Late Winter-early Spring Research Articles

Influence of environmental factors, season and size at deployment on growth and retrieval of postlarval lion's paw scallop Nodipecten nodosus (Linnaeus, 1758) from a subtropical environment

The effect of seasonal variation of environmental factors on daily shell growth rates (DGR) of postlarval Nodipecten nodosus was studied at the southern distribution limit of the species in Santa Catarina State, Brazil. Five deployments of hatchery produced postlarvae (initial shell height 0.5 mm) in the sea-based nursery were carried out from August 2000 to September 2001, and DGR and percent retrievals were recorded. Chlorophyll- a, seston, salinity, dissolved oxygen and turbidity were measured weekly, and temperature was recorded hourly. Additionally, DGR and retrievals were compared for postlarvae maintained simultaneously in the sea- and land-based nurseries (initial shell height 0.5 mm), and also for post-larvae deployed in the sea-based nursery at different initial sizes (0.29–1.1 mm). Mean DGR was significantly lower in late winter–early spring 2000 (0.045 mm day −1), intermediate in late winter–early spring 2001 (0.078 mm day −1) and significantly higher in the other seasons (late spring–early summer, 0.152 mm day −1; late summer–early autumn, 0.149 mm day −1 and late–autumn early winter, 0.130 mm day −1). Temperature was the best predictor of growth, which was least at temperatures below 20 °C. Growth rate was also minimal during a period of low salinity and high turbidity. Mean DGR was significantly higher in postlarvae deployed in the sea-based nursery than in those maintained in the land-based nursery. Loss of postlarvae in the sea-based nursery was initially higher in collectors transferred earlier to the sea (ca. 2–3 weeks post-set; shell height 0.5–0.8 mm), but percent retrievals were similar after postlarvae deployed to the sea ca. 4–5 weeks post-set (shell height 1.1 mm) were retrieved simultaneously with those deployed earlier. At retrieval, postlarvae deployed approximately 2 weeks post-set were larger than those deployed subsequently, but spat deployed 1 week post-set attained a similar size to those deployed 2 weeks post-set. A strategy to deploy postlarvae in the sea-based nursery at a size circa 0.5 mm is proposed as more advantageous than keeping them longer in land-based facilities. In southern Brazil, there is a wide window of opportunity to deploy post-larval scallops in the sea-based nursery in which growth is maximized, except when water temperatures drop below 20 °C.

Differences in light and temperature responses determine autumn versus spring germination for seeds of Schoenolirion croceum

Seeds of the southeastern North American Schoenolirion croceum (Michx.) Wood are dormant when dispersed in late spring to early summer. Fresh seeds buried in soil after dispersal germinate in autumn, whereas those sown on the soil surface do so the following late winter – early spring. To understand this difference in germination phenology, we examined the light and temperature requirements for dormancy break and germination. Seeds germinated to high percentages in darkness over 12:12 h thermoperiods ranging from 15:6 to 35:20 °C following warm stratification (25:15 °C) in darkness, whereas no seeds germinated in light following stratification in light. On the other hand, seeds germinated to high percentages in light and in darkness following cold stratification (5 °C) in light or darkness. Seeds exposed to light during autumn germinated in winter–spring regardless of the light regime in summer or winter–spring, whereas those in darkness during autumn germinated in autumn regardless of the light regime in summer. Thus, light conditions during autumn are critical for determining whether seeds will germinate in autumn versus early spring. In contrast with many other species in which germination phenology is mostly temperature controlled, timing of germination for S. croceum depends on the light conditions in relation to temperatures experienced during dormancy release.Key words: dark, germination phenology, Hyacinthaceae, negative photoblastic seeds, photoecology, seed dormancy.

