Variations in the age and growth of yellowfin tuna larvae,Thunnus albacares,collected about the Mississippi River plume

Synopsis Eight hundred and one yellowfin tuna larvae ranging from 2.57–7.48 mm SL were collected near the Mississippi River discharge plume in the Gulf of Mexico during July and September, 1987. Larvae were most abundant at intermediate salinities (i.e. frontal waters) where chlorophylla and macrozooplankton displacement values were also highest. Using sagittal otolith microstructure, we estimated larval ages ranging from 3–14 d. These ages were used to back calculate spawning dates from 13–24 July and 22–31 August. Mean absolute individual growth rate (length age^–1) was 0.47 mm d^–1, with the least squares linear regression SL = 1.67 + 0.47 AGE (r² = 0.60, Pr> F = 0.0001) representing the best growth curve. Highest growth occurred at intermediate salinities near 31%, and temperatures near 29° C. There was significant temporal variation in growth, with larvae collected in July growing slower than those from September (0.37 and 0.48 mm d^–1, respectively). The pooled instantaneous daily mortality rate (Z) of the larvae was estimated to be 0.33 d^–1 (0.16 d^–1 in July and 0.41 d^–1 in September). These results show that significant spawning of yellowfin tuna may occur in the northern Gulf of Mexico in the vicinity of the Mississippi River discharge plume, and suggest that larval growth and survival may be enhanced in the plume frontal waters.     

The gene fl(2)d is required for various Sxl-controlled processes in Drosophila females

Summary In Drosophila melanogaster, the gene Sex-lethal (Sxl) controls the processes of sex determination, dosage compensation, oogenesis and sexual behaviour. The control of Sxl is by alternative splicing of its primary RNA. We have identified a gene, female-lethal-2-d (fl(2)d), which is needed for the female-specific splicing of Sxl RNA and which also has a vital function independent of Sxl. Here we analyse other aspects of the gene fl(2)d. Specifically, we have analysed the effect of the temperature-sensitive mutation fl(2)d ¹ on the viability of adult flies homozygous for this mutation. We have found that the viability of the mutant females is reduced, while that of the mutant males is not affected. In addition, the capacity of the mutant females to be inseminated is considerably reduced, whilst all the mutant males are able to inseminate females. These effects on females are suppressed by Sxl ^M1. However, the fat body cells of fl(2)d ¹ homozygous females are able to synthesize yolk proteins at the restrictive temperature. We have also carried out, in males, a clonal analysis of fl(2)d ², a mutation lethal in both sexes. We have found that the clones are fully viable. We conclude that the gene fl(2)d seems to be necessary during the adult life of females for the processes that require Sxl ⁺ activity. Moreover, the Sxl-independent vital function of fl(2)d seems to be required in both sexes only during larval development. Offprint requests to: L. Sánchez     

On the interpretation of some planktonology equations

Summary The concept of the mean value of a function is used to interpret some population-dynamics equations. The well-known formula for the per capita growth rate r gives a precise mean value for any (not only exponentially growing) populations. This result is used to derive the birth and death rate equations of Paloheimo (1974) with minimal initial limitations.Abbreviations t time - N number of animals - E number of eggs - r specific (i.e. per capita) population growth rate - b specific birth rate - d specific death rate - D duration of embryonic development     

Leptin controls rabbit ovarian function in vivo and in vitro: Possible interrelationships with ghrelin

