This project will use a long-term field study of littoral populations of two asterinid sea stars Astrina gibbosa and Asterina phylactica to assess the demographic and genetic consequences of a recent environmental disaster, the Sea Empress oil spill of 1996, and will examine the processes which have led to the current distribution and genetic diversity of these species. The 'Lusitanian' ranges of these echinoderms completely overlap, and stretch from the Atlantic to the eastern Mediterranean. The most intensively studied population, in West Angle Bay , Wales, was dramatically affected by the oil spill and has become the focus of conservation measures and demographic monitoring. This project will assess the genetic effects of the population bottlenecks induced by the oil spill on both species and examine the effects of ongoing demographic changes on population viability. By examining two species which, although congeners, have very different life history strategies (including in reproduction, dispersal and habitat specificity), a deeper understanding of the processes shaping diversity in populations of marine invertebrates will be gained which will also assist in the conservation of the 'type' population of A. phylactica, a recently discovered and scarce species nearly extirpated by the oil spill. The applicant will be trained in a wide variety of techniques in molecular ecology and conservation biology. Firstly, a range of molecular ecological methods will be employed with which the applicant is not currently familiar. These include isolation and characterization of micro satellite markers, population screening and data analysis (standard population genetics and Bayesian, likelihood-based approaches). Second, the applicant will become familiar with the use of such data in conservation management and the assessment of population viability. For the host, the applicant's previous knowledge of molecular biology applied to immunology will be beneficial, since we wish to apply molecular techniques to assess immunodiversity in endangered species, which are often immunocompromised due to inbreeding.