THE EFFECT OF BIOREGULATORS, NITROGEN, LEAF REMOVAL, AND BRANCH TIPPING ON FLORAL BUD DISORDER OF JAPANESE PEAR 'HOSUI' (PYRUS PYRIFOLIA NAKAI)

ISHS IX International Symposium on Plant Bioregulators in Fruit Production THE EFFECT OF BIOREGULATORS, NITROGEN, LEAF REMOVAL, AND BRANCH TIPPING ON FLORAL BUD DISORDER OF JAPANESE PEAR 'HOSUI' (PYRUS PYRIFOLIA NAKAI)

Picoplankton community structure along the northern Iberian continental margin in late winter-early spring

The surface distribution of autotrophic and heterotrophic picoplankton was assessed in 24 transects perpendicular to the coast along the N and NW Iberian peninsula shelf in late winter and early spring 2002. Community structure was analyzed by flow cytometry (FC) and found to be strongly influenced by hydrography. Typical late winter conditions were found during the survey, characterized by the presence of the poleward Portugal coastal counter current (PCCC) in the west and an increasing stratification eastwards. Cyanobacteria (mostly Synechococcus) dominated at low chlorophyll a (Chl a) concentration whereas both the total and relative abundance of picoeukaryotes generally increased with total phytoplankton biomass. Differences in the cell size of most FC-defined picoplanktonic groups were also observed along the longitudinal and coastal‐offshore gradients. The presence of Prochlorococcus (<10 3 cells mL � 1 ) coincided with the core of the PCCC and its significant correlation with salinity suggests its possible use as a tracer of this current. Two groups of heterotrophic bacteria were distinguished according to their relative DNA content. High DNA bacteria dominated the community (60¯� 1% SE of total numbers), reaching maximum values in areas under riverine influence with presumed higher inputs of organic matter. Picoplankton biomass was dominated by heterotrophic bacteria in the western region (58¯� 3%) while autotrophic groups contributed on average 66¯� 2% in the southern Bay of Biscay. The heterotrophic bacteria to phytoplankton biomass ratio decreased significantly along the measured range. Yet showing regional differences, the estimated contribution of picophytoplankton to total algal biomass was high (mean 59¯� 4%), indicating the important role of small cells at the onset of the spring bloom in these temperate shelf waters.

Seasonal changes in angiotensin converting enzyme activity in male and female frogs ( Rana esculenta)

Gonad, lung, kidney and serum angiotensin converting enzyme (ACE) activities were determined by specific substrate hydrolysis in male and female Rana esculenta over 1 year. Ovary ACE activity showed the highest values among the different tissues, with a significant peak (223±52 nmol min −1 mg protein −1) in late winter-early spring. Testis ACE activity followed a significant seasonal cycle, increasing from September to peak in April (2.5±0.8 nmol min −1 mg protein −1) and then decreased in the post-reproductive period. Lung and kidney ACE activities were not correlated with the annual reproductive cycle phases. In serum a peak of activity was present in the post-reproductive period both in male and female frogs. The present data show a correlation between ACE and the annual reproductive cycle of R. esculenta.

Recent, Large-Scale Changes in the Extratropical Southern Hemisphere Atmospheric Circulation

The zonal anomalies in the 500-hPa geopotential height field of the Southern Hemisphere are examined using the National Centers for Environmental Prediction–National Center for Atmospheric Research reanalyses, 1958–96. The zonal anomalies were constructed by removing the zonal mean from each grid point, and principal components analysis was performed on the resulting spatial anomalies. The principal components of the leading EOF of the seasons March–April–May (MAM) to September–October–November (SON) indicate that a change has occurred in the extratropical, large-scale, atmospheric circulation of the Southern Hemisphere. It is estimated to have begun after 1975 and is limited to the southern late fall, winter, and early spring. The elements of this change are a deeper Pacific trough and higher Indian Ocean ridge at subtropical latitudes. At higher latitudes the ridge over the Pacific strengthened and shifted east while troughing occurred in the southwest Atlantic–Weddell Sea region. Consistent with the changes in the zonal anomalies, zonal wave 1 experienced a large increase in amplitude in the late winter–early spring. On the other hand, zonal wave 3 reached its maximum one month earlier, shrank more quickly, and reached lower-than-average amplitudes in spring after 1975.

