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Association of Southeast Asian Coastal Resources Management

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4.1 JUH r 8 1990 Seagrasses: A Resource Unknown

in the ASEANRegion MIGUEL D. FORTES 1989

Published by the International Center for Living Aquatic Resources Management 00 behalf of the Association of Southeast Asian Nations/United States Coastal Resources Management Project

Printed in Manila, Philippines.

Fortes, M.D. 1989. Seagrasses: a resoUlCe unknown in the ASEAN region. ICLARM Education Series 5, 46 p. International Center for Living Aquatic Resources Management, Manila, Philippines.

Cover photo: During low tide, shallow seagrass beds are often exposed and walked on by people looking for edible marine life. Dumaguete, Philippines,

Color photos are by A. T. White, unless otherwise

noted.

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Contents Acknowledgements

vii:

Foreword

ix

Introduction What are seagrasses? Why are seagrassesimportant? Where are seagrassesfound in the ASEAN region?

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Status of Seagrass Beds as a Resource Reasons for neglect. ., Uses of seagrassbeds """"'!""J"' Resource potential ".\,..' "/;;',.,...,;(.6)".I~"...,y1 ~~""""i

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Monetary value

8 '.8 9, 12

Biology and Ecology of Seagrasses: A Case Study in the Philippines Biological and ecological basesfor management Flowering, fruiting and adaptation Seagrassdensity, biomass and production Seagrassesin Philippine coastal food chains

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Resource Components of a Seagrass Ecosystem

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13 13 15 16

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Benthic seaweeds

Epibenthicinvertebrates ,

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19

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Fish

21

Reptiles and mammals

23

Threats t Natural threats

Mining activities Coastal aquaculture

Deforestation Blast fishing

Manage Conclusion References "

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Appendices'"'"'" 1. Atlas 0

2. Philip

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Acknowledgements I wish to thank Dr. Chua Thia-Eng (ICLARM) for the encouragementin writing this book, Drs. Alan T. White (ICLARM) and Mark S. Fonseca(US Departmentof Commerce,National Oceanicand Atmospheric Administration) for the insights and critical review of the manuscript,and my studentsfor having been my source of inspiration. Gratitude likewise goes to the United Nations Environment Programme (Nairobi) and the ASEAN-Australia Coastal Living ResourcesProject for giving me the rare opportunity to be in direct contactwith the seagrassscientistsof the region.

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Foreword

The coastalwaters of SoutheastAsian countrieshave some of the world's richest ecosystemscharacterizedby extensivecoral reefs and densemangrove forests.Blessed with warm tropical climate and high rainfall, thesewaters are further enriched with nutrients from land which enablethem to supporta wide diversity of marinelife. Becauseeconomicbenefitscould be derived from them, the coastalzonesin thesecountriesteem with humansettlements.OverJO% of the population in the regionlive in coastalareaswhich have beenrecentlycharacterized by high-level resourceexploitation. This situation became apparent betweenthe 1960sand 1970s when socioeconomicpressureswere increasing. Large-scaledestructionof the region's valuable resourceshilS causedserious degradationof the environment,thus affecting the economiclife of the coastal inhabitants,This lamentablesituationis mainly the result of ineffective or poor managementof the coastalresoQrces, It is essentialto considercoastalresourcesasvaluableassetsthat should be utilized on a sustainablebasis. Unisectoral overuse of some resources has caused grave problems. Indiscriminate logging and mining in upland areas might have brought large economic benefits to companiesundertaking these activities and, to a certain extent, increasedgovernme~trevenues,but could prove detrimental to 1owland activities such as fisheries, aquacultur~;and coastal-tourismdependentindustries.Similarly, unregulatedfishing efforts and the-use of destructive fishing methods, such as mechanizedpus_h-ne~and dynamiting, have causedserious destructionof fish habitatsand reduction of fish stocks. Indiscriminate cutting of mangroves for aquaculture, fuel wood, timber and the like have brought temporarygains in fish production, fuel wood and timber supply but lossesin nurseryareas of commercially important fish and shrimp, coastalerosionand land accretion. The coastalzonesof mostnations in ASEAN are subjected to increasing populationand economicpressuresmanifestedby a variety of coastalactivities, notably, fishing, coastalaquaculture,wastedisposal,salt-making,tin mining, oil drilling, tanker traffic, rural constructionand industrialization.This situationis aggravatedby the expandingeconomic activities attempting to uplift the standard of living of coastalpeople, the majority of which live below the official

