGG PRODUCTION IN FORTH ESTUARY RETUSA OBTUSA (MONTAGU) (GASTROPODA: OPISTHOBRANCHIA)

Retusa obtusa held individually in the laboratory carried largeoocytes in the gonad but did not spawn in December-late January.In late Jan-early Feb, however, the first few individuals producedbatches of 8–17 eggs and, by early February, most individualswere producing means of 2–4 eggs d^–1 and maximain late Feb of <7.9 d^–1. Spawning declined to low levelsin few individuals in late March. By early April, spawning hadvirtually ceased prior to the drastic loss of adults in thepopulation by May. Larger R. obtusa generally produced more eggs than smaller onesand the few specimens shorter than 3.8 mm produced markedlyfewer than those of 3.8–5.0 mm shell length. Twenty of the 34 R. obtusa held in the main breeding period(4 sets started 29 Jan-3 Mar) spawned in 3 or more successiveweeks whereas only 6 of them failed to spawn in 2 consecutiveweeks, so indicating that several successive batches of eggsare commonly produced. Yet in virtually all individuals (exceptat the start of breeding) more eggs were produced in the firstweek of captivity than subsequently. These first-week valuesimply total production by individuals in the spawning seasonof some 112-305 eggs comprising about 2.8-7.6 mg dry weightor, by the Forth estuary population, of 26880-73200 eggs m^–2comprising 0.67-1.83 g dry weight m^–2. (Received 19 August 1988; accepted 30 September 1988)     

Mechanisms Controlling Changes in Water Movement Through the Roots of Helianthus annuus L. During Continuous Exposure to Oxygen Deficiency

The effects of oxygen deficiency on suction-induced water flux(Jv) through detached roots of hydroponically-grown sunflowerwere investigated over a period of up to 6 d. Jv was reducedby the time the oxygen partial pressure in the solution, spargedwith oxygen-free N₂, had fallen below 2 kPa (air – 20.6kPa). This reduction resulted from a decline in the hydraulicconductivity of the radial pathway for water movement (Lp),although up to 46% of the decline was attributable to changesin the osmotic component of the driving force (). Lp (mm s^–1MPa^–1), for aerobic roots was 2.23 ? 10^–5 and foranaerobic roots during the initial 16 h, 1.21 ? 10^–5. At 22 h after the onset of anaerobic treatments, Jv and Lp increased,with Lp values becoming 3 times greater than those measuredbetween 4 h and 16 h of treatment and 1.4 times greater thanin aerated roots. However, Lp increased a further 15-fold whenroots were killed by immersion in boiling water for 2 min. Duringand up to 6 d of anaerobic treatment, some roots retained Lpvalues similar to those at 22 h, while others displayed characteristicstypical of dead roots. At no time was there any indication ofreduced axial conductivity due to xylem vessel blockage. The results are discussed in terms of possible energy sourcesfor the maintenance of root integrity and their importance toplant survival during long periods of severe oxygen shortage. Key words: Anaerobiosis, oxygen deficiency, hydraulic conductivity, osmotic potential, water     

Growth, reproduction and feeding behavior of the planktonic shrimp, Lucifer faxoni Borradaile, off the Texas coast

The planktonic shrimp, Lucifer faxoni, lives to an age of 30–40days off the Texas coast. In the laboratory, the shrimp took28.9 and 18.9 days to reach sexual maturity at 22 and 30°Crespectively. Oviposition was observed at night between 20.00and 23.00. Females attach eggs to the 3rd pereiopods and broodthem until the nauplii emerge. Multiple broods are produced,giving a maximal lifetime fecundity of >140 eggs per female.In addition, females may also be able to synchronize the timeof their hatching to occur at night, perhaps to further reducemortality due to predation and cannibalism. A rapid turnoverof generations, each with a short adult lifespan, sequentialspawnings, and protection of eggs until hatching, characterizesthe life strategy of this small shrimp. Adult L.faxoni are carnivorous.However, their feeding appendages do not exclude the possibilityof omnivory. The maximal, dry-weight-based, specific ingestionrate was 0.7 day^–1. Feeding activity was not affectedby either time of day or light regime.     

