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- Ehrenberg, Sigrid Z., 1964-
(författare)
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The neglected ecology of the sand goby: Abundance and feeding in the Baltic sublittoral
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- I investigated the ecology and population density of the sand goby, Pomatoschistus minutus, at sub-thermocline depth in the north-western Baltic proper. Most previous research on the sand goby, and the co-occurring closely related common goby, P. microps, has focused on their stay in shallow waters, while important parts of their life cycles have been largely neglected.Photography was used to assess goby population density and size distribution, a basis for estimations of the potential annual food consumption of the goby community. Diet analysis of the most abundant goby, the sand goby, was combined with the population censuses to estimate the contribution of different prey to the goby consumption. Both benthic and pelagic prey were consumed, including two non-indigenous species. The amphipod Monoporeia affinis was by far the most important prey for the overall consumption, while pelagic and benthic copepods, and naidid oligochaetes were important prey for sand gobies < 3.5 cm. Goby predation is likely to influence the populations of naidid oligochaetes and the amphipod M. affinis, as large parts of their production may be consumed.The potential goby consumption was calculated to be about 72 kJ m-2 yr-1, which corresponds to 14-60 % of the annual production on soft bottoms in the area. In a laboratory study of the sand goby activity, active swimming occurred preferentially at night and burying in the sediment mostly at day. Both behaviours may lead to underestimates in photographic censuses of up to 40 %. The goby community in the sublittoral links the benthic and pelagic sub-systems in the area by being able to remove a substantial amount of energy from the benthic production, by inclusion of pelagic prey, and by holding an intermediate position in the coastal marine food web of the Baltic Sea. Consequently, their role in the flow of energy, elements and substances, some potentially harmful, between the pelagic and benthic ecosystem should be further investigated.
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| 2. |
- Hansen, Joakim, 1978-
(författare)
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Effects of morphometric isolation and vegetation on the macroinvertebrate community in shallow Baltic Sea land-uplift bays
- 2010
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Shallow sheltered Baltic Sea bays are ecologically important habitats that harbour a unique vegetation community and constitute vital reproduction areas for many coastal fish species. Knowledge about the invertebrate community in these bays is, however, limited. This thesis examines the macroinvertebrate community in shallow sheltered Baltic Sea bays and how it is affected by: (1) the natural morphometric isolation of bays from the sea due to post-glacial land uplift; and (2) differences in vegetation types. The invertebrate biomass and number of taxa was found to decrease with increased bay isolation. The taxon composition changed from dominance by bivalves and gastropods in open bays to a community composed of a larger proportion of insects in isolated bays. Stable isotope analysis indicated epiphytes and periphyton as the major energy resources for most of the examined consumers, but the relative importance of these in relation to larger plants decreased for some consumers with increased bay isolation. A comparison of invertebrate abundance between plants revealed a close relationship with morphological complexity of the plants. More complexly structured plants had higher invertebrate abundance than plants with simpler morphology. The results suggest that management of these coastal habitats should be dynamic and take into consideration the natural change in invertebrate community resulting from the slow bay isolation process. In addition, the results imply that changes in the aquatic vegetation due to anthropogenic influences could induce changes in the invertebrate community as the plant habitat structure is altered. A changed invertebrate community may in turn affect higher trophic levels since invertebrates are important food for many fish and waterfowl species.
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| 3. |
- Bergström, Lena, 1973-
(författare)
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Macroalgae in the Baltic Sea : responses to low salinity and nutrient enrichment in Ceramium and Fucus
- 2005
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The brackish Baltic Sea is a marginal environment for both marine and freshwater species. The rate of ecological differentiation is presumably high due to strong selection pressure from a gradient of decreasing salinity that has been present in its current state for only about 3 000 years. Even more recently, increased nutrient loading due to human activities has affected the growth rate of species, with potential effects on their competitive interactions and responses to other regulating factors. I have investigated the potential effects of low salinity and nutrient enrichment on the distributional ranges of two marine macroalgae with a wide distribution in the Baltic Sea, the red alga Ceramium tenuicorne (Kütz.) Wærn and the brown alga Fucus vesiculosus L. A field study in the northern Baltic Sea indicated a strong relationship between the community structure of macroalgae and abiotic factors even on a small, local scale. The abiotic factors are potentially modulated by eutrophication, which may have a strong effect on the depth distribution and abundance of macroalgae. On a regional scale, laboratory experiments suggested that nutrient enrichment is unlikely to affect the distribution of Ceramium and Fucus along the salinity gradient. Growth in Ceramium from the Baltic Proper was enhanced by nitrate and phosphate, but the response did not override growth constraints due to low salinity. Ceramium from the Gulf of Bothnia had an inherently lower growth rate that was not positively affected by nitrate and phosphate increase. In Fucus vesiculosus, reproductive performance was impaired by nitrate and phosphate levels corresponding to ambient levels in eutrophicated areas of the Baltic Sea, when measured by their effect on zygote attachment, germination, and rhizoid development.The wide distribution of Ceramium in the inner Baltic Sea is probably related to local adaptation, rather than a generalized tolerance of different salinity levels. Ecotypic differences were observed when comparing strains from the Baltic Proper (salinity 7 psu) and the Gulf of Bothnia (4 psu). A high rate of vegetative reproduction was evident, although sexual reproduction was occasionally observed in salinity 4. In Fucus vesiculosus, genetic and morphological analyses of sympatric and allopatric populations of the common, vesicular, morphotype and a dwarf morphotype, characteristic for the Gulf of Bothnia, showed that the dwarf morphotype represents a separate evolutionary lineage. Also, vegetative reproduction was observed in Fucus for the first time, as supported by genetic and experimental data. The results show that the biota of the inner Baltic Sea may have unique adaptive and genetic properties, and that it is highly relevant to consider subspecies diversity in Baltic Sea management.
