The major zones in marine ecosystems are littoral, neritic, pelagic and benthic.
The littoral zone is the shoreline between land and the open sea. It is subjected to the physical violence of waves, tides and t o fluctuations, sometimes extreme of temperature, moisture and light intensity. Along rocky shores we find more sessile organisms(algae, barnacles, star fish) than in any other type of ecosystem. Along sandy shores organisms are adopted but burrowing in or adhering to sand (ghost, carbs, sand dollars, polycharts). Mud flats which occur in base, harbour algae on the surface and often phytosynthetic bacteria beneath the algae, along with the abundance of calms, worms, and crustacia . Coral reefs ,fringes of coral formed around the island by colonial coelenterates may also be regarded as littoral ecosystems. Because of the ir higher temperatures, depths of light penetration and richer in nutrient levels, coral reefs are amongst the most highly productive of all ecosystems.
The neritic zone is underlain by a continental shelf extending outward to its edge to a water depths of about 200 meters. This zone is relatively in rich in species and high in productivity owing to depth of light penetration and the presence of nutrients washed from the land. This richness and productivity decreases gradually towards the deeper water of the zone. Extensive algal communities of the jiant kelps as well as of smaller of uni and multi cello forms along with clams, snails, worms, and echinoderms dominate the bottom. Phytoplankton and Zooplankton are relatively abundant and supports some of the greatest fishing grounds in the world.
The pelagic zone is the open sea constituting of about 90% of the total ocean surface. Photosynthesis occurs in the surface pelagic region primarily by planktonic diatoms and dinoflagelates. Opepods and arrow worms are the major types of zooplankton along with active swimming forms such as shrimps, jelly fish and ctenophorous , this zone is low in nutrients and hence in primary and secondary productivity. The organisms in the pelagic zone below the level of light penetration are completely dependant on the rain of detritus from the upper region and are wholly heterotropic, carnivores copepods and other crustacia are abundant in the upper waters of this non photosynthetic zone. In deeper waters many animals have reduced vision, others including many fish are bioluminescant and some deep water fish have light producting organisms.
The benethic zone extense from the edge of continental shelf to the deepest ocean trenches. Organisms here are heterotropic many being anchored in the muddy ooze made of largely of siliceous and calcarious shells of fermanifera, snails, radiolarians and diatoms. Among these rooted animals are sea-lilies, sea-fans, sponges and brachiopods. Snails and the clams embeded in the mud while star fish, sea cucumbers and sea urchins move on its surface.