Karachaliou, Eleana2025-09-172025-09-172025-08-182025-08-192025-09-17http://hdl.handle.net/1993/39385Maintaining healthy oceans and the services they provide relies on safeguarding marine biodiversity. Genetic diversity is the foundation of biodiversity, underlying adaptive potential and population persistence, ecosystem resilience and stability. Planning for future genetic diversity conservation will be multifaceted. My thesis aims to uncover both patterns and drivers of global genetic diversity in marine fishes and the population genetics of a single species, taking a simultaneously global and single species approach to conservation genetics in the marine environment. I initially used a synthesis methodology, taking advantage of the large amount of publicly available genetic data. My aim was to determine global patterns of genetic diversity for marine fishes and their drivers. I found that global patterns of genetic diversity seemingly follow a west to east direction along global coastlines. I also uncovered human-caused declines in genetic diversity but not population differentiation. I detected variation in genetic diversity and gene flow levels connected to oceanographic parameters. I also found that species richness is correlated with higher genetic diversity, more genetically similar populations and lower effective population size. I then focused on a single species, anadromous sea lamprey Petromyzon marinus. The aim of my study was to apply a conservation genetics approach to this widely distributed species. As part of my study, I uncovered sea lamprey population genetic structure, status, demographic and evolutionary history, and likelihood of future maladaptation. I identified distinct sea lamprey management units across the species’ native range. I identified locations at which sea lamprey are vulnerable, both currently and under future climate change scenarios. I reconstructed deep demographic history and timed the split between sea lamprey populations on the two Atlantic coasts. I also uncovered that in recent evolutionary time, sea lamprey have faced population declines connected to human activity. My research has extended understanding of genetic diversity across global marine fish species, sea lamprey genetic structure, evolutionary trajectory and vulnerability across their native range. I interpret my results from a conservation genetics point of view, aiming to inform efforts for biodiversity conservation and show the importance in accounting for both the detail and the greater picture.engbiodiversitygenetic diversityconservation genomicsmarine biology