Understand the role and types of plankton in aquatic ecosystems.
Identify the factors influencing phytoplankton biodiversity and their importance in the carbon cycle.
Recognize the role of zooplankton in marine food webs and ecosystem health.
Describe the significance, functions, and threats to sea grasses and seaweeds.
Plankton
Plankton encompasses the diverse organisms floating in the surface waters of rivers, lakes, and oceans. This group includes microscopic plants like algae (phytoplankton) and animals such as crustaceans and protozoans (zooplankton). They inhabit nearly all aquatic ecosystems, except for some fast-flowing waters. Their locomotion is limited, making their distribution heavily dependent on water currents. Tropical waters, especially mangrove areas, showcase high growth rates, productivity, and diversity of plankton.
Phytoplankton
Phytoplankton, derived from Greek “phyto” (plant) and “plankton” (drifting), are microscopic plant organisms found in both saline and freshwater environments. They encompass various types like cyanobacteria, silica-encased diatoms, dinoflagellates, green algae, and coccolithophores. These organisms play a crucial role in oxygen production and the carbon cycle.
Characteristics:
Possess chlorophyll to capture sunlight for photosynthesis, consume carbon dioxide, and release oxygen.
Include bacteria, protists, and predominantly single-celled plants.
Their biomass exceeds that of terrestrial plants, serving as “pasture grounds” in oceans.
Distribution:
Occupy the euphotic zone of seas and oceans, thriving where light intensity suffices for photosynthesis.
Highest concentrations are at high latitudes and upwelling areas on continental shelves, with lower concentrations in tropics and subtropics.
Factors Affecting Phytoplankton Biodiversity
Light: Restricted to the ocean’s uppermost layers where light intensity supports photosynthesis. The rate of photosynthesis varies with light intensity.
Nutrients: Require inorganic nutrients like nitrogen and phosphorus for growth and reproduction. Specific types like diatoms also need silicate (SiO₂). Low iron concentrations in oceans can limit phytoplankton growth.
Temperature: Influences photosynthetic production, generally increasing the rate with rising temperatures but decreasing sharply beyond a certain point. Seasonal variations in temperate latitudes affect production rates.
Salinity: Alongside light and temperature, salinity impacts primary production.
Grazing by Zooplankton: Zooplankton’s grazing rate significantly affects the phytoplankton’s standing crop size and production rate.
Distribution: Influenced by wind, waves, nutrients, temperature, salinity, and exposure to UV-B radiation. Productivity is limited to the euphotic zone, influenced by wind and waves.
Important Note: High exposure to solar UV-B radiation in the tropics and subtropics might affect phytoplankton distribution.
Importance of Phytoplankton
The Food Web:
Foundation of aquatic food webs.
Primary producers feeding everything from zooplankton to whales.
Carbon Cycle and Climate Change:
Responsible for transferring carbon dioxide from the atmosphere to oceans during photosynthesis.
A “biological carbon pump” that moves about 10 gigatonnes of carbon annually to the deep ocean.
Changes in phytoplankton growth can impact global carbon dioxide levels, influencing surface temperatures.
Zooplankton
Zooplankton play an integral role in the aquatic food web, facilitating nutrient recycling and transferring organic matter from primary producers to secondary consumers like fish. They are more prevalent in mangrove waterways than in adjacent coastal waters. Their quality and species diversity are key indicators of an ecosystem’s productivity, fertility, and health.
Distribution and Abundance:
Abundant in mangrove waterways, where many juvenile fish are zooplanktivorous.
Their population determines the quantum of fish stock in an ecosystem.
Important Note: Zooplankton communities reflect the ecosystem’s productivity, aiding in fisheries resource assessment.
Sea Grass
Sea grasses are marine angiosperms resembling grass. They produce flowers, have strap-like or oval leaves, and possess root systems. Sea grasses grow in shallow, calm coastal waters with sandy or muddy bottoms, being the only higher plants fully adapted to saltwater.
Distribution:
Commonly found along the southeast coast of Tamil Nadu, Lakshadweep lagoons, and some regions around the Andaman and Nicobar Islands in India.
Thrive in areas with high salinity, water clarity, and sandy substratum.
Functions:
Physically reduce wave and current energy.
