Aquatic ecosystem - Oceans

MARINE ECOSYSTEMS ((OCEANS)
Oceans cover more than two third of the earth's surface. Ocean environment is characterized by a high concentration of salts and minerals. It supplies a large variety of sea products and drugs. Among others, it is a reservoir of magnesium, iron, phosphorus and natural gas.

STRUCTURE AND FUNCTION OF OCEAN ECOSYSTEMS

Abiotic components
Ex: Temperature, Light, NaCl, K, Ca, and Mg salts, Alkalinity

Biotic components

1.  Producers: Ex: Phytoplankton (diatoms, unicellular algae, etc) and marine plants (sea weeds, chlorophyceal, Phaeophycaea)
2. Consumers: They are heterotrophic macroconsumers and depend on producers for their food.
1. Primary consumers (herbivores) feed on producers. Ex: Crustaceans, molluscs, fish
2. Secondary consumers (Carnivores) feed on herbivores. Ex: Herring, sahd, mackerel, etc
3. Tertiary consumers are the top consumers. They feed on small fishes. Ex: Cod, Haddock, etc.
3. Decomposers: They decompose dead organic matter. Ex: Bacteria and some fungi. 

MARINE ECOSYSTEM

• Marine ecosystem is the largest of all ecosystems in the world
• It is the most stable ecosystem
• Marine ecosystem has more variations than the land ecosystems
• Characteristics of the marine ecosystem are:
• Relatively constant salt content of 3 to 3.7%
• Surface waters have more sunlight which is responsible for photosynthesis of phytoplanktons, algae and aquatic plants
• The deep layers of marine ecosystem are totally dark
• The average depth of the ocean is 4 km
• The ocean floor is made up of shelves, plains and mountain ranges
• Temperature varies from 2 C at the bottom to 30 C at the top surface
• Pressure increases with depth
• The ocean contains lesser species than on land. But they have more diversity of species
• Only organisms that can withstand high osmotic potential of water live in marine ecosystems
• Marine algae supply much of the world's oxygen supply.
• Evaporation of seawater brings rain on land
• The following physical factors control life forms in the ocean
• Waves
• Tides
• Currents
• Salinity
• Temperature
• Pressure
• Light intensity

ZONES OF THE OCEAN
Oceans have five zones with great species diversity:

Intertidal or littoral zone:

• This is the shoreline between land and the open sea
• Mass movement of water in this zone is caused by the gravitational effects of the sun and the moon. This zone is affected by waves and tides
• Habitat of this zone may consist of mud, sand or shingle
• This zone has plenty of light, nutrients and oxygen. However, it is the most stressed environment in the ecosystem due to fluctuations in temperature, light intensity and moisture
• Sometimes, the zone is submerged while at other times it is exposed as waves and tides keep coming in and out.
• Due to the above conditions, communities inhabiting this zone keep changing
• At the bottom of this zone, many invertebrates, fishes and sea weed can be found

Neretic zone:

•     This zone extends from the littoral zone to a depth of 200 m.
•     This zone consists of 7.5% of the total ocean area
•     Species richness and productivity are relatively high in this zone
•     Species richness and productivity decrease gradually towards the deep

Pelagic zone:

• This zone mainly consists of the open ocean
• This zone is generally cold
• There is thermal stratification with constant mixing of warm and cold ocean currents
• This zone occupies 92% of the total area of the total area of the marine environment and its
• Net Primary Productivity (NPP) varies from 2 to 400 g/m2
• This zone consists of less mineral nutrients
• Flora in this zone consists of surface sea weeds
• Fauna in this zone includes many species of fish and some mammals such as whales and dolphins

Benthic zone:

• This is the zone with homogenous and stable physico-chemical conditions of a marine ecosystem
• Bottom of this zone consists sand, silt and dead organisms
• Temperature of this zone is very less and it decreases as depth increases. Temperature is less than 4 C
• High pressure is exerted in this zone due to weight of water above it.
• Light cannot penetrate into deep waters
• Flora present is primarily sea weed and fauna includes all sorts of bacteria, fungi, sponges, sea anemones, worms, sea sters and fishes

Abyssal zone:

•     This zone includes the deepest parts of the marine ecosystem
•     The temperature in this zone is about 3 C
•     The water in this zone has high pressure and high oxygen content
•     This zone consists less nutrients as compared to other zones
•     It supports many species of invertebrates and fishes
•     Mid-ocean ridges are found in the abyssal zone along the ocean floor