The aim of these in vivo and in vitro studies was to examine the role of leptin in the control of plasma hormone concentrations, reproduction, and secretory activity of ovarian granulosa cells.In in vivo experiments, 15 female European domestic rabbit (Oryctolagus cuniculus) were treated with leptin (5 μg animal⁻¹ d⁻¹ for 1 wk before induction of ovulation with 25 IU equine chorionic gonadotropin and 0.25 IU human chorionic gonadotropin), and 15 females constituted the control group (treated with phosphate-buffered saline). Plasma concentrations of progesterone (P₄), testosterone (T), estradiol (E₂), estrone sulfate (ES), and insulin-like growth factor I (IGF-I) were determined at the estimated day of ovulation by radioimmunoassay (RIA), and number, viability, and body weight of newborns were recorded at parturition. In in vitro experiments, granulosa cells were isolated from periovulatory ovarian follicles of five control and five females treated with ghrelin (10 μg animal⁻¹ d⁻¹ for 1 wk before induced ovulation). Isolated cells were cultured for 2 d with and without leptin (0, 1, 10, or 100 ng/mL medium). Secretion of P₄, T, E₂, IGF-I, and prostaglandin F (PGF) was assessed in culture medium by RIA.In in vivo experiments, leptin administrations reduced plasma P₄, T, E₂, ES, and IGF-I levels. Leptin treatments did not affect ovarian weight or total number and body mass of newborns, but the proportion of pregnant females and number of live newborns were significantly higher in leptin-treated females than that in control females. In in vitro experiments, leptin significantly decreased (at 1 and 10 ng/mL) or increased (at 100 ng/mL) P₄ secretion, promoted E₂ and IGF-I (both at 100 ng/mL) secretion, and reduced T (at 1 and 10 ng/mL) and PGF (at 10 ng/mL) secretion. Granulosa cells from ghrelin-treated animals secreted less P₄, T, E₂, and PGF, but not IGF-I, than that secreted by granulosa cells from control animals. Furthermore, pretreatment of animals with ghrelin suppressed or even reversed subsequent leptin effects on P₄, T, E₂, IGF-I, and PGF secretion by cultured granulosa cells.These observations (1) show for the first time that leptin can increase the number of live newborns in rabbits, (2) confirm previous data on the ability of leptin to control ovarian secretory activity both directly and via upstream mechanisms, (3) demonstrate the involvement of ghrelin in the control of rabbit ovarian secretory functions, and (4) suggest an antagonistic interrelationship between leptin and ghrelin in the rabbit.     

A bioenergetic study of a benthic nematode,plectus palustris de man 1880, throughout its life cycle

Summary Growth and reproduction of the parthenogenetic freshwater nematode,Plectus palustris, were studied at different controlled levels of food densities at 20° C. A bacteria-sloppy agar mixture was used as substrate and food medium. No growth or reproduction occurred at the lowest food density (8.10⁷ bacterial cells ml^-1). At 8.10⁸ cells ml^-1, the larval duration was 18.5 days, the instantaneous growth rate (g) of young larvae 0.2 d^-1 and the daily fecundity rate during a prolonged period of constant egg production 12.6 eggs·d^-1. At a food density of 8.10⁹ cells ml^-1, the corresponding values are 12.5 days, 0.4 d^-1 and 37.7 eggs d^-1.By including the data on respiration from a previous paper (Klekowski et al., 1979), the energetics of the species at different food densities can be discussed: production processes are apparently more dependent on food supply than respiration. However, prolongation of the larval phase in lower food densities greatly increases the cumulated respiratory costs per unit production. A second point is the ability to produce smaller-sized primiparous females in sub-optimal food which shortens the immature life period and serves to reduce the burden of cumulated metabolic costs for attaining sexual maturity.A comparison of the range of food densities used in the experiments with bacterial densities known from lake sediments of different trophic type suggests that food is likely to be the main factor governing the population dynamics of bacterivorous species under field situations.     

Annual growth rate of the calcareous red alga Lithothamnion corallioides (Corallinales,Rhodophyta) in the Bay of Brest,France

Lithothamnion corallioides Crouan et Crouan (Rhodophyta, Corallinales) is the main constituent of the maerl beds of the Bay of Brest (Atlantic coast of western Brittany). Its growth rate was measured monthly in situ during one year. Growth rates were obtained by an adaptation of the buoyant weight technique. The highest daily growth rate was observed in July and reached 0.26 % d^–1 (S.D. = 0.06), when expressed as the increase of calcium carbonate weight. The average daily growth rate was 0.12% d^–1 (S.D. = 0.04) for a period of 275 days (summer and autumn 1988, winter 1989). Using this preliminary data, the calcium carbonate accretion rate can be estimated provisionally: 876 g m^–2 year^–1, a rate much lower than that of tropical reef coralline algae, but higher than that of Lithophyllum incrustans, the well known temperate European reef-builder.     

On an interacting particle system modeling an epidemic

We consider an interacting particle system onZ ^dto model an epidemic. Each site ofZ ^dcan be in either one of three states: empty, healthy or infected. Healthy and infected individuals give birth at different rates to healthy individuals on empty sites. Healthy individuals get infected by infected individuals. Infected and healthy individuals die at different rates. We prove that in dimension 1 and with nearest-neighbor interactions the epidemic may persist forever if and only if the rate at which infected individuals give birth to healthy individuals is high enough. This is in sharp contrast with models analysed by Andjel and Schinazi (1994) and Sato et al. (1994) where infected individuals do not give birth. We also show that some results in the latter reference can be obtained easily and rigorously using probabilistic coupling to the contact process.     

