| 1. |
- Crona, Beatrice, 1974-
(författare)
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Of Mangroves and Middlemen : A study of social and ecological linkages in a coastal community
- 2006
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis studies some of the links between the social and ecological components in a coastal Social-Ecological System (SES) of East Africa to gain insight into factors affecting natural resource management at a community level. It does so by assessing the return of ecosystem goods and services in restored mangroves through both ecological and socio-economic measurements, and by empirically studying variations and diversity in content of local ecological knowledge among resource users, its relation to valuation of ecosystem goods and services and its distribution across a social network.Taking its starting point in a study of the return of ecological functions in restored mangroves (Paper I) the main results of the thesis are presented in three sections. The ecological perspective, showing restored mangroves as nursery grounds for juvenile shrimp communities, is complemented by findings from interviews with local user groups revealing a range of ecosystem goods and services associated with natural and replanted forests (Paper II). The thesis moves on to show heterogeneity in local ecological knowledge held by groups of resource users (Paper III) and how this can be correlated with structure of the social network for transferring such information and knowledge (Paper IV). This network structure is elaborated upon in the third and final section to look at the role it might play for community social capital and for structurally well positioned individuals to access such capital and initiate collective action for natural resource management (Paper V). The role played by social capital in shaping the informal institution represented by middlemen in the study area is also touched upon as is the function of middlemen in linking social and ecological dynamics of the coupled Social Ecological System (Paper VI). Finally, the implications of these findings are discussed in the context of natural resource management with focus on co-management and community involvement.
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| 2. |
- de la Torre-Castro, Maricela, 1965-
(författare)
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Humans and Seagrasses in East Africa : A social-ecological systems approach
- 2006
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The present study is one of the first attempts to analyze the societal importance of seagrasses (marine flowering plants) from a Natural Resource Management perspective, using a social-ecological systems (SES) approach. The interdisciplinary study takes place in East Africa (Western Indian Ocean, WIO) and includes in-depth studies in Chwaka Bay, Zanzibar, Tanzania. Natural and social sciences methods were used. The results are presented in six articles, showing that seagrass ecosystems are rich in seagrass species (13) and form an important part of the SES within the tropical seascape of the WIO. Seagrasses provide livelihoods opportunities and basic animal protein, in from of seagrass associated fish e.g. Siganidae and Scaridae. Research, management and education initiatives are, however, nearly non-existent. In Chwaka Bay, the goods and ecosystem services associated with the meadows and also appreciated by locals were fishing and collection grounds as well as substrate for seaweed cultivation. Seagrasses are used as medicines and fertilizers and associated with different beliefs and values. Dema (basket trap) fishery showed clear links to seagrass beds and provided the highest gross income per capita of all economic activities. All showing that the meadows provide social-ecological resilience. Drag-net fishery seems to damage the meadows. Two ecological studies show that artisanal seaweed farming of red algae, mainly done by women and pictured as sustainable in the WIO, has a thinning effect on seagrass beds, reduces associated macrofauna, affects sediments, changes fish catch composition and reduces diversity. Furthermore, it has a negative effect on i.a. women’s health. The two last papers are institutional analyses of the human-seagrass relationship. A broad approach was used to analyze regulative, normative and cultural-cognitive institutions. Cooperation and conflict take place between different institutions, interacting with their slow or fast moving characteristics, and are thus fundamental in directing the system into sustainable/unsustainable paths. Ecological knowledge was heterogeneous and situated. Due to the abundance of resources and high internal control, the SES seems to be entangled in a rigidity trap with the risk of falling into a poverty trap. Regulations were found insufficient to understand SES dynamics. “Well” designed organizational structures for management were found insufficient for “good” institutional performance. The dynamics between individuals embedded in different social and cultural structures showed to be crucial. Bwana Dikos, monitoring officials, placed in villages or landing sites in Zanzibar experienced four dilemmas – kinship, loyalty, poverty and control – which decrease efficiency and affect resilience. Mismatches between institutions themselves, and between institutions and cognitive capacities were identified. Some important practical implications are the need to include seagrass meadows in management and educational plans, addressing a seascape perspective, livelihood diversification, subsistence value, impacts, social-ecological resilience, and a broad institutional approach.
