This session will present currently important contrasts between ecological processes in marine and inland seas (Great Lakes) and introduce a number of key concepts in aquatic ecology to a more general ecological audience. The theme is comparison between ecological processes in marine and Great Lakes ecosystems. The Laurentian Great Lakes are inland seas subject to meso-oceanic physical factors such as strong wind-driven currents, earth-spin, and waves large enough to sink large ships. These physical factors have prevented establishment in Great Lakes’ main basins of many organisms found in smaller lakes, such as vascular macrophytes and littoral zone fishes. Unlike the African Great Lakes and Lake Baikal, which are relatively old, and support diverse and endemic species, the Laurentian Great Lakes are only ~10,000 years old. Great Lakes native biota are primarily species that survived Pleistocene glaciation in river refugia and marine glacial relict species. Physical factors may promote success of freshwater-tolerant, marine coastal invasive species (e.g., sea lamprey, alewife, dreissenid mussels, and Cladophora). Comparison of diverse marine ecosystems and the comparatively depauperate Great Lakes ecosystems will provide insights into critical ecological “services” of marine systems that are lacking, or are less efficient in the Great Lakes. However, interaction between ecologists working in the Great Lakes and coastal marine environments is not common. The purpose of the session is to encourage interaction and communication between marine and Great Lakes ecologists working with complementary ideas. The session will explore some important and currently relevant and emerging themes, including invasive species, effects of invasive species on nutrient cycling, ecological change in upper trophic levels, ecological stoichiometry, the ecological role of aquatic viruses in marine and freshwater ecosystems, the peculiar ecology of sea mounts, physical processes shaping Great Lakes ecology, and population ecology of marine and Great Lakes fishes.