Any species which fall into the categories Vulnerable, Endangered or Critically Endangered are considered to be at risk of extinction. Of the nearly 60,000 species assessed so far, this equates to a staggering 20,222 species, from the majestic tiger to the enormous giant clam.
(Photo: Elkhorn Slough NERRS site). An estuary is a partially enclosed body of water, and its surrounding coastal habitats, where saltwater from the ocean mixes with fresh water from rivers or streams. In fresh water the concentration of salts, or salinity, is nearly zero.The salinity of water in the ocean averages about 35 parts per thousand (ppt).ruly, no two estuaries are the same. Yet they are typically classified based on two characteristics: their geology and how saltwater and fresh water mix in them. However, not all estuaries contain brackish waters. There are a small number of ecosystems classified as freshwater estuaries.
Economics of Estuaries. Estuaries, the transition zones where rivers meet the sea, provide the focal point around which coastal communities grow. The local bay or sound nurtures a high quality of life and maintains the health and traditions of our communities. An estuary is also a tremendous economic resource which provides jobs to coastal communities. The U.S. coasts generate more than 28 million jobs. These jobs come from commercial and recreational fishing, which alone employ 1.5 million people and contribute $111 billion to the nation's economy.