Temporal variations in carbon isotope ratio of phytoplankton in a eutrophic lake

Temporal variations in carbon isotope ratio of phytoplanktonand dissolved inorganic carbon (DIC) in Lake Suwa were reported.In summer, blooming of Microcystis spp. resulted in low concentrationsof DIC and high pH, and HCO₃^– was the prominent speciesof DIC. Chlorophyll-specific rates of photosynthesis were relativelyconstant irrespective of the algal biomass during summer. Carboxylationin photosynthesis of Microcystis spp. was mainly catalyzed byribulose bisphosphate carboxylase (RuBPCase). Carbon isotopediscrimination between ¹³C of phytoplankton and DIC was considerablysmall in early summer and appeared to be negatively correlatedto DIC concentration. We concluded that carbon fixation by phytoplanktonin Lake Suwa is controlled not by the switch of photosyntheticpathways, but by low DIC concentration and high pH, suggestingthat photosynthesis of Microcystis spp. in Lake Suwa is governedby uptake kinetics other than the carboxylation step.     

ASPECTS OF THE LIFE CYCLE, POPULATION DYNAMICS,GROWTH AND SECONDARY PRODUCTION OF THE EDIBLE SNAIL HELIX LUCORUM LINNAEUS, 1758 (GASTROPODA, PULMONATA) IN GREECE

This paper examines the biology and ecology of Helix lucorumL. which lives in mainland Greece, as well as its growth andsecondary production. A demographic study revealed that (a)3 cohorts exist at any time during the year (when adults ofall generations belong to the same cohort) (b) egg-laying andhatching occur during the months of July and August respectively,(c) the most rapid growth takes place during spring. Study ofH. lucorum genitalia in relation to age showed that the snailsaxe sexually mature 3 years after hatching, when the largestdiameter of their shell (D) is equal to or greater than 35 mm Von Bertallanffy's method suggests that Helix lucorum may liveup to 14 years or more in order to reach its possible maximumsize (48.80 mm) The study of relative growth of D in relation to P_s (peristomesurface) of Helix lucorum shows that D grows faster than P_swhen D12.50 mm; juveniles change their growth rate when theirD arrives at 22.05 mm, and growth becomes slower when adultsarrive at 36.27 mm Annual secondary production calculated by the size frequencymethod gave a mean annual density of 3.39 individuals per m²,a mean annual crop (biomass) of 4.04 g-m^–2 and an annualproduction (P) of 5.02 g · m^–2. The annual turnoverratio (P//b) is equal to 1.24 (Received 23 June 1987;     

Vertical distribution and seasonal abundance of Aglantha digitale (O.F. Muller) (Coelenterata: Trachymedusae) and other planktonic coelenterates in the northeast Atlantic Ocean

The vertical distribution and seasonal variability in abundanceof the hydromedusa Aglantha digitale (O.F. Müller) andother coelenterates from the north-east Atlantic Ocean are described.The coelenterates were abundant from May to September and reachedpeak numbers in June, July and September when concentrationof 40 individuals m^–1 were recorded. A. digitale numericallydominated the codenterate population and accounted for over80% of the dry weight biomass in hauls taken from 1971 to 1974.The data suggests a 2 month development period for this medusafrom egg to mature adult (8 mm) which supports previous publisheddata. During the growth of the medusa there were considerablechanges in the ratios of wet to dry weights. At a bell-heightof 1 mm the mean dry weight was 22% of mean wet weight and at8 mm the mean dry weight was 5% of mean wet weight; the percentagedecreased further in the largest specimens to 2% at 25 mm. Themajority of A. digitale occurred in the upper 100 m but in lateJuly the larger specimens extended their distribution to thelimit of sampling (500 m). The two most abundant siphonophores, Dimophyes arctica(Chun) and Nanomia cara A. Agassiz, werefound deeper than the main population of A. digitale. It issuggested that coelenterates could be an important source ofnitrogen for the development of the late bloom of phytoplanktonin the north-east Atlantic Ocean.     

