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.
Estuaries are partially enclosed bodies of water along coastlines where fresh water and salt water meet and mix. They act as a transition zone between oceans and continents. An estuary has a free connection with the ocean.Fresh water input from land sources (usually rivers) dilutes the estuary's salt content.stuaries are important for the health of the oceans. Estuaries can filter sediment and pollutants from the water before it flows into the oceans. Excess nutrients are removed in bordering salt marshes, resulting in cleaner water for people and marine organisms. Estuaries act as a buffer between the ocean and the land.