Filter suspended sediments and stabilize bottom sediments to prevent erosion.
Provide habitat for marine invertebrates and fish.
Act as nutrient sinks near reef flats and estuaries, buffering and filtering nutrients and chemicals.
Important Note: Sea grasses significantly contribute to lagoon ecosystems by supporting fish and migratory bird populations.
Threats to Sea Grass Beds
Eutrophication: Excessive nutrients in water bodies lead to dense plant growth and oxygen depletion.
Siltation: Increased sediment deposit can bury sea grass beds.
Trawling: Disturbs the seabed, destroying sea grass.
Coastal Engineering: Constructions can alter water flow and habitat conditions.
Over-exploitation: Harvesting for commercial use impacts sea grass populations.
Concept: IUCN prioritizes sea grass conservation due to their ecological importance and the declining populations of species like the Dugong, which depend on sea grasses for food.
Management
Mapping: Identify and map major sea grass beds for preservation.
Controlled Dredging: Conduct dredging activities far from sea grass beds to prevent siltation and turbidity.
Seaweeds
Seaweeds are macroscopic algae without differentiation into true tissues (roots, stems, and leaves). They attach to rocks, corals, and submerged substrates in the intertidal and shallow subtidal zones.
Classification: Based on pigmentation, seaweeds are categorized into blue-green, green, brown, and red varieties.
Functions:
Serve as food for marine organisms.
Provide habitat for fish breeding grounds.
Act as sediment sources.
Uses:
Food for humans and feed for animals.
Fertilizer for plants.
Provide extracts (agar-agar, alginates, iodine) used commercially.
Biodegradation produces economically valuable gases like methane.
Extracts exhibit antibacterial properties.
Indicators of coastal ecosystem pollution due to their metal-binding and accumulating abilities.
Harmful Effects:
Rotting seaweed emits hydrogen sulfide, a toxic gas that can cause health issues like vomiting and diarrhea.
Threats to Seaweeds
Similar to those faced by sea grasses, including eutrophication, siltation, and over-exploitation.
Important Note: Seaweeds act as pollution indicators, especially for heavy metal pollution in coastal ecosystems.
Comparative Overview
Type
Distribution
Importance
Threats
Phytoplankton
Upper oceanic layers
Oxygen production, base of food web, carbon cycle
Nutrient scarcity, light, temperature
Zooplankton
Mangrove waterways, oceans
Nutrient recycling, food for fishes
Ecosystem changes, habitat loss
Sea Grass
Shallow coastal waters
Habitat, nutrient sinks, erosion control
Eutrophication, siltation, trawling
Seaweeds
Intertidal, subtidal zones
Food, habitat, pollution indicators
Siltation, eutrophication, harvesting
Concept: Seaweeds and sea grasses, despite similarities, have distinct roles and ecological functions within marine environments.
Did you know? The five sea turtle species nesting on Indian coasts are Leatherback, Green, Olive Ridley, Hawksbill, and Loggerhead turtles.
Important Note: Sea snakes, typically found in the Indian and Pacific Oceans, have adapted to lay eggs on land or give birth in water, depending on the species.
Do you know? The “ampullae of Lorenzini” is a sensory organ in sharks used to detect electrical fields from prey.
Interesting Fact: Silverfish, an insect found in old books, demonstrate the surprising variety of organisms influenced by marine ecosystems.
IUCN: Has accorded high priority to conserve sea grass due to its importance in marine ecosystems.
Sea Grass Note: Out of 58 global species, 14 species of sea grasses are recorded along the Indian coast.
Endangered Species: Dugong, a marine mammal reliant on sea grass for food, faces extinction.
Threat Mitigation: Mapping and preservation of sea grass beds are crucial, alongside controlled dredging to maintain ecosystem balance.
Conservation Priority: Both sea grasses and seaweeds require active management to mitigate threats from human activities and environmental changes.
Impactful Role: The collective roles of plankton,
PLANT CLASSIFICATION
Plants can be classified into different categories based on their structure, growth patterns, and nutritional strategies. Below is a structured classification with defining characteristics of each category:
Herb: Plants with a green, tender stem that rarely exceeds 1 meter in height.
