1,720,977 research outputs found
Nutritional regulation of egg production of Calanus Finmarchicus in the North Atlantic
Full text linkShip-board experiments in the North Atlantic were used to study how food quality influences the egg production of Calanus finmarchicus feeding on natural planktonic diets. Food quality was expressed in terms of carbon (C), nitrogen (N), and the essential fatty acids eicosapentaenoic acid (EPA; 20:5(n-3)) and docosahexaenoic acid (DHA; 22:6(n-3)). Five consecutive 24 hr bottle incubations were conducted in April and July/August 2002 under in situ conditions to determine egg production rates and the ingested quantities of C, N, EPA and DHA. Biomass contributions towards growth were determined and the biochemical composition of the eggs was examined. In order to accurately determine ingestion rates, a method to account for microzooplankton grazing in particle removal experiments was developed.Balanced physiological budgets were compiled for C. finmarchicus in both seasons. The input terms of these budgets consisted of ingestion and the use of biomass, and the outputs were growth, respiration, excretion and egestion. Respiration and
excretion were not determined experimentally, and were therefore determined by mass balance and compared to literature-derived values.In April, close agreement between literature- and mass balance-derived rates of respiration and excretion demonstrated that the experimentally determined components of the budget were accurate. Ingestion rates were low, and > 80 % of the C utilised was derived internally from somatic biomass. The absence of storage fatty acids and the low C:N ratio (~ 4 µg µg-1) of the biomass lost from the females indicated that these animals had been catabolising structural protein and were close to exhaustion. This suggests that when food is scarce, C. finmarchicus adopts a semelparous reproductive strategy. In July/August, the observed growth exceeded the estimated ingestion rates. This shortfall was possibly provided by cannibalising eggs.Assuming that EPA and DHA were used with high efficiency (0.9), the stoichiometric analysis predicted that these compounds were non-limiting in April. Using typical maximum growth efficiencies for C (< 0.6) and N (0.4), the former was predicted to be limiting because the biomass utilised was rich in N, EPA and DHA relative to the demand for C
End of century ocean warming and acidification effects on reproductive success in a temperate marine copepod
No full textWe examined how predicted end of century ocean warming and acidification scenarios affected the incidence of apoptosis in the eggs and nauplii of the copepod Calanus helgolandicus. Offspring viability was not affected by 1000 ppm CO2-acidified seawater, whereas the effects of 2 and 4°C warming were dependent upon the batch of eggs used; warming increased viability in the second batch. This context-dependency highlights the need for cautious interpretation and application of data from individual climate-change studies
CO2-induced acidification affects hatching success in Calanus finmarchicus
No full textBottle incubations were conducted to examine how exposure to seawater containing 8000 ppm carbon dioxide (CO2; pH 6.95) influenced the growth and reproduction of the keystone copepod Calanus finmarchicus. The chosen concentration of CO2 is expected to occur over 100s of cubic kilometres of seawater as a result of marine CO2 storage/disposal, and is also representative of the predicted ‘worst-case’ atmospheric CO2 scenario in the year 2300. Growth (egg production and biomass loss) in adult female copepods was not affected by the simulated ocean acidification. In contrast, a maximum of only 4% of the eggs successfully yielded nauplii after 72 h in the experimental treatment. Our results demonstrate that environmental risk assessments for marine CO2 storage/disposal must look beyond adult mortality as an endpoint. Furthermore, if CO2 is to be disposed of in the deep sea, the location and timing of such activities must take into consideration the overwintering populations of C. finmarchicus
Effects of copper and the sea lice treatment Slice® on nutrient release from marine sediments
No full textCopper-based antifoulant paints and the sea lice treatment Slice® are widely used, and often detectable in the sediments beneath farms where they are administered. Ten-day, whole sediment mesocosm experiments were conducted to examine how increasing sediment concentrations of copper or Slice® influenced final water column concentrations of ammonium–nitrogen (NH4–N), nitrate + nitrite–nitrogen (NOX–N) and phosphate–phosphorus (PO4–P) in the presence of the non-target, benthic organisms Corophium volutator and Hediste diversicolor. Nominal sediment concentrations of copper and Slice® had significant effects on the resulting concentrations of almost all nutrients examined. The overall trends in nutrient concentrations at the end of the 10-day incubations were highly similar between the trials with either copper or Slice®, irrespective of the invertebrate species present. This suggests that nutrient exchange from the experimental sediments was primarily influenced by the direct effect of copper/Slice® dose on the sediment microbial community, rather than the indirect effect of reduced bioturbation/irrigation due to increased macrofaunal mortality
Acute toxicity of some treatments commonly used by the salmonid aquaculture industry to Corophium volutator and Hediste diversicolor: whole sediment bioassay tests