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Introduction

Paradoxically, the greatest contribution of seagrassecosystemto the chains of life...is death.58 c' What

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Seagrasses are the only group of submergedflowering plants in the marine environment..They thrive in shallow-watercoastalhabitats.Like the terrestrial grassesfrom which they originated,they possesserectleafy shootsand creeping stems or r:hizomes(Fig. 1) which are effective for propagation.In contrast to , .", other submergedmarine plants (e.g., seaweedsor algae), seagrassesflower, develop fruit and produce seeds. They also have true roots andari internal systemfor the transportof gasesand nutrients. ",:, '. Why are SeagrassesImportant. ?

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Thereare only about50 speciesof seagrasses in the world"but.'~i$'number is not proportional to their abundance,as well as to their economicand ecological importance.Usually existing in enormousquantitiesand often!orrning large, densemeadows in tropical areas,seagrassesperform a wide spectrumof biological and physical functions. The traditional and contemporaryapplicationsof mainly nontropical seagrassecosystems,56 summarizedbelow, are also applicable in the ASEAN regionJt shouldbe noted,however,that the secondcategory of usesis only anticipated(Fonseca,pers.comm.). Traditional uses: 1. woveninto baskets 2. burned for salt,sodaand warmth 3. stuffing for mattresses 4. roof thatch 5. upholsteryand packingmaterial 6. compostfor fertilizer

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Cymodocea rotundata

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prophyllum bud leaf scale rhizome single root

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7. insulation for soundand temperature 8. fiber substitutein making nitrocellulose 9. piles to build dikes 10.cigarsand children'stoys .;,

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Contemporaryuses: 1. sewagefilters 2. coastalstabilizers 3. papermanufacture 4. sourceof usefulchemicals 5. fertilizer and fodder 6. food and medicine for man

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Seagrasses have beenknown to serve as food for turtles since the time of

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Darwin. However, it was Petersen65 who fIrst evaluatedthe contribution of the eelgrassto coastalfisheries. Seagrassbedsserveas nursery,shelterand food for fish, invertebrates42and dugong or sea cow.47They alsoproduce sedimentSand interact with coral reefs and mangrovesin reducingwave energyand regulating water flow. 87

Seagrasshabitatscan be viewed at two levels:86 .As a community -where a seagrassbed is a structural framework with plant and animal interrelationships;and .As an ecosystem-where theseinterrelationshipsare viewed as discrete processes,controlled by the interactive effects of both biological and physico-chemicalfactors. Seagrassbiomass is a primary factor in determining the organization of marine macrofaunal communities,82as it controls the habitat complexity, speciesdiversity and abundanceof associatedinvertebrates.39It is this ecological role of seagrassesthat links them directly to the improvementin thelivelihood of many coastalinhabitantsof the ASEAN region. The well documentedcatastrophiceffectSof the "wasting disease"of eelgrassbeds alongthe coastsof the North Atlantic in the early 1930sattestto the fundamentalecological importance of a seagrasscommunity. With its demise, not only were the structure and composition of the associatedfauna altered,81 but regimes in salinity, temperatureand nutrientload in the affectedwaterswere changedJ2Fisheries production in the area declinedand fisheries management strategieshad tobe reoriented.This ecological disaster,coupledwith the advent of scuba diving in the early 1970s,triggeredrenewed interest in seagrassesin mostparts of the world. , "