Shrub: Woody perennial plants branching from the base with a persistent woody stem, generally not taller than 6 meters.
Tree: Large woody perennials with a single, well-defined stem and crown.
Parasites: Plants that rely on other living organisms (hosts) for nourishment:
Total Parasites: Obtain all their nutrients from the host.
Partial Parasites: Draw only part of their nutrients from the host.
Epiphytes: Plants growing on other plants for support but not nourishment. Their roots help establish them on branches and absorb moisture from the air. Example: Vanda.
Climbers: Herbaceous or woody plants that climb other structures using tendrils, hooks, aerial roots, or twining stems.
Important Note: Bats are unique among mammals as they are the only ones capable of sustained flight. They are warm-blooded, nurse their young with milk, and possess fur.
EFFECT OF ABIOTIC COMPONENTS ON PLANTS
Abiotic factors like light, temperature, frost, and snow significantly influence plant growth and survival. Each of these components affects plant physiology and ecosystem distribution in various ways.
Intensity of Light on Plant Growth
High Light Intensity: Promotes root growth, leads to increased transpiration, shorter stems, and thicker leaves.
Low Light Intensity: Hinders growth, flowering, and fruiting, causing CO₂ accumulation which can be fatal.
Light Spectrum: Only red and blue light are effective in photosynthesis; blue light causes small growth, while red light leads to cell elongation.
Ultraviolet Light: Leads to dwarf growth in plants.
Effect of Frost on Plants
Killing of Young Plants: Freezing of soil moisture, combined with morning sunlight, increases transpiration and kills plants.
Cell Damage: Frost causes water in intercellular spaces to freeze, leading to dehydration, coagulation, and eventual plant death.
Canker Formation: Frost can also cause mechanical injury to plant tissues.
Important Note: Frogs, in most species, do not tend to their eggs post-fertilization, leaving them to survive on their own.
Effects of Snow on Plants
Influences the distribution of species like deodar, fir, and spruce.
Acts as a blanket, protecting seedlings from extreme cold.
Shortens vegetative growth periods and mechanically bends tree stems.
Effect of Temperature on Plants
High Temperature: Causes plant death due to protein coagulation, dehydration, and increased susceptibility to pathogens.
Disturbs the balance between respiration and photosynthesis, leading to food depletion.
Dieback
A natural adaptive mechanism where plants die back from the tip to survive adverse conditions. The roots may remain alive for years while shoots die.
Causes:
Dense canopy blocking light.
Weak plant growth.
Frost, drought, and grazing pressures.
Important Note: Elephants have an exceptional memory and intricate social structures. Males usually live alone or in loose bachelor groups.
INSECTIVOROUS PLANTS
Insectivorous plants have developed specialized mechanisms to trap insects for supplementary nutrition. These plants thrive in nutrient-poor soils and can be active or passive in their trapping mechanisms.
The Indian Hunters
Drosera (Sundew): Found in wet, infertile soils; traps insects using sticky, dew-like secretions on leaf tentacles.
Aldrovanda: A rootless, free-floating aquatic plant in the Sunderbans; traps insects using sensitive hairs on leaf blades.
Nepenthes (Pitcher Plant): Found in the high rainfall hills of northeastern India; traps insects using pitcher-like structures filled with digestive enzymes.
Utricularia (Bladderworts): Inhabits freshwater wetlands; uses bladder traps with sensitive hairs to suck in and digest insects.
Pinguicula (Butterwort): Grows in Himalayan alpine heights; traps insects with sticky leaves that roll up when prey lands on them.
Medicinal Uses: Drosera can be used for curdling milk and treating blisters. Nepenthes’ liquid helps with urinary troubles, while Utricularia is used for coughs and wound dressing.
Important Note: Tigers mark their territory using urine, and conflicts often arise when another male encroaches on this space.
INVASIVE ALIEN SPECIES
Alien species are non-native organisms introduced to new environments, where they lack natural predators and threaten biodiversity.
Invasion and Species Richness
Invasions can increase species richness initially but often lead to native species’ extinction due to competition and predation.
Effects of Invasive Species
Loss of Biodiversity: Native species decline due to competition and habitat loss.
Habitat Degradation: Ecosystem balance is disrupted.