An immunofluorescent survey of the brown tide chrysophyte Aureococcus anophagefferens along the northeast coast of the United States

Surveys were conducted along the northeast coast of the USA.between Portsmouth, NH, and the Chesapeake Bay in 1988 and 1990,to determine the population distribution of Aureococcus anophagefferens,the chrysophyte responsible for massive and destructive ‘browntides’ in Long Island and Narragansett Bay beginning in1985. A species-specific immunofluorescent technique was usedto screen water samples, with positive identification possibleat cell concentrations as low as 10–20 cells ml^–1.Both years.A.anophagefferens was detected at numerous stationsin and around Long Island and Barnegat Bay, NJ, typically athigh cell concentrations. To the north and south of thus ‘center’,nearly half of the remaining stations were positive for A.anophagefferens,but the cells were always at very low cell concentrations. Manyof the positive identifications in areas distant from Long Islandwere in waters with no known history of harmful brown tides.The species was present in both open coastal and estuanne locations,in salinities between 18 and 32 practical salinity units (PSU).The observed population distributions apparently still reflectthe massive 1985 outbreak when this species first bloomed, giventhe number of positive locations and high abundance of A.anophagefferensin the immediate vicinity of Long Island. However, the frequentoccurrence of this species in waters far from this population‘center’ is disturbing. Aureococcus anophagefferensis more widely distributed than was previously thought. Numerousareas thus have the potential for destructive brown tides suchas those associated with the sudden appearance of the speciesin 1985.     

Structure of the major neutral oligosaccharide-alditols released from the egg jelly coats ofAxolotl maculatum. Characterization of the carbohydrate sequence GalNAc({eta}l-4)[Fuc({alpha}l-3)] GlcNAc({eta}l-3 6)

Several O-linked oligosaccharides of the jelly coat surroundingthe eggs of Axolotl maculatum were analysed by ¹H-NMR spectroscopy.The four major oligosaccharide-alditols released by reductive-elimination display either the Lewis^x(Le^x) determinant or thesequence GalNAc(l-4)[Fuc(l-3)]GlcNAc This last structure haspreviously been characterized in allergenically active oligosaccharidesisolated from the sea squirt H-antigen, and hi the N-linkedglycans of Schistosoma mansoni and human urokinase. It representsthe major carbohydrate chain found in A.macu-latum,the oviductof which constitutes an excellent source of l-4-acetylgalactosaminyltransferase activity. Moreover, the carbohydrate chains isolatedfrom A.maculatum are quite different from those found hi sevenother amphibian species, in which the presence of species-specificmaterial has been characterized. The role of carbohydrates appearsmore and more apparent during the fertilization process, andthe diversity of the O-linked oligosaccharides supports sucha biological role. amphibian egg jelly coats Axolotl maculatum/Hnmr/oligosccharide structure     

禾谷缢管蚜和麦长管蚜玻璃管药膜法敏感毒力基线的建立

【目的】建立禾谷缢管蚜Rhopalosiphum padi（Linnaeus）和麦长管蚜Sitobion avenae（Fabricius）对常用杀虫剂的相对敏感基线。【方法】从田间采集麦蚜在实验室内饲养30代以上,利用玻璃管药膜法测定其对杀虫剂的敏感度,每条毒力基线为2次以上独立测定数据合并后的计算结果。【结果】用玻璃管药膜法建立了包括新烟碱类、吡啶类、氨基甲酸酯类、有机磷类和拟除虫菊酯类共22个药剂品种对禾谷缢管蚜和麦长管蚜3 h的敏感毒力基线。禾谷缢管蚜对新烟碱类药剂吡虫啉和啶虫脒的LC₅₀值分别为0.02和0.007 μg/cm²;对吡啶类药剂吡蚜酮的LC₅₀值为0.124 μg/cm²;对氨基甲酸酯类药剂丁硫克百威、硫双灭多威、灭多威、抗蚜威、西维因的LC₅₀值为0.0026~0.70 μg/cm²;对有机磷类药剂三唑磷、丙溴磷、氧乐果、乐果、马拉硫磷、辛硫磷、敌敌畏、毒死蜱的LC₅₀值为0.005~0.065 μg/cm²;对拟除虫菊酯类药剂三氟氯氰菊酯、高效氯氰菊酯、溴氰菊酯、联苯菊酯、氰戊菊酯、氯氰菊酯的LC₅₀值为0.033~0.240 μg/cm²。麦长管蚜对新烟碱类药剂吡虫啉和啶虫脒的LC₅₀值分别为0.15和0.12 μg/cm²;对吡啶类药剂吡蚜酮的LC₅₀值为0.41 μg/cm²;对氨基甲酸酯类药剂丁硫克百威、硫双灭多威、灭多威、抗蚜威、西维因的LC50值为0.005~0.76 μg/cm²;对有机磷类药剂三唑磷、丙溴磷、氧乐果、乐果、马拉硫磷、辛硫磷、敌敌畏、毒死蜱的LC₅₀值为0.018~0.36 μg/cm²;对拟除虫菊酯类药剂三氟氯氰菊酯、高效氯氰菊酯、溴氰菊酯、联苯菊酯、氰戊菊酯、氯氰菊酯的LC50值为0.20~2.94 μg/cm²。【结论】建立的两种麦蚜对22种杀虫药剂的相对敏感基线,包括当前所有可能用于防治麦蚜的药剂,可以用于以后麦蚜抗药性监测或其他相关研究的参照;禾谷缢管蚜对药剂的敏感度高于麦长管蚜。     

