<P> Classes of organisms found in marine ecosystems include brown algae, dinoflagellates, corals, cephalopods, echinoderms, and sharks . Fishes caught in marine ecosystems are the biggest source of commercial foods obtained from wild populations . </P> <P> Environmental problems concerning marine ecosystems include unsustainable exploitation of marine resources (for example overfishing of certain species), marine pollution, climate change, and building on coastal areas . </P> <P> Freshwater ecosystems cover 0.78% of the Earth's surface and inhabit 0.009% of its total water . They generate nearly 3% of its net primary production . Freshwater ecosystems contain 41% of the world's known fish species . </P> <P> There are three basic types of freshwater ecosystems: </P>

List the abiotic factors that are used to classify aquatic ecosystems