Correlation between the presence of Gonyaulax fragilis (Dinophyceae) and the mucilage phenomena of the Emilia-Romagna coast (northern Adriatic Sea)

The formation of massive amounts of suspended mucilaginous organic matter which periodically affects the Adriatic Sea, has been regarded as a complex physico-chemical phenomenon resulting from the production of extracellular material by phytoplankton. Although the exact cause has remained obscure, the mechanism of its formation has usually been considered to be a long-term process, starting after the late winter-early spring blooms, and involving the participation of various algal species, mainly within the diatom group. In this paper we report on the results of a phytoplankton monitoring programme in northern Adriatic seawaters off the Emilia-Romagna coast of Italy which revealed the constant concomitant presence of the dinoflagellate Gonyaulax fragilis (Schütt) Kofoid and mucilaginous formations. In the early stages of the phenomenon the dinoflagellate was clearly observable by microscopic examination in the mucilage, but as the mucilage aged this alga almost completely decomposed and diatom cells increased in number and became predominant. Although characterized by a slow growth rate in culture, in natural seawater G. fragilis was observed to reach cell densities of up to 7.0×10 6 cells l −1. The results of this study lead us to propose the hypothesis that the appearance of mucilage in the water column of the Adriatic Sea is the consequence of a seasonal growth of this dinoflagellate favoured by specific environmental circumstances.

Development and recovery from winter embolism in silver birch: seasonal patterns and relationships with the phenological cycle in oceanic Scotland.

Silver birch (Betula pendula Roth) is increasingly used in the United Kingdom for reforestation. However, recent evidence indicates that, under some circumstances, planted birch can suffer serious and repeated mortality of the apical leaders and branches, with consequent loss of apical dominance and the formation of a contorted stem. Plants from 37 seed sources of silver birch from Scotland and northern England planted at two sites were compared for several characteristics related to hydraulic architecture, vulnerability to freeze-thaw cycle induced embolism and spring recovery from winter embolism during the period 2000-2002. Phenological rhythms were also monitored in late winter-early spring to document relationships between phenology and water relations parameters. Significant differences were found across seed sources in stage of bud flushing for four dates in spring. Early flushing seed sources differed by about 1 to 2 weeks from late-flushing seed sources across the two sites. Wintertime xylem embolism in stems reached a peak of about 50 to 70% loss of xylem hydraulic conductivity, depending on the size and position of the sample shoots in the canopy. Small apical shoots were significantly more embolized than large basal shoots. Development of winter embolism was coupled to the occurrence of frost events. As percent loss of hydraulic conductivity increased during the winter, wood relative water content declined. Embolism reversal occurred rapidly in spring at the time of development of positive root pressure. No significant differences in the degree of winter embolism in 2001 were found among the three seed sources examined. The investigation was expanded in the winter-spring of 2002 to include 10 seed sources across both sites. Significant differences were found in degree of winter embolism across sites, dates and seed sources. For each date, there was a significant relationship between flushing scores and wood relative water contents across the two sites and all seed sources, suggesting that differences in time of flushing across sites and seed sources were likely caused by differences in the time of occurrence of root pressure, a necessary precondition to flushing.

Historical changes in lake ice‐out dates as indicators of climate change in New England, 1850–2000

AbstractVarious studies have shown that changes over time in spring ice‐out dates can be used as indicators of climate change. Ice‐out dates from 29 lakes in New England (USA) with 64 to 163 years of record were assembled and analysed for this study. Ice‐out dates have become significantly earlier in New England since the 1800s. Changes in ice‐out dates between 1850 and 2000 were 9 days and 16 days in the northern/mountainous and southern regions of New England respectively. The changes in the ice‐out data over time were very consistent within each of the two regions of New England, and more consistent than four air‐temperature records in each region. The ice‐out dates of the two regions had a different response to changes in air temperature. The inferred late winter–early spring air‐temperature warming in both regions of New England since 1850, based on linear regression analysis, was about 1.5°C. Published in 2002 by John Wiley &amp; Sons, Ltd.

Habitat Use by Striped Bass in Relation to Seasonal Changes in Water Quality in a Southern Reservoir

Adult striped bass Morone saxatilis (n = 61; 597-914 mm total length) were captured by hook and line throughout Lake Murray, South Carolina, and by electrofishing in the Greenwood Dam tailrace and upper Saluda River above Lake Murray, implanted with temperature-sensitive radio transmitters, and tracked biweekly. During late winter-early spring, striped bass were concentrated in the upstream portions of the reservoir. By midsummer, they were primarily located in the lower embayment of the reservoir, but several fish remained in the tailrace of the upstream dam as well as in a thermal refuge in the Saluda River. After the reservoir began to cool in fall, fish dispersed from the lower embayment and moved upstream toward the headwaters of the reservoir, where they had been captured the previous spring. Several fish returned to locations within 10 m of their original capture locations. Mean movement rates were lowest in winter and summer and highest in spring and fall. Low movement rates in summer were associated with a severe reduction of suitable habitat. In addition to the standard biweekly sampling, a 7.5-km2 section of the lower embayment of Lake Murray was searched every 2 h over a continuous 48-h period from 10 to 12 August 2000. During this period, striped bass were observed to use the same areas on a seasonal basis as they did on a diel basis. However, mean hourly rates of movement were greater than the movement rates calculated for the normal 2-week interval between samples. Changes in location between biweekly samples may not indicate displacement but rather only randomly chosen locations in normal use areas.

