The Bryozoa consist of over 4,000 living species which form small sessile colonies displaying a wide range of form, including encrusting calcareous or gelatinous patches, long branching chains, apparently jumbled heaps, or bushy branching growths, some of which superficially resemble corals. As little research has been done on the ecology of this group, it is unknown whether any particular species is under threat of extinction, but it can be inferred that many species could be vulnerable to a variety of adverse factors, such as: pollution; increased turbidity, sedimentation, and siltation; changes in salinity and temperature; and the loss of substrate caused by dredging and kelp harvesting.