定义：A habitat that is in or on a body of water containing low concentrations of dissolved salts and other total dissolved solids (<0.5 grams dissolved salts per litre).
定义：This organism produces this material or substance, either during its life or after death. A produces B if some process that occurs in A has output B.
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)
