| 1. |
- Dinasquet, Julie, et al.
(author)
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Cascading effects of the ctenophore Mnemiopsis leidyi on the planktonic food web in a nutrient-limited estuarine system
- 2012
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In: Marine Ecology Progress Serie. - : Inter-Research Science Center. - 0171-8630 .- 1616-1599. ; 460, s. 49-61
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Journal article (peer-reviewed)abstract
- Increasing biomasses of gelatinous zooplankton presumably have major implications for the structure and function of marine food webs at large; however, current data on lower trophic levels are scarce, as most studies have focused on the immediate effects on zooplankton and fish larvae only. We examined the short-term impact of larvae and adults of the invasive ctenophore Mnemiopsis leidyi on a summer planktonic food web in the estuarine southern Baltic Sea, with special emphasis on the microbial loop. Grazing by M. leidyi reduced the mesozooplankton biomass, followed by increased dinoflagellate biomass in treatments with M. leidyi. While chlorophyll a increased most in the treatments with M. leidyi, small phytoplankton and ciliates decreased in all treatments. M. leidyi had a slight effect on bacterial abundance, but not on bacterial production, ectoenzymatic activities, or community composition. Undetectable levels of phosphate and a gradual accumulation of dissolved organic carbon during the experiment suggested a malfunctioning microbial loop scenario. The experiment shows that direct and indirect short-term effects of M. leidyi on the estuarine food web are limited to higher trophic levels and indicates that top-down and bottom-up consequences of M. leidyi expansions on the microbial loop will likely depend on local nutrient conditions.
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| 2. |
- Flores, H., et al.
(author)
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Impact of climate change on Antarctic krill
- 2012
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In: Marine Ecology-Progress Series. - : Inter-Research Science Center. - 0171-8630 .- 1616-1599. ; 458, s. 1-19
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Journal article (peer-reviewed)abstract
- Antarctic krill Euphausia superba (hereafter 'krill') occur in regions undergoing rapid environmental change, particularly loss of winter sea ice. During recent years, harvesting of krill has in creased, possibly enhancing stress on krill and Antarctic ecosystems. Here we review the overall impact of climate change on krill and Antarctic ecosystems, discuss implications for an ecosystem-based fisheries management approach and identify critical knowledge gaps. Sea ice decline, ocean warming and other environmental stressors act in concert to modify the abundance, distribution and life cycle of krill. Although some of these changes can have positive effects on krill, their cumulative impact is most likely negative. Recruitment, driven largely by the winter survival of larval krill, is probably the population parameter most susceptible to climate change. Predicting changes to krill populations is urgent, because they will seriously impact Antarctic ecosystems. Such predictions, however, are complicated by an intense inter-annual variability in recruitment success and krill abundance. To improve the responsiveness of the ecosystem-based management approach adopted by the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR), critical knowledge gaps need to be filled. In addition to a better understanding of the factors influencing recruitment, management will require a better understanding of the resilience and the genetic plasticity of krill life stages, and a quantitative understanding of under-ice and benthic habitat use. Current precautionary management measures of CCAMLR should be maintained until a better understanding of these processes has been achieved. [GRAPHICS] .
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| 3. |
- Flores, Hauke, et al.
(author)
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The Association of Antarctic Krill Euphausia superba with the Under-Ice Habitat
- 2012
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In: PLoS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 7:2
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Journal article (peer-reviewed)abstract
- The association of Antarctic krill Euphausia superba with the under-ice habitat was investigated in the Lazarev Sea (Southern Ocean) during austral summer, autumn and winter. Data were obtained using novel Surface and Under Ice Trawls (SUIT), which sampled the 0–2 m surface layer both under sea ice and in open water. Average surface layer densities ranged between 0.8 individuals m−2 in summer and autumn, and 2.7 individuals m−2 in winter. In summer, under-ice densities of Antarctic krill were significantly higher than in open waters. In autumn, the opposite pattern was observed. Under winter sea ice, densities were often low, but repeatedly far exceeded summer and autumn maxima. Statistical models showed that during summer high densities of Antarctic krill in the 0–2 m layer were associated with high ice coverage and shallow mixed layer depths, among other factors. In autumn and winter, density was related to hydrographical parameters. Average under-ice densities from the 0–2 m layer were higher than corresponding values from the 0–200 m layer collected with Rectangular Midwater Trawls (RMT) in summer. In winter, under-ice densities far surpassed maximum 0–200 m densities on several occasions. This indicates that the importance of the ice-water interface layer may be under-estimated by the pelagic nets and sonars commonly used to estimate the population size of Antarctic krill for management purposes, due to their limited ability to sample this habitat. Our results provide evidence for an almost year-round association of Antarctic krill with the under-ice habitat, hundreds of kilometres into the ice-covered area of the Lazarev Sea. Local concentrations of postlarval Antarctic krill under winter sea ice suggest that sea ice biota are important for their winter survival. These findings emphasise the susceptibility of an ecological key species to changing sea ice habitats, suggesting potential ramifications on Antarctic ecosystems induced by climate change.
