The recent efforts of Tamil Nadu in the restoration of seagrasses, particularly in the Gulf of Mannar, have drawn attention to the importance of these marine flowering plants. These plants provide integral ecological functions and services, but are also facing various threats that can potentially lead to their extinction.
Understanding Seagrasses: Definition, Evolution and Reproduction
Seagrasses are unique flowering plants that are specifically adapted to grow submerged in shallow marine environments, such as bays and lagoons. Displaying tiny flowers and strap-like or oval leaves, seagrasses originated from terrestrial plants that recolonised the ocean around 70 to 100 million years ago.
Not unlike land-based plants, seagrasses rely on sunlight to photosynthesise, an essential process that allows them to manufacture their own food and release oxygen. Seagrasses reproduce through both sexual and asexual means. Sexual reproduction involves the transfer of pollen from the male plant’s flower to the female’s ovary, a process known as submarine pollination. Meanwhile, asexual reproduction happens when seagrasses branch off at their rhizomes, allowing them to recover from grazers’ damages or storms.
There are roughly 60 species of seagrasses which belong to four families under the order Alismatales. Some significant examples include Sea Cow Grass, Thready Seagrass, Needle Seagrass, and Flat-tipped Seagrass.
Habitat and Distribution of Seagrasses
Seagrasses can thrive in all types of substratas, such as mud and rock. However, lush green seagrass beds are predominantly found in muddy and sandy substratas. In India, they are abundant along coastal areas especially in the Palk Strait and Gulf of Mannar in Tamil Nadu.
Ecological Significance of Seagrasses
Often described as ‘Ecosystem Engineers’ or ‘lungs of the sea,’ seagrasses have crucial roles in ecosystem functioning and services. Even though they cover only 0.1% of the ocean floor, they bury up to 11% of the organic carbon in the ocean and remove 83 million tonnes of carbon from the atmosphere annually, with a carbon capture rate that is 35 times faster than tropical rainforests.
Seagrasses contribute greatly to water quality by trapping fine sediments and filtering nutrients from land-based industries before they can reach sensitive habitats like coral reefs. They also prevent soil erosion through their extensive root systems that stabilise the sea bottom and serve as a source of food and habitat for various marine organisms.
Threats to Seagrasses
Despite their importance, seagrass beds are currently declining globally at an annual rate of 2-5%. An estimated 30,000 square kilometres of seagrass have been lost recently due to natural disturbances such as grazing, storms, ice-scouring, and desiccation, and human activities like eutrophication, habitat destruction, overfishing, coastal construction, pollution, and nutrient release.
Protecting the Future of Seagrasses
The loss of seagrass habitats compromises the survival of dependent marine organisms and contributes to the loss of marine ecosystem productivity. The protection and restoration of these habitats should be pursued globally, given their notable role in climate change mitigation. Immediate action is required to conserve seagrasses and their habitats, necessitating the intervention of conservation bodies such as the International Union for the Conservation of Nature (IUCN) to study the status of different seagrass species and prevent their extinction.