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  • Hansson, Lars-Anders, et al. (författare)
  • Food-chain length alters community responses to global change in aquatic systems
  • 2013
  • Ingår i: Nature Climate Change. - Nature Publishing Group. - 1758-678X. ; 3:3, s. 228-233
  • Tidskriftsartikel (refereegranskat)abstract
    • Synergies between large-scale environmental changes, such as climate change(1) and increased humic content (brownification)(2), will have a considerable impact on future aquatic ecosystems. On the basis of modelling, monitoring and experimental data, we demonstrate that community responses to global change are determined by food-chain length and that the top trophic level, and every second level below, will benefit from climate change, whereas the levels in between will suffer. Hence, phytoplankton, and thereby algal blooms, will benefit from climate change in three-, but not in two-trophic-level systems. Moreover, we show that both phytoplankton (resource) and zooplankton (consumer) advance their spring peak abundances similarly in response to a 3 degrees C temperature increase; that is, there is no support for a consumer/resource mismatch in a future climate scenario. However, in contrast to other taxa, cyanobacteria-known as toxin-producing nuisance phytoplankton(3)-benefit from a higher temperature and humic content irrespective of the food-chain composition. Our results are mirrored in natural ecosystems. By mechanistically merging present food-chain theory with large-scale environmental and climate changes, we provide a powerful framework for predicting and understanding future aquatic ecosystems and their provision of ecosystem services and water resources.
  • Hansson, Lars-Anders, et al. (författare)
  • Consumption patterns, complexity and enrichment in aquatic food chains
  • 1998
  • Ingår i: Proceedings of the Royal Society, London, B. - Royal Society Publishing. - 1471-2954 (Online) .- 0962-8452 (Print). ; 265:1399, s. 901-906
  • Tidskriftsartikel (refereegranskat)abstract
    • The interactions between consumers and prey, and their impact on biomass distribution among trophic levels, are central issues in both empirical and theoretical ecology. In a long-term experiment, where all organisms, including the top predator, were allowed to respond to environmental conditions by reproduction, we tested predictions from `prey-dependent' and `ratio-dependent' models. Prey-dependent models made correct predictions only in the presence of strong interactors in simple food chains, but failed to predict patterns in more complex situations. Processes such as omnivory, consumer excretion, and unsuitable prey-size windows (invulnerable prey) increased the complexity and created patterns resembling ratio-dependent consumption. However, whereas the prey-dependent patterns were created by the mechanisms predicted by the model, ratio-dependent patterns were not, suggesting that they may be right for the wrong reason'. We show here that despite the enormous complexity of ecosystems, it is possible to identify and disentangle mechanisms responsible for observed patterns in community structure, as well as in biomass development of organisms ranging in size from bacteria to fish.
  • Lindegren, Martin, et al. (författare)
  • Towards sustainable fisheries of the Oresund cod (Gadus morhua) through sub-stock-specific assessment and management recommendations
  • 2013
  • Ingår i: ICES Journal of Marine Science. - Oxford Univ. Press. - 1054-3139. ; 70:6, s. 1140-1150
  • Tidskriftsartikel (refereegranskat)abstract
    • Fisheries management traditionally relies on stock assessments assuming discrete populations within large administrational areas. However, failing to account for sub-stock structuring may result in overestimation of the stocks' true harvest potential and unsustainable exploitation of small stock elements. Atlantic cod (Gadus morhua) frequently occurs in spatially segregated populations, some of which exhibit fine-scaled stock structuring within current management boundaries. Here we use the locally spawning cod stock in the Sound ("Oresund") as a case study, and perform a sub-stock-specific assessment to evaluate biological and economic effects of managing the Sound cod as a separate stock. Our results indicate that reducing exploitation pressure, particularly through technical regulations i. e. increasing gill-net mesh sizes, would not only enhance the stock age distribution, but yield long-term net benefits to the local gill-net fishery. Furthermore, our study emphasizes the need for developing sub-stock-specific management recommendations in order to ensure the maintenance of fisheries resources in general, and the persistence of sub-stock structuring in particular.