Component community of larval trematodes in the mudsnail Hydrobia ventrosa: temporal variations in prevalence in relation to host life history.

Temporal variations in the prevalence of larval trematodes in the short-lived prosobranch mudsnail Hydrobia ventrosa (Montagu) were investigated in relation to host life history and season for 4 successive years in temperate windflats of the southern Baltic Sea. The component community of trematode larvae in H. ventrosa comprises at least 10 species; families (and species) represented include Notocotylidae (1), Echinostomatidae (1 or 2), Heterophyidae (2), Monorchidae (1), Microphallidae (3 or 4), Psilostomatidae (1), and Hemiuridae (1). The notocotylid Paramonostomum alveatum was the most prevalent species, followed by the microphallids Maritrema subdolum and Microphallus sp. Trematode prevalence in H. ventrosa fluctuated seasonally. Prevalence usually peaked in summer between July and September-October and decreased in late winter-early spring. This seasonal change is chiefly explained by the life history patterns of the semelparous snail host. Hydrobia ventrosa has a maximum life span of about 2 yr and reproduces between June and November of its second calendar year. The first trematode infections appeared annually in May when the most abundant cohort of H. ventrosa, the second-calendar-year snails, mature. The prevalence continued to increase until August-September, throughout the reproductive period of the second-calendar-year snails, Prevalence decreased during winter, when most of the second-calendar-year snails died after reproduction. On the basis of longterm laboratory experiments, it has been shown that the late autumn-winter mortality was not the result of trematode infections. Seasonal patterns of prevalence were similar among the trematode species except for the monorchid Asymphylodora demeli, the only one using fish definitive hosts. Species-specific differences in the seasonal occurrence of prepatent infections and the predominance of certain larval stages in winter are interpreted as different strategies of the trematode species to survive the harsh winter conditions, or to survive the death of the first intermediate host in autumn-winter, or both.

Fine-fraction carbonate stable isotopes as indicators of seasonal shallow mixed-layer paleohydrography

We have measured stable isotopic compositions of Miocene pelagic fine-fraction (<63 μm) carbonates from oligotrophic deep-sea sites in the Pacific and Atlantic oceans and compared them with those of coexisting foraminifers to test their utility as near sea-surface indicators. Fine-fraction carbonates (primarily polyspecific nannofossils) and surface-dwelling planktic foraminiferal ( Globigerinoides) stable isotopes both have been considered to reflect surface-water hydrographic conditions. However, our results indicate that fine-fraction stable isotopes are offset from and do not correlate well with those of Globigerinoides. In contrast, stable isotopic records of the deep-dwelling planktic foraminifer Globoquadrina are in good correspondence with the fine-fraction records in terms of long-term (ca. >1 m.y.) trends and temporal variability. On the basis of a time-series hydrography and flux study site in the oligotrophic subtropical North Atlantic, we interpret the isotopic discrepancies between fine-fraction and Globigerinoides as resulting primarily from season of calcification, as well as possible vital effects. We suggest that fine-fraction stable isotope values from oligotrophic waters reflect late winter–early spring relatively cool, nutrient-rich shallow mixed-layer conditions during the time of deep mixing (i.e., spring bloom), whereas Globigerinoides stable isotope values record conditions that prevailed in the stratified surface waters in the warmer late spring–fall. This implies that paired analyses of fine-fraction and surface-dwelling planktic foraminiferal δ 18O could be applied to reconstruct paleoseasonality of the open oceans. However, because the fine-fraction δ 13C values are not representative of the annual mean surface-water δ 13C, we recommend use of near surface-dwelling planktic foraminiferal δ 13C as a proxy for δ 13C of stratified surface waters that are more or less in equilibrium with the atmosphere with respect to pCO 2.

