This volume presents selected contributions to the 38th European Marine Biology Symposium, held in Aveiro, Portugal, in September 2003. Understanding the functioning of Marine Ecosystems is the first step to measure and predict the influence of humanity, and to find solutions for the enormous array of problems we face today. The book is organized according to the four sub-themes of the symposium and to issues commonly perceived as relevant by scientists concerned with the study, protection and management of Marine Biodiversity: patterns and processes, assessment, threats and management and conservation. The 32 papers that make up this book represent the current research and concerns about Marine Biodiversity in Europe, and will appeal to all those interested in understanding and preserving the marine ecosystems of the world's oceans.