Greeve, Youk2025-03-212025-03-212025-03-21https://hdl.handle.net/2077/85234Bivalves are common animals in coastal ecosystems that alter energy flows and the characteristics of their surroundings, which contributes to ecosystem functions and services. Most bivalve species are suspension-feeders, clearing the water from organic particles and phytoplankton and thereby lowering water turbidity and exert top-down control on phytoplankton communities. Faeces are deposited on the sea floor, coupling the pelagic and benthic ecosystem components and enhancing the long-term storage and remineralization of nutrients which is important for mitigating negative effects of eutrophication. The infaunal species’ burrowing behaviour reworks the sediment which increases the flux of oxygen and other solutes between sediments and water, while epifaunal species create complex reef structures that can be utilized by other species promoting biodiversity. Globally, much of the epifaunal bivalve reefs have been greatly diminished, resulting in a loss of function and services, while invasive species have been introduced in many areas causing shifts in ecosystems. The aim of this thesis was to describe the coastal bivalve communities on the Skagerrak coast in terms of species composition, distribution, abundances and biomass. This was done in order to identify key species, functional groups and habitat types that contribute to ecosystem functions and services. Recently collected data was contrasted against older records to access temporal changes in the structure of the bivalve populations. The possible underlying mechanisms to these changed and the potential consequences for ecosystem functioning was also explored. The results showed that populations are shaped by a combination of environmental factors, species habitat preference and the availability of those habitats. While epifaunal species are overall more ecologically relevant than infaunal species, the later can be locally more impactful. Since the invasive Pacific oyster arrived it has become the dominant species in terms of biomass which has, together with a general decline of infaunal bivalves, likely caused shifts in bivalve ecosystem functions and services. The methods and analyses described provide an important current baseline for the bivalve populations in this area and to compare further changes to in the future.engmussels, oysters, species distribution models, niche, invasive species, predation, filamentous algae, ecosystem functions, ecosystem servicestext