Functional characterization of the neuronal-specific K-Cl cotransporter: implications for [K+]o regulation

The neuronal K-Cl cotransporter isoform (KCC2) was functionallyexpressed in human embryonic kidney (HEK-293) cell lines. Two stablytransfected HEK-293 cell lines were prepared: one expressing anepitope-tagged KCC2 (KCC2-22T) and another expressing theunaltered KCC2 (KCC2-9). The KCC2-22T cells produced aglycoprotein of ~150 kDa that was absent from HEK-293 control cells.The ⁸⁶Rb influx in both cell lineswas significantly greater than untransfected control HEK-293 cells. TheKCC2-9 cells displayed a constitutively active⁸⁶Rb influx that could beincreased further by 1 mMN-ethylmaleimide (NEM) but not by cellswelling. Both furosemide [inhibition constant (K_i) ~25µM] and bumetanide (K_i~55 µM) inhibited the NEM-stimulated ⁸⁶Rb influx in the KCC2-9cells. This diuretic-sensitive⁸⁶Rb influx in theKCC2-9 cells, operationally defined as KCC2 mediated, required external Clbut not external Na⁺ and exhibiteda high apparent affinity for externalRb⁺(K⁺)[Michaelis constant(K_m) = 5.2 ± 0.9 (SE) mM; n = 5] but alow apparent affinity for externalCl(K_m >50 mM). Onthe basis of thermodynamic considerations as well as the unique kineticproperties of the KCC2 isoform, it is hypothesized that KCC2 may servea dual function in neurons: 1) themaintenance of low intracellularCl concentration so as toallow Cl influx vialigand-gated Cl channelsand 2) the buffering of externalK⁺ concentration([K⁺]_o) in the brain.

     

Development, growth and egg production of Centropages abdominalis in the eastern subarctic Pacific

Centropages abdominalis is a neritic, omnivorous, temporallyabundant copepod present throughout the subarctic Pacific andits marginal seas. The two main objectives of this study wereto determine how temperature influences the development of C.abdominalis and whether growth rates of in situ populationsmay be limited by available food. At 6.9°C, median developmenttime from eggs laid to 50% adults was 42 days and the averageweight-specific somatic growth rate was 0.17 day^–1. At4.6°C, median development time to adult was 59 days (projected)and growth rate averaged 0.08 day^–1, suggesting that 4.6°Cmay be approaching the lower temperature for development andgrowth in this species. The functional relationship betweendevelopment time and temperature was established over the temperaturerange in which this species occurs. The in situ adult growthrates between 10 and 13°C averaged 0.14 day^–1 andwere generally lower than the laboratory-reared juvenile growthrates, which may indicate that adult C. abdominalis are foodlimited in the field during summer and autumn.     

