*This article is excerpted from oneocean.org booklet (Why protect seagrass beds)

Seagrasses are seed-producing marine plants that occur in shallow, nearshore waters, the only group of submerged flowering plants in tropical and marine environments. Thriving in the shallow waters lining the shore, they have adapted life in saline waters with a root system that can withstand wave action and a reproductive system that distributes pollen by water. They are normally found in areas where light can easily penetrate (shallow, clear and calm waters) enabling photosynthesis to occur. Seagrass beds are often found between coral reefs and mangrove areas, colonizing the soft, shallow and sandy-muddy bottom.

Seagrasses have very high primary productivity that helps support and provides nutrients and physical habitat to a variety of organisms. Their main role as a nutrient source occurs when the dead seagrass decomposes and releases it nutrients to the water. Important fish species such as rabbitfishes (siganids), rely completely upon the seagrasses. Shrimps, sea cucumbers, sea urchins, seahorses, crabs, scallops, mussels and snails are economically important and abundant. Many resident and transient species also use the seagrass for refuge, spawning and nursery activities.

The
Philippines has extensive seagrass and algal beds and soft-bottom communities
that often occur in close proximity to mangroves and coral reefs. Soft-bottom
communities made up of sand or muddy substrates occur in many shallow sub-tidal
areas. Some are dominated by seagrass and algal beds while others are not
vegetated. Organisms that inhabit soft-bottom areas are influenced by particle
size and stability of the sediment, light, and temperature. Although not
obvious, the unvegetated soft-bottom areas have a variety of organisms that are
in-fauna, benthic animals that burrow or dig in the sediment. Some animals live
on the surface such as clumps of seaweeds, mollusks, flat fishes, and rays.
Typical in-fauna include various worms, bivalves, heart urchins, sand dollars,
some sea cucumber, and shrimps. All depend to some degree on detritus for food
and are easily disturbed if the sediment is moved or churned up

Seagrass ecosystems have very high primary productivity. It is
this capacity which helps to support and provide nutrients and physical habitat
to a variety of organisms. Seagrasses can grow quickly without fertilizers or
modern cultivation techniques. Some species can grow as much as 8 cm/day
(Fortes 1995). They also produce multiple crops (2-4 times annually). Their
high productivity includes not only their own high growth rates but also the
many small plants and other organisms that attach to their surfaces and live
among them.

Relatively few animals actually eat seagrasses. The main role of seagrasses as a nutrient source occurs when the dead seagrass decomposes and releases its nutrients to the water. The seagrass food web is illustrated in Fig. 1 Important fish species, such as some rabbitfishes (siganids), rely completely upon the seagrasses. Shrimps, sea cucumbers, sea urchins, seahorses, crabs, scallops, mussels, and snails are economically important and abundant in seagrasses. Many resident and transient species use the seagrasses for refuge, spawning, and nursery activities. Large animals like dugong and green sea turtles also graze extensively in seagrass beds. Seahorses, a tourist attraction and of medicinal value, reside in seagrass beds (see Fig. 1)

The
Value of Seagrasses.

“Within seagrass communities, a single acre
(half a hectare) of seagrass can produce over 10 tons of leaves per year. This vast biomass provides food, habitat, and nursery areas
for a myriad of adult
and juvenile vertebrates and invertebrates. Because seagrasses support such high
biodiversity, and because of their sensitivity to changes in water quality, they have become recognized as important indicator
species that reflect the overall health of coastal ecosystems” (Smithsonian Marine Station).

“Fish species such as rabbit fish spend t heir whole life cycle in seagrass beds; where they spawn, protect their eggs from predators and grow to maturity”

.

Seagrass
Resources in the Philippines.

The Philippines with its 18,000
km coastline, has sizeable seagrass
areas spread discontinuously along
the shallow portions
of its coastline. Sixteen
species that have been identified (Fortes 1986) are variably distributed in all parts of
the country… From surveys in 96 sites, a total of 978 sq km of seagrass beds have been identified in the country, mostly
in northwestern, western and southern portions, with outlying islands
having sizeable beds.

A significant portion
of the coastal habitats is at high risk of being lost in the next decade. About half have either been lost or severely
degraded during the past 56 years (Fortes
and Santos 2004).

Table 1. Traditional and
contemporary uses for seagrasses.

Source:
(Fortes 1989)

Management issues

Seagrass beds and
soft-bottom communities are often forgotten during preparation of various
management plans because their values and functions are not as well recognized.
The many coastal activities having major impacts on littoral basins also cause
loss of seagrass habitat or damage to soft-bottom communities.