大兴安岭北部天然针叶林土壤氮矿化特征

采用顶盖埋管法对大兴安岭地区天然针叶林(樟子松林、樟子松-兴安落叶松混交林和兴安落叶松林)土壤铵态氮(NH~+_4-N)、硝态氮(NO~-_3-N)、净氮矿化速率进行研究,并探索土壤理化性质与氮矿化之间的相关性,为大兴安岭地区森林生态系统土壤养分管理及森林经营提供帮助。结果表明:观测期内(5—10月)3种林型土壤无机氮变化范围为31.51—70.42 mg/kg,以NH~+_4-N形式存在为主,占比达90%以上,且与纯林相比混交林土壤无机氮含量较高。3种林型土壤净氮矿化、净氨化、净硝化速率月变化趋势呈V型,7、8月表现为负值,其他月份为正值。净氮矿化速率变化范围樟子松林为-0.54—1.28 mg kg~(-1) d~(-1)、樟子松-兴安落叶松混交林为-0.13—0.55 mg kg~(-1) d~(-1)、兴安落叶松林为-0.80—1.05 mg kg~(-1) d~(-1)。土壤净氨化过程在土壤氮矿化中占主要地位,占比达60%以上。3种林型土壤净氮矿化、净氨化及净硝化速率垂直差异显著,0—10 cm土层矿化作用明显高于10—20 cm土层(P0.05)。土壤氮矿化速率与土壤含水量、土壤有机碳含量、土壤C/N、枯落物全氮含量和枯落物C/N均存在显著相关性。不同类型的森林土壤及枯落物的质量也存在差异,进而影响土壤氮矿化特征。     

AGE,GROWTH, AND REPRODUCTIVE PATTERNS OF DALL'S PORPOISE (PHOCOENOIDES DALLI) IN THE CENTRAL NORTH PACIFIC OCEAN

Life history parameters were estimated for Dall's porpoise, Phocoenoides dalli, from biological specimens collected in the western Aleutian Islands, during 1981–1987. Of 2,033 males and 3,566 females examined, reproductive data were available for 1,941 males and 1,906 females; ages were determined for 813 males and 1,297 females. Female sexual maturity was based on the presence of one or more corpus on either ovary; 845 were sexually immature and 1,061 were sexually mature. Two estimates of female average age at sexual maturity (ASM) were 3.8 and 4.4 yr; average length at sexual maturity (LSM) was 172 cm. Males were considered sexually mature when evidence of spermatogenesis was detected; 1,136 were sexually immature and 805 were sexually mature. Two estimates of male ASM were 4.5 and 5.0 yr; LSM was 179.7 cm. Physical maturity was assessed for 246 males and 446 females by examining the degree of fusion in thoracic vertebral epiphyses. For both sexes, the average age at physical maturity was 7.2 yr. Average length at physical maturity was 202.6 cm for males and 192.7 cm for females. Average lengths of physically mature males (x?= 198.1 cm, SE = 0.8566) and females (x?= 189.7 cm, SE = 0.4002) were significantly different(P < 0.0001). Early postnatal growth was rapid in both sexes. A secondary growth spurt in both mass and length was characteristic for both sexes; the increase in length preceded the mass increase by 1–2 yr. Average length at birth (LOB) was approximately 100 cm; birth mass averaged 11.3 kg (SE = 0.0772). By the time the umbilicus had healed (<2 mo), the average length and mass had increased to 114.1 cm and 23.8 kg, respectively. Gestation period based on projections using LOB was 12 mo, but this was considered an overestimate. Calving was modal, centered in early July; an annual reproductive interval was indicated. Among the sexually mature females, 120 were pregnant, 55 were pregnant and lactating, 321 were pregnant with colostrum, and 33 were “resting.” By 3 July (95% CI =x? 1 d), 50% of births had occurred, during each of the seven years sampled. The ovulation rate was estimated at 0.914 ovulations per average reproductive year. Enlarged follicles and recent ovulations were observed in postpartum females in late July.     