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| 4. |
- Eklöf, Johan S., 1978-
(författare)
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Anthropogenic Disturbances and Shifts in Tropical Seagrass Ecosystems
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Seagrasses constitute the basis for diverse and productive ecosystems worldwide. In East Africa, they provide important ecosystem services (e.g. fisheries) but are potentially threatened by increasing resource use and lack of enforced management regulations. The major aim of this PhD thesis was to investigate effects of anthropogenic distur-bances, primarily seaweed farming and coastal fishery, in East African seagrass beds. Seaweed farming, often depicted as a sustainable form of aquaculture, had short- and long-term effects on seagrass growth and abundance that cascaded up through the food web to the level of fishery catches. The coastal fishery, a major subsistence activity in the region, can by removing urchin predators indirectly increase densities of the sea urchin Tripneustes gratilla, which has overgrazed seagrasses in several areas. A study using simulated grazing showed that high magnitude leaf removal – typical of grazing urchins – affected seagrasses more than low magnitude removal, typical of fish grazing. Different responses in two co-occurring seagrass species furthermore indicate that high seagrass diversity in tropical seagrass beds could buffer overgrazing effects in the long run. Finally, a literature synthesis suggests that anthropogenic disturbances could drive shifts in seagrass ecosystems to an array of alternative regimes dominated by other or-ganisms (macroalgae, bivalves, burrowing shrimp, polychaetes, etc.). The formation of novel feedback mechanisms makes these regimes resilient to disturbances like seagrass recovery and transplantation projects. Overall, this suggests that resource use activities linked to seagrasses can have large-scale implications if the scale exceeds critical levels. This emphasizes the need for holistic and adaptive management at the seascape level, specifically involving improved techniques for seaweed farming and fisheries, protection of keystone species, and ecosystem-based management approaches.
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| 7. |
- Hedman, Jenny E, 1972-
(författare)
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Fate of contaminants in Baltic Sea sediment ecosystems : the role of bioturbation
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Aquatic sediments are of major importance for the cycling of environmental pollutants, acting as both sinks and secondary sources of contaminants to the ecosystem. Sediment-living organisms can affect the fate and transport of contaminants through activities like feeding and burrowing, collectively called bioturbation. Apart from high contaminant levels, the Baltic benthic ecosystem is affected by stressors such as eutrophication-induced anoxic conditions and invading alien species. The main objectives of this thesis were to determine the effects of bioturbation on contaminant fluxes in Baltic Sea sediments and to increase the understanding of how these other stressors act together upon contaminant fate in the benthic ecosystem. Bioturbation affected contaminants in a species-specific way. The native species Monoporeia affinis and Macoma balthica increased the incorporation of BDE-99 and Cd deposited on the sediment surface, enhancing their retention in the sediment. The invasive polychaete Marenzelleria sp. did not contribute to the incorporation of surface-deposited contaminants, however, significantly increased the release of contaminants back to the water column. Reoxygenation of anoxic laminated sediments and bioturbation by Marenzelleria increased the sediment-to-water flux of dissolved organic contaminants. When the bioturbation-driven release of PCB was compared to the release caused by physical sediment resuspension, results indicated that the continuous activities of benthic infauna can be just as, or even more, important than physical disturbance for the remobilization of sediment-bound contaminants. Bioaccumulation was significantly higher when contaminants were deposited associated to phytoplankton compared to lignin or sediment, suggesting that there are likely seasonal differences in the mobilization of contaminants in the benthic ecosystem. In summary, bioturbation is an important process influencing contaminant fate in Baltic Sea sediments, and the risk of remobilization of historically buried contaminants may increase with improved benthic redox conditions and the invasion of new deeper-digging species, such as Marenzelleria.
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| 8. |
- Mörk, Erik, 1978-, et al.
(författare)
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Top–down and bottom–up regulation of macroalgal community structure on a Kenyan reef
- 2009
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Ingår i: Estuarine, Coastal and Shelf Science. - : Elsevier BV. - 0272-7714 .- 1096-0015. ; 84:3, s. 331-336
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Tidskriftsartikel (refereegranskat)abstract
- Top–down and bottom–up regulation in the form of grazing by herbivores and nutrient availability areimportant factors governing macroalgal communities in the coral reef ecosystem. Today, anthropogenicactivities, such as over-harvesting of herbivorous fish and sea urchins and increased nutrient loading, arealtering the interaction of these two structuring forces. The present study was conducted in Kenya andinvestigates the relative importance of herbivory and nutrient loading on macroalgal communitydynamics, by looking at alterations in macroalgal functional groups, species diversity (H0) and biomasswithin experimental quadrats. The experiment was conducted in situ for 42 days during the dry season.Cages excluding large herbivorous fish and sea urchins were used in the study and nutrient addition wasconducted using coated, slow-release fertilizer (nitrogen and phosphorous) at a site where herbivory isgenerally low and nutrient levels are relatively high for the region. Nutrient addition increased tissuenutrient content in the algae, and fertilized quadrats had 24% higher species diversity. Herbivoreexclusion resulted in a 77% increase in algal biomass, mainly attributable to a >1000% increase in corticatedforms. These results are in accordance with similar studies in other regions, but are unique in thatthey indicate that, even when prevailing nutrient levels are relatively high and herbivore pressure isrelatively low, continued anthropogenic disturbance results in further ecological responses and increasedreef degradation.