The role of mesoscale processes controlling biological variability in the Black Sea coastal waters: inferences from SeaWIFS-derived surface chlorophyll field

Several different time series of chlorophyll images from the 1997–2000 Seaviewing Wide Field-of-view Sensor data set have been analysed to gain a perspective on the dynamical and biological variability in the Black Sea, particularly on its northwestern shelf region and along the Anatolian coastal zone. The images are interpreted in terms of documenting the close link between biological production and physical dynamics of the boundary system, and of emphasizing the role of eddy processes on controlling mesoscale chlorophyll distributions. It is shown that western coastal waters of the Black Sea are characterized by permanently high chlorophyll concentrations of more than 4.0 mg m −3, often subject to considerable dynamical transformations, and modulated by mesoscale structures including southward elongated filament-like features extending up to 100 km offshore with a lifetime of up to a month. Filaments, meanders, offshore jets and other forms of mesoscale and sub-mesoscale structures appear as a common signature of the system along the Anatolian coast. They play an important role in the cross-stream transport of biota and chemical constituents, and thus supporting productivity within the interior parts of the basin. The images reveal phytoplankton blooms lasting several months in all three autumn seasons. During autumn 1999 to winter 2000, the phytoplankton biomass declines in December, and then increases to form another bloom in February–March 2000, albeit somewhat weaker. For the previous 2 years (1997, 1998), the autumn bloom is extended towards the first half of the winter but the late winter–early spring bloom is absent.

Seasonal Variation in Sex Ratio and Asynchronous Presence at Ponds of Male and Female Triturus Newts

Adult Triturus newts show spatial and temporal variation in sex ratio at the aquatic breeding site, to the extent that contrasting scenarios on the evolution of mating systems appear to be supported. I collected data for the five western European species (Triturus alpestris, Triturus cristatus, Triturus helveticus, Triturus marmoratus, and Triturus vulgaris) over 500 ponds and 27 yr in two areas in France, to test the hypothesis that the phenology of pond presence is independent of gender. Approximately equal numbers of males and females were found. However, in T. marmoratus males outnumbered females, which could be explained by a proportion of females skipping annual breeding opportunities. In the hybrid T. cristatus × T. marmoratus, females were twice as numerous as males, in accordance with Haldane's rule. A trend was observed for a male-biased sex ratio at the start of the aquatic season (late winter–early spring) and for a female bias toward the end of the aquatic season (early summer), suggesting that males mostly arrive and leave the breeding sites ahead of the females. The data do not support evolutionary scenarios selecting for the early breeding of female T. vulgaris.

The long-term impact of nitrogen fertiliser on perennial ryegrass tiller and white clover growing point densities in grazed dairy pastures in south-western Victoria

A 3-year grazing experiment determined the impact of multiple applications of different rates of nitrogen (N) fertiliser, applied over autumn and winter in 1997, 1998, and 1999, on perennial ryegrass (Lolium perenne)/white clover (Trifolium repens) tiller and growing point densities (stolon apices with at least 2 nodes). Annual pasture dry matter (DM) yields were also monitored. Four treatments were replicated 3 times in a randomised block design and included: 0 N (A); 3 applications of 25 kg N/ha (B); 3 applications of 50 kg N/ha (C); and 3 applications of 75 kg N/ha (D). Urea (46% N) was the N source. Grazing of treatment plots occurred at a pre-grazing herbage mass of 2200–2500 kg DM/ha.Over 3 years, N applications consistently increased annual pasture DM yields by 0.9–3.3 t/ha when a total of 75–225 kg N/ha was applied annually.Generally, treatments B, C, and D resulted in higher perennial ryegrass tiller densities than treatment A. An exception occurred from July 1998 in Year 2 to July 1999 in Year 3, when all perennial ryegrass densities were similar. Nitrogen fertiliser generally produced no consistent effect on white clover growing point density, with the exception of July–December in Year 2 when treatments B, C, and D resulted in lower growing point densities than treatment A. Clover growing point density decreased over the trial period irrespective of treatment. There were no N fertiliser effects on 'other' grasses and broadleaved weeds. 'Other' grasses (mainly winter grass, Poa annua) did, however, peak in density (up to 2500 tillers/m2) from July to September each year.Seasonally, the peak perennial ryegrass tiller density was similar each year and occurred during late winter–early spring (5450 tillers/m2 in July 1997; 6200 tillers/m2 in August 1998; 5400 tillers/m2 in July 1999). This was followed by a trough over midsummer (800 tillers/m2 in January 1998; 725 tillers/m2 in January 1999). White clover growing point density declined over 3 years. During this decline there were peaks in June 1997 (2650 growing points/m2), November 1997 (1600 growing points/m2), June 1998 (1250 growing points/m2), April 1999 (1050 growing points/m2), and November 1999 (850 growing points/m2). Troughs occurred in January 1998 (530 growing points/m2) and February 1999 (380 growing points/m2).It is concluded that although increasing applications of N increased annual pasture DM yields and generally increased perennial ryegrass tiller densities, with little effect on clover growing point densities, there is little to suggest that N fertiliser alone would enhance the persistence of these pasture species. Persistence is likely to be influenced by a combination of factors including grazing management and climatic effects, rather than N fertiliser alone.

