Trophic role of Atlantic cod in the ecosystem

As the world's oceans continue to undergo drastic changes, understanding the role of key species therein will become increasingly important. To explore the role of Atlantic cod ( Gadus morhua Gadidae) in the ecosystem, we reviewed biological interactions between cod and its prey, predators and competitors within six ecosystems taken from a broad geographic range: three are cod-capelin ( Mallotus villosus Osmeridae) systems towards cod's northern Atlantic limit (Barents Sea, Iceland and Newfoundland–Labrador), two are more diverse systems towards the southern end of the range (North Sea and Georges Bank–Gulf of Maine), and one is a species-poor system with an unusual physical and biotic environment (Baltic Sea). We attempt a synthesis of the role of cod in these six ecosystems and speculate on how it might change in response to a variety of influences, particularly climate change, in a fashion that may apply to a wide range of species. We find cod prey, predators and competitors functionally similar in all six ecosystems. Conversely, we estimate different magnitudes for the role of cod in an ecosystem, with consequently different effects on cod, their prey and predator populations. Fishing has generally diminished the ecological role of cod. What remains unclear is how additional climate variability will alter cod stocks, and thus its role in the ecosystem.     

Performance evaluation of a crop/weed discriminating microsprayer

An intelligent real-time microspraying weed control system was developed. The system distinguishes between weed and crop plants and a herbicide (glyphosate) is selectively applied to the detected weed plants. The vision system captures 40 RGB images per second, each covering 140 mm by 105 mm with an image resolution of 800 × 600 pixels. From the captured images the forward velocity is estimated and the spraycommands for the microsprayer are calculated. Crop and weed plants are identified in the image, and weed plants are sprayed. Performance of the microsprayer system was evaluated under laboratory conditions simulating field conditions. A combination of maize (Zea mays L.), oilseed rape (Brassica napus L.) and scentless mayweed (Matricaria inodora L.) plants, in growth stage BBCH10, was placed in pots, which were then treated by the microspray system. Maize simulated crop plants, while the other species simulated weeds. The experiment were conducted at a velocity of 0.5 m/s. Two weeks after spraying, the fraction of injured plants was determined visually. None of the crop plants were harmed while 94% of the oilseed rape and 37% of the scentless mayweed plants were significantly limited in their growth. Given the size and shape of the scentless mayweed plants and the microsprayer geometry it was calculated that the microsprayer could only hit 64% of the scentless mayweed plants. The system was able to effectively control weeds larger than 11 mm × 11 mm.     

Stress response of Crassostrea virginica (Gmelin, 1791) oysters following a reciprocal transfer between upriver and downriver sites

This study was designed to assess the physiological impact of transferring oysters between upriver and downriver aquaculture sites, a common practice in North America that is primarily aimed at reducing disease infections and predation on cultured stocks. In May 2009, oysters (Crassostrea virginica) were reciprocally transferred between an upriver and a downriver site in the Richibucto estuary in eastern Canada. Mortality, tissue and cellular stress responses were subsequently evaluated in August and October 2009. Overall, oyster mortality remained low (~5%) throughout the 5‐month study period with no significant difference between sites or oyster sources. However, by October oysters reared at the upriver site, regardless of their origin, had significantly higher levels of lysosomal membrane destabilization (63.6%, SE = 1.9) and digestive tubule atrophy (33.3–42.4%, SE = 3.6) than oysters reared at the downriver site (47.5%, SE = 1.8; 15.6–19.1%, SE = 3.8 respectively). They also exhibited a greater salinity differential between their mantle/haemolymph fluids and the ambient seawater, possibly indicating more restricted exchange with the environment. In general, the transfer of upriver oysters to a downriver site had a positive impact, i.e. lower levels of lysosomal destabilization and tubule atrophy, whereas transfer of downriver oysters upriver had the opposite effect. These results suggest that upriver environmental conditions negatively impact cellular and tissue integrity in oysters without leading to mortality during the summer–autumn period.     

Effects of variable egg incubation temperatures on the embryonic development in Arctic charr Salvelinus alpinus

An evaluation of different thermal regimes during incubation of Arctic charr Salvelinus alpinus L. egg was conducted with regard to embryo survival and development. The study consisted of two major parts: In experiment A, a range of commonly used thermal regimes, constant and variable ranging from 2.7°C to 7°C, were tested for differences in embryo survival and developmental status of newly hatched alevins. Experiment B assessed the timing of a shift from autumn (6°C) to winter temperature (2.5°C) and its effect on embryo survival and the occurrence of spinal deformities in newly hatched alevins. In general, incubations that were initiated at temperatures below 3°C resulted in significantly higher mortality rates and spinal deformity frequencies than other treatments. Hence, Arctic charr eggs require an initial warmer period for unimpaired embryonic development. A general negative correlation was found between the duration of this warmer period (6°C) and both mortality rates and frequency of spinal deformities. The total absence of the 6°C period had the most detrimental effect, with deformity frequencies at least four times higher than all treatments with an initial warmer period. The upper incubation temperature threshold was not reached in the study. The highest temperature tested (7°C) did not result in excess mortality or increased deformity frequency. Higher incubation temperature resulted in less developed alevins at hatching, i.e. alevins were smaller with more yolk remaining. However, measurements on alevins from incubations at variable temperatures revealed different temperature effects on growth and yolk consumption during different parts of embryonic development.     

