Interactions between algae and nematodes: habitat provision and detrital driven processes

The overall aim of this thesis was to investigate marine nematode-algae interactions using a twofold approach: habitat provision by algae and the role of algal detritus in structuring nematode assemblages. Nematode assemblages living in algae on the south and east coast of Korea were compared using a hierarchical sampling design with those from the south coast of the British Isles in order to investigate nematode diversity and functional traits at different spatial scales (patch, shore, region and biogeographic realm). The cosmopolitan genus Corallina and Sargassum muticum, a native of Korea and an invader in the British Isles were investigated as algal habitat providers for nematodes. The species composition and functional traits of nematode assemblage in both species of macroalgae were significantly different at all spatial scales. The alpha, beta and gamma biodiversity of nematodes in each macroalgae were also measured at all spatial scales. The alpha, beta and gamma diversity of nematodes across four spatial scales in two different habitats are an alpha dominant relationship indicating random colonization and high species turnover at small scales. Nematode species composition and diversity on the wrack-loaded sandy shore were explored using field experiments. Mesh bags filled with three different types of macroalgae (brown, green and red) were used to test the effects of diversity of algal detritus on nematode assemblages involved in decomposition processes. The detrital treatments consisted of 10 combinations of macroalgae (monoculture, two and three species treatments), containing different proportions of algal material in order to test the impacts of detrital diversity on nematode assemblages. The density, diversity and species composition of nematodes in combinations of algae were higher than with single types of macroalgae. This indicated that the combination of two algae mixtures offered more favourable environments than the single species bags. Overall this thesis demonstrated the high diversity of nematodes inhabiting seaweeds and the role of detrital composition in driving nematode assemblages.