Impact of Microzooplankton and Copepods on the Growth of Phytoplankton in the Yellow Sea and East China Sea

Dilution and copepod addition incubations were conducted in the Yellow Sea (June) and the East China Sea (September) in 2003. Microzooplankton grazing rates were in the range of 0.37–0.83 d⁻¹ in most of the experiments (except at Station A3). Correspondingly, 31–50% of the chlorophyll a (Chl a) stock and 81–179% of the Chl a production was grazed by microzooplankton. At the end of 24 h copepod addition incubations, Chl a concentrations were higher in the copepod-added bottles than in the control bottles. The Chl a growth rate in the bottles showed good linear relationship with added copepod abundance. The presence of copepods could enhance the Chl a growth at a rate (Z) of 0.03–0.25 (on average 0.0691) d⁻¹ ind⁻¹ l. This study, therefore parallels many others, which show that microzooplankton are the main grazers of primary production in the sea, whereas copepods appear to have little direct role in controlling phytoplankton.     

Growth of the Barents Sea capelin,Mallotus villosus,in relation to climate

Synopsis In order to investigate a possible relationship between temperature and fish length growth in the Barents Sea capelin stock, estimates of environmental temperature in the feeding season were compared to estimates of length growth during the same season. The mean temperature of the capelin feeding area was calculated by averaging the temperatures in September for the depth interval 10–200 m in statistical rectangles. The estimates of capelin growth were obtained for the same rectangles using backcalculation of length from otoliths. Correlation coefficients for the relationship between water temperature and growth were 0.70 and 0.53 for two- and three-year-olds, respectively, when all the material was considered, and between 0.85 and 0.91 for within-year data. In addition, a close correspondence between feeding area and growth rates was found.     

Viral Production, Decay Rates, and Life Strategies along a Trophic Gradient in the North Adriatic Sea

Although the relationships between trophic conditions and viral dynamics have been widely explored in different pelagic environments, there have been few attempts at independent estimates of both viral production and decay. In this study, we investigated factors controlling the balance between viral production and decay along a trophic gradient in the north Adriatic basin, providing independent estimates of these variables and determining the relative importance of nanoflagellate grazing and viral life strategies. Increasing trophic conditions induced an increase of bacterioplankton growth rates and of the burst sizes. As a result, eutrophic waters displayed highest rates of viral production, which considerably exceeded observed rates of viral decay (up to 2.9 × 10⁹ VLP liter⁻¹ h⁻¹). Viral decay was also higher in eutrophic waters, where it accounted for ca. 40% of viral production, and dropped significantly to 1.3 to 10.7% in oligotrophic waters. These results suggest that viral production and decay rates may not necessarily be balanced in the short term, resulting in a net increase of viruses in the system. In eutrophic waters nanoflagellate grazing, dissolved-colloidal substances, and lysogenic infection were responsible together for the removal of ca. 66% of viral production versus 17% in oligotrophic waters. Our results suggest that different causative agents are primarily responsible for the removal of viruses from the water column in different trophic conditions. Factors other than those considered in the past might shed light on processes responsible for the removal and/or decay of viral particles from the water column.     

Photoadaptation of sea-ice microalgae in the Barents Sea

Summary Variations in under-ice scalar irradiance, P vs I parameters and the CHLa C^–1 ratio of natural assemblages of sea-ice microalgae from the Barents Sea growing at -1.8°C in May and September 1988 are described, including one diurnal station. CHLa C^–1 ratios of 0.031–0.071 mg mg^–1 indicate shade adaptated assemblages both in May and September. Values for ^B (photosynthetic efficiency) were generally low, e.g. 0.0025–0.0078 mg C (mg CHLa)^–1 h^–1 (mol m^–2 s^–1)^–1, and should be typical for self-shaded algae in mats or aggregates of about 4 mm thickness. Provided no self shading and the typical spectral distribution of light under ice without algae, ^B would, however, be about 2.5 times higher. Photoinhibition of the photosynthetic response was negligible. Maximum carbon uptake P _m ^B was 0.15–0.24 and 0.032–0.088 mg C (mg CHLa)^–1 h^–1 in May and September, respectively. Diurnal variations were small, particularly for P _m ^B . Calculations of the maximum specific gross growth rate yielded an upper limit of 0.20–0.24 and 0.01–0.04 d^–1 for assemblages in May and September, respectively; the latter may have been in a resting stage.Contribution No. 245, Trondhjem Biological Station     