Estrous asynchrony causes low birth rates in wild female chimpanzees

Estrous cycle asynchrony likely functions to elevate individual females' sexual attractiveness during female mate choice. Female chimpanzees show physiological estrus as anogenital swelling. Copulations are concentrated during the period of maximal tumescence, which is called the estrous period. A group of female chimpanzees in Mahale Mountains National Park, Tanzania, was shown to display asynchrony in both maximal tumescence and periovulatory periods. We tested the hypothesis that females establish asynchronous maximal tumescence or periovulatory periods with respect to other females to increase copulation frequency and birth opportunities (Hypothesis 1). We analyzed differences in birth rates between four asynchronous years and five nonasynchronous years. Counter to Hypothesis 1, females in periovulatory periods during asynchronous years showed significantly lower birth rates than those in nonasynchronous years. In addition, periovulatory females copulated more frequently on days on which no other female in a periovulatory period was present. These results suggest that birth rates tend to decrease when females experience nonoverlapping ovulation cycles, although copulation frequency is high. Such a decrease in the birth rate may have resulted from the cost associated with multiple copulations. We tested two other hypotheses: paternity confusion (Hypothesis 2) and sperm competition (Hypothesis 3). Both of these hypotheses were partially supported. The highest‐ranking male most effectively monopolized access to receptive females when relatively few other males and receptive females from the party (or subgroup) were present. The viability of Hypotheses 2 and 3 requires that dominant males are able to hinder a female from mating with other males. Given that the male‐biased operational sex ratio created by female asynchrony is likely to reduce the efficiency of mate guarding by dominant males, an asynchronous female may gain a fitness benefit by increasing the probability of mating with at least one male who produces superior sperm. Am. J. Primatol. 73:180–188, 2011. © 2010 Wiley‐Liss, Inc.     

Effects of the sea louse Lepeophtheirus salmonis on temporal changes in cortisol,sex steroids,growth and reproductive investment in Arctic charr Salvelinus alpinus

Groups of mature (5+ year old) Arctic charr Salvelinus alpinus held in sea water were exposed for 34 days to either a high (mean ±s.e . 0·15 ± 0·01 sea lice Lepeophtheirus salmonis g^?1 fish mass) (HI), medium (0·07 ± 0·00 sea lice g^?1 fish mass) (MI) or no [control (C)] sea‐lice infection during early stages of gonad development (June to July). Infection with sea lice resulted in increased plasma cortisol concentrations and this was related to intensity of infection; females tended to have higher cortisol concentrations than males at high infection intensities (HI group: female c. 130 ng ml^?1; male c. 80 ng ml^?1). Plasma osmolality (C c. 330, MI c. 350 and HI c. 415 mOsm) and chloride concentrations (C c. 135, MI c. 155 and HI c. 190 mM) increased significantly with infection intensity, indicating osmoregulatory problems in infected fish. A strong positive relationship between plasma osmolality and cortisol concentration was recorded. Plasma sex‐steroid concentrations were influenced negatively by sea‐lice infection, particularly in the HI group, and were inversely related to plasma cortisol concentrations. The most heavily infected fish postponed the initiation of reproductive development until exposed to fresh water and timing of ovulation tended to be delayed in these fish. Growth rate and condition were negatively influenced by sea‐lice infection and growth rate was inversely related to plasma cortisol concentrations. Sea‐lice infection resulted in mortality among females in the HI group, and the proportion of maturing females was lower in the MI group (46%) than in the controls (85%). Egg production in the MI and HI groups was c. 50 and 30% of the C group. Egg size, embryonic survival and fry mass did not differ across groups. Sea lice influence reproductive development and egg production in S. alpinus, and consequently these parasites may influence populations via sublethal effects on broodfish, affecting growth and condition, and their reproductive output.     

尕海湿地草甸土退化过程土壤氮矿化演变特征

氮矿化是生态系统循环的重要环节之一,影响着生态系统功能和氮素生物地球化学循环,因此研究高寒湿地退化过程中土壤氮矿化演变特征,对揭示气候变化和人为活动干扰背景下的湿地土壤氮素循环过程具有重要意义。以尕海湿地4种不同退化梯度(未退化、轻度退化、中度退化、重度退化)土壤为研究对象,采用野外树脂芯原位培养方法,通过对植物生长季不同生长阶段(生长初期、生长盛期、枯萎期)土壤氮素矿化作用研究,分析湿地退化演替过程中土壤氮矿化时空变化特征及其与土壤环境因子和酶活性之间的关系。结果表明：尕海湿地退化对土壤氮矿化过程有显著抑制作用,与未退化(0.143 mg kg^-1 d^-1)相比,轻度退化、中度退化、重度退化的土壤净氮矿化速率分别减小了0.018 mg kg^-1 d^-1、0.025 mg kg^-1 d^-1、0.020 mg kg^-1 d^-1;随着退化程度加剧,土壤净氨化速率逐渐减小或者不变,而净硝化速率却增大。随时间推移,各退化...     

