Introduction

The ocean ecosystem is the largest of all the ecosystems in the world and is located in the largest surface area of the world. The total volume of all oceans is about 15 times that of land. There are a total of five oceans on this planet. About 70% of the earth’s surface is covered by oceans and these oceans are extremely large and deep. The temperature and salinity of ocean water vary based on depth. The biodiversity of these oceans is very high, as it is home to millions of aquatic plants and animals. These species make up the ocean food chain. The ocean food chain is discussed below (2) & (3).

Definition of the food chain in the ocean

In the ocean ecosystem, food energy is transferred at a declining rate from the lowest trophic level (producer) to the highest trophic level (decomposer) among the various food and consumer groups. This flow is called the food chain of the ocean. Ocean food chain is a periodic process by which the food energy is transported from microscopic plants (phytoplankton) to large aquatic animals (big fish) in the ocean ecosystem. The nature of the ocean food chain is very complex. The combination of many food chains with the environment can be seen here (1).

Classification of ocean organisms

The food chain of the ocean is formed with different weeds, different creatures, etc. located in the ocean. These living organisms are divided into three parts: plankton, nekton, and benthos. These living organisms survive on each other and thus control the ocean food chain. Some of the characteristics and locations of these ocean organisms are described below (2) & (4).

1. Plankton

Planktons are tiny creatures that float on the surface of ocean water. Their mobility is determined by the direction of ocean currents. These are of three types according to shape (4) & (5).

• Nano plankton

Their diameter is less than 0.06 mm. Nano plankton is mainly phytoplankton. Bacteria such as diatoms, unicellular algae, cocolithopthores, etc., and several types of protozoa belong to this class.

• Micro plankton

They range in diameter from 0.06 mm to 3 mm. Diatoms, dinoflagellates, etc. belong to this category.

• Macro plankton

Their diameter is more than 3 mm. Mysids, slaps, jellyfish, etc. belong to this category.

2. Nekton

This layer is made up of Mollusca, fish, turtles, seabirds, various mammals, etc. Among the fishes, herring, sardines, anchovies, etc. are particularly noteworthy. They mainly consume plankton as food. These foods are also used as human food. Some species of fish live together in groups. Seasonal migration can be observed in some species. High-altitude fish lay their eggs in the open sea but do not try to maintain them. On the other hand, low-altitude fish lay their eggs under the sea and maintain the eggs. Some seabirds are good at swimming and live on the surface of the ocean. They feed on fish and other creatures. Among the mammals, seals, whales, dolphins, etc. are particularly noteworthy. They eat fish, turtles, etc. (5).

3. Benthos

They live at the bottom of the ocean. Organisms such as limpets, corals, crabs, shrimps, flatfish, etc. are members of this class. Some of these animals live by digging holes in the deep ocean (5).

Structure of the ocean food chain

Like the food chain structure of each ecosystem, the food chain of the ocean ecosystem has a specific structure. The ocean food chain also has several trophic levels. These are-

1. Producer

The first food layer of the ocean food chain is made up of autotrophic organisms. This food layer is called the producer level. And the autotrophic organisms are called producers. The phytoplankton is the main producer of the ocean food chain. These phytoplankton float on the ocean surface. They usually range in diameter from 0.06 mm to 3 mm. Sometimes the diameter of the phytoplankton is more than 3 mm.

Also, some types of algae, seaweed, unicellular plants, bacteria, etc. are the producers of the ocean food chain. These ocean producers can produce their own food. They make food in the process of photosynthesis with the help of sunlight. They convert solar energy into chemical energy while making food with the help of sunlight. This phytoplankton after using the generated food energy for their own work, transfers the remaining energy to the next level (2) & (5).

2. Primary consumer

Animals that are directly dependent on producers for food are the primary consumers. They cannot make their own food. They complete their physiological process by absorbing the food energy that producers produce. Zooplankton, small fish, crustaceans, etc. are the primary consumers of the ocean food chain.

The zooplankton is an aquatic animal that floats on the surface of the ocean. They feed on various phytoplankton, unicellular plants, algae, etc. floating on the sea surface (2) & (4).

3. Secondary consumer

Some animals present in an ecosystem that takes primary consumers as food are called secondary consumers. Some animals in this food chain use primary consumers as food to store energy for their own bodies. All of these animals are called secondary consumers in the ocean food chain. These animals include fish, corals, penguins, whales, and some other species. They survive by eating floating zooplankton, small fish, etc. (3) & (5).

4. Tertiary consumer

Animals that survive by feeding on primary and secondary consumers as food are called tertiary consumers. The larger fish such as tuna, barracuda and groupers, seals and sea lions, jellyfish, dolphins, sharks, killer whales, etc. are the tertiary consumers of the ocean food chain. They survive by eating primary consumers (zooplankton) and secondary consumers (fish, corals, penguins, etc.).

Thus in an ocean food chain, food flows from the producer level to the tertiary consumer level in a circular way. On the other hand, there are some organisms at the tertiary consumer level, which are known as apex predators. Tiger sharks, killer whales, etc. are the apex predators of the ocean food chain (4) & (5).

5. Decomposer

The primary decomposer in the ocean food chain is bacteria. Fungi, ocean worms, echinoderms, mollusks, echinoderms, etc. are the other decomposers of the ocean ecosystem. All these fungi and bacteria cause the decay of the producers and consumers of the ocean ecosystem (1).

Importance of the food chain in the ocean

• Ocean food chains are an important source of food. This food chain is much larger than the food chain of all ecosystems, as millions of aquatic species are found here. All these organisms survive by eating each other. So this food chain is a very important source of food.
• Organisms cannot directly absorb gaseous nitrogen in the atmosphere. Plants take up nitrogen only when it is converted to ammonium or nitrate. This process of conversion of gaseous nitrogen to ammonium or nitrate is called nitrogen fixation. There are some bacteria in the ocean that participate in this nitrogen fixation and play an important role in the environment.
• If this is destroyed, there will be a crisis for the survival of the ocean ecosystem. Even the ecosystem will be ruined forever.
• The ocean food chain maintains the balance of the ocean ecosystem of the world. Therefore, the existence of the ecosystem is endangered as the ocean food chain is destroyed. So when the ocean food chain is decreased the ecological balance is maintained (1) & (5).

Q&A

1. What is phytoplankton?

The microscopic plants floating on the surface of the water are called phytoplankton. Volvox, Chlamydomonas, green algae, silica-encased diatoms, etc. are examples of phytoplankton (5).

2. What is zooplankton?

Zooplankton are small microscopic animals that float on the surface of the water. They survive by eating the phytoplankton. Forams, radiolaria, Antarctic krill, jellyfish, cyclops strenuous, etc. are zooplankton (5).

3. What are the differences between phytoplankton and zooplankton?

4. What is nekton and benthos?

Nekton

Aquatic animals that swim in the water are called nekton. They mainly consume plankton as food.  Example: – fish, whales, dolphins, etc. (5).

Benthos

Aquatic animals that live underwater are called benthos. They often live by digging deep holes in the water. Example: – snails, oysters, etc. (5).