Marine ecosystems are among the Earth’s aquatic ecosystems. They include: oceans, estuaries and lagoons, mangroves and coral reefs, the deep sea and the sea floor. These are the gigantic reservoirs of water covering approximately 71% of the Earth’s surface (an area of some 361 million square kilometers).
These ecosystems are different from freshwater ecosystem mainly because of its salty water. The salt concentration in an open sea is usually 3.5% (35 parts per thousand (ppt)). Dominant ions are sodium and chloride. Average temperature of Marine ecosystem is 2-3 degree centigrade, devoid of light.
It includes phytoplanktons (diatoms, dinoflagillates), large seaweeds (mainly algae like chlorophyceae, phaeophyceae and rhodophyceae; angiosperms like Ruppia, Zostera, posidonia), and mangrove vegetation (like Rhizophora, Carapa etc.)
(a) Primary consumers:
These are herbivores and feed directly on producers (Crustaceans, Mollusks, fish etc.)
(b) Secondary consumers:
These are carnivorous fishes (Herring, Sahd and Mackerel)
(c) Tertiary consumers:
These are top carnivorous fishes (Cod, Haddock, etc.)
These are micro-organisms like bacteria, fungi.
High Na, Ca, Mg and K salt concentration, variable dissolved oxygen content, light and temperature make a unique physiochemical conditions in marine water.