OceanThe open ocean is the most extensive biome on earth.

Ocean

• The open oceans or pelagic ecosystems are the areas away from the coastal boundaries and above the seabed. It encompasses the entire water column of the seas and the oceans and lies beyond the edge of the continental shelf. It extends from the tropics to the polar regions and from the sea surface to the abyssal depths. It is a highly heterogeneous and dynamic habitat.

Geography

• The world ocean covers over 360 million km2

of earth’s surface and consists of one continuous, interconnected mass of water. This water is spread among three major ocean basins:

Pacific AtlanticIndian

• Marine scientists divide the ocean environment into zones. Marine Zones are areas with uniform physical conditions. Common classifications are based on physical factors such as depth, light, temperature, salinity, etc. The most basic zonation is based on substrate: exclusively water environment (pelagic) and bottom interface (benthic).

Classification of the Marine Environment Classification of the Marine

• The pelagic zone is divided by depth into: nerithic zone, which includes the nearshore areas over the continental shelves; and the oceanic zone,the areas seaward of the continental shelves. The oceanic zone is further divided into epipelagic zone (same as photic zone), mesopelagic, bathypelagic, and abyssopelagic zones. Abyssopelagic zone is water in the deep ocean trenches. The last three zones are all at aphotic depths.

• * Supralittoral - bottom substrate above high tides (not part of ocean).* Littoral - bottom substrate within the intertidal zone.* Sublittoral - bottom substrate below the lowest tides.

The shallowest benthic environments (below the neritic zone) are:

• * the Bathyal zone (ocean bottom down to the abyssal plain or the average depth of the ocean floor), * the Abyssal zone (from 4,000 - 6,000 m depths), and * the Hadal zone representing the deepest ocean bottom in the deepest trenches.

Beyond the continental shelf break are:

• Physical factors affecting Marine LifeAny factor of the physical environment that affects the survival of marine organisms are physical factors. These physical factors form barriers between various communities of marine organisms. The most important of these are:

• Light the primary importance of light is photosynthesis.

– The depth of penetration of light will determine the birth of a food chain sequence.

Most marine organisms live in the well-lighted neritic zone and in the epipelagic zone where food is abundant.

Some deep water fish use light for body orientation (even dim light), feeding, and predator avoidance.

Some marine organisms produce their own light by biochemical reaction, known as bioluminescence. Organisms typically living at depths within the aphotic zone, (or those that are active at night) such as squids, some fish and shrimps, are bioluminescent. They use light to see, to communicate, and to facilitate predation.

• Temperature - the metabolic rate of organisms increases

with the temperature of their bodies. Temperature range in the oceans is -50 to

40 C, except around hydrothermal vents where temperatures can be as high as 110 C. So in general, marine organisms live within a much narrower temperature range than land organisms.

• Dissolved Nutrients - Nutrients are chemical substances that

play vital role in the growth and general functioning of an organisms.

In the oceans, nutrients in short supply are nitrogen (N) and phosphorus (P).

• Salinity - marine salinity varies from 6 - 40 ppt. This large range is controlled by evaporation rates, sea ice formation, and freshwater supply rates. The greatest impact of salinity variation is at the ocean surface, whereas deeper ocean salinity (below the halocline), is far less variable. Salinity affects the tissues of organisms thorough osmosis.

• Most marine organisms are isotonic and no special salinity problems are imposed on them. But marine fish (bony fish) is hypotonic, that is, their body fluids are less salty than seawater. Hence, they are constantly losing water and are threatened by dehydration.

• Dissolved gases - gases dissolve more in cold water than in warm water. The two most important gases to marine organisms are: O2, and CO2. O2 is essential for respiration and CO2 for photosynthesis. O2 is less soluble is seawater and tends to be in abundance only in surface waters. Why? CO2 is more soluble in seawater and its concentration increases with depth. Why?

• PlanktonsIn the biosphere, nearly all living organisms use converted solar energy as the primary fuel to facilitate their daily activities.

• In the oceans, the organisms that capture solar energy and bind it into usable energy for their own use as well for the use of other organisms are known as phytoplanktons and seaweed.

• Planktons represent a community of organisms associated solely on their mode of locomotion. All planktons drift or swim very weakly, moving around with the currents or waves. Many can move vertically through the water column.

• In general, planktons live in the euphotic zone, in the upper layers of the open ocean down to the compensation depth. This is the depth to which 1% of surface light penetrates and photosynthetic organisms produce just enough carbohydrate to serve all the organisms' needs (zero net productivity). Although the compensation depth is variable, it averages about 150 m from the ocean surface.

• Planktons are generally diverse, ranging from those with soft, gelatinous bodies with little or no hard parts, to those encrusted in hard parts. The common planktons are drifting jellyfish, arrowworms, single-celled organisms, some crustaceans, a few marine mollusks, some algae, etc. Hence both animals (zooplanktons) and plants are part of the plankton community.

• There are, at least, eight major types of phytoplanktons (the plant variety) responsible for the nearly all the oceans primary productivity. These phytoplanktons are mostly single-celled, microscopic organisms that include diatoms, dinoflagellates, cocclithophores, silicoflagellates, and extremely very minute varieties called nannoplanktons and picoplanktons.

• PhotosynthesisPhotosynthesis is the process used by primary producers to manufacture their own food in the presence of light. These organisms possess a green dye, called chlorophyll, which is the molecule that traps sunlight and converts it to chemical energy in chemical bonds of substances called carbohydrates. When these bonds are broken, the energy is released and used in a variety of ways by organisms.

• Carbohydrates are assembled from small, simple, low-energy molecules such as water and CO2, to produce large, high-energy molecules (sugar) and oxygen.

• 6CO2 + 6H2O --> C6H12O6 + 6O2

• Chemosynthesis This is another energy binding process performed by organisms that do not use light to harness energy for living organisms. Instead, because these organisms live in the aphotic zone, they capture energy from breaking down chemical bonds of simple molecules (such as hydrogen sulfide), and use the energy obtained to synthesize carbohydrates from carbon dioxide and water. Chemosynthesis is estimated to contribute 2% to 8% of the ocean's primary productivity.

StructureThe oceans can be divided into

several vertical and horizontal zones.

Structure

• Litoral zone- the shallow shoreline under the influence of the rise and fall of the tides

• Neritic zone- extends from the coast to the margin of the continental shelf

• Oceanic zone- beyond the continental shelf• Epipelagic zone- is the surface layer of the

ocean that extends to a depth of 200m• Mesopelagic zone- extends from 200m to

1000m

Structure

• Bathypelagic zone- extends from 1000 to 4000m

• Abyssal zone- the layer from 4000to 6000m• Hadal zone- the deepest part of the ocean

Structure

Ocean Light Zone

• 1. Sunlit Zone: This is the top layer, nearest the surface. It is also called the euphotic zone. Here there is enough light penetrating the water to support photosynthesis.

2. Twilight Zone: Only a small amount of light can penetrate the water at this depth. As the water becomes deeper, the pressure increase, too. Plants do not grow here. Only animals that have adapted to little light survive.

• 3. Midnight Zone: Ninety percent of the ocean is in the midnight zone. It is entirely dark—there is no light. The water pressure is extreme. The temperature is near freezing.

Ocean Light Zone

Human ImpactHumans have a lot of 'waste' that is often disposed of in the ocean - trash, sewage, oil, chemicals, heat, and even 'noise' to

name a few.

Human Impact

• Over fishing• Climate change• Oil spills• Noise pollution• Habitat destruction• Introduction of alien species• Sewage and trash