定义：microscopic algae, typically found in freshwater and marine systems, living in both the water column and sediment. They are unicellular species which exist individually, or in chains or groups.
定义：A landform consisting of loose rock particles such as sand, gravel, shingle, pebbles, cobble, or even shell fragments along the shoreline of a body of water.
定义：An organism that moves through the water column via movements of its fins, legs or appendages, via undulatory movements of the body or via jet propulsion; includes pelagic phases during reproduction (swarming at the surface)
定义：A group of species that exploit the same food resources, and/or use the same feeding or foraging methods. http://en.wikipedia.org/wiki/Guild_(ecology)
