What is Seagrass? Role & Global Distribution

What is seagrass?

Seagrass refers to a unique group of flowering plants that have adapted to thrive underwater, dating back to the era of dinosaurs. Unlike true grasses, they are more closely related to plants like lilies and gingers. These plants anchor themselves in the seabed using rhizomes—root-like structures—while their long, slender leaves extend into the water.

Seagrass meadows are found in shallow coastal waters across various continents, playing a crucial role in marine ecosystems. They serve as a primary food source for marine herbivores such as dugongs and green turtles. Additionally, they offer shelter and breeding grounds for numerous smaller aquatic species, including commercially valuable fish and shrimp. Beyond their ecological significance, seagrasses contribute to water clarity by stabilising sediments and absorbing excess nutrients from coastal runoff.

What are the characteristics of seagrass?

Seagrass has various features given below in the table:

Global Distribution and Growth Factors

Seagrasses are found in near-shore waters worldwide, thriving in environments that meet specific conditions:

• Physical Factors: Temperature, salinity, wave action, depth, and day length
• Photosynthetic Constraints: Light availability, nutrients, epiphytes, and diseases
• Human-Induced Threats: Pollution, sedimentation, and coastal development

Seagrass Habitat

• Found in shallow, sheltered marine coastlines and estuaries
• Form monospecific (single species) or multispecies meadows
• Depth range is determined by light availability and wave action
• Survive in intertidal zones with trapped water during low tide

Why is seagrass important?

Seagrass meadows are super helpful to the environment and the economy. It provides:

1. Biodiversity Hotspots

• Seagrass meadows host 40 times more marine animals than bare-sand
• Provide nursery grounds for prawns, fish, and other marine species
• Support diverse food chains based on herbivores and detritivores

2. Coastal Protection

• Stabilize sediments, preventing coastal erosion
• Reduce wave and tidal energy, acting as natural buffers

3. Carbon Sequestration

4. Water Quality Improvement

• Absorb excess nutrients from land-based runoff
• Trap fine sediments, enhancing water clarity
• Reduce harmful bacterial pathogens in adjacent coral reefs

5. Economic Value

• Seagrass/algae meadows are the third most valuable ecosystem globally
• Estimated value of $19,004 per hectare annually for nutrient cycling and raw materials (1994 valuation)
• Directly supports fisheries and coastal economies

Ecological Connections

Seagrass interacts closely with mangroves and coral reefs.

1. Connectivity with Mangroves and Coral Reefs

• Mangroves: Trap sediment from land, preventing smothering of seagrass and corals
• Seagrasses: Reduce sediment loads in water, benefiting coral reefs
• Coral Reefs: Protect coastlines, allowing seagrass and mangroves to thrive

2. Benefits to Coral Reefs

• Improves water clarity, enhancing coral health
• Increases local pH, aiding coral calcification
• Reduces disease-causing bacterial pathogens by over 50%

What is the role of seagrass in marine food chains?

Seagrass meadows support a rich and diverse range of marine life, providing both food and shelter to various species, from small invertebrates to large fish, crabs, turtles, marine mammals, and birds. These underwater plants play a vital role in maintaining healthy ecosystems by offering breeding and nursery grounds for many aquatic organisms.

Beyond their ecological benefits, seagrasses also provide valuable services to humans, including coastal protection, carbon sequestration, and supporting fisheries. However, extensive loss of seagrass habitats has occurred due to human activities such as pollution, coastal development, and destructive fishing practices, threatening the balance of marine ecosystems.

Seagrass meadows are a vital part of marine food chains by providing food, habitat, and nutrients. 

1. Food 

• Nursery grounds: Seagrass meadows provide safe areas for fish and invertebrates to grow and develop
• Grazing areas: Seagrass meadows provide food for herbivores
• Organic carbon sources: Seagrass meadows provide organic carbon for food webs

2. Habitat

• Shelter: Seagrass meadows provide shelter for fish and invertebrates 
• Predation refuge: Seagrass meadows provide areas where fish and invertebrates can hide from predators 

3. Nutrients 

• Nutrient pump: Seagrass meadows absorb nutrients from the soil and release them into the water

Seagrass meadows are among the most productive marine ecosystems in coastal waters. They are found in shallow seas on all continents except Antarctica.

Primary Food Source

Oxygen Production

• 1 m² of seagrass produces up to 10 liters of oxygen per day
• Converts CO₂ and water into sugar and oxygen via photosynthesis

Seagrass Conservation: Why It Matters

Threats to Seagrass

• Climate Change: Seawater temperatures above 40°C stress seagrass; death occurs at 43°C
• Coastal Development: Pollution and habitat destruction reduce seagrass cover
• Overgrazing: Excessive feeding by herbivores disrupts ecosystems

The Role of Sharks in Seagrass Protection

• Sharks regulate herbivore populations, preventing overgrazing
• Maintain a balanced seagrass ecosystem, ensuring even grazing distribution

Conclusion

Seagrasses are among the most productive and valuable ecosystems in the world. Their ability to store carbon, protect coastlines, and support marine biodiversity makes their conservation a priority. Protecting seagrass meadows ensures a healthy marine environment and benefits economies and coastal communities.

By understanding the significance of seagrass and implementing conservation efforts, we can safeguard these "pastures of the ocean" for future generations.