Aquatic Ecosystem
Intended Learning Outcomes
At the end of this Lecture, students will be able to
• Explain Aquatic ecosystem
• Discuss the characteristic features of Aquatic ecosystem
• Discuss the structure and functional of the Aquatic ecosystem
Aquatic Ecosystem
• Aquatic ecosystems constitute the marine environments of the seas and the fresh water systems in lakes, rivers, ponds and wetlands
• Provide human beings with a wealth of natural resources (food such as fish and crustaceans)
• Natural aquatic systems such as rivers and seas break down chemical and organic wastes created by man
• If aquatic ecosystems are misused or over utilized, their ability to provide resources suffers in the long term
• Over-fishing leads to a fall in the fish catch
What is an aquatic ecosystem?
• In aquatic ecosystems, plants and animals live in water
• These species are adapted to live in different types of aquatic habitats
• Aquatic ecosystems may be classified as being stagnant ecosystems or running water ecosystems
• The mud gravel or rocks that form the bed of the aquatic ecosystem alter its characteristic and influence its plant and animal species composition
• The aquatic ecosystems are classified into freshwater, brackish and marine ecosystems, which are based on the salinity levels
• The fresh water ecosystems that have running water are streams and rivers
• Ponds, tanks and lakes are ecosystems where water does not flow
• Wetlands are special ecosystems in which the water level fluctuates dramatically in different seasons
• They have expanses of shallow water with aquatic vegetation, which forms an ideal habitat for fish, crustacea and water birds
• Marine ecosystems are highly saline, while brackish areas have less saline water such as in river deltas
• Coral reefs are very rich in species and are found in only a few shallow tropical seas
• Richest coral reefs in India are around the Andaman and Nicobar islands and in the Gulf of Kutch
• Brackish water ecosystems in river deltas are covered by mangrove forests and are among the world’s most productive ecosystems in terms of biomass production
• The largest mangrove swamps are in the Sunderbans in the delta of the Ganges
Types of aquatic ecosystem
Pond Ecosystem
• Pond is the simplest aquatic ecosystem to observe
• There are differences in a pond that is temporary and has water only in the monsoon and a larger tank or lake that is an aquatic ecosystem throughout the year
• Most ponds become dry after the rains are over and are covered by terrestrial plants for the rest of the year
• When a pond begins to fill during the rains, its life forms such as the algae and microscopic animals, aquatic
insects, snails, and worms come out of the floor of the pond where they have remained dormant in the dry phase
• Gradually more complex animals such as crabs frogs and fish return to the pond
• As the pond fills in the monsoon a large number of food chains are formed
• Algae is eaten by microscopic animals, which are in turn eaten by small fish on which larger carnivorous fish depend, these are in turn eaten by birds such as kingfishers, herons and birds of prey
• Aquatic insects, worms and snails feed on the waste material excreted by animals and the dead or decaying plant and animal matter
• They act on the detritus, which is broken down into nutrients which aquatic plants can absorb, thus completing the nutrient cycle in the pond
• The temporary ponds begin to dry after the rains and the surrounding grasses and terrestrial plants spread into the moist mud that is exposed
• Animals such as frogs, snails and worms remain dormant in the mud, awaiting the next monsoon
Lake Ecosystem
• Lake Ecosystem functions like a giant permanent pond
• Large amount of its plant material is the algae, which derives energy from the sun, which transferred to the microscopic animals and feed on the algae
• Fish that are herbivorous and are dependent on algae and aquatic weeds
• Small animals such as snails are used as food by small carnivorous fish, which in turn are eaten by larger carnivorous fish
• Specialised fish, such as catfish, feed on the detritus on the muddy bed of the lake
• Energy cycles through the lake ecosystem from the sunlight that penetrates the water surface to the plants
• From plants energy is transferred to herbivorous animals and carnivores
• Animals excrete waste products, which settle on the bottom of the lake
• This acts as the nutrient material that is used by aquatic plants for their growth
• During this process plants use Carbon from CO2 for their growth and in the process release Oxygen
• This Oxygen is then used by aquatic animals, which filter water through
Streams and Rivers Ecosystem
• Streams and rivers are flowing water ecosystems in which all the living forms are specially adapted to different rates of flow
• Some plants and animals such as snails and other burrowing animals can withstand the rapid flow of the hill streams
• Other species of plants and animals such as water beetles and skaters can live only in slower moving water
• Some species of fish, such as Mahseer, go upstream from rivers to hill streams for breeding, they need crystal clear water to be able to breed
• As deforestation occurs in the hills the water in the streams that once flowed throughout the year become seasonal
• This leads to flash floods in the rains and a shortage of water once the streams dry up after the monsoon
• The community of flora and fauna of streams and rivers depends on the clarity, flow and oxygen content as well as the nature of their beds