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| 4. |
- Haraldsson, Matilda, 1980, et al.
(author)
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Emerging niche clustering results from both competition and predation
- 2023
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In: Ecology Letters. - 1461-023X. ; 26:7, s. 1200-1211
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Journal article (peer-reviewed)abstract
- Understanding species coexistence has been a central question in ecology for decades, and the notion that competing species need to differ in their ecological niche for stable coexistence has dominated. Recent theoretical and empirical work suggests differently. Species can also escape competitive exclusion by being similar, leading to clusters of species with similar traits. This theory has so far only been explored under competition. By combining mathematical and numerical analyses, we reveal that competition and predation are equally capable to promote clusters of similar species in prey-predator communities, their relative importance being modulated by resource availability. We further show that predation has a stabilizing effect on clustering patterns, making the clusters more diverse. Our results merge different ecological theories and bring new light to the emergent neutrality theory by adding the perspective of trophic interactions. These results open new perspectives to the study of trait distributions in ecological interaction networks.
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| 5. |
- Haraldsson, Matilda, 1980, et al.
(author)
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Environmental constraints of the invasive Mnemiopsis leidyi in Scandinavian waters
- 2013
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In: Limnology and Oceanography. - : Wiley. - 0024-3590. ; 58:1, s. 37-48
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Journal article (peer-reviewed)abstract
- We studied the seasonal dynamics of the invasive ctenophore Mnemiopsis leidyi over its distribution range from Skagerrak into the Baltic Proper during 1 yr and related this to ambient physical and biological variables. The appearance of M. leidyi was sporadic in the Baltic Proper, with 60-fold lower abundance than in the Skagerrak and Kattegat (mean 0.02 individual m−3 and 1.16 individual m−3, respectively). M. leidyi typically resided above the halocline (10–20 m depth), except in the Baltic Proper where they were found deeper. Smaller size classes were underrepresented in the Baltic Proper, indicating failed reproduction or high mortality of the younger life stages. Ninety percent of the M. leidyi were observed at salinities of 22–29 and 75% of the individuals in water masses warmer than 11°C, i.e., typical late summer to autumn temperatures. Results of a Generalized Additive Model (GAM) indicate that the spatio-temporal distribution of M. leidyi might be explained by advection of M. leidyi from the Skagerrak and Kattegat area to the Baltic Proper. We conclude that the low salinity (< 9) of the Baltic Proper is likely to restrict successful reproduction and establishment of M. leidyi and that the advection of individuals from higher saline source areas sustained the observed Baltic Proper occurrence.
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| 6. |
- Haraldsson, Matilda, 1980, et al.
(author)
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Evidence of diel vertical migration in Mnemiopsis leidyi
- 2014
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In: PLoS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 9:1
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Journal article (peer-reviewed)abstract
- The vertical distribution and migration of plankton organisms may have a large impact on their horizontal dispersal and distribution, and consequently on trophic interactions. In this study we used video-net profiling to describe the fine scale vertical distribution of Mnemiopsis leidyi in the Kattegat and Baltic Proper. Potential diel vertical migration was also investigated by frequent filming during a 24-hour cycle at two contrasting locations with respect to salinity stratification. The video profiles revealed a pronounced diel vertical migration at one of the locations. However, only the small and medium size classes migrated, on average 0.85 m h-1, corresponding to a total migration distance of 10 m during 12 h. Larger individuals (with well developed lobes, approx. >27 mm) stay on average in the same depth interval at all times. Biophysical data suggest that migrating individuals likely responded to light, and avoided irradiance levels higher than approx. 10 µmol quanta m-2 s-1. We suggest that strong stratification caused by low surface salinity seemed to prohibit vertical migration.
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| 7. |
- Haraldsson, Matilda, 1980, et al.