Particle Transport, Nutrient Cycling, and Algal Community Structure Associated with a Major Winter-Spring Sediment Resuspension Event in Southern Lake Michigan

Over the past decade, intermittent satellite imagery revealed the presence of an extensive plume of resuspended sediments in late winter-early spring with a clear offshore projection coinciding with the region of maximum sediment accumulation in the lake. The large scale of the plume implied that this process was important in sediment, and associated constituent, cycling and transport, but it had never been sampled due to severe conditions. The onset of the 1996 event coincided with a major March storm. Within a few days the plume was approximately 10 km wide and over 300 km in length, implying that the source of the reflective materials was widely distributed. An estimate of the total mass of resuspended sediment, 12 days after the storm, was similar to the annual external load of (sand-free) particulate material to the southern basin. The high turbidity plume persisted for over a month, progressing northward along the eastern shore with a major offshore transport feature. Sediment traps within this feature recorded a major mass flux event. The plume was sampled on two occasions and was found to contain 5 to 10 times as much suspended matter as open-lake locations outside the visible plume. Total particulate phosphorus was high within the plume making this episodic process important in sedimentwater exchange. The diatom community structure within the plume was significantly different from outside the plume and was characteristic of more eutrophic waters. Abundance of non-diatom phytoplankton and microbial food web organisms were highest at the plume edge. The episodic nature of this process makes it difficult to sample, but the scale makes it important in designing monitoring programs and massbalance modeling efforts.

Prevalence of sensitization to Cupressus sempervirens: a 4-year retrospective study

In the last few years Cupressus sempervirens has been identified as the cause of an increasing number of cases of late winter-early spring pollinosis in Mediterranean countries. We conducted a 4-year retrospective study of a large group of subjects with documented allergic respiratory disease in order to determine the prevalence, clinical significance and annual rate of sensitization to C. sempervirens pollen. Anamnestic data and skin prick tests (SPT) with common aeroallergens and C. sempervirens extract were collected from 1397 subjects (712 male and 685 female) resident in Latium, a region in central Italy, with complaints related to upper- or lower-respiratory-tract disorders or conjunctival disease. Two hundred and forty-three subjects (17.4%) showed positive results to C. sempervirens extract; 47 (19.3%) of them were monosensitized. The annual sensitization rate of SPT positivity to C. sempervirens varied from 7.2% in 1995 to 22% in 1998. All the subjects monosensitized to cypress pollen had symptoms from January through April. Our study suggests that sensitivity to C. sempervirens is responsible for respiratory symptoms in an increasing percentage of subjects. Further studies are needed to determine its frequency at the national level.

Post-weaning growth of cattle in northern New South Wales. 2. Growth pathways of steers