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Where are SeagrassesFound in the ASEAN Region? Seagrasses, .together with mangrovesand coral reefs, have a center of genericrichnessand diversity in the Indo-WestPacific..Table l,which gives the number of seagrassspecies from 27 countries,reflects,this. It also shows the similarities in the numbers of species among the-'countries in the region. Province A of Fig. 2 shows the 15 countrieslying in the areaof highest number of seagrassspecies.This biogeographicarea exhibits characteristicpatternsof climate, habitat conditions and perhaps,productivity. The expansivenature of the seagrasssystemhasdevelopedextensivefaunal communicationand material exchangewith other habitats(Fonseca,pers.comm.). For example,Province A holds about30% of the coral reefsof the world.46Seagrasses are closely associ,. ated with the corals and yet they cover much more areaon many fringing reefs thando the corals.S3Vast seagrassmeadowsareofteniound betweencoral reefs and the coastalfringes that supportmost of the region'smangroves.In this tran'" sition zone,characterizedby shallow, soft, sandy-muddybottom,the plantshave colonized all environmentallysuitableareas.

No.,of species Province A Philippines

Malaysia-Singapore Indonesia New Caledonia PapuaNew Guinea Queensland Micronesia VieUiarn Ryukyu Island Thailand Borneo India Sri Lanka Burma Hongkong

ProvinceG WesternAustralia New SouthWales SouthAustralia Tasmania-Victoria

Province B Kampuchea

aThe 27 countries of the Indo-West Pacif'tcgrouped by cluster analysis into major provmces showing the number of seagrassspeciesrecordedfor eachcountry and Sorensen'ssirriilarity iIidex (%CCs) with the Philippine flora.34

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Indian Ocean

Fig. 2. The sevenseagrass provinces in the Indo-W cst Pacific region (A through G) dclineatedby '" cluster analysis.34

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The most authoritativeaccounton the distribution of seagrasses (including the ASEAN .-egion)was made by Den Hartog.20lIt the Philipp~es,Mefiez~d.: co-workersS8 publisheda comprehensiveaccounton the local flora, andFortes31' producedthe latest complete work on the taxonomyand ecology of Philippine seagrasses, adding three new taxa to the list. With the 16 taxa now recorded,the" country has the second highest number of seagrassspecies in the wor14 [WesternAustraliahas 17(Crossland,pers.comm.)]. The seagrassspeciesreport for the ASEAN region(fable 2) is summarized thus:

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.Brunei Darussalam-Four speciesreported. These are the tropical eelgrass,spoon-grass,curled-basedspoon-grassand dugonggrass.The exposure and substrate condition of this country's coast appear unfavorablefor seagrass growth. IS ~ , .Indonesia -Twelve speciesknown. Seagrassbeds were sighted at the Flores Strait, Jakarta Bay and Seribu Island. Densebeds of tropical , 5 "

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Table2. Seagrassspeciesreportedfor the ASEAN region.20,3l Bnmei Indooesia Darussalam

~ilippines

Singapore

Thailand

Round-tippedseagrass (Cymodocearotundata)

x

x

x

x

x

Toothedseagrass (C. serrulata)

x

x

x

x

x

x

x

x

Fiber-strandgrass (Halodule pinifolia)

x

x

Fiber-strandgrass (H, uninervis)

x

x

x

x

Tropical eelgrass (Enhal~ acoroides)

Estuarinespoon-grass (Halophila beccarii)

x

Veinless spoon-grass (H, decipiens)

x

Small spoon-grass (H. minor)

x

x

Small spoon-grass

x

x

x

x

x

' x

(H. minor), a new variety Spoon-grass (H. ovalis)

x

x

Curled-basespoon:'grass (H. spinulosa) Halophila sF. Ruppia maritima Syringe grass (Syringodiwn isoetifoliwn) Dugong grass (Thalassia hemprichii)

x

x

x

Woody seagrass (Thalassodendronciliatwn) Total

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seagrass are associated with estuaries in Benten Bay and Riau Archipelago. Thinner beds of dugong grass, tropical eelgrass, fiberstrand grass, round-tipped seagrass and syringe grass are common among the coral islands in eastern Indonesia. 45

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.Malaysia -Nine s~ies known. There are recent records of tropical eelgrass in Cape Rachado and Port Dickson, spoon-grass in a shallow bay in Kuah and a new variety of spoon-grass in Tanjung Rhu.67 .Philippines -Sixteen species are variably distributed in Bolinao Bay in the north, Palawan, Cuyo Islands, and the Cebu-Bohol-Siquijor area at the center and Zamboanga and Davao in the south. Other seagrass beds are scattered throughout the coastal expanse of the islands. .Singapore -Eleven species are distributed in Pulau Sem*u,

Pulau

Tekong, Terembu Jarat, Labrador :Beach and Cyrene Reefs.41 .Thailand -Ten species reported. Dugong grass was sighted in the Andaman Sea together with spoon-grass, tropical eelgrass, round.' tipped grass and toothed seagrass.70 -.. The apparent discontinuity in the distribution of seagrasses in the region reflects more the lack of integrated and systematically collected data than their true pattern of distribution.