Phytoplankton Growth and Microzooplankton Grazing in the Subtropical Northeast Atlantic

Dilution experiments were performed to estimate phytoplankton growth and microzooplankton grazing rates during two Lagrangian surveys in inner and eastern locations of the Eastern North Atlantic Subtropical Gyre province (NAST-E). Our design included two phytoplankton size fractions (0.2–5 µm and >5 µm) and five depths, allowing us to characterize differences in growth and grazing rates between size fractions and depths, as well as to estimate vertically integrated measurements. Phytoplankton growth rates were high (0.11–1.60 d⁻¹), especially in the case of the large fraction. Grazing rates were also high (0.15–1.29 d⁻¹), suggesting high turnover rates within the phytoplankton community. The integrated balances between phytoplankton growth and grazing losses were close to zero, although deviations were detected at several depths. Also, O₂ supersaturation was observed up to 110 m depth during both Lagrangian surveys. These results add up to increased evidence indicating an autotrophic metabolic balance in oceanic subtropical gyres.     

春季赤潮频发期东海微型浮游动物摄食研究

2002年4～5月在东海长江口及其邻近水域的8、11、14、23和28号5个典型站位采样。用现场稀释法对春季东海水域浮游植物的生长率和微型浮游动物对浮游植物的摄食压力等方面进行了研究．结果表明,微型浮游动物的摄食行为在东海赤潮过程起到关键作用．各站位微型浮游动物主要以急游虫、红色中缢虫和夜光藻为主,在种类上砂壳纤毛虫是主要的类群．微型浮游动物的摄食速率范围在0．28～1．13d-1,对浮游植物现存量的摄食压力范围在35．14％～811．69％。对浮游植物潜在初级生产力的摄食压力范围在74．04％～203．25％,对浮游植物碳的摄食率范围在9．58～97．91μg·L-1·d-1,靠近岸边的站位,微型浮游动物的摄食速率、对浮游植物现存量的摄食压力和对浮游植物碳的摄食率相对较高。而远离岸边的站位对浮游植物潜在初级生产力的摄食压力却较高．与世界其它海区比较此水域微型浮游动物摄食压力处于较高水平．急游虫是控制东海主要赤潮原因生物具齿原甲藻生长的关键种类．     

Sea ice primary productivity in the northern Barents Sea,spring 2004

The biomass and productivity of sea ice algae was assessed in the northwestern Barents Sea in May 2004. Sea ice algal pigment content was patchy with a mean of 18.5 ± 8.9 mg Chla m⁻². The algal community was dominated by the diatom Nitzschia frigida. Primary production measured by ¹⁴C incubations was between 0.37 and 2.8 mg C m⁻² h⁻¹, which compared well with oxygen-based methods using the diffusive boundary layer approach (0.071–1.1 mg C m⁻² h⁻¹). Given the differences in the irradiances under which these two sets of measurements were made, there was a strong level of consistency between the two sets of results. Measurements of primary production were consistent with previous Arctic measurements but high spatial heterogeneity made a regional estimate of production inappropriate.     

