Aquatic Ecosystem
Environment
An aquatic ecosystem is an ecosystem where the main habitat is water. The major differences between various aquatic zones arise due to:
• Salinity
• Levels of dissolved nutrients
• Water temperature
• Depth of sunlight penetration
Types of Aquatic Ecosystem
Freshwater Ecosystem
• Salt content is less than 5 ppt.
• Two types:
– Lentic (static water): pond, lake, bogs, swamps
– Lotic (running water): springs, streams, rivers, mountain brooks
Brackish Water Ecosystem
• Salt concentration between 5 to 35 ppt.
• Includes estuaries, salt marshes, mangrove swamps.
• Estuaries: where river water meets sea water, mixed by tides; highly productive.
Marine Ecosystem
• Salt concentration 35 ppt or more.
• Includes shallow seas and open oceans.
Aquatic Organisms (Based on Zone of Occurrence)
Neuston
• Live at air–water interface.
• Examples: floating plants, water striders, beetles.
Periphyton
• Attached to stems/leaves of rooted plants or other substrates.
• Includes sessile algae and small animals.
Plankton
• Microscopic plants (phytoplankton) and animals (zooplankton).
• Found in all aquatic ecosystems except fast-moving streams.
Nekton
• Strong swimmers; can overcome currents.
• Example: fish.
Benthos
• Organisms living at the bottom of the water body.
• Example: sea grass communities.
Corals
• Corals are living animals with symbiotic algae (zooxanthellae).
• Corals get their colour from algae.
• Two types: hard corals (reef-builders) and soft corals.
• Found mainly in shallow tropical waters.
• Types of reefs: fringing, barrier, patch, atoll.
Factors Affecting Aquatic Productivity
Temperature
• Water temperature changes slowly due to high specific heat.
• Aquatic species have narrow tolerance ranges.
Sunlight
• Determines plant distribution.
• Zones:
– Photic zone: light penetrates; supports photosynthesis.
– Aphotic zone: insufficient light; only respiration occurs.
Dissolved Oxygen (DO)
• Enters water through air–water interface and photosynthesis.
• Used up by respiration of organisms and decomposition.
Transparency
• Affected by silt, clay, phytoplankton.
• Determines light penetration and photosynthesis.
Lake Ecosystem
Zones:
• Littoral zone (shallow edges)
• Open-water zone (deep water)
• Benthic zone (lake floor)
Based on salinity:
• Freshwater lakes
• Brackish lakes
• Saline lakes
Based on nutrients:
• Oligotrophic (low nutrients)
• Mesotrophic (moderate)
• Eutrophic (high nutrients)
Eutrophication
• Natural eutrophication: slow nutrient enrichment over time.
• Cultural eutrophication: accelerated by human activities (fertilizers, sewage).
• Leads to algal blooms.
Algal Blooms
• Rapid growth of algae due to excess nutrients.
• Some algae produce toxins harmful to fish, birds, mammals, humans.
Estuarine Ecosystem
• Formed where river meets sea.
• Ecotone between freshwater and marine systems.
• Highly productive; act as natural filters.
• Examples: tidal marshes, lagoons, deltas.
Formation of Estuaries
• Rising sea levels
• Sand movement and sandbar formation
• Glacial and tectonic processes
Mangroves
• Found on tropical/subtropical coasts.
• Adapted to saline conditions.
• Protect coasts from cyclones and tsunamis.
• Key features:
– Pneumatophores for respiration
– Vivipary (seeds germinate on tree)
• Abundant along eastern India (Ganga, Mahanadi, Godavari, Krishna, Cauvery deltas)
Wetland Ecosystem
• Swamps, marshes, mangroves.
• Periodically inundated areas supporting aquatic flora/fauna.
• Nutrient-rich and highly productive.
Functions of Wetlands
• Habitat for diverse species
• Filtration of sediments
• Nutrient recycling
• Water purification
• Flood control
• Groundwater recharge
• Shoreline protection
Adaptations in Aquatic Organisms
• Floating plants/animals: lightweight bodies
• Osmoregulation: tolerance to varying salt levels
• Streamlined bodies for swimming
• Deep-sea organisms show bioluminescence
• Dependence on upper sea zones for food
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Subject: Environment
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