- Seagrasses are the exclusive flowering plants capable of thriving in saltwater environments.
- There are approximately 60 known species of entirely marine seagrasses, classified into four families: Posidoniaceae, Zosteraceae, Hydrocharitaceae, and Cymodoceaceae.
- The term “seagrass” encompasses a diverse range of species characterized by long, slender leaves and the ability to spread extensively across vast “meadows,” resembling terrestrial grasslands.
- Visually, many of these seagrass species bear a resemblance to land-based grasses.
DISTRIBUTION
- Seagrasses are globally distributed, thriving in brackish (semi-salty) and salty waters, primarily along gently sloping and protected coastlines.
- These aquatic plants prefer shallow depths with abundant light, as photosynthesis, a vital process for their growth, relies on light availability.
- The deepest-dwelling seagrass, Halophila decipiens, has been identified at depths of 190 feet.
- However, the majority of seagrass species are typically found at depths ranging from 3 to 9 feet (1 to 3 meters), although some can extend down to 58 meters.
- Coastal areas usually feature dominant seagrass species, but in the tropical waters of the Indian and western Pacific oceans, up to 14 different seagrass species can coexist harmoniously.
- Notably, Antarctica is the only continent without seagrasses.
- In India, significant seagrass beds are located along the coastline in various regions, including the lagoons of the Andaman and Nicobar Islands in the Bay of Bengal, the Gulf of Mannar and Palk Bay areas on the east coast, and the Gulf of Kachchh region on the west coast.
CHARACTERISTICS
Seagrass species exhibit distinctive features that aid in their identification:
Underwater Pollination:
- Seagrasses utilize specialized pollen for pollination beneath the water’s surface.
- Seeds produced by underwater plants are distributed through a combination of biotic and abiotic processes.
Photosynthetic Tissue and Leaves:
- The principal photosynthetic tissue and leaves of seagrass species are characterized by the epidermis.
- The epidermis lacks stomata and features specialized leaves with a reduced cuticle.
Rhizomes for Anchoring:
- Rhizomes, commonly known as subterranean stems, play a crucial role in anchoring seagrasses.
Nutrient Transfer Processes:
- Nutrient transfer processes are vital for seagrasses, with roots playing a crucial role.
- Seagrass roots can survive in an anoxic environment and depend on leaves and rhizomes for oxygen delivery.
Impact on Coastal Seas:
- Seagrasses significantly influence the physical, chemical, and biological conditions of coastal seas.
Their presence has a substantial impact on the overall ecological dynamics of coastal marine environments.
ECOSYSTEM SERVICES
- Ecosystem Engineers:
- Seagrasses are acknowledged as “Ecosystem Engineers” for their remarkable contributions to various ecosystem services.
- Lungs of the Sea:
- Termed “the lungs of the sea,” seagrasses utilize photosynthesis to release oxygen into the water, enhancing the aquatic environment.
- Carbon Sequestration:
- Despite covering only 0.1% of the ocean floor, seagrasses annually absorb 83 million tonnes of carbon from the atmosphere, sequestering up to 11% of the organic carbon in the water.
- Efficient Carbon Absorption:
- Surpassing tropical rainforests, seagrasses absorb carbon from the atmosphere up to 35 times faster, showcasing their efficiency in carbon capture.
- Water Quality Enhancement:
- Seagrasses contribute to water clarity by trapping fine sediments and suspended particles, playing a vital role in maintaining water quality.
- Filtration Mechanism:
- Acting as natural filters, seagrasses intercept fertilizers from land-based industries before they reach vulnerable ecosystems like coral reefs.
- Soil Erosion Prevention:
- The extensive root systems of seagrasses, both vertically and horizontally, stabilize the ocean floor, preventing soil erosion.
- Diverse Habitat Providers:
- Seagrasses serve as habitats for a plethora of marine life, including fish, octopuses, shrimp, blue crabs, and oysters, offering a diverse ecosystem.
- Protection of Endangered Species:
- Grazing on seagrass fronds is essential for endangered marine species such as dugongs, green turtles, and bottlenose dolphins, forming a crucial part of their diet.
- Nutrient Cycling and Release:
- Decomposed seagrass detritus provides nutrition for creatures like worms and sea cucumbers, and upon decomposition, seagrasses release nitrogen and phosphorus into the ecosystem.
- Defense Mechanism:
- Seagrasses act as shields, protecting young and small fish from predators and creating a barrier against strong currents for creatures like worms, crabs, starfish, sea cucumbers, and sea urchins.
- Nursery Sites for Commercial Species:
- Seagrasses ensure the availability of ideal nursery sites for commercially valuable marine life such as squids and cuttlefish, contributing to marine biodiversity and economic activities.
Threats to Seagrasses: Unravelling the Challenges
- Global Deterioration:
- Seagrass beds worldwide face an alarming degradation rate of 2–5% annually, leading to substantial losses.
- Widespread Disappearance:
- A staggering 30,000 square kilometers of seagrass have vanished globally in recent decades, signaling a concerning trend.
- Geographical Factors:
- Seagrasses are vulnerable to natural disturbances like grazing, storms, ice-scouring (erosion by glaciers), and desiccation (extreme dryness), influenced by geographical conditions.
- Anthropogenic Activities:
- Human-induced threats significantly contribute to seagrass decline, including eutrophication, mechanical habitat loss, overfishing, discharge of nutrients, and coastal infrastructure construction.
- Eutrophication Impact:
- The influx of excessive nutrients, often from agricultural runoff, fuels eutrophication, negatively impacting seagrass health and contributing to their decline.
- Mechanical Habitat Loss:
- Destructive activities such as trawling and dredging result in mechanical habitat loss, disrupting seagrass ecosystems and reducing their resilience.
- Overfishing Pressures:
- Overfishing depletes populations of herbivores that play a crucial role in maintaining seagrass health, disrupting the delicate balance within the ecosystem.
- Nutrient Discharge:
- Discharge of nutrients, particularly from urban and industrial areas, contributes to water pollution, affecting seagrasses and their associated fauna negatively.
- Coastal Infrastructure Impact:
- Construction projects along coastlines, including ports and urban development, lead to habitat destruction, fragmenting seagrass beds and hindering their ability to recover.
- Pollution Consequences:
- Pollution from various sources, including oil spills and plastic debris, poses direct threats to seagrasses, impeding their growth and compromising ecosystem integrity.
- Climate Change Effects:
- Seagrasses are susceptible to climate change impacts, including rising sea temperatures and ocean acidification, which further exacerbate their vulnerability.
- Inadequate Conservation Measures:
- The lack of effective conservation measures, including designated protected areas and sustainable management practices, contributes to the ongoing decline of seagrass ecosystems.
FAQs
1. What makes seagrasses unique among flowering plants?
A: Seagrasses are distinctive as they are the only flowering plants capable of thriving in saltwater environments.
2. How many species of marine seagrasses are known, and how are they classified?
A: There are approximately 60 known species of entirely marine seagrasses, classified into four families: Posidoniaceae, Zosteraceae, Hydrocharitaceae, and Cymodoceaceae.
3. What is the distribution of seagrasses globally?
A: Seagrasses are globally distributed, thriving in brackish and salty waters primarily along gently sloping and protected coastlines.
4. How do seagrasses reproduce?
A: Seagrasses can reproduce both sexually and asexually. Sexual reproduction involves subaquatic pollination, while asexual reproduction occurs through rhizome branching.
5. What is the ecological impact of seagrasses?
A: Seagrasses significantly influence the physical, chemical, and biological conditions of coastal seas, playing a crucial role in the overall ecological dynamics of marine environments.
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