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Threereasonsmay be cited why in SoutheastAsia, seagrasses are the least studie~ amongthe living reso~s of the coastalenvironment: FIrst, people perhaps think that seagrassesare not as Important as coral reefs or mangroves. Second,the main interestsof marine and fisheries biologists working on seagrasshabitatshave beenfocusedon the algae,animals or fish that either live there or are associatedwith the beds. It was only in the mid-1960s that the shallow benthic coastalfringe was recognizedby oceanographersas a discrete ecosystem,forming a part of the largeroceansystems.68 Third, researchand developmentpriorities in ASEAN countriesare usually directed towards other resourceswith immediate impact and which are easily measuredin terms of monetaryvalue.

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Uses of SeagrassBeds Seagrassbedshave so far been valued for their role as fISh nurseryareas and as a source of food and nutrientsfor coastalecosystems,but their economic importance to the region has not yet beenquantified. Trying to determine the monetary value of an obviously rich and biologically diverse resource may indeed be a waste of time (Fonseca,pers. comm.), for this will only further delay its development Policymakers should, therefore, give higher priority to researchand developmentof the seagrassresource,despite the lack of documentationof its economicvalue,so that it can be usedmore productively for the service of humansand the environment Seagrassbeds are nursery areas for young fish and foraging grounds for food fish (e.g., snapperand emperorfish), dugong,turtles and wading birds.78In remote parts of Indonesia, d~gongand sea ~es are cl~sely associ~ted",:ith seagrassbeds.46Around Pan Island, Indonesia,78 specIesof fish, mcluding somevaluable food fish like the white-dottedrabbitfish,Japanesefllefish, cardinal fish and mojarra, were found in large numbers on seagrassbeds.44In the

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trawl catches from Bolinao and Ulugan Bay in the Philippines, shrimp in the mysis stage were the most abundant (53%) of all the juvenile stages of fish, shrimp and other invertebrates colIected.32 At these sites, seagrass beds yielded faunal densities at least three times higher than those yielded by nonseagrass areas. It is no wonder that in many coastal towns in the region, the collecting areas for fish and shrimp fry are iIi close association with either mangroves or seagrassbeds. There is a significant coincidence between the shrimp exploitation areas in the East Asian seas46and the known occurrence of seagrassesin the region (see Fig. 3). Although there is a high coincidence between areas in Indonesia where dugong17 and turtIes49 occur and where seagrasses are repqrted, dugong has become an endangered species in the region. Seagrasseshave other uses in the ASEAN region: .Thailand -At the Phuket Marine Biological Center, dugong reared in captivity are fed spoon-grass.13 .Indonesia -At the Ancol Oceanarium in Jakarta, the animals are fed syringe grass at a rate of 50 kg wet wt/day.45 In some places, thefnrits of tropical eelgrass are eaten by people. .Philippines -Fruits of tropical eelgrass are eaten raw, cooked or boiled. Together with the leaves, they are chewed or macerated and the spat mixture placed over wounds to check profuse bleeding.5 Tropical eelgrass and dugong grass are pqtential sources of fodder and fer:tilizer. Crude protein levels from their leaves reach as high as 23% of dry weight,30 higher than those of terrestrial forage grasses.64SmaIl amounts of sixmonth old leaf compqsts, when mixed with garden soil, appear to increase growth, pod fecundity and leaf chlorophyll content in mungbeans.l0 Interestingly, seagrasseshave been used as substitute for animal straw and as a fertilizer compqnent in coastal Denmark.52.88 In Florida, fruit production in both tomatoes and strawberries was highest with mulch from syringe grass.88In Germany, the grass has been used in papermaking and as a substitute for cotton in the manufacture of nitrocellulose.19 In the United States, dried seagrassesare used as fire retardant (Fonseca, pels. comm.). C ' , ,:."