Influence ofMyriophyllum aquaticum cover onAnopheles mosquito abundance,oviposition, and larval microhabitat

Summary The surface cover produced by aquatic macrophytes is the primary habitat for immature stages (eggs, larvae, and pupae) ofAnopheles mosquitoes. We hypothesized that both the abundance of immatureAnopheles and the recruitment ofAnopheles (from oviposition or larval movement) is positively related to the amount of surface cover present. Field sampling documented a positive correlation betweenAnopheles egg and larval abundance and the amount of vegetative cover present (measured as the number of emergent stems m^-2) in monospecific beds ofMyriophyllum aquaticum in a California, USA, wetland. Experiments conducted to determine the influence ofMyriophyllum stem density on selection of oviposition sites by adultAnopheles females clearly indicate that oviposition rate (eggs m^-2 d^-1) increases as stem density increases from 0 to 1000 stems m^-2 but decreases as stem density approaches 2000 stems m^-2. In selecting microhabitats,Anopheles larvae preferred patches with high stem densities over patches with few or no plant stems; this preference correlates with differences in habitat quality (e.g., increased refuge from predation and enriched food sources). The optimal habitat for anopheline mosquitoes apparently occurs above a threshold plant density of approximately 500Myriophyllum stems m^-2. Habitat heterogeneity produced by variability in the distribution and structure of aquatic vegetation strongly influences the local distribution and abundance of anopheline mosquitoes.     

Biogeochemical cycling of methylmercury at Barn Island Salt Marsh,Stonington, CT,USA

Monomethylmercury (MMHg) is toxic, and is the primary form of Hg thatbioaccumulates in the food web. An understanding of its distribution,production, and transport is needed. Prior investigations indicate thatmethylation is mediated by sulfate-reducing bacteria, yet limited in highsulfate environments. High rates of microbial respiration and strong oxygengradients are found in salt marshes. It is hypothesized that significant in situ methylation takes place in the redox transition zone of sulfate rich( 28 mM) salt marsh sediment. Results from a water column surveyof Barn Island Salt Marsh in October 1996 showed that ca. 61pmol m^-2 d^-1 of dissolved MMHg were discharged toadjacent coastal waters, while 16 pmol m^-2 d^-1 ofparticulate MMHg were entrained in the marsh, implying an in situsource. In-sediment MMHg production rates were determined by²⁰³Hg radiotracer studies. At the surface, methylation rates variedover both long (i.e., 100's m; 11–1120 pmol m^-2 d^-1) andshort (i.e., 10 cm; 11–108 pmol m^-2 d^-1) spatial scales. Methylation rate profiles from both low and high MMHg production sitesexhibited an exponential decrease below the redox transition zone. Porewater was collected with multi-chambered in situ dialysis (30 kDa)samplers [Peepers] and analyzed for MMHg. Temporal differences in porewater MMHg accumulation (i.e., May > September > November)were found. Results from May showed a significant gradient at thesediment water interface. The transport out of the sediments estimated byFick's Law (ca. 390 pmol MMHg m-2 d^-1) suggeststhat MMHg entered the marsh water by diffusion. This workdemonstrates the potential for elevated in situ Hg methylation in highsulfate environments.     

