6.3. The biosfere like an ecosystme (II). Marine ecosystems

water_mapThe distribution of marine biodiversity varies widely throughout ocean basins. The abundance and diversity of most taxa tends to be highest near continental and island margins that are less than 2,000 meters deep.

These areas experience nutrient enrichment from upwelling processes and terrestrial runoff. Areas where significant upwelling occurs are often extraordinarily productive in tropical, temperate, and polar regions. Within major habitat types, species richness and endemism also vary enormously around the globe.

Species endemism tends to be less pronounced in marine ecosystems than in terrestrial or freshwater ecoregions, but several regional centers of endemism are recognized, including the southern coast of Australia, New Caledonia, Lord Howe and Norfolk Islands, the northern coast of South America, the Yellow and East China Seas, the Red Sea, the Mediterranean Sea, the Sea of Cortez, the Great Barrier Reef, and tropical Pacific Islands such as Hawaii, Marquesas, the Tuamotus and Societies, and Easter Island.

In general, marine ecoregions associated with isolated islands and enclosed seas tend to display higher levels of endemism.


Ocean habitats can first be broken down into 2 groups, the benthonic province (sea bottom) and the pelagic province, from the water column. Thus separating organisms into bottom dwellers and those that dwell in the water such as fish. Each of these areas can then be subdivided into different zones depending on their depth or in some cases the amount of light they receive.


  • The benthonic environment is divided by depth into the:
    Littoral zone                  Inter tidal zone
    Sublittoral zone,                 0 to 200m     (continental shelf)
    Bathyal zone,                 200 to 2000m    (shelf wall)
    Abyssal zone,              2000 to 6000m    (abyssal plains)
    and the Hadal zone.              >  6000m    (deep sea trenches)
  • The pelagic environment is divided into the:Neritic Zone       (water over the continental shelf, no sub divisions)
    and the
    Oceanic Zone.  (water beyond the shelf break, deep ocean water)

because of the range in depths, the oceanic zone is subdivided further into the:

  • Epipelagic                 0     to  200m
  • Mesopelagic         200     to  1000m
  • Bathypalagic       1000m  to  2000m
  • Abyssalpelagic   2000m   to  6000m
  • Hadelpelagic                    >  6000m

The oceanic zone can also be divided into different zones based upon depth of light penetration.

  • The photic zone is the depth where light is sufficient for photosynthesis during the day.    ( 0 to 100m)
  • The dysphotic zone (twilight zone) is where illumination is too weak for photosynthesis.   (100 to 450m approx)
  • The aphotic zone receives no light from the surface because it is all absorbed by the water above. ( > 450m)

Inter Tidal Zone

intertidalzonesregThe intertidal area (also called the littoral zone) is where the land and sea meet, between the high and low tide zones. This complex marine ecosystem is found along coastlines worldwide. It is rich in nutrients and oxygen and is home to a variety of organisms.


  • sandy beaches
  • rocks
  • estuaries
  • mangrove swamps
  • coral reefs

Some of these regions are very productive. Many of their inhabitants have adaptations that enable them to survive periodic exposure to the air and wave action.

Spray zone

Tidal rush over mussels and goose barnacles in high tide spray zone.Spray Zone : Also called the Upper Littoral, the Supralittoral Fringe, the Littorina Zone (because it is often dominated by Littorina species) the Splash Zone,upper Balanoid and the upper Barnacle Belt. This area is dry much of the time, but is sprayed with salt water during high tides. It is only flooded during storms and extremely high tides. Organisms in this sparse habitat include barnacles, isopods, lichens, lice, limpets, periwinkles, and whelks. Very little vegetation grows in this area.

Sublittoral Zone

sublittoralThis zone is in the lower shore and is permanently under water. The highest reaches of the sublittoral zone are defined as the point where the low water spring tides fall, or where the water level falls to on the lowesttide of the month. Life here is abundant and diverse because it is a proper marine habitat.

Other than wave action, this is a very stable environment, and competition is fierce as a result. In order to thrive, organisms must be ideally suited to this zone. The optimum living conditions for species are subtly different and through fierce competition these differences make or break an organisms success.

One other problem for life in the lower zones is changes in light intensity. When plants are covered by water, the light intensity is reduced. Plants here develop special pigments to absorb wavelengths of light that would be reflected by their land relatives.

Perwinkles, kelp fish, chitons, sea urchins, sponges as well as corals live in the sublittoral zone. There is a great abundance of plant and animal life in this zone because the sunlight can reach the bottom in most areas, and there is a large amount of nutrients.