(author)
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How to model social-ecological systems? – A case study on the effects of a future offshore wind farm on the local society and ecosystem, and whether social compensation matters
- 2020
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In: Marine Policy. - : Elsevier BV. - 0308-597X. ; 119
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Journal article (peer-reviewed)abstract
- Models of social-ecological systems (SES) are acknowledged as an important tool to understand human-nature relations. However, many SES models fail to integrate adequate information from both the human and ecological subsystems. With an example model of a future Offshore Wind Farm development and its effects on both the ecosystem and local human population, we illustrate a method facilitating a “balanced” SES model, in terms of including information from both subsystems. We use qualitative mathematical modeling, which allows to quickly analyze the structure and dynamics of a system without including quantitative data, and therefore to compare alternative system structures based on different understandings of how the system works. By including similar number of system variables in the two subsystems, we balanced the complexity between them. Our analyses show that this complexity is important in order to predict indirect and sometimes counterintuitive effects. We also highlight some conceptually important questions concerning social compensations during developmental projects in general, and wind farms in particular. Our results suggest that the more project holders get involved in various manner in the local socio-ecological system, the more society will benefit as a whole. Increased involvement through e.g. new projects or job-opportunities around the windfarm has the capacity to offset the negative effects of the windfarm on the local community. These benefits are enhanced when there is an overall acceptance and appropriation of the project. We suggest this method as a tool to support the decision-making process and to facilitate discussions between stakeholders, especially among local communities.
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| 8. |
- Haraldsson, Matilda, 1980, et al.
(author)
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Seasonal distribution and life history of Thysanoessa macrura (euphausiacea, crustacea) in high latitude waters of the Lazarev Sea, Antarctica
- 2014
-
In: Marine Ecology Progress Series. - : Inter-Research Science Center. - 0171-8630 .- 1616-1599. ; 495, s. 105-118
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Journal article (peer-reviewed)abstract
- Although Thysanoessa macrura is one of the most abundant and widely distributed euphausiid species in the Southern Ocean, knowledge about its seasonal distribution and overwintering strategy remains sparse. We describe the variation in abundance, demography, and distribution of T. macrura during 3 seasons in the Lazarev Sea, located in the south-east Atlantic sector of Antarctica. Adult and larval T. macrura were widely distributed across the Lazarev Sea in all seasons, but with large seasonal variability in the adult population. Mean summer densities (4.9 and 7.0 ind. m-2 in 2005/06 and 2007/08, respectively) were 20-fold higher than densities recorded during autumn (0.4 ind. m-2) and winter (0.2 ind. m-2). Comparison of length-frequency distributions and sex ratios, particularly between shallow (0-200 m) and deep (0-2000 m) samples taken during winter, suggest a seasonal vertical migration. A large proportion of the adult population seems to migrate to greater depth during winter, possibly as an overwintering strategy. Further, the demographic data and a set of growth models suggest that females and males have deviating life history traits. Females grow to larger size but their growth rate is slower, and they may mature later than males. The presence of mature males and females with spermatophores attached during late June to August indicated that spawning had already started during mid-winter conditions. These data, which were uniquely sampled in the same region from summer to winter, provide a new perspective on the seasonal behavior and general life history of T. macrura. © Inter-Research 2014.
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| 9. |
- Haraldsson, Matilda, 1980, et al.
(author)
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The relationship between fish and jellyfish as a function of eutrophication and water clarity
- 2012
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In: Marine Ecology Progress Series. - : Inter-Research Science Center. - 0171-8630 .- 1616-1599. ; 471, s. 73-85
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Journal article (peer-reviewed)abstract
- There is a concern that blooms of cnidarians and ctenophores, often referred to as jellyfish, are increasing in frequency and intensity worldwide and that there is a shift from fish- to jellyfish-dominated systems. We present an idealized analysis of the competitive relationship between zooplanktivorous jellyfish that is based on a generic model, termed ‘Killing the Winner’ (KtW), for the coexistence of 2 groups utilizing the same resource. Tactile predation by jellyfish makes them less dependent on water optics than fish using vision, and we modified the KtW model to account for this particular trait difference. Expectations of the model are illustrated by use of observations from the Baltic Sea. The model predicts a general succession on how mass of the system distributes when going from an oligotrophic to a eutrophic system. Initially the mass of the system accumulates at the level of the common resource (zooplankton) and planktivorous fish (sprat/herring). At one point, with increased eutrophication, mass starts to accumulate at the level of the top predator (cod) and at a later point, at the level of the jellyfish. For those organisms utilizing vision (fishes) an optimal degree of eutrophication and water clarity is predicted due to a 2-sided effect of eutrophication.
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| 10. |
- Hosia, A, et al.