Resource Potential

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In order to evaluate the resource pqtentia1 of seagrasses, their coverage area must be determined. In the Philippines, mapping of seagrassbeds has been done using digitizer analysis of landsat images and low altitude photography, ,

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supplementedby intensiveground truth surveysandplanimetry. In Bolinao Bay, northernPhilippines (plate 1), seagrassbeds (green bands)abound in shallow portions, totalling 37 km2. This total comprises 14 km2 of truly dense seagrasses(> 400 shoots/m2)and 23 km2 of less densebeds « 400 shoots/m2). Theseare delineatedby the dark greenbandsand light-to-greenish-bluebands, respectively(the dark greenbandsare moreaccurate). At six. sites in the country, seagrasss~eys yielded ~ total area of 50.88 km2 of WhICh2.56 km2 covered the specific transectstations. These figures, broken down below, representonly a small percentageof the entire areawhere seagrasses abound. Studysite

Seagrasses can grow as fast as cultivated com, rice, hayfields or tall grass prairies68 even without the benefit of fertilizers. Per area production can be higher than phytoplanktonproduction off Peru, one of the mostproductive areas in the world's oceans.74The production rate of trppical eelgrassin the Philippines (1.08 g C/m2/day)25is comparableto those of wheat, com, rice, hay and other crops.57,61Indeed, seagrassecosyste~sare one of the richest and most productive, rivaling tropical agriculture, with a prod1,lctivity apparently approachingthe theoretical maximum for natural ecosystems.57,93 It is this physiological adaptabilitywhich remains to be the mostprobablekey to the high diversity of plantsaild animals in seagrassecosystems. The extremely prolific seagrassbeds at Bolinao Bay produc~ at .least. 18,900kg C/day (basedon 0.9 g C/m2idayproduction rate),31 with the dense beds contributing two-thirds of gross production. This suggeststhat a squaremeterarea of the bedproduces8,635 calories daily or roughly 20% of the daily caloric requirement per kilogram of an ordinary individual. Thus, the daily caloric need of an adult individual weighing 70 kg is equivalentto that which is naturallyprocesseddaily by seagrasstissueswithin a 350 m2 areaof the bed. If productivity data for the whole region are considered,seagrassbedsas nutrient providers might very well be the most in1portantecosystemin the marineenvironmentof ASEAN countries. ,

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At the First SoutheastAsian SeagrassResourcesResearchand Management Workshop (SEAGREM 1) held at the University of the Philippines (17-22 January1989), the sustainableand elimination usesof seagrassesin the region were assessed(seeTable 3). Table3. Potentially sustainableandelimination usesof seagrasses in the ASEAN reg.ion. Indooesia Sustainableuses Food/drinks Fenilizer Fodder Medicine Construction Toys Footwear Fish Crustacean SheMlSh Use of otherfauna Recreation Education PreselVation Shorelineprotection

WI X X --X --I --X --X W2 WI LI LI X LI L3 X

Elimination uses Aquaculture fish crabs shrimp Ricefields Sugarcane Palm plantation Other agriculture Pasture Solar salt Industrial development Urban development Ports Airports Recreation

X X X --X --X --X -X --X --L X X X X X

Mining Wastedisposal Flood runoff engineering Boat traffice

X -W --L2 L

Legend: L, use is localized W, useis widespread X, information is inadequate

.

Malaysia

Philippines

Singapore

Thailarid

-Ll -W2 -LI

-W3 -W2 -W3 -W3 -LI W2 X -W3

LI LI

-LI -LI -LI

----LW -LW -LW --LI -LI LI -X

L W -W3 -LI W

W2 L2 W2

-LI -LI .; .LW .----W3 W3 W3 L3 W2

X

L3 W2

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X

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W2

LI

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LI LI L2

LI

I, a minor use 2, a moderateuse 3, a major use

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MonetaryValue

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Monetary values have been assigned to seagrassbeds, based primarily on the fiSheries they support. At Cairns North Queensland, fiSheries supported by seagrass beds produce about A$700,OOO (US$540,OOO) annually.16 In Puget Sound, Washington, a 0.4 ha of eelgrass bed has a value of approximately US$412,325 annually, estimated from the amount of energy derived from the system as well as the nutrition it generated for oyster culture,40 comme~ial and sport fisheries, sport charters and waterfowl. Judging from the revenues derived from seagrass fisheries alone, the economic value of seagrass beds in the ASEAN region could be substantial.

