ENVIRONMENT: COASTAL ECOSYSTEMS ON THE BRINK (Last of Three Parts)

Like the two other marine habitats — the coral reefs and mangroves — the seagrasses are in deep trouble.

Dr. Theresa Mundita S. Lim, director of Biodiversity Management Bureau, sounded the alarm during the International Coral Reef Symposium (ICRS) a few years back.  “In spite of the ecological and economic value of seagrasses, between 30% to 50% of the seagrass beds have been lost due to industrial development, ports, and recreation in the last 50 years.”

Dr. Miguel D. Fortes, the country’s foremost expert on seagrasses, echoed the same concern.  “Despite their high biodiversity and abundance, seagrass habitats are still poorly understood in our country,” he said. “Hence, it appears only marginally useful when, in fact, the ecosystem plays significant economic and ecological roles.”

Dr. Fortes, who presented a paper during a mini-symposium on seagrasses and seagrass ecosystems during the ICRS conference, said that seagrasses are among the most productive of coastal ecosystems, matching coral reefs and mangroves in terms of environmental and economic importance.  “As meadows, seagrasses are an important link between land and ocean and support a high primary production,” he pointed out.

Since the time of the dinosaurs, three groups of flowering plants colonized the oceans. Seagrasses, however, are the only flowering plants that can live underwater. More closely related to terrestrial lilies and gingers than to true grasses, they grow in sediment on the sea floor with erect, elongate leaves.

Dr. Fortes described seagrasses in these words: “Just like the grasses that we normally see outside our homes, they are flowering plants. But the only difference is that they complete their life history submerged in seawater, forming extensive meadows on sandy to muddy sediments in shallow coastal waters.”

Seagrasses — commonly known as isay or lusay — are quite different from seaweeds, which are algae. Seagrasses produce flowers, fruits, and seeds while seaweeds make spores. Seagrasses have separate roots, leaves and underground stems called rhizomes (which form an extensive network below the surface). Seaweeds rarely have “roots” below the surface.   Unlike seaweeds, seagrasses are vascular plants – they have a network of veins to move nutrients and dissolved gases around the plant.

On the Great Barrier Reef of Australia, over 500 species of algae can be found but only 14 species of seagrasses inhabit.  In comparison, the Philippines has 18 species thriving along its coasts.  This makes the Philippines as having the second highest species of seagrasses around the world.  Western Australia leads — with more than 30 species of seagrasses.

According to Lim, the country has a total seagrass area of 978 square kilometers.  Seagrasses are widely distributed throughout the country – from Bolinao Bay (Pangasinan) in the north, Palawan and the Cebu-Bohol-Siquijor area to the center, and Zamboanga and Davao in the South.

Based on the degree and nature of alteration and general community response to habitat conditions, seagrasses in the country are classified into pristine, disturbed, altered and emergent.

Pristine means “with high or low diversity of species, far removed from human habitations, disturbed only by the normal intensity of natural elements.  Considered disturbed are “high or low diversity beds occupying bays and coves, adjacent to human habitation.”

Altered are “low species diversity areas, permanently and completely changed or converted to other coastal uses” while emergent means “community diversity is low, controlled in part by extreme physico-chemical conditions.”

The majority of seagrass beds in the country have been disturbed and altered. So far, only those in Palawan, or other remote areas, could be considered pristine.

“Seagrasses are the least studied among the habitats in our coastal zones,” deplored Dr. Fortes. “As such, we know less than we need to in order to use them in solving coastal environmental as well as societal problems.”

Seagrasses are sometimes labeled ecosystem engineers, because they partly create their own habitat: the leaves slow down water-currents increasing sedimentation, and the seagrass roots and rhizomes stabilize the seabed. Their importance for associated species is mainly due to provision of shelter (through their three-dimensional structure in the water column), and for their extraordinarily high rate of primary production. As a result, seagrasses provide coastal zones with a number of ecosystem goods and ecosystem services.

Seagrasses provide food and shelter for many organisms, and are a nursery ground for commercially important prawn and fish species. The high primary production rates of seagrasses are closely linked to the high production rates of associated fisheries.

Among the diversified species found in the seagrass beds are fishes, sea cucumbers, sea urchins, crabs, scallops, mussels and snails.  Shrimps spend the early stages of their lives in seagrass areas.  Large animals like sea cow (dugong) and green sea turtles graze extensively in seagrass beds.

Seahorses, a tourist attraction and of medicinal value, reside in seagrass beds. A study done in five seagrass sites in the country identified a total of 1,384 individuals and 55 species from 25 fish families.

“All have economic value mostly as food and aquarium specimens,” Dr. Fortes reported. “Five times as many fish live in seagrass beds as above sea floors of mud, shells, and sand.”

Dr. Fortes, however, believed seagrasses are resilient. Compared with mangroves and coral reefs, seagrasses can even thrive on harsh conditions that may bring out by sea level rise caused by climate change.

In fact, seagrasses are hardly affected by climate change as they easily develop and reproduce underwater. Some marine life would still exist – thanks to seagrasses. “Species that thrive in mangroves, they can thrive in seagrasses. Mangroves and corals may be gone, but in seagrasses, they can still live,” said Dr. Fortes, who authored of Seagrasses: A Resource unknown in the ASEAN Region. — ###