(author)
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Interactions between native and alien ctenophores: Beroe gracilis and Mnemiopsis leidyi in Gullmarsfjorden
- 2011
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In: MARINE ECOLOGY-PROGRESS SERIES. - 0171-8630. ; 422, s. 129-138
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Journal article (peer-reviewed)abstract
- We experimentally quantified predation rates between the native North Sea ctenophore Beroe gracilis and the introduced Mnemiopsis leidyi. A series of incubation experiments with varying M. leidyi prey concentrations (0.15 to 2.37 ind. l–1) and sizes (mean oral-aboral length: 5.9 to 20.6 mm) was conducted, and digestion rates were measured. B. gracilis fed readily on M. leidyi and reproduced on this diet. However, B. gracilis were unable to entirely ingest M. leidyi approaching their own size, resulting in a size refuge from predation. Larger prey were often partially consumed, and the proportion of prey that was only partially eaten increased with prey size. Observed maximum clearance rates for whole prey were from 0.42 to 0.97 l ind.–1 h–1. Ingestion rates of whole prey increased linearly with prey concentration for the smaller prey, but leveled off at the higher prey concentrations for the larger sizes, indicating handling limitation. The handling limitations probably largely stemmed from digestion time (1.6 to 8.4 h for 4 to 12 mm prey) and gut volume. Applying the determined clearance rates to concurrent in situ abundances of M. leidyi and B. gracilis suggested a slight predation impact on the M. leidyi population (overall mortality: 8.8 × 10–4 d–1). The predatory interactions between the 2 species are further complicated by transitional and lobate stage M. leidyi being able to feed on young B. gracilis.
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| 11. |
- Jaspers, Cornelia., et al.
(author)
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Ctenophore population recruits entirely through larval reproduction in the central Baltic Sea
- 2012
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In: Biology Letters. - : The Royal Society. - 1744-9561 .- 1744-957X. ; 8:5, s. 809-812
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Journal article (peer-reviewed)abstract
- The comb jelly Mertensia ovum, widely distributed in Arctic regions, has recently been discovered in the northern Baltic Sea. We show that M. ovum also exists in the central Baltic but that the population consists solely of small-sized larvae (less than 1.6 mm). Despite the absence of adults, eggs were abundant. Experiments revealed that the larvae were reproductively active. Egg production and anticipated mortality rates suggest a self-sustaining population. This is the first account of a ctenophore population entirely recruiting through larval reproduction (paedogenesis). We hypothesize that early reproduction is favoured over growth to compensate for high predation pressure.
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| 12. |
- Jaspers, Cornelia, et al.
(author)
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Seasonal dynamics of early life stages of invasive and native ctenophores give clues to invasion and bloom potential in the Baltic Sea
- 2013
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In: Journal of Plankton Research. - : Oxford University Press (OUP). - 0142-7873 .- 1464-3774. ; 35:3, s. 582-594
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Journal article (peer-reviewed)abstract
- Recently, both the invasive ctenophore Mnemiopsis leidyi and the arctic Mertensia ovum were discovered in the Baltic Sea but their range expansion remains unclear due to misidentification of their larval stages. Supported by molecular species verification we describe seasonal abundance and distribution of larvae and eggs of these two species. We show that their occurrence is significantly but inversely related to salinity. Mertensia ovum was present year round throughout the brackish Baltic Sea but also occurred in high-saline areas during cold seasons. Larvae of M. leidyi occurred throughout all seasons in high-saline areas but never extended further into the central Baltic. Highest ctenophore egg abundances were observed in high-saline areas during summer along with the first appearance of M. leidyi adults. The M. leidyi population peaked 2 months after the first occurrence of adults in high-saline areas, suggesting these areas as a source for lower saline regions. Low larvae abundances and a reduced transitional-to-adult ratio in the southern Baltic point to reduced or no active recruitment, suggesting that drift of animals from high-saline into lower saline regions sustains the M. leidyi population in the southern Baltic such as the Arkona and Bornholm basins.
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| 13. |
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| 14. |
- Niquil, N., et al.
(author)
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Shifting levels of ecological network's analysis reveals different system properties
- 2020
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In: Philosophical Transactions of the Royal Society B-Biological Sciences. - : The Royal Society. - 0962-8436 .- 1471-2970. ; 375:1796
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Journal article (peer-reviewed)abstract
- Network analyses applied to models of complex systems generally contain at least three levels of analyses. Whole-network metrics summarize general organizational features (properties or relationships) of the entire network, while node-level metrics summarize similar organization features but consider individual nodes. The network- and node-level metrics build upon the primary pairwise relationships in the model. As with many analyses, sometimes there are interesting differences at one level that disappear in the summary at another level of analysis. We illustrate this phenomenon with ecosystem network models, where nodes are trophic compartments and pairwise relationships are flows of organic carbon, such as when a predator eats a prey. For this demonstration, we analysed a time-series of 16 models of a lake planktonic food web that describes carbon exchanges within an autumn cyanobacteria bloom and compared the ecological conclusions drawn from the three levels of analysis based on inter-time-step comparisons. A general pattern in our analyses was that the closer the levels are in hierarchy (node versus network, or flow versus node level), the more they tend to align in their conclusions. Our analyses suggest that selecting the appropriate level of analysis, and above all regularly using multiple levels, may be a critical analytical decision. This article is part of the theme issue 'Unifying the essential concepts of biological networks: biological insights and philosophical foundations'.
