Between the seas and the continents lies a band of diverse ecosystems that are not just transition zones but have ecological characteristics of their own. Whereas physical factors such as salinity and temperature are much more variable near shore than in the sea itself, food conditions are so much better that the region is packed with life. Along the shore live thousands of adapted species that are not to be found in the open sea, on land, or in fresh water. A rocky shore, a sand beach, a sand beach, an intertidal mud flat, and a tidal estuary dominated by salt marshes are shown in this post illustrate four kinds of marine inshore ecosystems. The word ‘’estuary’’ (from Latin aestus, tide) refers to a semi enclosed body of water, such as a river mouth or coastal bay where the salinity is intermediate between the sea and fresh water, and where tidal action is an important physical regulator and energy subsidy.

Estuaries and inshore marine waters areamong the most naturally fertile in the world

       Estuaries and inshore marine waters are among the most naturally fertile in the world. Three major life forms of autographs are often intermixed in an estuary and play varying roles in maintaining a high gross production rate; these are (1) phytoplankton; (2) benthic micro flora – algae living in and on mud, sand, rocks or other hard surfaces, and bodies or shells of animals; and (3) macroflora – large attached plants – the seaweeds, submerged eel grasses, emergent marsh grasses, and , in the tropics, mangrove trees. An estuary is often an efficient nutrient trap that is partly physical (differences in salinities retard vertical but not horizontal mixing of water masses) and partly biological, as was illustrated by the example of the mussel population. As discussed in the next post this property enhances the estuary’s capacity to absorb nutrients in wastes provided organic matter has been reduced by secondary treatment estuaries peovide the ‘’nursery grounds’’ (that place for young stages to grow rapidly) for most coastal shellfish and fish that are harvested not only in the estuary but offshore as well.

       Organisms have evolved many adaptions to cope with tidal cycles, thereby enabling them to exploit the many advantages of living in an estuary. Some animals, such as fiddler crabs, have internal ‘’biological clocks’’ that help to time their feeding activities to the most favorable part of the tidal cycle. If such animals are experiment tally removed to a constant environment they continue to exhibit rhythmic activity synchronous with the tides. Estuaries have been traditionally the most used, but least appreciated, free sewers for man’s great coastal developments. As symptoms of overuse appear (the decline in seafood yield is often a first symptom) government becomes concerned with ‘’coastal management.’’ An economic approach to proper evaluation of estuaries is discussed in the next post.