Bathyal zone

Extending down from the edge of the continental shelf to the depth at which the water temperature is 4° C (39° F). Both of these limits are variable, but the bathyal zone is generally described as lying between 200 and 2,000 m (660 and 6,600 feet) below the surface.

Photosynthesis does not occur in bathyal waters as a rule, the zone being characteristically dark except in the clear, virtually lifeless waters of the tropics, where small amounts of sunlight can penetrate as deeply as 600 m (2,000 feet).

It is known as the Twilight zone because of this feature. Because of the lack of light, some species do not have eyes, however those possessing eyes in this zone include the viperfish and the frill shark. Many forms of nekton live in the bathyal zone, such as squid, large whales and octopuses, but this zone is difficult for fish to live in. Sponges, brachiopods, sea stars, and echinoids are also common in the bathyal zone. The fish in this zone have become very energy efficient, since it is especially hard to find nutrients. Many have slow metabolic rates to conserve energy. The fish here have weak muscles, soft skin and slimy bodies. Animals in the bathyal zone are not threatened by predators that can see them, so they do not have powerful muscles. There are few plants because of lack of sunlight, as they need sunlight to produce their food through photosynthesis. The bathyal zone holds some of the world’s largest whales.

Bathyal zones (both temperate and tropical) have greater biodiversity than coral reefs, according to a 1995 study by the Natural History Museum in London. Maximum biodiversity occurs between 1,000 m/3,280 ft and 3,000 m/9,800 ft

Abyssal zone

Dark ocean region 2,000–6,000 m/6,500–19,500 ft deep; temperature 4°C/39°F. Three-quarters of the area of the deep-ocean floor lies in the abyssal zone, which is too far from the surface for photosynthesis to take place. Some fish and crustaceans living there are blind or have their own light sources. The region above is the bathyal zone; the region below, the hadal zone.

Abyssal hills are low hills that occur on the deep ocean floor. Large stretches of the Atlantic and Indian Ocean floors and more than three-quarters of the Pacific floor are covered by such hills, which rise no higher than about 1,000 meters (3,000 ft). They tend to occur as a series of parallel ridges 1–10 km across, and represent the roughed topography of mid-ocean ridgessubdued by burial beneath thick layers of sediment.

Abyssal plains are very flat areas of the deep ocean floor which may extend for more than 1,000 km (600 miles). They typically have slopes with gradients of less than 1 in 1000 and are found off continental margins where sediments can enter the deep sea unobstructed. They are common in the Atlantic and Indian Oceans, but rare in the Pacific, where deep trenches and island arcs serve as barriers to the transport of sediment from the continents and marine snow.

Its permanent inhabitants (for example, the black swallower, tripod fish, deep-sea anglerfish and the giant squid) are able to withstand the immense pressures of the ocean depths, up to 76 megapascals (11,000 psi).Many abyssal creatures have underslung jaws to sift through the sand to catch food. The deep trenches or fissures that plunge down thousands of meters (feet) below the ocean floor (for example, the midoceanic trenches such as the Mariana Trench in the Pacific) are almost unexplored. Only the bathyscaphe Trieste, the remote control submarine Kaiko and the Nereushave been able to descend to these depths. These regions are also characterized by continuous cold and lack of nutrients. The abyssal zone has temperatures around 2 to 3 degrees Celsius through the large majority of its mass.

Hadal zone

The Hadal zone is made up of the very deepest parts of the ocean, causing it to be totally dark, and constantly cold, with a very intense pressure.  You may think that the Hadal zone is lifeless, due to the conditions, but it was proven that there was life when Jaques Piccard and Don Walsh reached the Marianas Trench in 1960. This trench is the deepest trench with a depth of 10,900 m, yet Piccard and Walsh sighted shrimp and flounder-like fish. (see side bar)

The deep-sea creatures have adapted to the darkness by reducing their use of eyesight.  The fish do have eyes, though, and they are usually enormous, which indicates that there are enough flashes of bioluminescent light to keep their eyes from totally deteriorating.  The animals that live near the bottom have a reddish or pinkish coloration, possibly because the red light waves are absorbed in the topmost layers of the ocean.  So the creatures don’t look any different than the black ones with no red light to be reflected!

Creatures removed from this zone will die in the lower-pressure areas above. The most common creatures include jellyfish, viperfish, tube worms, sea cucumbers, and the deep sea angler fish. The hadal zone can reach far below 6,000 meters (20,000 feet) deep; the deepest known is at 10,911 meters (35,814 ft). At such depths, e.g., 36k ft. below sea level, the pressure in the Hadal zone will reach over 1,100 standard atmospheres (110 MPa; 16,000 psi).

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