Seagrass

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Seagrass

Seagrass

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Seagrasses are marine angiosperms (flowering plants) that resemble terrestrial grass in appearance.Seagrasses produce true flowers and seeds, possess strap-like or oval leaves, and develop root and rhizome systems that anchor them to the seabed.They are the only flowering plants which grow in marine environments.Seagrasses reproduce both sexually and asexually. In sexual reproduction, submarine pollination transfers male pollen to female flowers underwater. Asexually, they propagate through rhizomes-horizontal underground stems, that enable regeneration after disturbances like grazing or storms.

Habitat and Distribution

Seagrasses grow in shallow, calm coastal waters with sandy or muddy substrates. They are the only group of higher plants adapted to life in saltwater.
Global Habitat Range
- Seagrasses are found in saline and brackish waters across the world, primarily along gently sloping, sheltered coastlines. These areas provide the calm and stable conditions essential for their growth and reproduction.
Light Requirement and Depth
- Being photosynthetic plants, seagrasses require sunlight and are usually restricted to shallow waters where light can penetrate easily.
- Most species grow at depths of 1 to 3 metres (3 to 9 feet).
- Some exceptional species, like Halophila decipiens, have been found at depths of up to 58 metres (190 feet)—the deepest recorded for any seagrass.
Biodiversity Hotspots
- While most coastal zones host only one or a few species, tropical regions—especially in the Indian and western Pacific Oceans—support the highest diversity.
- In these hotspots, up to 14 different species of seagrass can be found growing together in the same area.
Geographic Exclusion
- Antarctica is the only continent where seagrasses are completely absent due to extreme cold and lack of suitable light and coastal conditions.
Seagrass Distribution in India
- Southeast coast of Tamil Nadu
- Lagoons of Lakshadweep Islands
- Selected coastal zones of the Andaman and Nicobar Islands
- The dense growth along Tamil Nadu and Lakshadweep is attributed to favourable environmental factors, including clear water, high salinity, and sandy seabeds.

Ecological Roles & Functions

Ecosystem Support & Biodiversity
- Seagrass meadows support high biodiversity, providing habitat for 750+ fish species and 121 threatened species such as dugongs, sea turtles, seahorses, and shellfish .
- A single hectare can support 80,000 fish and hundreds of millions of invertebrates — a biodiversity comparable to coral reefs .
Carbon Sequestration & Climate Impact
- Act as carbon sinks, removing carbon dioxide from the atmosphere and sequestering it in sediments.
- Seagrasses sequester carbon up to 35 times faster than tropical rainforests.
- Seagrasses accounts for 10 per cent of the ocean’s capacity to store carbon—so-called “blue carbon”—despite occupying only 0.2 per cent of the sea floor.
Coastal Protection & Water Quality
- They prevent coastal erosion by stabilizing the seabed with their root systems.
- Seagrasses improve water clarity and quality by filtering pollutants, absorbing excess nutrients .
Fisheries & Livelihood Security
- Acting as nursery grounds, they enhance fish recruitment and support fisheries that account for over 20% of global landings .
- These ecosystems support coastal economies and food security through healthy fish stocks and interlinked marine biodiversity .
Foundation Species and Ecosystem Engineers
- Seagrasses are known as foundation species or ecosystem engineers because they actively modify their environment, creating distinct and stable habitats. These modifications not only support the survival of seagrasses themselves but also offer critical ecosystem services for marine organisms and human communities alike.

Threats & Conservation Challenges

Seagrass habitats are declining globally—some estimates record a loss rate of up to 7% per year—due to pollution, coastal development, eutrophication, and destructive fishing practices such as bottom trawling.

Pollution & Poor Water Quality
- Nutrient runoff (nitrogen, phosphorus) from agriculture and sewage causes eutrophication, leading to algal blooms and hypoxia (low oxygen) conditions harmful to seagrass survival .
- Industrial and plastic pollution also reduce water clarity and light penetration, impacting photosynthesis .
Coastal Development & Sedimentation
- Dredging, land reclamation, coastal infrastructure, and aquaculture result in sediment deposition and burial of seagrass beds, suffocating plants even at burial depths.
Physical Damage by Boats and Fishing
- Propeller scarring and bottom trawling physically uproot seagrass, creating barren zones from which recovery is difficult .
Climate Change & Temperature Stress
- Rising temperatures, sea-level rise, and increased storm intensity stress seagrass species.
Disease, Predation & Invasive Species
- Wasting disease, invasive crabs, or pests can erode habitat edges and reduce root stability, accelerating erosion and decline .

Seagrasses are unsung heroes of coastal ecosystems. By providing biodiversity support, climate resilience, coastal protection, and livelihood benefits, they play a crucial role in environmental sustainability.

FAQs on Seagrass

Q1. What exactly is a seagrass meadow?

Seagrass meadows are underwater ecosystems formed by flowering marine plants with root-rhizome systems anchoring them in shallow coastal sediments .

Q2. Why are seagrasses referred to as “lungs of the sea”?

Because they photosynthesize, producing oxygen and helping regulate carbon dioxide levels in coastal waters—playing a critical role in ocean health .

Q3. How do seagrasses support fisheries?

Seagrass beds act as nurseries for juvenile stages of many commercially important fish and shellfish, significantly contributing to fisheries productivity .

Q4. What is “blue carbon” and how do seagrasses contribute?

Blue carbon refers to carbon captured by coastal ecosystems. Seagrass meadows account for 10–18% of ocean carbon storage and sequester carbon much faster per unit area than terrestrial forests .

Q5. What threats are seagrass ecosystems facing?

Major threats include sedimentation, nutrient pollution, coastal infrastructure development, destructive trawling, and rising sea temperatures, all leading to habitat degradation and loss

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