Naphthalene,phenanthrene and surfactant biodegradation

The impact of surfactants on naphthalene and phenanthrene biodegradation and vice versa after surfactant flushing were evaluated using two anionic surfactants: sodium dodecyl sulfate (SDS) and sodium dodecyl benzene sulfonate (SDBS); and two nonionic surfactants: POE (20) sorbitan monooleate (T-maz-80) and octylphenol poly(ethyleneoxy) ethanol (CA-620). Naphthalene and phenanthrene biodegradation varied differently in the presence of different surfactants. Naphthalene biodegradation was not impacted by the presence of SDS. In the presence of T-maz-80 and CA-620, naphthalene biodegradation occurred at a lower rate (0.14 d^-1 for T-maz-80 and 0.19 d^-1 for CA-620) as compared to un-amended control (0.29 d^-1). Naphthalene biodegradation was inhibited by the presence of SDBS. In the presence of SDS, phenanthrene biodegradation occurred at a lower rate (0.10 d^-1 as compared to un-amended control of 0.17 d^-1) and the presence of SDBS, CA-620 and T-maz-80 inhibited phenanthrene biodegradation. The surfactants also responded differently to the presence of naphthalene and phenanthrene. In the presence of naphthalene, SDS biodegradation was inhibited; SDBS and T-maz-80 depleted at a lower rate (0.41d^-1 and 0.12 d^-1 as compared to 0.48 d^-1 and 0.22 d^-1). In the absence of naphthalene, CA-620 was not degradable, while in the presence of naphthalene, CA-620 began to degrade at a comparatively low rate (0.12 d^-1). In the presence of phenanthrene, SDS biodegradation occurred at a lower rate (1.2 d^-1 as compared to 1.68 d^-1) and a similar trend was observed for T-maz-80. The depletion of SDBS and CA-620 did not change significantly. The choice of SDS for naphthalene-contaminated sites would not adversely affect the natural attenuation of naphthalene, in addition, naphthalene was preferentially utilized to SDS by naphthalene-acclimated microorganisms. Therefore, SDS was the best choice. T-maz-80 was also found to be usable in naphthalene-contaminated sites. For phenanthrene contaminated sites, SDS was the only choice.     

Metabolic costs of viviparity in yellowtail rockfish,Sebastes flavidus

Synopsis We estimated the energy utilized by developing embryos and larvae of yellowtail rockfish,Sebastes flavidus, by determining the routine metabolic rate of adult females throughout gestation and subtracting the mean metabolic rate of non-gestating fish. The pattern of maternal oxygen consumption during gestation was such that metabolic demands did not become significantly elevated until intra-ovarian embryos had hatched and larvae were being incubated (i.e. 24–28 d post-fertilization). Metabolic rates of females in this latter stage of gestation were 82% higher than spent females and 101% higher than those of non-reproductive males. We determined that 0.08996 cal embryo^-1 was consumed during gestation as compared to the change in energy content of embryos from fertilization to birth which was 0.08690 cal embryo^-1. The difference between the energy consumed and the energy lost during the 29 d gestation period indicated that extra embryonic sources contributed only 3.4% or 0.00306 cal embryo^-1 of the energy utilized after fertilization. Our observations agree with previous work which determined that embryos and larvae ofS. flavidus are primarily lecithotrophic and that the relatively high fecundity ofS. flavidus coupled with a small egg size, rapid embryogenesis and brief gestation period characterize this species as a relative r-strategist within a genus whose species range broadly over the K end of the r-K continuum.     

PRODUCTIVITY OF PODOSTEMUM CERATOPHYLLUM IN THE NEW RIVER,VIRGINIA

Productivity of Podostemum ceratophyllum, the dominant aquatic macrophyte in the New River, was measured at four sites representing soft- and hardwater reaches of the river. Available dissolved inorganic carbon (DIC) was 4–5 times greater in the hardwater reach. The difference in available DIC was reflected in standing crop and productivity of P. ceratophyllum. Maximum standing crops of P. ceratophyllum at the two hardwater sites (Sites 1 and 2) were 244.8 ± 30.7 g ash-free dry wt (AFDW) m^−-2 and 193.8 ± 18.7 g AFDW m^−-2 compared to 128.5 ± 14.9 g AFDW m^−-2 and 101.3 ± 6.9 g AFDW m^−-2 for the softwater sites (Sites 3 and 4). Productivity, based on differences in standing crops, was: Site 1, 1.08 ± 0.12 g C m^−-2 d^−-1; Site 2, 0.86 ± 0.08 g Cm^−-2d^−-1; Site 3,0.58 ± 0.06 g C m^−-2 d^−-1; Site 4,0.45 ± 0.03 g C m^−-2 d^−-1. Corresponding values for productivity as ¹⁴C uptake were: 2.77 ± 0.44 g C m^−-2 d^−-1; 2.10 ± 0.45 g C m^−-2 d^−-1; 0.34 ± 0.04 g C m^−-2 d^−-1; 0.28 ± 0.03 g C m^−-2 d^−-1. Productivity/biomass (P/B) based on ¹⁴C uptake and standing crop revealed that P. ceratophyllum productivity was inhibited at the softwater sites perhaps due to carbon limitation. Because of its abundance and its high productivity, P. ceratophyllum is hypothesized to contribute significantly to the New River organic matter budget.     

