The edible cockle, Cerastoderma eduleis an ecological and commercially importantbivalve that occupiesmuddy and sandy tidal flats and estuaries in the temperate regions along the North East Atlantic coastlines and adjoining seas. By forming dense aggregations over large areas, C. edulesupports a highlyvaluable shellfish fishing industry and is vital to the survival of other marine organisms that rely on its ecological functioning. This thesis has looked at the spatial and temporal variability ofsome of thebiological and environmental processes that affectC. eduleat different lifestages. It has used two sitesin North Wales, the Dee estuary and Traeth Melynog for providing samples for the experiments. Adult cockles collected in the spring 2015were spawned in the laboratory. Their larvae were rearedat three temperatures:10, 15 and 20°C and fed 2different food concentrations. After 21days, larvae from Traeth Melynog were larger at 20°C than any other temperature and suffered less mortalitycompared to those from the Dee estuary. Noeffect of feedwas observed between temperatures or site.Each fishery was assessed for the parasite and pathogen community of which C. eduleare known to host. C. edulewere collectedbetween the autumn, 2014 to the end of summer, 2015 and divided into two separate halves. The first was processed for histopathology screening. Seventeen differentparasite groups were identifiedacross both sites, and six of theseare known to cause significant harm at the individual or population levelto C. edule. Overall,a difference in community structure was observed between the sites and the prevalence of the different groups was highly variable over the seasons. The second underwent biochemical analysis to measure the total energetic content using the Cellular Allocation Methodology(CEA). Cockles from Traeth Melynog were found to have more energy available to them but the energy consumedwas the same between sites. High variability in the total lipid content and total carbohydrate content was observed across each season at both sites. Results from the three experiments arediscussed in relation to the main objective of this thesis. The long-term management of cockle fisheries in North Wales and across the UK relieson the understanding of the complex processes that take place at all temporal and spatial scales.