This dissertation investigates the role of climate and ocean conditions on the marine survival of Atlantic salmon. The overall objective was to identify the relevant environmental variables controlling salmon marine survival, in order to establish predictive models of marine recruitment. These models are required to improve the management process of the Irish and European salmon resources. I first explored the levels of synchrony in the marine survival of European salmon, in order to assemble evidence on the spatial scale of the processes controlling survival. I demonstrate that these levels of synchrony are low and I conclude that large scale events are not directly exerting a control on the rates of salmon survival, perhaps indicating the presence of several intermediary processes. Using information from a scale analysis of a monitored Irish population, I then explore the hypothesis that marine survival is linked to marine growth. I present evidence that the level of marine recruitment of 1 SW salmon is linked to growth during the marine residency, and that decreasing growth over the last 30 years explains the observed decrease in salmon recruitment. Finally, I explore the role of several environmental variables on salmon marine survival, by constructing semi-parametric models (GAMs) of marine survival for wild and hatchery Irish populations. These models explain an important part of the inter-annual variability in survival and provide a capability to forecast survival. These models also help to identify the role of specific variables, more specifically the North Atlantic Oscillation, sea surface temperatures, and the abundance of zooplankton, to explain the variations in survival. I conclude that the changes in climate in the northeast Atlantic have affected the salmon via bottom-up effect, by affecting the abundance, distribution and phenology of key zooplankton species in the northern North Sea and southern Norwegian Sea.

This dissertation is the first critical analysis of patterns of species diversity in a deep-sea taxon (the Gastropoda) on a global scale. My analysis is based on 85 epibenthic sled samples collected from soft sediments in ten deep-sea regions of the Norwegian Sea and Atlantic Ocean. Over 21,000 gastropod individuals were sorted to species and their mode of larval development was documented. The basins from which the samples were taken represent a broad range of ecological circumstances that may affect species diversity and taxonomic composition. Bathymetric patterns of species diversity were shown to vary significantly among deep-sea basins. Unusually high or low values of diversity appear to be associated with environmental disturbance or rates of nutrient input. The most important and unexpected finding was that on a global scale there are latitudinal gradients in deep-sea species diversity similar to those in shallow-water and terrestrial environments. Gastropods show a clear and highly significant latitudinal decrease in diversity from the equator to 77$\sp\circ$N in the North Atlantic and a significant decrease from the equator to 37$\sp\circ$S in the South Atlantic. Depressed diversity at higher latitudes in the deep-sea, in part, may be related to seasonal nutrient loading and frequent physical disturbance from bottom currents. At lower latitudes, these same ecological factors may become less intense and variable. A multiple regression analysis showed that the North Atlantic local (sample) diversity is highly correlated with regional (basin) diversity suggesting that evolutionary-historical processes play a role in the development of deep-sea diversity through the mechanism of regional species enrichment. The percentage of species with planktotrophic development in the regional species pool was also correlated with local diversity. For the South Atlantic, the pattern of latitudinal diversity is less clear. On global scales, diversity gradients may be shaped by the interplay between the ecological potential and the history of evolutionary diversification at different latitudes. Underlying evolutionary processes that influence local diversity are difficult to recognize on a local scale, but may be revealed through large-scale patterns of species diversity. (Abstract shortened with permission of author.)