1. Encroachment and
   seagrass modification.
   Encroachment by “land reclamation” for development of shore
   facilities has reduced the habitat for seagrasses. Both dredging and filling
   greatly disturb the bottom and largely remove that area as a potential seagrass
   area and area for soft-bottom organisms. Shrimp and fish farming have displaced
   many hectares of seagrass beds and mangroves.
2. Sedimentation. Excessive sedimentation
   can physically smother the seagrasses or it can cause such turbidity in the
   water that photosynthesis is impaired and filter feeders die. Major sediment
   sources include improper mining, agriculture, or forestry practices. Large
   areas of seagrasses have been smothered by mining runoff in Marinduque Island
   and other areas (Fortes 1989).
3. Introduction of
   waterborne pollutants. Pollution of nearshore waters occurs from
   domestic waste, oil and gas from boats and ships, and the accumulation of solid
   waste in shallow areas. In highly polluted waters, concentrations of
   herbicides, heavy metals, and detergents may be elevated enough to cause tissue
   damage to seagrasses (Fortes 1989). However, the major long-term threat to
   seagrasses in the world is from coastal eutrophication. Surface water runoff
   and groundwater containing excessive nutrients from fertilizers or sewage
   create conditions that promote algal blooms. Excessive algal growth shades the
   seagrasses on the bottom, interfering with light passage and the photosynthesis
   process. In addition, excessive amounts of dying algae will strip the oxygen
   from the water causing anoxic (no or low oxygen content) conditions in waters
   and sediments. The two actions combined may severely limit seagrass survival,
   either killing everything or leaving only those species that are hardy enough
   to survive
4. Destruction of submerged
   and fringing vegetation. Destruction of fringing vegetation, such
   as mangroves, allows additional sediment and pollutants to enter the water. It
   also removes significant sources of nutrients that help to sustain the
   seagrasses and coral reefs. Blast fishing gouges large holes in the bottom, not
   only killing the plants but also creating erosion sites that may remove more
   plants. Dragging boats, nets, anchors, and other gear can dislodge seagrass as
   can the churning of shallow waters from small boats and jet skis. In addition,
   planting of mangroves in seagrass beds is destructive to seagrasses and not
   appropriate.

Management interventions

Management interventions
for addressing the loss of seagrass and soft-bottom habitats include:

• Mapping and identification of
  beds to catalogue the extent and location of the resource;
• Zoning to prioritize use of
  space between pristine seagrass meadows versus those that are disturbed,
  altered, or newly emergent;
• Controlling of fishing methods
  to ban bottom trawling, blast fishing, and other methods of harvesting
  which tear up the bottom and cause turbidity;
• Reducing pollution by enforcing
  prohibitions against discharge of urban and industrial effluent and sea
  dumping of solid waste or dredge spoils and by reducing the amount of
  impervious surface area in the upland areas abutting the shoreline.
  Maintaining vegetated buffers along the shoreline and around disturbed
  sites to filter the runoff and promote infiltration of water into the
  ground; improve logging, mining, and agriculture practices to prevent erosion;
• Control coastal construction
  and beach nourishment;
• Transplanting shows signs of
  success from experimental transplanting; however, careful selection of the
  transplant site in regard to light, nutrients, and sediment type and
  stability is important while considering relative cost and benefits; and
• Recreation and tourism
  opportunities can provide opportunities for alternative sources of income
  to replace income generated by activities that degrade seagrass beds.

An example of a
successful intervention to protect seagrass beds is at the village of Handumon
on Handayan Island in Getafe, Bohol, where a municipal seahorse sanctuary was
established with assistance from the Visayan Seahorse Project of Haribon
Foundation. Ordinarily, a fisherman would receive Php10 per
seahorse from a broker feeding a lucrative market supplying Chinese folk
medicines. Through the Visayan Seahorse Project, fishermen learned to let the
animals mature to reproductive size and to allow pregnant males to deliver
their young. Tourists can arrange to go with a fisherman on a seahorse catch
and release night expedition. The Php300 fee compensates the fisherman (Php250)
for his catch and contributes Php50 to the project. Visitors stay in basic
accommodations built by the project that are priced high enough (Php750
including meals) to increase benefits to the community. Additional bungalows
are added as profits from the venture permit. Local residents also are learning
to create alternative products for sale, including woven bags and pillows
stuffed with old fish nets, rattan products, wooden boat models, and assorted
fish and squid “snack foods” for local consumption.