Masked,diluted and drowned out: how global seafood trade weakens signals from marine ecosystems

Nearly 40% of seafood is traded internationally and an even bigger proportion is affected by international trade, yet scholarship on marine fisheries has focused on global trends in stocks and catches, or on dynamics of individual fisheries, with limited attention to the link between individual fisheries, global trade and distant consumers. This paper examines the usefulness of fish price as a feedback signal to consumers about the state of fisheries and marine ecosystems. We suggest that the current nature of fisheries systems and global markets prevent transmission of such price signals from source fisheries to consumers. We propose several mechanisms that combine to weaken price signals, and present one example – the North Sea cod – to show how these mechanisms can be tested. The lack of a reliable price feedback to consumers represents a challenge for sustainable fisheries governance. We therefore propose three complimentary approaches to address the missing feedback: (i) strengthening information flow through improved traceability and visibility of individual fishers to consumers, (ii) capitalizing on the changing seafood trade structures and (iii) bypassing and complementing market mechanisms by directly targeting citizens and political actors regarding marine environmental issues through publicity and information campaigns. These strategies each have limitations and thus need to be pursued together to address the challenge of sustainability in global marine fisheries.     

Effects of nurse trees,spacing, and tree species on biomass production in mixed forest plantations

Growing concern about increasing concentrations of greenhouse gases in the atmosphere, and resulting global climate change, has spurred a growing demand for renewable energy. In this study, we hypothesized that a nurse tree crop may provide additional early yields of biomass for fuel, while in the longterm leading to deciduous stands that are believed to better meet the demands for other ecosystem services. Ten different species combinations were planted, with two different stocking densities, at three different sites in Denmark. Significant differences, with regard to biomass production, were observed among the different sites (P?P??1?yr^?1 more biomass. The additional biomass production was similar to what was obtained in stands with conifers only (Sitka spruce, Douglas-fir and Japanese larch), which produced 4.9–6.1?t ha^?1yr^?1 more biomass than the pure beech stands. No effects of initial planting density (P?=?.19), or of initial weeding (P?=?.81), on biomass production were observed. Biomass production of the broadleaved crop was in most cases reduced due to competition. However, provided timely thinning of nurse trees, the qualitative development of the trees will allow for long-term timber production.     

ABA signaling inhibits oxalate-induced production of reactive oxygen species and protects against <Emphasis Type="Italic">Sclerotinia sclerotiorum</Emphasis> in <Emphasis Type="Italic">Arabidopsis thaliana</Emphasis>

Oxalic acid is an essential virulence factor of Sclerotinia sclerotiorum that elicits wilting symptoms in infected host plants. Foliar wilting in response to oxalic acid is known to be dependent on an increase in stomatal conductance. To determine whether stomatal regulation controls susceptibility to S. sclerotiorum, abscisic acid-insensitive and open stomata mutants of Arabidopsis thaliana were analyzed. Whereas abscisic acid-insensitive mutants were hypersusceptible to S. sclerotiorum, open stomata mutants were as susceptible as wild type. It was concluded that stomatal regulation does not control susceptibility to S. sclerotiorum because open stomata mutants are known to only impair guard cells whereas abscisic acid-insensitive mutants also affect other cell types. Guard cell-independent processes also control sensitivity to oxalic acid because oxalic acid was more toxic to abscisic acid-insensitive mutants than to open stomata mutants. To explore a possible mechanism of toxicity, production of reactive oxygen species was measured in plant cells after exposure to oxalic acid. Oxalic acid was found to elicit reactive oxygen species production independently of abscisic acid. Nevertheless, cancellation of reactive oxygen species elicitation after co-stimulation of wild-type guard cells with oxalic acid and abscisic acid provided evidence for antagonistic interaction between both molecules.     

Effect of biochar on aerobic processes,enzyme activity,and crop yields in two sandy loam soils

Biochar added to agricultural soils may sequester carbon and improve physico-chemical conditions for crop growth, due to effects such as increased water and nutrient retention in the root zone. The effects of biochar on soil microbiological properties are less certain. We addressed the effects of wood-based biochar on soil respiration, water contents, potential ammonia oxidation (PAO), arylsulfatase activity (ASA), and crop yields at two temperate sandy loam soils under realistic field conditions. In situ soil respiration, PAO, and ASA were not significantly different in quadruplicate field plots with or without biochar (20 Mg ha^?1); however, in the same plots, volumetric water contents increased by 7.5 % due to biochar (P?=?0.007). Crop yields (oat) were not significantly different in the first year after biochar application, but in the second year, total yields of spring barley increased by 11 % (P??1, applied during two consecutive years, substantiated that biochar was not inhibitory to PAO and ASA as reference plots consistently showed lowest activities. For PAO, it was found that soil pH, rather than biochar rates, was a driving environmental variable. For ASA, the methodological approach was challenged by product sorption, but results did not suggest that biochar significantly stimulated the enzyme activity. Crop yields of maize in field experiments with 10–100 Mg biochar ha^?1 were unaffected by biochar except for a negative effect of the highest annual rates of 50 Mg ha^?1 in the first year after application. In conclusion, the present wood-based biochar poorly affected the measured microbial processes and generally resulted in similar crop yields in reference and biochar-amended soil plots.     

Statistical Modelling of Neighbor Treatment Effects in Aquaculture Clinical Trials

In the design of clinical trials involving fish observed over time in tanks, there may be advantages in housing several treatment groups within the same tank. In particular, such “within-tank” designs will be more efficient than designs with treatment groups in separate tanks when substantial between-tank variability is expected. One potential problem with within-tank designs is that it may not be possible to include all treatments in one tank; in statistical terms this means that the blocks (tanks) are incomplete. In incomplete block designs, there may be a concern that the treatments present in the same tank (denoted here as “neighbors”) affect each other in their performance; thus the need for an assessment of neighbor effects. In this paper, we propose two statistical approaches to assess and account for neighbor effects. The first approach is based on a non-linear mixed model and the second involves cross-classified and multiple membership models. Both approaches are illustrated on simulated data as well as data from a clinical ISAV (Infectious Salmon Anaemia Virus) trial; corresponding computer code is available online.