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| 9. |
- Norling, Pia, 1974-
(författare)
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Importance of blue mussels for biodiversity and ecosystem functioning in subtidal habitats
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Blue mussels, Mytilus spp., occur on rocky and sedimentary shores worldwide where they often form dense aggregates. These assemblages change the local environment and create unique habitats. By extensive filter-feeding, the mussels regulate availability and flow of resources such as nutrients and organic material, and are thereby important in benthic-pelagic coupling. This thesis investigates the role of Mytilus spp. for the diversity of associated species, ecosystem functioning and services that the mussels provides. My results show that Mytilus habitats support highly diverse associated communities, especially in subtidal sediment habitats in the Skagerrak and Baltic Sea. The macrofauna species richness was shown to correlate with mussel patch size and biomass. Structural properties of Mytilus spp. provide substrate for attachment, shelter and increase habitat complexity in the system, which was found to enhance species diversity. Biological activities of the mussels, e.g. filter-feeding, biodeposition and nutrient regeneration, seemed to determine the abundance, biomass and functioning of the associated plant and animal communities. The communities are dependent on import of energy resources through the mussels filter-feeding from the pelagic system, which increase contents of organic carbon and nitrogen in sediments by biodeposition even in very small patches. At larger scale, the role of Mytilus spp. as a habitat-modifying species varied between substrate types. On soft substrate, where physical structure is scarce, Mytilus spp. had strong positive effects on the associated algal community, while on hard substrate much less influence was found. In Flensborg fjord, when coexisting with eelgrass, Zostera marina, presence of Mytilus edulis influenced the grain size and biogeochemistry of the sediment, which in turn, seemed to induce sulphide stress in the plants and change plant performance. Due to its biomass dominance and substantial water-filtering capacity, Mytilus sp. tends to counteract eutrophication and maintain water quality maintenance services in the Baltic Sea. The mussels' filtration of plankton and particulate organic material from the pelagic system improves the light climate for benthic algae and increase production of other benthic organisms. This promotes a shift from a turbid plankton dominated system to a highly diverse and productive benthic system. I conclude that Mytilus spp. is important for sustaining biodiversity and ecosystem functioning of subtidal habitats, especially in the Baltic coastal zone.
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| 15. |
- Stark, Karolina, 1978-
(författare)
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Risk from radionuclides: a frog's perspective : Accumulation of 137Cs in a riparian wetland, radiation doses, and effects on frogs and toads after low-dose rate exposure
- 2006
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Threats from man-made radionuclides include waste issues, increasing number of power plants, underground bomb testing, nuclear weapons, and “dirty bombs”. Until recently the ionizing radiation protection system focused on protecting humans with an implied protection of biota. However, goals of sustainable development and precautionary principles for human activity are leading to an inclusion of plant and animal populations in the protection system.From this perspective, the present thesis examines wetlands that function as sinks for the radionuclide 137Cs, and describes calculated and measured radiation doses to residing biota. Also, multi-level effects from exposure to low-dose rate ionizing radiation were studied. Accumulation of 137Cs after the Chernobyl accident fallout was studied in a riparian wetland with a mean activity concentration of 1 200 kBq m-2 in Sweden (paper I). A mass balance budget of 137Cs showed that the sedimentation of new material was balanced by the decay process of 137Cs in parts of the wetland (paper I).Frogs were identified as organisms of concern in this wetland. Internal radiation doses, based on whole body measurements of frogs, were estimated to be lower than external doses based on soil samples (paper II). Current dose models for biota resulted in a wide range of doses depending on different levels of conservatism in the models. Therefore, in situ measurements with frog-phantoms were found to provide valuable dose information (paper III). Measured doses using frog-phantoms were lower than calculated doses using several dose models. Although a dose conversion factor by FASSET was found to be useful for comparison with measurements in the field. A higher dose was measured to the phantom surface in comparison to inner parts, i.e. the sensitive skin of frogs receives the highest dose. Estimated and measured radiation doses to frogs were below suggested dose rate limits.Low-dose rate 137Cs exposure of eggs and tadpoles from three amphibian species, Scaphiopus holbrookii, Bufo terrestris, and Rana catesbeiana, showed no increased levels of strand breaks in red blood cells, and no effects on development, survival or growth up to metamorphosis (paper IV). The ecological factor larval density had a stronger effect on metamorphic traits than low-dose rate radiation. Higher levels of strand breaks were detected after an acute dose in R. catesbeiana than after a chronic dose supporting a dose rate limit for protection of amphibians rather than a dose limit (paper IV).Based on current knowledge, frogs in the contaminated wetland are probably not exposed to radiation doses from 137Cs that are harmful for the population. However, variations in sensitivity between populations and species, and adaptive responses have been shown for amphibians exposed to other stressors. This supports further research on effects of chronic low-dose rates of ionizing radiation on amphibians.
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| 16. |
- Walker, Brian, et al.
(författare)
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Looming Global-Scale Failures and Missing Institutions
- 2009
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Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 1095-9203 .- 0036-8075. ; 325:5946, s. 1345-1346
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Navigating global changes requires a coevolving set of collaborative, global institutions.
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