Horizontal distribution and dominant species of heteropods in the East China Sea

This article discusses the horizontal distribution and dominantspecies of heteropods in the East China Sea. The ecologicalcharacteristics of heteropods and their adaptability to theenvironments were also considered. Oceanographic census wascarried out in the East China Sea (23°30 '33° N and118°30'128° E) in four seasons from 1997 to 2000. Itwas found that the total abundance showed obvious seasonal variations.It peaked in autumn with a mean value of 21.03 ind. (100 m³)^–1,followed by summer (4.89 ind. (100 m³)^–1). The lowestabundance occurred in winter and spring. As to the horizontaldistribution, abundance in summer and autumn was higher in thenearshore than in the offshore of the East China Sea. In winterand spring, heteropods were barely found in the northern nearshore.Three dominant species were observed in four investigated seasons,in which only Atlanta rosea dominated in winter, spring andsummer while Atlanta peroni and Atlanta lesueuri mainly dominatedin autumn. These two dominant species observed in autumn exhibiteda rather higher occurrence frequency than A. rosea. Temperaturewas found to be a major influencing factor whereas salinitywas a minor one. Comparing their adaptability, A. rosea cansurvive in a wider temperature range (1628°C), which enablesit to dominate in four seasons, while A. peroni survives ina relatively narrow temperature range (1928°CC) and therange for A. lesueuri was even more narrow (2128°CC). Moreover,A. rosea was also adapted to a wider range of salinity. However,the abundance of A. rosea in autumn was lower than those ofA. peroni and A. lesueuri. It can be thereby inferred that themultiplication speed of A. rosea was lower than the other twospecies within the same favorable temperature range. Due totheir adaptability to high salinity, the distribution of heteropodswas closely related to the domain of the Taiwan Warm Currentand Kuroshio. Especially for A. peroni and A. lesueuri, theirhigh abundance areas are always indicative of the lasting existenceof strong warm currents. The negative values of aggregationindices indicated relatively even distribution of heteropodsin the East China Sea. The high abundance area (31°00' N,126°00' E) of heteropods in autumn is on the migration pathwayof the mackerel (Scomber japonicus Houttuyn). Thus, there isalso a fishing ground of the mackerel. This suggested that thehigh abundance area of heteropods in autumn is important tothe fisheries in the East China Sea. Comparing with the historicalrecords, the abundance of heteropods appeared to increase inthe past 40 years. This may be a result of strengthened warmcurrents due to global warming.     

The annual cycle of planktonic ciliates in nearshore waters at Signy Island, Antarctica

The abundance and biomass of marine planktonic ciliates in BorgeBay, Signy Island, were determined at monthly intervals betweenApril 1990 and June 1991. At least 24 different ciliate taxawere recorded from samples preserved in Lugol's iodine, includingthe tintinnids Codonellopsis balechi, Cymalocylis convallaria,Laackmaniella naviculaefera and Salpingella sp., and the aloricatetaxa Didinium sp. and Mesodinium rubrum. Ciliate abundance andbiomass exhibited a clear seasonal cycle with high values duringthe austral summer and low values in the austral winter. Abundanceranged from 0.3 10³l^–1 in September to 2.3 10³l^–1in January, while biomass ranged from 0.5 µg C l^–1in October to 12.6 µg C l^–1 in December. Small ciliatesdominated abundance throughout the year, and biomass duringwinter. Larger ciliates contributed most to biomass during summer.Aloricate ciliates were common throughout the year, while tintinnidscontributed substantially to abundance and biomass only duringsummer. Salpingella sp. was the commonest tintinnid, but C.convallariacontributed most to tintinnid biomass. The seasonal patternof ciliate abundance and biomass matched that of chlorophylla concentration and bacterial biomass, suggesting tight trophiccoupling between ciliates and other components of the pelagicmicrobial community. ¹Present address: Scott Polar Research Institute, Universityof Cambridge, Lensfield Road, Cambridge CB2 1ER, UK     

Seasonal variation of reproduction rates and body size of Calanus sinicus in the Southern Yellow Sea, China

