This book discusses ecological perspectives, biodiversity and management of the Baltic and Black Seas. Chapter One reviews the role of the Russian section of the Gulf of Finland and its basin in the ecosystems of the Baltic Sea. Chapter Two studies spatio-temporal dynamics of ichthyoplankton biodiversity in different biotopes of the Baltic Sea. Chapter Three explores the abnormalities in the amphids of free-living nematodes in the Black Sea. Chapter Four discusses the role of defense systems to the adaptation to ecological conditions in the Black Sea ecosystem.