  • Ljungberg, Peter, 1976-, et al. (författare)
  • Effects of small-scale habitat fragmentation on predator–prey interactions in a temperate sea grass system
  • 2013
  • Ingår i: Marine Biology. - 0025-3162. ; 160:3, s. 667-675
  • Tidskriftsartikel (refereegranskat)abstract
    • During the last decades, fragmentation has become an important issue in ecological research. Habitat fragmentation operates on spatial scales ranging over several magnitudes from patches to landscapes. We focus on small-scale fragmentation effects relevant to animal foraging decision making that could ultimately generate distribution patterns. In a controlled experimental environment, we tested small-scale fragmentation effects in artificial sea grass on the feeding behaviour of juvenile cod (Gadus morhua). Moreover, we examined the influence of fragmentation on the distribution of one of the juvenile cod’s main prey resources, the grass shrimp (Palaemon elegans), in association with three levels of risk provided by cod (no cod, cod chemical cues and actively foraging cod). Time spent by cod within sea grass was lower in fragmented landscapes, but total shrimp consumption was not affected. Shrimp utilised vegetation to a greater extent in fragmented treatments in combination with active predation. We suggest that shrimp choose between sand and vegetation habitats to minimize risk of predation according to cod habitat-specific foraging capacities, while cod aim to maximize prey-dependent foraging rates, generating a habitat-choice game between predator and prey. Moreover, aggregating behaviour in grass shrimp was only found in treatments with active predation. Hence, we argue that both aggregation and vegetation use are anti-predator defence strategies applied by shrimp. We therefore stress the importance of considering small-scale behavioural mechanisms when evaluating consequences from habitat fragmentation on trophic processes in coastal environments.
  • Ljungberg, Peter, et al. (författare)
  • Prey selectivity by juvenile Atlantic cod Gadus morhua in three coastal habitat types
  • 2012
  • Ingår i: Marine Ecology: Progress Series. - Inter-Research. - 0171-8630. ; 466, s. 215-223
  • Tidskriftsartikel (refereegranskat)abstract
    • Coastal habitats are heavily subjected to eutrophication and commercial fisheries, and such alterations can affect organism interaction strengths and potentially influence trophic dynamics. A key species inhabiting coastal environments in temperate waters is the Atlantic cod Gadus morhua, which utilises coastal areas for food and shelter. We used an experimental mechanistic approach to assay prey selectivity by juvenile cod when foraging on grass shrimp Palaemon elegans and brown shrimp Crangon crangon, under light and dark conditions, in 3 of the most abundant habitat types in temperate coastal environments-sand, eelgrass (artificial vegetation mimicking Zostera marina), and bladderwrack Fucus vesiculosus. Using functional response relationships from single-prey experiments, we calculated the energetically best foraging strategy for cod in the 3 habitats, i.e. feeding selectively on either of the shrimp species or on a combination of both. These predictions were tested in experiments where the cod predator was offered both prey species. Cod selected both prey species in accordance with our predictions in eelgrass and in bladderwrack under light conditions, but a lower than predicted consumption of grass shrimp was found in sand and in bladderwrack under dark conditions. Cod decreasingly selected grass shrimp with increasing habitat complexity, i.e. the highest selectivity was in sand and the lowest selectivity was in bladderwrack. As the 2 shrimp species have different trophic roles, cod selective predation may have effects on lower trophic levels. We provide a quantitative prediction of cod selective predation in habitat types that undergo degradation, and suggest that such predation can influence the trophic consequences from environmental change.
  • Persson, Anders, et al. (författare)
  • Effects of enrichment on simple aquatic food webs
  • 2001
  • Ingår i: American Naturalist. - University of Chicago Press. - 0003-0147. ; 157:6, s. 654-669
  • Tidskriftsartikel (refereegranskat)abstract
    • Simple models, based on Lotka-Volterra types of interactions between predator and prey, predict that enrichment will have a destabilizing effect on populations and that equilibrium population densities will change at the top trophic level and every second level below. We experimentally tested these predictions in three aquatic food web configurations subjected to either high or low nutrient additions. The results were structured by viewing the systems as either food chains or webs and showed that trophic level biomass increased with enrichment, which contradicts food chain theory. However, within each trophic level, food web configuration affected the extent to which different functional groups responded to enrichment. By dividing trophic levels into functional groups, based on vulnerability to consumption, we were able to identify significant effects that were obscured when systems were viewed as food chains. The results support the prediction that invulnerable prey may stabilize trophic-level dynamics by replacing other, more vulnerable prey. Furthermore, the vulnerable prey, such as Daphnia and edible algae, responded as predicted by the paradox of enrichment hypothesis; that is, variability in population density increased with enrichment. Hence, by describing ecosystems as a matrix of food web interactions, and by recognizing the interplay between interspecific competition and predation, a more complete description of the ecosystem function was obtained compared to when species were placed into distinct trophic levels.