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| 15. |
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| 16. |
- Siegel, Volker, et al.
(author)
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Distribution and abundance of Antarctic krill (Eupausia superba) along the Antarctic Peninsula
- 2013
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In: Deep Sea Research Part I: Oceanographic Research Papers. - : Elsevier BV. - 0967-0637. ; 77, s. 63-74
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Journal article (peer-reviewed)abstract
- Net-based data on the abundance, distribution, and demographic patterns of Antarctic krill are quantified from a contemporaneous two ship survey of the Antarctic Peninsula during austral summer 2011. Two survey areas were sampled focussed on Marguerite Bay in the south, and the tip of the Antarctic Peninsula in the north. Data from 177 stations showed that the highest concentrations of krill were found in the southern sampling area. Differences between areas were associated with a few large catches of one year old krill found in anomalously warm and productive waters in Marguerite Bay, and small krill catches in the less-productive, offshore waters in the north. Estimated krill density across the survey area was 3.4 krill m−2, and was low compared to the long-term average of 45 krill m−2 for the Elephant Island area. Overall recruitment between the two survey regions was similar, but per capita recruitment was about 60% lower than historical mean recruitment levels measured at Elephant Island since the late 1970s. Demographic patterns showed small krill concentrated near the coast, and large krill concentrated offshore on the shelf and slope all along the survey area. The offshore distribution of adult krill was delineated by the warm (∼1 °C), low salinity (33.8) water at 30 m, suggesting that most krill were present shoreward of the southern boundary of Antarctic Circumpolar Current Front. Distributions of larvae indicated that three hotspot areas were important for the production of krill: slope areas outside Marguerite Bay and north of the South Shetland Islands, and near the coast around Antarctic Sound. Successful spawning, as inferred from larval abundance, was roughly coincident with the shelf break and not with inshore waters. Given the rapid changes in climate along the Antarctic Peninsula and the lower per capita recruitment observed in recent years, studies comparing and contrasting production, growth, and recruitment across the Peninsula will be critical to better understand how climate change will impact krill populations and their dependent predators in the Scotia Sea.
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| 17. |
- van Der Heijden, L. H., et al.
(author)
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Quantitative food web modeling unravels the importance of the microphytobenthos-meiofauna pathway for a high trophic transfer by meiofauna in soft-bottom intertidal food webs
- 2020
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In: Ecological Modelling. - : Elsevier BV. - 0304-3800. ; 430
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Journal article (peer-reviewed)abstract
- Meiofauna are known to have an important role on many ecological processes, although, their role in food web dynamics is often poorly understood, partially as they have been an overlooked and under sampled organism group. Here, we used quantitative food web modeling to evaluate the trophic relationship between meiofauna and their food sources and how meiofauna can mediate the carbon flow to higher trophic levels in five contrasting soft-bottom intertidal habitats (including seagrass beds, mudflats and sandflats). Carbon flow networks were constructed using the linear inverse model-Markov chain Monte Carlo technique, with increased resolution of the meiofauna compartments (i.e. biomass and feeding ecology of the different trophic groups of meiofauna) compared to most previous modeling studies. These models highlighted that the flows between the highly productive microphytobenthos and the meiofauna compartments play an important role in transferring carbon to the higher trophic levels, typically more efficiently so than macrofauna. The pathway from microphytobenthos to meiofauna represented the largest flow in all habitats and resulted in high production of meiofauna independent of habitat. All trophic groups of meiofauna, except for selective deposit feeders, had a very high dependency on microphytobenthos. Selective deposit feeders relied instead on a wider range of food sources, with varying contributions of bacteria, microphytobenthos and sediment organic matter. Ecological network analyses (e.g. cycling, throughput and ascendency) of the modeled systems highlighted the close positive relationship between the food web efficiency and the assimilation of high-quality food sources by primary consumers, e.g. meiofauna and macrofauna. Large proportions of these flows can be attributed to trophic groups of meiofauna. The sensitivity of the network properties to the representation of meiofauna in the models leads to recommending a greater attention in ecological data monitoring and integrating meiofauna into food web models.
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