Seagrass: Evolution, Reproduction, Significance – UPSC

In this article, You will read everything about Seagrass: Evolution, Reproduction, Significance – for UPSC IAS.

Seagrass

• These are flowering plants that grow submerged in shallow marine waters like bays and lagoons.
• These have tiny flowers and strap-like or oval leaves.
• Seagrasses are found in shallow salty and brackish waters in many parts of the world, from the tropics to the Arctic Circle, except Antarctica.
• Even though seagrasses and seaweeds look superficially similar, they are very different organisms. Seagrasses have leaves, roots, and veins, and produce flowers and seeds.
• The roots and rhizomes (thicker horizontal stems) of seagrasses extend into the sediment of the seafloor and are used to store and absorb nutrients, as well as anchor the plants.
• Seagrasses are known as the “lungs of the sea” because one square meter of seagrass can generate 10 liters of oxygen every day through photosynthesis. Seagrass leaves also absorb nutrients and slow the flow of water, capturing sand, dirt, and silt particles.

Evolution:

• Terrestrial plants evolved about 850 million years ago from a group of green algae and seagrasses evolved from terrestrial plants that recolonised the ocean 70-100 million years ago.

Food Production:

• Like terrestrial plants, seagrasses also require sunlight for photosynthesis from which these manufacture their own food and release oxygen.

Reproduction:

• Sexual Reproduction Method: The pollen from the flower of the male plant is transferred to the ovary of the female flower through this method.
  • This is known as submarine pollination. Most species undergo this process and complete their life cycle underwater.
• Asexual Reproduction Method: Seagrasses can also reproduce asexually by branching off at their rhizomes (modified subterranean plant stem that sends out roots and shoots from its nodes).
  • Because of this character, they can recover after being cut by grazers or disturbed by storms.

Order and Species:

• There are 60 species belonging to four families in the order Alismatales.
• Some of the important seagrasses are Sea Cow Grass (Cymodocea serrulata), Thready Seagrass (Cymodocea rotundata), Needle Seagrass (Syringodium isoetifolium), Flat-tipped Seagrass (Halodule uninervis), etc.

Habitat:

• Though seagrasses inhabit all types of substratas (layers) from mud to rock, the lush green seagrass beds are found extensively in muddy and sandy substratas.
• These occur all along the coastal areas of India and are abundant in the Palk Strait and Gulf of Mannar in Tamil Nadu.

Significance:

• Seagrasses are considered ‘Ecosystem Engineers’ as they are known for providing many ecosystem services and are also called ‘the lungs of the sea’ as they release oxygen into the water through photosynthesis.
• Sequesters up to 11% of the organic carbon buried in the ocean even though they occupy only 0.1% of the ocean floor and absorb 83 million tonnes of carbon from the atmosphere annually.
• Seagrasses can capture carbon from the atmosphere up to 35 times faster than tropical rainforests. They are one of the most productive ecosystems in the world.
• Help maintain water quality by trapping fine sediments and suspended particles in the water column and increase water clarity.
• Filter nutrients released from land-based industries before they reach sensitive habitats like coral reefs.
• Prevent soil erosion as the extensive vertical and horizontal root systems of seagrasses stabilise the sea bottom.
• Seagrasses provide food as well as habitat for fishes, octopuses, shrimp, blue crabs, oysters, etc.
  • Endangered marine organisms like dugong (Sea Cow), green turtle, etc, graze directly on seagrass leaves.
  • Bottle-nosed dolphins feed on the organisms that live in seagrass areas.
  • Detritus (natural waste) of decomposed dead seagrass supplies food for worms, sea cucumbers, crabs, etc.
  • After decomposition, it releases nutrients like nitrogen and phosphorus which are absorbed by seagrasses and phytoplankton.
• Protect juvenile and small adult fish from large predators and also protect worms, crabs, starfishes, sea cucumbers, sea urchins, etc, from strong currents.
• Provide ideal nursery sites for important commercial marine life like squids and cuttlefish.

Threats:

• Seagrass beds are facing decline all over the world at the rate of 2-5% annually.
  • Around 30,000 square kilometres of seagrass has been lost during recent decades at a global level.
• These face natural disturbances like grazing, storms, ice-scouring (abrasion and erosion of seabeds by glaciers.), and desiccation (extreme dryness).
• Human disturbances like eutrophication, mechanical destruction of habitat, overfishing, the release of nutrients, coastal engineering construction, pollution, etc are destructive for them.

1. They are found from the tropics to the Arctic and Antarctica.
2. They do not have roots and derive all the nutrition from petals.
3. They are called “lungs of the sea” as they generate substantial oxygen through photosynthesis.

Which of the above statements is/are correct?

•  a) 1, 3
•  b) 3 only
•  c) 1, 2
•  d) 1 only

Solution: (b)