This paper describes the post-weaning growth of Bos taurus and Bos taurus x Bos indicus-derived steers grazing temperate perennial pasture in northern New South Wales. These cattle were either autumn weaners from spring-calving herds in summer rainfall environments, or summer weaners from autumn-calving herds in winter rainfall environments. Autumn weaners were grown out on 3 pasture systems: (i) pasture only (P1), (ii) pasture supplemented in late winter–early spring with formulated pellets of high protein content (P2), or (iii) pasture supplemented with a nitrogen-fertilised forage crop (P3) to provide different growth pathways towards entry to the finishing phase. Over the 3-year study, seasonal liveweight gain on P1 varied between –0.21 and 1.05 kg/head.day; liveweight gain was generally low (about 0.5 kg/head.day) in winter and high (about 0.8 kg/head.day) in spring. Bos taurus autumn weaners achieved feedlot entry specifications for the domestic market (300 kg liveweight) in 6–8 weeks by the end of winter, and feedlot entry specifications for the export market (400 kg liveweight) in 17–27 weeks by the end of summer. For B. taurus x B. indicus-derived autumn weaners, the period to feedlot entry was 19 and 33 weeks for domestic and export feedlot entry specifications, respectively. Supplementary feeding generally increased post-weaning growth in late winter–early spring and reduced the period to feedlot entry for export steers. Summer weaners were grown out on pasture in P1, P2 or P3 pasture systems, met domestic feedlot entry specifications on arrival, but did not reach export feedlot entry specifications before the onset of winter imposed liveweight stasis. The most effective grow-out system was based on Bos taurus autumn weaners with supplementary feeding in winter–spring to overcome the limitations of the winter feed gap.

Nitrogen uptake kinetics in the Ross Sea, Antarctica

Abstract The first estimates of uptake kinetic parameters for NH4+, NO3−, and urea in the Ross Sea, Antarctica were measured on three cruises during austral late winter–early spring 1996 (pre-bloom), late spring 1997 (bloom development), and summer 1997 (bloom decline). Nitrogen (N) uptake experiments were conducted with water collected at the 50% light penetration depth using trace-metal clean protocols and 15N tracer techniques. At all sites, ambient NO3− concentrations ranged from 5.8 to 30.5 μg-at N l−1 and silicic acid concentrations were greater than 62.0 μg-at Si l−1. The following trends were observed. First, based on maximum uptake rates (Vmax), apparent N utilization followed the order NO3−>NH4+>urea during the pre-bloom and bloom development cruises. During the summer cruise, as the bloom was declining, the apparent order of utilization was NH4+>NO3−>urea. Second, evidence for possible repression of NO3− uptake by elevated NH4+ concentrations was only observed at one site. Third, the kinetic parameters of NH4+ uptake rates corrected for isotope dilution were compared with the kinetic parameters determined from uncorrected rates. In this comparison, the measure of substrate affinity, α (α=Vmax/Ks) increased by an average of 4.6-fold when rates were corrected for isotope dilution, but values of Vmax remained unchanged. Fourth, using bacterial production data, the magnitude of bacterial N uptake was estimated. Assuming that all bacterial N demands were met with NH4+, the estimated bacterial portion of NH4+ uptake ranged from

Early spring phosphorus limitation of primary productivity in a NW Mediterranean coastal zone (Gulf of Lions)

Evidence of phosphorus limitation of algal C- and N-uptake in a NW Mediterranean coastal area (Gulf of Lions) was obtained from a field survey of inorganic and organic N, P and C and from bioassays carried out during the late winter-early spring 1998. Dissolved inorganic nitrogen (ΣDIN = NO3 + NO2 + NH4) and phosphorus (DIP) distributions showed a clear DIP depletion in the inorganic fractions available for primary production. While below the 150 m depth, the mean ΣDIN to DIP ratio was close to the typical Mediterranean ratio of 22, while values found in the upper layer (0 to 150 m) were about 3 times higher (68.4:1 on average). In this upper layer, N:P (19.9:1) and C:P (159.7:1) ratios in the particulate organic matter were higher than the Redfield ratio and also indi- cated P depletion in this fraction. In the dissolved organic pool, P depletion was higher than in the particulate organic pool, since the mean C:N:P ratios were 1674:75:1 in the photic layer. Dissolved organic forms of C and N represented the bulk (ca 94 and 86%, respectively) of the total organic matter, while ca 31% of the organic P was in particulate fraction. The apparent imbalance between N and P in the inorganic fraction was partly attributed to an imbalance in the corresponding nutrient utilization by the phytoplanktonic community, and partly due to the influence of the Rhone River. Additions of small amounts of DIP to surface samples led (1) to a decrease in C-uptake (o30%) dur- ing the first 24 h incubation, (2) to a rapid increase in chlorophyll biomass and (3) to stimulate nitrate uptake (o60%), suggesting DIP limitation of new production and of algal biomass during the spring 1998 in the Gulf of Lions.