Annual variations of egg production rate (EPR) and clutch sizeof Calanus sinicus, as well as body size of females (prosomelength and dry weight), were investigated at a series of stationsin the Southern Yellow Sea by onboard incubation. Calanus sinicuswas spawning in all the 11 cruises investigated, and the annualvariation of EPR was bimodal. Monthly average EPR was highestfrom May to July, respectively, 5.97, 5.36 and 6.30 eggs female^–1d^–1, then decreased dramatically to only 1.37 eggs female^–1d^–1 in August and attained the lowest 1.07 eggs female^–1d^–1 in October. In November, average EPR increased againto 4.31 eggs female^–1 d^–1. Seasonal variation ofclutch size was similar to EPR, except that it decreased graduallyafter August rather than dramatically as did EPR. Prosome lengthof females was maximum in May and minimum in October, but dryweight was highest in November. Monthly average EPR correlatedbetter with prosome length than dry weight, while clutch sizewas rather determined by dry weight of females. It is suggestedthat egg production of C. sinicus was active during two discontinuousperiods when both surface and bottom temperature fell into itsfavorite range (i.e. 10–23°C), and different reproductivestrategies were adopted in these two reproductive peaks: otherthan the highest EPR, longer prosome length was also achievedby C. sinicus from May to July, while females in November developedshorter bodies but accumulated more energy for reproduction.     

Fractionation of Nitrogen Isotopes during the Uptake and Assimilation of Ammonia by Plants

Two varieties (Nihonbare and Koshihikari) of rice plants (Oryzasativa L.) were grown hydro-ponically with two levels (20 and100 mg N liter ^–1) of ammonia. Variations in levels ofnatural abundance of ¹⁵N (¹⁵N) were analyzed in the ammoniaand organic nitrogen of shoots and roots, as well as in theammonia in the culture solution. There was substantial fractionationof nitrogen isotopes during the uptake of ammonia. When plantsabsorbed a large proportion of ammonia from a solution witha low concentration, less negative ¹⁵N values in plants andhigh positive ¹⁵N values in the ammonia remaining in solutionwere observed. The reverse was found when a smaller fractionof ammonia was absorbed from a solution with a higher concentrationof ammonia. The ^l5N values of ammonia in shoots and roots werehigher than in the respective constituent organic nitrogen,suggesting the fractionation of nitrogen isotopes during theassimilation of ammonia. Wild-type and mutant cells of the cyanobacterium(blue-green alga) Synechococcus PCC 7942 were grown in nitrate-or ammonia-containing medium as the source of nitrogen. Fractionationof nitrogen isotopes during the uptake of nitrate was limited,whereas that during the uptake of ammonia was considerable. ¹ In this report, the term ammonia refers indiscriminately toboth NH₃ or NH₄⁺. (Received June 13, 1991; Accepted September 12, 1991)     

Nitrogen regeneration by the subtropical marine copepod Eucalanus pileatus

Ammonium release rates by individual marine copepods (Eucalanuspileatus) were examined kinetically over successive 10-min intervalsafter the animals were exposed to three concentrations of thediatom Thalassiosira fluviatilis as food. Food concentrationsspanned those expected in the natural environment. "Well-fed"(3 mm³ T. fluviatilis l^–1) copepods released ammoniumsignificantly (p<0.05) faster than those fed zero or lowconcentrations of food, but differences were not dramatic. Meanexcretion rates (± SE) for animals removed from foodfor 18 –22 h [30 ± 6 nmol NH₄(mg ash free dry weight)^–1h ^–1] were 60% of those for "well-fed" animals [49 ±8 nmol NH₄ (mg ash free dry weight)^–1 h^–1]. Continuedhigh release rates after extended periods without food suggestthat E. pileatus must feed frequently in nature to maintainan adequate nitrogen balance. Depending on food concentration,animals released ammonium at rates ranging from 40 to > 100%of their N ingestion rates over the previous 18–22 h.Long-term (4–6 h) kinetic excretion experiments with "well-fed"animals indicated that, on average, release rates decreasedwith time after food removal, but patterns varied among individualcopepods. In addition to ammonium release, o-phthalaldehydereactive amino acid nitrogen was occasionally released by E.pileatus in large "spurt events" lasting from 20 to 60 min. ¹GLERL Contribution No. 283