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| 4. |
- Bergström, Ulf, 1971-
(författare)
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Spatial heterogeneity and biotic interactions : scaling from experiments to natural systems
- 2004
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Much of current ecological theory stems from experimental studies. These studies have often been conducted in closed systems, at spatial scales that are much smaller than the systems of interest. It is known that the outcome of these experiments may be seriously affected by artefacts associated with the caging procedures, as well as by the actual difference in spatial scale between experimental and target system. Yet, quantitative methods for estimating and removing artefacts of enclosure and for extrapolating experimental results to the scales of natural systems are largely lacking.The aim of this thesis was to confront some of the problems encountered when scaling from experiments to nature in studies on predator-prey systems, with focus on effects of changes in spatial heterogeneity. Specifically, I examined mechanisms that may cause consumption rate estimates to depend on the size of the experimental arena. I also studied methods for scaling up these process rate estimates to natural predator-prey systems. The studies were performed on invertebrate predator-prey systems found in the northern Baltic Sea. Initially, a descriptive study of small-scale distribution patterns was performed, in order to get background information on how the behaviour of the organisms was manifested in the spatial structure of the community. Experimental studies of two predator-prey systems exposed an artefact that may be widespread in experiments aiming at quantifying biotic interactions. It is caused by predator and prey aggregating along the walls of the experimental containers. This behaviour affects the encounter rate between predator and prey, thereby causing consumption rates to be scale-dependent. Opposing the common belief that larger arenas always produce less biased results, this scale effect may instead be reduced by decreasing arena size. An alternative method for estimating the magnitude of, and subsequently removing, the artefact caused by aggregation along the arena wall was presented.Once unbiased estimates of process functions have been derived, the next step is to scale up the functions to natural systems. This extrapolation entails a considerable increase in spatial heterogeneity, which may have important implications for the dynamics of the system. Moment approximation provides a method of taking the heterogeneity of natural populations into account in the extrapolation process. In the last study of the thesis, the concepts of moment approximation and how to estimate relevant heterogeneity were explained, and it was shown how the method may be used for adding space as a component to a dynamic predator-prey model. It was concluded that moment approximation provides a simple and useful technique for dealing with effects of spatial variation, and that a major benefit of the method is that it provides a way of visualising how heterogeneity affects ecological processes.
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| 5. |
- Yletyinen, Johanna, 1977-
(författare)
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The Impact of Multiple Drivers on Marine Systems : Novel approaches for studying structural changes
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Human action is transforming the species composition, biogeochemistry and habitats of the world’s oceans at unprecedented rates. The cumulative effect of natural and anthropogenic drivers is challenging to measure, in part due to indirect effects and the complexity of marine systems. Building on the theory of complex adaptive systems, this thesis aims to increase our understanding of how complex, heterogeneous marine social-ecological systems (SES) may respond to changing conditions. This thesis integrates resilience research with network science and describes change and structural patterns at several SES scales in order to advance our knowledge on the effects of multiple drivers.Paper I proposes a new, quantitative fish stock collapse definition, that accounts for fish stock dynamics and enables standardization and thus comparability across a large number of commercial fish stocks. Recognizing that substantial ecosystem changes are part of SES dynamics, in Paper II we review marine regime shifts worldwide to specify how co-occurring bundles of drivers are related to degraded ecosystem services for management purposes. A more detailed ecological study on regime shifts was performed in Papers III and IV. Paper III describes the late-1980s central Baltic Sea regime shift based on a food-web model. Paper IV uses a novel structural network analysis approach to detect functional shifts in complex food webs. The results of Paper IV imply that the Baltic Sea regime shift may not be a systemwide shift. Paper V uses a network approach to analyze fishing strategy diversification and social-ecological connectivity among Swedish Baltic Sea fishers, indicating that natural resource management evaluations should not be limited only to ecosystem conditions but also take account of social conditions.Overall, this thesis provides empirical evidence for the emerging perspective that marine resource science and management must account for the complexity of system elements in order to ensure the provision of ecosystem services in the future. The first application of Exponential Random Graph Modeling in ecology and an improved fish stock collapse definition provide new advanced tools for studying oceans from an SES perspective in the future.
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