His main research areas include understanding the responses and vulnerabilities of marine ecosystems and fisheries to global change, and examining trade-offs in managing and conserving living marine resources. His works cut across multiple disciplines, from oceanography to ecology, economics and social sciences, and range from local to global scales. William has published over 150 peer-reviewed publications, including papers in leading international journals. William is also actively involved in international and regional initiatives that bridge science and policy. For instance, he was a Lead Author in the Working Group II of the Fifth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC), a Coordinating Lead Author of the Intergovernmental Platform on Biodiversity and Ecosystem Services (IPBES) and Global Biodiversity Outlook. He serves as member of the editorial board of Fish and Fisheries, Fisheries Oceanography and Frontier in Marine Sciences, and as scientific advisors in a number of international and local organizations including BioDiscovery, IUCN and WWF Canada.