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.
An estuary is a partially enclosed body of water formed where fresh water from land meets and mixes with salt water from the ocean. Estuaries come in all shapes and sizes and can be called bays, lagoons, harbours, inlets, sounds, wetlands and swamps. Introduction. Estuaries are unique environments to which plants and animals have specially adapted. Transition from land to sea and fresh water to salt water. Estuaries are protected from ocean forces by reefs, barrier islands, headlands and deltas.