Pelagic Bacteria–Particle Interactions and Community-Specific Growth Rates in Four Lakes along a Trophic Gradient

Abstract The relationships between bacterial concentration, bacterial production, and cell-specific activity of both free and attached bacteria and environmental factors such as suspended solids, nutrients, and temperature were examined in four lakes, two in New Zealand and two in Switzerland. Estimates of cell-specific production were obtained by microautoradiographic counts of [³H]thymidine-labeled cells. Bacteria attached to particles accounted for only 1.3 to 11.6% of the total bacterial abundance, but showed overall 20-fold higher specific growth rates and were relatively more active than their free counterparts. On average, 80 to 100% of epibacteria were attached to organic particles. The abundance and production of free and attached bacteria were positively correlated; however, relationships between these fractions and some environmental variables differed. Cell-specific activities of active bacteria were not equivalent to mean cellular activities of the entire bacterial community and differed in their relationship to trophic state. [³H]Thymidine-positive bacteria were more tightly linked to chlorophyll a than were total bacteria. Our findings indicate that production by attached bacteria, fueled by phytoplankton carbon, supplies ``new' free bacteria to the bacterial community. Our results support the idea that particulate organic matter acts as a source of dissolved nutrients to free bacteria. Bottom-up control of bacterial biomass, as shown by regressions of biomass vs production, appeared to be stronger in two ultraoligotrophic lakes than in two more eutrophic ones. Received: 17 April 1998; Accepted: 24 August 1998     

Compliance and Postagreement Bargaining in the Barents Sea Fisheries

States’ failure to comply with their international obligations has been viewed by institutional theory as problems to be solved, rather than as wrongs to be punished. This article reviews how Norway has employed different postagreement bargaining strategies in the Joint Norwegian-Russian Fisheries Commission in order to enhance Russian compliance with the bilateral fisheries agreements in the Barents Sea and with the precautionary approach more widely.     

Phytoplankton of the Barents Sea - the end of a growth season

 Few phytoplankton investigations have been carried out at the end of the growth season, particularly in the Arctic. In the present study, we monitored the phytoplankton distribution in relation to environmental conditions in the Barents Sea in September 1988 and October 1987. An ice-edge bloom was found in September at 80° N in a stratified meltwater layer, lasting until new ice formation and southward advection of the ice cover commenced in the middle of the month. Phytoplankton populations in the marginal ice zone at this time were not nutrient limited, but biomass was probably reduced due to grazing by small copepods. Lower chl/C and chl/N ratios in the phytoplankton above the pycnocline than below in September indicated light-adapted populations. In October the particulate matter was rich in carbon, but had low chlorophyll content, indicating high levels of detritus. The hydrographic conditions in October differed greatly from those observed in September. The combination of freezing and mixing resulted in higher salinity and nutrient concentrations, and caused a homogeneous distribution, as well as reduction, of the phytoplankton stocks in the upper water column. During late October, low incoming radiation, combined with deep vertical mixing, resulted in light-limiting conditions for the algae, eventually stopping photosynthesis and terminating the growth season in the northern Barents Sea. Received: 1 March 1996/Accepted: 19 May 1996     

Estimating the Barents Sea polar bear subpopulation size

A large-scale survey was conducted in August 2004 to estimate the size of the Barents Sea polar bear subpopulation. We combined helicopter line transect distance sampling (DS) surveys in most of the survey area with total counts in small areas not suitable for DS. Due to weather constraints we failed to survey some of the areas originally planned to be covered by DS. For those, abundance was estimated using a ratio estimator, in which the auxiliary variable was the number of satellite telemetry fixes (in previous years). We estimated that the Barents Sea subpopulation had approximately 2,650 (95% CI approximately 1,900–3,600) bears. Given current intense interest in polar bear management due to the potentially disastrous effects of climate change, it is surprising that many subpopulation sizes are still unknown. We show here that line transect sampling is a promising method for addressing the need for abundance estimates.     

Sea ice resource selection models for polar bears in the Barents Sea subpopulation