• Stream or river can have a sandy, rocky or muddy bed, each type having its own species of plants and animals
Marine Ecosystem
• Indian Ocean, Arabian Sea and Bay of Bengal constitute the marine ecosystems
• The producers in this ecosystem vary from microscopic algae to large seaweeds
• Millions of zooplankton and a large variety of invertebrates and marine mammals are available
• Shallow areas near Kutch and around the Andaman and Nicobar Islands are some of the most incredible coral reefs in the world
• Coral reefs are only second to tropical evergreen forests in their richness of species
• Fish, crustacea, starfish, jellyfish and polyps that deposit the coral are a few of the thousands of species that form this incredible world under the shallow sea
• Deforestation of adjacent mangroves leads to silt being carried out to sea where it is deposited on the coral which then dies
• Marine ecosystem is used by coastal fisherfolk for fishing which forms their livelihood
• Marine ecosystem continued to maintain its abundant supply of fish over many generations
Seashore Ecosystem
• Beaches can be sandy, rocky, shell covered or muddy
• On each of these different types, there are several specific species which have evolved to occupy a separate niche
• There are different crustacea such as crabs that make holes in the sand
• Various shore birds feed on their prey by probing into the sand or mud on the sea shore
• Several different species of fish are caught by fishermen
• In many areas the fish catch has decreased during the last decade or two
How are aquatic ecosystems used?
• Man uses aquatic ecosystems for the clean freshwater on which his life is completely dependent (water to drink and for other domestic uses)
• Water is essential for agriculture
• Fisher folk use the aquatic ecosystems to earn a livelihood
• People catch fish and crabs
• They also collect edible plants (used locally as food or for sale in the market)
• Over fishing leads to a serious decline
in the catch and a long-term loss of income for fisher folk
• Marshes and wetlands are of great economic importance for people who live on their fish, crustacea, reeds, grasses and other produce
• Agriculture and industry are highly dependent on large quantities of water
• These dams make rich people richer in the farmland and supports people in large urban centres that use enormous quantities of water
• The poor tribal folk become even poorer as the natural resources they depend on are taken away as their lands are submerged under the water of the dam
• Dams are built across rivers to generate electricity
• Large proportion of this energy is used by urban people, by agriculturists in irrigated farmlands and in enormous quantities for industry
• Large dams have serious ill effects on natural river ecosystems
• This makes such lands gradually more and more saline and unproductive
What are the threats to aquatic ecosystems?
• Water pollution occurs from sewage and poorly managed solid waste in urban areas when it enters the aquatic ecosystem of lakes and rivers
• Sewage leads to a process called eutrophication, which destroys life in the water as the oxygen content is
severely reduced
• Fish and crustacea cannot breathe and are killed (foul odour is produced)
• Gradually the natural flora and fauna of the aquatic ecosystem is destroyed
• In rural areas the excessive use of fertilisers causes an increase in nutrients, which leads to eutrophication
• Pesticides used in adjacent fields pollute water and kills off its aquatic animals
• Chemical pollution from industry kills a large number of life forms in adjacent aquatic ecosystems
• Contamination by heavy metals and other toxic chemicals affects the health of people who live near these areas as they depend on this water
How can aquatic ecosystems be conserved?
• For sustainable use of an aquatic ecosystem, water pollution must be prevented
• It does not make sense to allow water to be polluted and then try to clean it up
• Changing the nature of the aquatic ecosystem from a flowing water ecosystem to a static ecosystem destroys its natural biological diversity
• Thus dams across rivers decrease the population of species that require running water, while favouring those that need standing water
• Aquatic ecosystems, especially wetlands, need protection by including them in Sanctuaries or National Parks in the same way in which we protect natural forests
• These sanctuaries in aquatic ecosystems protect a variety of forms of life as well as rare fish which are now highly endangered such as the Mahseer
• Wetland Sanctuaries and National Parks are of greatest importance as this is one of the most threatened of our ecosystems
• As the proportion of the earth’s surface that is naturally covered by wetlands is very small compared to forests or grasslands, the wetland ecosystems are very highly threatened
Summary
• Aquatic ecosystems constitute the marine environments of the fresh water systems in lakes, rivers, ponds and wetlands the seas and
• In aquatic ecosystems, plants and animals live in water
• Pond is the simplest aquatic ecosystem to observe
• Lake Ecosystem functions like a giant permanent pond
• Streams and rivers are flowing water ecosystems
• Indian Ocean, Arabian Sea and Bay of Bengal constitute the marine ecosystems
• Man uses aquatic ecosystems for the clean freshwater, agriculture etc.,
• Water pollution occurs from sewage and poorly managed solid waste in
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