Function and Role of Seagrass Ecosystems to Climate Change Mitigation

Seagrasses are a vital part of the marine ecosystem. Seagrasses are often called foundation plant species or ecosystem engineers because they modify their environments to create unique habitats. They are often confused with seaweeds, but are actually more closely related to the flowering plants that you see on land. Even though seagrasses and seaweeds look superficially similar, they are very different organisms.  Seagrasses have roots, stems and leaves, and produce flowers and seeds. They evolved around 100 million years ago, and today there are approximately 72 different seagrass species that belong to four major groups. The 72 species of seagrasses are commonly divided into four main groups: Zosteraceae, Hydrocharitaceae, Posidoniaceae and Cymodoceaceae. Their common names, like eelgrass, turtle grass, tape grass, shoal grass, and spoon grass, reflect their many shapes and sizes and roles in marine ecosystems.

Seagrasses provide a wide range of ecosystem services, here defined as natural processes and components that directly or indirectly benefit human needs. Seagrasses support commercial fisheries and biodiversity, clean the surrounding water and help take carbon dioxide out of the atmosphere. Because of these benefits, seagrasses are believed to be the third most valuable ecosystem in the world (only preceded by estuaries and wetlands). Seagrasses support commercial fisheries and biodiversity, clean the surrounding water and help take carbon dioxide out of the atmosphere. Because of these benefits, seagrasses are believed to be the third most valuable ecosystem in the world (only preceded by estuaries and wetlands).

Fungction and role seagrass

1. Key service

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. Their roots trap and stabilize the sediment, which not only helps improve water clarity and quality, but also reduces erosion and buffers coastlines against storms.

2. Creation of Living Habitat

Seagrasses of nursery habitats because the leafy underwater canopy they create provides shelter for small invertebrates (like crabs and shrimp and other types of crustaceans), small fish and juveniles of larger fish species. A number of the species that depend on seagrasses are important for commercial and recreational fisheries. It is because of the wide variety of different species that live amongst the grasses that seagrass beds often form important "biodiversity hotspots".

3. Foundation of Coastal Food Webs

Seagrass beds are important feeding grounds for thousands of species around the world, and they support this diverse food webs. The epiphytic organisms growing on the surface of the seagrass blades provide other sources of food.  Some epiphytic bacteria can extract nitrogen from the environment and make it available to larger animals. Small invertebrate mesograzers, such as crustaceans and snails, feed on epiphytes, and in doing so can help keep the seagrass clean, acting as mutualistic partners (or housekeepers) that promote seagrass growth. They are in turn consumed by larger crustaceans, fish and birds and are important links in the coastal food web.

4. Blue Carbon

Carbon captured by living organisms in coastal-ocean ecosystems through photosynthesis process and accumulated in biomass (Mangrove, Seagrass, Seaweeds and Phytoplankton) and sediments.

As parts of the seagrass plants and associated organisms die and decay, they can collect on the seafloor and become buried, trapped in the sediment. It has been estimated that in this way the world's seagrass meadows can capture up to 83 million metric tons of carbon each year.  For seagrasses in Indonesia, median above- and below-ground biomass was 0.29 and 1.13 Mg C ha-¹ respectively; the median soil pool was 118.1 Mg C ha-¹. Combining plant biomass and soil, median carbon storage in an Indonesian seagrass meadow is 119.5 Mg C ha-1. Extrapolated to the estimated total seagrass area of 30,000 km², the national storage value is 368.5 Tg C (Alongi et al., 2015)

            Indonesia has explored the potency of our Coastal-marine Ecosystems as a carbon sink (Mitigation and Adaptation). This could support the global effort to maintain the temperature increase below 2 degree Celsius. The goal of blue carbon is to improve the national food security, livelihoods, and the resilience of coastal communities in Indonesia by integrated conservation and sustainable use of coastal and marine ecosystem services, while avoiding greenhouse gas emissions, increasing sequestration of carbon, and promoting alternative income opportunities.

Threat to seagrass:

Global seagrass coverage is diminishing at a rate of 1.5% a year, or about two football fields each hour. Estimates suggest that 29% of seagrass meadows have died in the past century. Unregulated coastal development and other human activities have resulted in severe damage to seagrass meadows and risk the sustainability of our coastal habitats. Several risks were observed for coastal seagrass ecosystems; in particular, coastal developments (road construction, reclamation and deforestation) have resulted in increased coastal turbidity and sedimentation from run-off, as well as reclamation of shallow coastal habitats that smothers seagrass beds, resulting in localised loss of seagrass habitat. This may have a significant socio-economic impact for coastal villages that rely on the seagrass meadows as a source of food.