The extent, thickness and age of Arctic sea ice has dramatically declined since the late 1990s, and these trends are predicted to continue. Exploring the habitat use of sea‐ice‐dependent species can help us understand which resources they use and how their distribution responds to a changing environment. The goal of this study was to develop predictive models of the habitat use of an Arctic apex predator. Polar bear Ursus maritimus habitat use in the Barents Sea subpopulation was modelled with seasonal resource selection functions (RSFs) using satellite‐linked telemetry data from 294 collars deployed on female polar bears between 1991 and 2015. Polar bears selected habitat in the Marginal Ice Zone, with a preference for intermediate sea ice concentrations (40–80%). They spent most time in areas with relatively short travel distances to 15 or 75% ice concentration, and during spring and autumn they exhibited a preference for sea ice areas over the continental shelf or over shallower bathymetry). Predictions of the distribution of polar bears in the Barents Sea area can be made for specific sea ice scenarios using these models. Two such predictive distribution maps based on the autumn seasonal model were made and validated against two independent polar bear survey datasets collected in August 2004 and August 2015. The distribution of optimal polar bear habitat has shifted strongly northwards in all seasons of the year during the 25 yr study period.     

Temporal Dynamics of Top Predators Interactions in the Barents Sea

The Barents Sea system is often depicted as a simple food web in terms of number of dominant feeding links. The most conspicuous feeding link is between the Northeast Arctic cod Gadus morhua, the world''s largest cod stock which is presently at a historical high level, and capelin Mallotus villosus. The system also holds diverse seabird and marine mammal communities. Previous diet studies may suggest that these top predators (cod, bird and sea mammals) compete for food particularly with respect to pelagic fish such as capelin and juvenile herring (Clupea harengus), and krill. In this paper we explored the diet of some Barents Sea top predators (cod, Black-legged kittiwake Rissa tridactyla, Common guillemot Uria aalge, and Minke whale Balaenoptera acutorostrata). We developed a GAM modelling approach to analyse the temporal variation diet composition within and between predators, to explore intra- and inter-specific interactions. The GAM models demonstrated that the seabird diet is temperature dependent while the diet of Minke whale and cod is prey dependent; Minke whale and cod diets depend on the abundance of herring and capelin, respectively. There was significant diet overlap between cod and Minke whale, and between kittiwake and guillemot. In general, the diet overlap between predators increased with changes in herring and krill abundances. The diet overlap models developed in this study may help to identify inter-specific interactions and their dynamics that potentially affect the stocks targeted by fisheries.     

Maritime Delimitation in the Arctic: The Barents Sea Treaty

During a visit to Norway by the Russian president in the spring of 2010, the president and the Norwegian prime minister surprisingly announced agreement on a delimitation line in the Barents Sea ending almost 40 years of negotiations. The agreement was signed in Murmansk on 15 September 2010. This article presents the background of the dispute and undertakes an assessment of the agreement and its implications for the Barents Sea, Svalbard, and other Arctic maritime delimitations.     

Morphometric differentiation of Pseudocalanus minutus populations in the Barents Sea

Dvoretsky VG. and Dvoretsky AG. 2011. Morphometric differentiation of Pseudocalanus minutus populations in the Barents Sea. —Acta Zoologica (Stockholm) 00 : 1–12. We investigated spatial variations in the morphometric characteristics (total length of body, lengths of cephalothorax, abdomen and antennules, and their relative proportions) of Pseudocalanus minutus, an abundant copepod species across the Barents Sea in August–September 2007. Females were found to have higher values for the measured parameters than males. The average absolute morphometric characters of both sexes increased from the south to the north. In most cases, parameters were similar in the southern, central, and eastern regions delineated by cluster analyses of oceanographic variables. The morphometric characteristics were strongly correlated with environmental variables in both males and females. Multiple regression analysis showed that temperature together with salinity explained 72–85% (in females) and 38–91% (in males) of the total variations in the log₁₀‐transformed morphometric parameters. According to principal component analysis and discriminant function analysis, two distinct groups could be separated in the Barents Sea. The first group included the copepods from the northern region; the other included populations from the southern, central, and eastern regions. The observed morphological variation can be interpreted as geographical variation connected with hydrological variability.     

A pH Gradient across the Root

A pH gradient across the intact root of Helianthus annuus hasbeen measured using pH microelectrodes. The results indicatea steady increase in pH from epidermis to protoxylem. Thereis evidence for the activity of a proton extrusion pump in someof the cells. The possibility that the pH gradient may be thebasis of centripetal ion transport across the root is discussed.