  • Persson, Anders, et al. (författare)
  • Foraging performance of juvenile cod (Gadus morhua) and profitability of coastal habitats
  • 2012
  • Ingår i: Marine Ecology Progress Series. - Inter-Research. - 0171-8630 .- 1616-1599. ; 456, s. 245-253
  • Tidskriftsartikel (refereegranskat)abstract
    • Overfishing and eutrophication affects coastal communities worldwide, leading to dwindling fish stocks and deteriorated habitats. Hence, attempts to rebuild overfished stocks to past fish productivities need to account for functional relations between habitat types and fish performance. Here we quantify resource availability, foraging performance and anti-predator behaviour of juvenile Atlantic cod (Gadus morhua) to assess the costs and benefits associated with different coastal habitats. In the laboratory, Atlantic cod foraged more efficiently in sand habitats compared to the structurally more complex habitats of eelgrass (Zostera marina) and the canopy forming bladderwrack (Fucus vesicolosus). Presence of chemical cues from a cannibal reduced Atlantic cod consumption rates in all habitats, but most pronounced in the sand habitat. Field observations in the three habitats showed highest resource density in the bladderwrack habitat and lowest in the sand habitat, irrespective of season. Habitat profitability, calculated by combining data from field estimates of prey density and experimental quantifications of foraging performance, revealed the bladderwrack habitat most profitable independent of season. The difference in profitability between the complex habitats was relatively small, suggesting that Atlantic cod in the field contributed to drive habitat profitability towards equalization. The results strengthen the view that the ongoing loss of seagrass and macroalgae habitats may have significant ramifications for juvenile Atlantic cod performance, which ultimately may lower the productivity of entire stocks. Consequently, future and ongoing rebuilding of commercial fish stocks should revise the expectations of stock productivity (and hence harvesting intensity) accordingly.
  • Schwenke, Jörg, et al. (författare)
  • Digital in-line holography on amplitude and phase objects prepared with electron beam lithography.
  • 2012
  • Ingår i: Journal of microscopy. - Royal Microscopical Society. - 1365-2818. ; 247:2, s. 196-201
  • Tidskriftsartikel (refereegranskat)abstract
    • We report on the fabrication and characterization of amplitude and phase samples consisting of well defined Au or Al features formed on ultrathin silicon nitride membranes. The samples were manufactured using electron beam lithography, metallization and a lift-off technique, which allow precise lateral control and thickness of the metal features. The fabricated specimens were evaluated by conventional microscopy, atomic force microscopy and with the digital in-line holography set-up at the Lund Laser Centre. The latter uses high-order harmonic generation as a light source, and is capable of recovering both the shape and phase shifting properties of the samples. We report on the details of the sample production and on the imaging tests with the holography set-up.
  • Waldo, Staffan, et al. (författare)
  • Swedish coastal herring fisheries in the wake of an ITQ system
  • 2013
  • Ingår i: Marine Policy. - Elsevier. - 0308-597X. ; 38, s. 321-324
  • Tidskriftsartikel (refereegranskat)abstract
    • The European common fisheries policy (CFP) advocates measures to sustain small-scale fisheries; hence, in the European Commission's proposal for a reformed CFP, these are exempted from a mandatory system with tradable fishing concessions. This opens up for management actions designed for small-scale fisheries, but also implies new management issues. This article provides insights into the topic based on a Swedish small-scale herring fishery in the western Baltic Sea that was exempted from an ITQ-system. The fishery has been profitable since the system was introduced, and the increasing effort of both incumbent fishermen and new entrants implies a situation where fishermen compete for a limited quota. The migratory pattern of the herring implies high densities in the southern parts of the fishing areas during spring and in the northern parts during autumn. This forms the basis for two different fisheries in the area, as well as for the current management proposal to divide the quota into a spring and an autumn part. This and other management proposals are discussed in the paper. The main conclusion from the case study is that, when exempting a fishery from tradable fishing concessions, it is important to build other institutions dealing with the fundamental problem of access to the quota. Failure to do so might result in an over-capacity issue and threaten the long-run development of an otherwise successful small-scale fishery. (C) 2012 Elsevier Ltd. All rights reserved.
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