Ulva rigida (Ulvales,Chlorophyta) tank culture as biofilters for dissolved inorganic nitrogen from fishpond effluents

Ulva rigida was cultivated in 7501 tanks at different densities with direct and continuous inflow (at 2, 4, 8 and 12 volumes d^–1) of the effluents from a commercial marine fishpond (40 metric tonnes, Tm, of Sparus aurata, water exchange rate of 16 m³ Tm^–1) in order to assess the maximum and optimum dissolved inorganic nitrogen (DIN) uptake rate and the annual stability of the Ulva tank biofiltering system. Maximum yields (40 g DW m^–2 d^–1) were obtained at a density of 2.5 g FW 1^–1 and at a DIN inflow rate of 1.7 g DIN m^–2 d^–1. Maximum DIN uptake rates were obtained during summer (2.2 g DIN M^–2 d^–1), and minimum in winter (1.1 g DIN m^–2 d^–1) with a yearly average DIN uptake rate of 1.77 g DIN m^–2 d^–1 At yearly average DIN removal efficiency (2.0 g DIN m^–2 d^–1, if winter period is excluded), 153 m² of Ulva tank surface would be needed to recover 100% of the DIN produced by 1 Tm of fish.Abbreviations DIN= dissolved inorganic nitrogen (NH _inf4 ^sup+ + NO _inf3 ^sup– + NO _inf2 ^sup– ); - FW= fresh weight; - DW= dry weight; - PFD= photon flux density; - V= DIN uptake rate     

Seasonal changes in glomerular filtration rate in Antechinus stuartii (Marsupialia: Dasyuridae)

The small marsupial Antechinus stuartii experiences a synchronised life cycle that culminates in complete male mortality (within 3 weeks) following the 1 week mating period in mid-August (late winter). There are pronounced physiological changes in male A. stuartii over the life cycle and renal function was assessed for correlation with these changes. Glomerular filtration rate and urine and plasma electrolytes were determined in male and female A. stuartii in February, May, July and August. Females showed little change in glomerular filtration rate, except for pre-mating values in August which decreased. In contrast, glomerular filtration rate of males decreased significantly in July and August. Plasma sodium and chloride levels were higher in males than females and were higher in animals in July and August than in February and May. Plasma potassium levels dropped in both males and females in July and August. Plasma osmolality was higher in animals in February compared to animals from May and August. However, there were no significant sex or seasonal differences in urine electrolytes, although urea concentration was higher in females than males. Urine osmolality was higher in both sexes in July and August. There were no significant differences in total excretory rates of sodium, potassium or chloride between sexes or between seasons. Many of the alterations in renal function are correlated with known physiological and hormonal profiles in A. stuartii. This is the first observation of seasonal changes in glomerular filtration rate that are unrelated to dietary and water stresses. Accepted: 8 September 1997     

Dynamics of coexisting Calanus finmarchicus, Calanus glacialis and Calanus hyperboreus populations in a high-Arctic fjord

We studied the population dynamics of Calanus finmarchicus, Calanus glacialis and Calanus hyperboreus in Billefjorden, Svalbard (78°40N). All three species reproduced in the fjord with different timing. The maximum abundance of Calanus spp. copepodite stages peaked on the 11th of July (29,000 ind m^–2). C. glacialis was the dominant species accounting for 60–80% of the total Calanus abundance. C. finmarchicus appear to thrive in the fjord despite the low temperatures (–1.86°C to 5°C) and accounted for 20–30% of the total population. C. hyperboreus contributed less to the total abundance (5–20%). A 1-year life cycle is suggested for C. finmarchicus and C. hyperboreus in the fjord, C. glacialis has a 1- to 2-year life cycle. Highest mortality rates were observed for copepodite stage CV in C. finmarchicus and C. glacialis (0.09 and 0.075 d^–1, respectively) and for females in C. hyperboreus (0.149 d^–1). Mortality of copepodite stages was substantially lower in C. glacialis than in the other species. This is particularly obvious in the early and numerous copepodite stages (CI + CII) during the period of recruitment to these stages. This suggests that differences in secondary production in Arctic pelagic ecosystems are controlled partly by population loss rates.