No full textThe commercial farming of Atlantic salmon, Salmo salar, typically requires the periodic application of copper-based anti-foulants and chemotherapeutic treatments, including Slice®, Excis®, Salmosan® and Aquatet®/Tetraplex® to reduce the effects of biological pests. Information on the environmental safety of any chemical agent released into the aquatic environment must be obtained before a product can be licensed for use, but such information typically exists only in confidential technical reports which can be difficult to obtain. Furthermore, different test organisms, experimental protocols and reporting procedures make comparison of the various compounds/studies difficult. Here we present a series of 10-day, whole sediment bioassay tests that determined the concentrations of emamectin benzoate (EB), cypermethrin (CP), azamethiphos (AZ) and oxytetracycline hydrochloride (OTC), the active ingredients of the aforementioned chemotherapeutants, and copper, that caused 50% mortality (LC50) in the non-target benthic crustacean, Corophium volutator. Additional whole sediment bioassays of identical design were conducted with the non-target polychaete worm, Hediste diversicolor exposed to copper and EB. C. volutator demonstrated similar sensitivity to EB and AZ, with LC50s of 153 (95% confidence intervals, CI = 119–198) and 182 (95% CI = 152–217) µg active ingredient [kg wet sediment]? 1 respectively. OTC caused 50% mortality of C. volutator at a concentration of 414 (95% CI = 233–734) µg OTC [kg wet sediment]? 1. The LC50 for H. diversicolor exposed to EB was 1368 (95% CI = 744–2516) µg EB [kg wet sediment]? 1, an order of magnitude greater than that for C. volutator. Conversely, C. volutator was able to tolerate much higher concentrations of copper than H. diversicolor, with LC50s of 193,326 (95% CI = 171,034–218,523) and 74,988 (95% CI = 61,192–91,895) µg Cu [kg wet sediment]? 1 respectively. CP was the most toxic to C. volutator of all compounds investigated, causing 50% mortality at a concentration of 5 (95% CI = 4–6) µg CP [kg wet sediment]? 1. These data allow direct inter-comparison of the toxicities of some of the commonly applied treatments used by the global salmonid aquaculture industry
Seasonal and spatial patterns of adult Antarctic krill at the Antarctic Peninsula: insights from a 41 year data analysis
No full textLocating the spawning grounds of Antarctic krill Euphausia superba is key to understanding their population dynamics and managing the commercial krill fishery. In the shelf waters of the Antarctic Peninsula where krill and their fishery are concentrated, a recent relaxation of fishing quotas has meant that locally successful spawning grounds could become increasingly targeted. This study revisits the existing paradigm that in summer, larger adult krill migrate awayfrom these shelf-based fishing grounds, out towards oceanic waters to spawn off the shelf break (>1000 m). Our findings support a seasonal on-shelf division of adult krill, with smaller krill closer inshore. However, contrary to current understanding, our results suggest that 85% of the largest and most fecund >50 mm krill remain on-shelf during the summer spawning season. All adults(>30 mm) were strongly concentrated over the shelf throughout the whole spring–summer–autumn transition, with no evidence for any summer redistribution off-shelf. The Western Antarctic Peninsula (WAP) has strong on-shelf–off-shelf gradients in chlorophyll a and sea surface temperature,and based on generalised additive models, our study suggests that the high food requirement of adult krill, coupled with an oligotrophic off-shelf environment, contributes to the distribution of krill observed at the Antarctic Peninsula. The concentration of large, nutritious krill over the shelf throughout the season may be advantageous to land-based predators but raises concern for the management of fisheries that are becoming increasingly concentrated within the key adult krill habitat along the northern shelf of the WAP
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Feeding strategies of deep-sea sub-Arctic macrofauna of the Faroe-Shetland Channel: Combining natural stable isotopes and enrichment techniques
No full textThe response of a sub-arctic, deep-sea macrofaunal community to a simulated food sedimentation event was studied by means of a stable isotope “pulse-chase” experiment. A food pulse was simulated by adding 500 mg C m?2 of 13C-labelled diatoms, Chaetoceros radicans, to sediment cores retrieved from 1080 m in the Faroe-Shetland Channel. Carbon uptake by specific macrofaunal groups was quantified after 3 and 6 days of incubation. The carbon uptake of the dominant taxon (Polychaeta) was quantified at the genus-, and where possible, species-level, representing a data resolution that is rare in deep-sea tracer studies. The macrofaunal community reacted rapidly to the diatom addition, with 47% and 70% of the animals illustrating 13C-enrichment after 3 and 6 days, respectively. Approximately 95% of C uptake was located in the upper 2 cm due to the particularly shallow vertical distribution of the macrofaunal community and the nonexistent tracer subduction by burrowing species. Polychaetes of the families Ampharetidae and Cirratulidae were among the most heavily labelled with above background enrichment reaching 1300‰. Approximately 0.8 and 2.0 mg C m?2 were processed by the macrofauna after 3 and 6 days, representing 0.2% and 0.4% of the added carbon, respectively. It was not possible to differentiate sub-surface deposit-feeding polychaetes from predator/scavenger- and omnivorous polychaetes using their natural ?15N signatures. However, the combination of natural abundance ?15N data and 13C-labelling experiments proved to be useful for elucidating trophic relations in deep-sea food webs. This study confirms that macrofauna play an active role in the short-term carbon cycling at bathyal depths even at sub-zero temperatures and highlights the need for detailed knowledge of the community structure in understanding carbon processing patterns and early diagenesis of organic matter in marine sediments
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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