They are akin to grass meadows on land and nurture many forms of sea life, playing a significant role in the ecological balance of our planet.
Today, sea grass areas are “among the most threatened ecosystems on earth with an estimated disappearance rate of 110 square kilometres per year since 1980,” marine scientist Hilconida Calumpong tells SciDev.Net.
Calumpong, a science professor at the Silliman University in the Philippines, is a member of the UN-mandated World Ocean Assessment (WOA) group of marine scientists that studied the state of the world’s oceans for five years (2011-2015).
“The rate of decline is accelerating from a median of 0.9 per cent per year before 1940 to 7 per cent per year since 1990. One-third of all the sea grass areas recorded around the world about a century ago in the 1870s have now disappeared,” says Calumpong, citing the WOA report.
The most intense destruction is in the China-Korea-Japan region where the highest decline of 80-100 per cent of all species is reported. The decline is associated with heavy coastal development and extensive coastal reclamation.
“Sea grass meadows are under siege by humans.”
By Crispin Maslog
The destruction of one species of sea grass meadows is intense in South-East Asia due to aquaculture, fisheries and heavy watershed siltation, notes Calumpong.
Another three species in Australia and four species in the Mediterranean are damaged by propellers and ship grounding, by degraded water quality, and competition with introduced sea life species.
Roles of sea grass meadows
Sea grasses are flowering plants found in shallow marine waters (like bays and lagoons) and the continental shelves. They provide food, habitat and nursery areas for numerous marine life — fishes, crabs, shrimps, shells, sea horses, sea urchins, sea turtles, dolphins, manatees, waterfowl, scallops, clams and sea cucumbers.
Sea grasses perform other important functions. They stabilise the sea bottom in a manner similar to the way land grasses prevent soil erosion. They also lessen the impact of strong currents at the bottom of the sea.
Sea grasses help maintain water quality in the coastal areas. They trap fine sediments and particles that are suspended in the water and increase water quality. Without the grasses, the sediments are stirred by winds and waves.
Sea grasses also filter nutrients that come from land-based industrial discharge and storm water runoff before these are washed out to sea and affect other sensitive habitats like coral reefs.
Sea grass destruction
These sea grass meadows are under siege by humans. A major human-made cause are plastics. The South-East Asian region has been reported to be the world’s worst plastic polluters of the oceans.
Scientists explain that plastics break into very tiny particles, competing with microscopic organisms that serve as food for larger marine animals and block the sunlight needed for the sea grass to survive.
Sea grass produces oxygen and absorbs carbon dioxide. With the loss of sea grass meadows, more carbon dioxide is released into the air, causing more heating in the oceans. With more heating, the climate becomes more extreme.
Sea grass loss will affect populations of some 115 marine species that live on sea grass beds, according to the International Union for the Conservation of Nature.
Reefs and mangrove ecosystems are also affected because many fish and invertebrate species found in coral reefs and mangroves spend their juvenile stages in sea grass beds.
The ocean is a complex system that is interconnected, and what goes wrong in one part of the ocean will affect the whole.
Reversing the tide of destruction
What can be done to mitigate the destruction?
“Many strategies have been employed in the management of sea grass meadows,” says Calumpong.
“These strategies include declaration of sanctuaries and protected areas, regulation of fishing methods destructive to kelps and sea grasses (such as trawls and seines), transplantation and restoration of sea grass beds.”
“But since sea grass meadows are catchments, an integrated approach is needed to regulate siltation-causing activities in the uplands such as deforestation, agriculture, mining plus reclamation,” she emphasises.
The UN has recognised the gravity of the destruction and organised the First Integrated World Ocean Assessment in 2011 to mitigate the problem. However, there is no specific date for the next WOA.
We think there is urgent need for action now, both at local and national government levels, and from the United Nations perspective, without waiting for the next WOA. The WOA report admits that some problems – such as those flowing from climate change and acidification – can only be dealt with at a global level.
As one of the 25 experts from the Asia-Pacific working with WOA 2011-2115, Calumpong says the experience has made her realise how small she is as a scientist and how huge “the challenge to act as a family of nations so that humans can survive as a species”.
This piece was produced by SciDev.Net’s South-East Asia & Pacific desk.