The only flowering plants that can grow in saltwater conditions are seagrasses. About 60 species of totally marine seagrasses from four families are known (Posidoniaceae, Zosteraceae, Hydrocharitaceae and Cymodoceaceae). The term "seagrass" refers to a variety of species that have long, narrow leaves and that spread widely across expansive "meadows" that resemble grassland. Many of these species visually resemble terrestrial grasses. This article will explain to you about Sea-Grass which will be helpful in preparing the Environment Syllabus for the UPSC Civil Service exam.

Sea-Grass

What exactly are Sea-Grasses?

• These are flowering plants that can be found on the seafloor and in our oceans.
• It belongs to the class of marine angiosperms. They frequently spend their entire lives underwater.
• They have tiny blooms and strap-like or oval leaves, and photosynthesis depends on sunshine.
• Despite the fact that seagrasses may grow on anything from mud to rock, muddy and sandy substrata are where the majority of the rich green seagrass beds are found.
• Important Species: Sea Cow Grass (Cymodocea serrulata), Thready Seagrass (Cymodocea rotundata), Needle Seagrass (Syringodium isoetifolium), Flat-tipped Seagrass (Halodule uninervis), Spoon Seagrass (Halophila ovalis), and Ribbon Grass are a few of the significant seagrass species (Enhalus acoroides).
• These are currently in danger despite once being in great abundance in the Gulf of Mannar region.

Sea-Grass - Distribution

• Around the world, seagrasses thrive in brackish (semi-salty) and salty waters, usually along gently sloping, protected coastlines.
• Since photosynthesis requires light, they are most frequently found in shallow depths with abundant light.
• The deepest growing seagrass, Halophila decipiens, has been discovered in depths of 190 feet, despite the fact that many seagrass species exist in depths of 3 to 9 feet (1 to 3 meters) (58 meters).
• While only one or a few seagrass species dominate most coastal areas, up to 14 species of seagrass can coexist peacefully in the tropical waters of the Indian and western Pacific oceans.
• The only continent without seagrasses is Antarctica.
• India: The main seagrass beds can be found along our coastline in the lagoons of the Andaman and Nicobar Islands in the Bay of Bengal, the Gulf of Mannar and Palk Bay regions on the east coast, and the Gulf of Kachchh region on the west coast.

Global Distribution of Sea-Grass

Sea-Grass - Features

• A seagrass species can be identified by the listed features.
• Specialized pollen is used for underwater pollination. Underwater plants produce seeds that are distributed by both biotic and abiotic processes.
• The principal photosynthetic tissue and the leaves of the seagrass species are the epidermis, which lacks stomata and has specialised leaves with a reduced cuticle.
• Rhizomes, often known as subterranean stems, are crucial for anchoring. The processes involved in the nutrient transfer are crucial for the roots since they can survive in an anoxic environment and rely on the leaves and rhizomes for oxygen delivery.
• The physical, chemical and biological conditions of coastal seas are significantly impacted by seagrasses.

Sea-Grass - Growth

• To absorb sunlight and nutrients from the water and sediment, seagrasses grow both vertically and horizontally—their blades extend upward, while their roots extend downward and sideways.
• Asexual Clonal Growth: Like grasses on land, seagrass shoots are interconnected underground by a network of substantial, rhizome-like structures.
• Under the silt, the rhizomes can disperse and sprout new shoots.
• Clonal growth refers to the phenomenon where many stems within a single meadow can really be a part of the same plant and have the same genetic makeup.
• The oldest known plant is actually a clone of the Mediterranean seagrass Posidonia oceanica, which dates back to the late Pleistocene ice ages and could be up to 200,000 years old.
• A meadow can emerge from a single plant in some seagrass species in less than a year, while in slow-growing species like Posidonia, it may take hundreds of years.

Sea - Grass - Reproduction

Seagrasses can reproduce both sexually and asexually.

Sexual Reproduction

• Through the process of sexual reproduction, the pollen from the male plant's flower is transmitted to the female plant's ovary.
• This process is called subaquatic pollination.
• The majority of organisms go through this procedure and finish their life cycle underwater.

