Like all seat creatures, seagrasses are destroyed by cyclones, over-grazing, fungal and other attacks. Seagrasses some times dry out in the inter-tidal areas. Have you seen them washed ashore? In estuaries, too much of freshwater and suit accumulation destroy seagrass beds.
The biggest seagrass enemy is human activity. We pollute the seawater when we use chemical pesticides and fertilizers and the water runs into seagrass beds on the coast. These chemicals support the growth of algae that block sunlight reaching seagrass. Sediments choke the leaves and sea dredging damages seagrass meadows. Boat anchors and large marine debris can kill sections of seagrass meadows.
Overfishing is bad too. Without fish, the sea-urchin population explodes. Sea urchins eat up seagrass. When large carnivorous fish like sharks are removed predators that eat invertebrates become more abundant. These in turn wipe out small pollinating creatures that the seagrass needs. An increase in herbivorous fish also kills off the seagrasses. You know of the food-chain, right?
Cyclones and tsunamis affect seagrasses. It takes time for left-over seagrasses to regenerate the meadow or for the seed-bank present in the sediment to give rise to new shoots.
Another big threat comes from global warming. When sea temperatures rise, marine heatwaves are created. These occur suddenly, spiking seawater temperature. Examples are the “record-breaking ‘Ningaloo Nino’ (2011) off Western Australia, the long-lasting ‘Blob’ (2013-2016) in the northeast Pacific ad El Nino-related extreme warming in 2016 that affected most of the Indo-Pacific. The number of marine heatwaves has increased around the world, and coral refs, seaweed beds and seagrass meadows are at maximum risk from marine heatwaves.
Biologists tell us that seagrasses bury carbon sediments faster than tropical forests do. When a tree dies, the carbon gets released into the atmosphere. in seagrass meadows, carbon gets stored in seabeds and even if the seagrass dies, carbon stays trapped inside the sediment. Destruction of the ocean food-chain, reducing ocean productivity. Even if protected areas are created for seagrasses, they will survive only if the seawater is clear.
Picture Credit : Google