Asexual Reproduction

• By branching off at their rhizomes, seagrasses can also reproduce asexually (modified subterranean plant stem that sends out roots and shoots from its nodes).
• They can recover from being injured by grazers like dugongs or disturbed by storms thanks to this quality.
• The National Centre for Sustainable Coastal Management calculated the size of the seagrass ecosystem in India to be 516.59 km2 based on field studies and satellite data.

Sea - Grass - Importance

• Ecosystem Engineers: Seagrasses are referred to as "Ecosystem Engineers" since they are known for offering a variety of ecosystem services.
• Lungs of the Sea: They are also known as "the lungs of the sea" because they use photosynthesis to release oxygen into the water.
• Carbon Sequestration: Despite taking up only 0.1 % of the ocean floor and annually absorbing 83 million tonnes of carbon from the atmosphere, they sequester up to 11 % of the organic carbon buried in the water.
• Absorption: Compared to tropical rainforests, seagrass may absorb carbon from the atmosphere up to 35 times faster.
• Water Quality: Clarity is improved and fine sediments and suspended particles are trapped, helping to maintain water quality.
• Filtration: Before fertilizers from land-based industries reach delicate environments like coral reefs, they filter them.
• Prevent Soil Erosion: As seagrasses' broad vertical and horizontal root systems stabilize the ocean floor, they help to prevent soil erosion.
• Habitat: They serve as a habitat for fish, octopuses, shrimp, blue crabs, oysters, etc., and as a source of food.
• Prevent Endangered Species: Grazing on seagrass fronds are endangered marine animals including dugongs (also known as sea cows), green turtles, and others.
• Bottlenose dolphins consume the creatures that inhabit seagrass habitats.
• Source of Nutrition: Detritus (natural waste) from dead seagrass that has decomposed provides food for creatures like worms and sea cucumbers.
• Release of Nutrients: Seagrasses and phytoplankton take nitrogen and phosphorus once it decomposes, releasing these nutrients.
• As a Defense: Protect young and small fish from huge predators, and keep powerful currents away from creatures like worms, crabs, starfish, sea cucumbers, and sea urchins.
• Ideal Nursery Sites: Ensure that vital marine life used for commerce, such as squids and cuttlefish, has ideal nursery sites.

Sea-Grass - Threats

• Seagrass beds are deteriorating at a rate of 2–5 % annually all across the world.
• Around 30,000 square kilometres of seagrass have disappeared globally in recent decades.
• Geographical Factors: These are subject to grazing, storms, ice-scouring (the abrasion and erosion of seabeds by glaciers), and desiccation, among other natural disturbances (extreme dryness).
• Anthropogenic Activities: They suffer damage from human activities such as eutrophication, mechanical habitat loss, overfishing, discharge of nutrients, construction of coastal infrastructure, pollution, etc.

Sea-Grass - Management

• The majority of seagrass management focuses on preserving their biodiversity and the benefits that these habitats offer to ecosystems and people.
• Since there is no international law governing seagrasses, local and regional organisations usually provide protection.
• Limiting hazardous behaviors including excessive trawling and dredging, runoff pollution, and unsustainable fishing methods are measures done to protect seagrasses (such as dynamite or cyanide fishing).
• Additionally, initiatives are made to repair and restore seagrass beds. Usually, this is done by sowing seeds, transplanting adult seagrasses from other healthy meadows, or growing seedlings in aquariums.
• The Eastern United States' Chesapeake Bay and coastal Virginia have some of the most inspiring restoration success stories.
• The Virginia Institute of Marine Science has seeded 456 acres with 7.65 million seagrass seeds there as of 2014.
• From these planted plots, the seagrass Zostera marina has expanded to span 6,195 acres as of 2015.
• The root reasons for the initial seagrass decline must also be dealt with in order for restoration to succeed.

Conclusion

Despite the fact that seagrasses support commercial fisheries and provide essential ecosystem services by serving as a breeding and nursery ground for a range of animals, many elements of their physiology remain poorly understood. There is a global decline in seagrass habitat, according to numerous research. Ten seagrass species, or 14% of all seagrass species, have a high risk of going extinct, with three of those species being endangered. The human population, which depends on the resources and ecosystem services that seagrasses provide, and marine biodiversity would both suffer significantly from seagrass loss and biodiversity deterioration. Therefore, for seagrass species to survive, appropriate conservation activities are imperative.