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Biology and Ecology of Seagrasses: ' A Case Study in the Philippines

Biological and Ecological Basesfor Management Although very little is known aboutthe biology and ecology of seagrasses in the ASEAN region, there is a practical need to incorporateall available scientific findings into their management.The coastal conditions are generally favorable to seagrassgrowth and development,as reflected partly in the high diversity of the seagrassflora. This diversitY results directly from the varied res~nses of the speciesto particular environmentalconditions alongthe coasts. The period of flowering and fruiting 'and adaptationsto different habitatconditions which control distribution, abundanceand production, are.im~rtant considerationsfor deriving maximumeconomicbenefitsfrom theseplarit resources.

Flowering, Fruiting and Adaptation Not much information is available on the time of flowering, fruiting and seed.dispersalof seagrasses. However, ecological studies on some Philippine species may reveal similar patterns in' closely related species present in the c

region. Tropical

eelgrass

starts to flower

in late April

and continues

until

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AuguSlThis processis directly related to progressionsin daylen~, temperature and rainfall. On the other hand, growth, biomass and production of the speciesare inversely related to suchprogressions.Fruiting occurs at the lattc.r half of the flowering period, with a peak in July when daylengthand rainfall have their highestvalues. In central Philippines, tropical eelgrassseedsgerminatein Augusl31 During the following months up to December.there are longer and more frequent low tides by day (day-minustides), suchthat the plants are exposedto air and sun for a maximumperiod. Thus,rapid growth and biomassincreasetake place during thesemonths,peakingin October. ,

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Survival strategiesof seagrasses consistof morphologicaland physiological or behavioraladaptations.The general form of a seagrassis itself the most remarkablefeature which adaptsthe plant to its environment.Flexible, grasslike leaves and an extensive root and rhizome system enable it to withstand the impact of waves, tides and shifting sedimentsin the shallow coastal habitat. Smaller-leafed varieties are more abundant in areas frequently subjected to higher temperatures.55

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.

Physiological or behavioraladaptationsare exhibited by tropical'eelgrass; toothedseagrass,fiber-strandgrassand small spoon-grass.Each of thesespecies has two varieties: one with a narrow range of tolerance (stenobiontic) to daylengtl1,tides, rainfall and temperature,and the other with a wide range of tolerance(eurybiontic) to thesefactors. The stenobionticvariety of tropical eelgrassesis seasonaland is narrow, thin-leafedand sparse,usually occupyingthe intertidal portions of openreefs.The eurybiontic variety, on the other hand, occurs throughout the year, and is wide and thick-leafed. This variety occupies subtidal habitatsand protectedembaymentsin dense~pulations. , '

DUring summer, anoxia or very low oxygen levels characteriZe'shallow intertidal habitatsdue to minimal water and wind movements,as well as "elevated ambient water temperatures,which reachan annualmaximum. Under this condition, seagrasses are overgrownby thick mats of blue-greenor greenalgae with associatedhigh turnover and oxygendemand;Consequently,the sediment becomeshighly reducingand acidic, indicated by the smeff of hydrogensulfide gas when the plants are uprooted.However, evenundersuchconditions, dugong grass,tropical eelgrassand round-tipped seagrassgrow and develop due to an apparentadaptive metabolic strategy (aerobic root microzones)which enables ,

14

them to colonize successfullysuch shallow-watermarine habitatsthat have excluded most other plant groups.It is in thesehabitatswhere the highestlevels in crude protein from the seagrasses havebeenrecorded.30

SeagrassDensity, Biomassand Production Density in local seagrassesis generally bimodal, with highest values in summer (March-May) and in the wet season(July-November).31Highest biomasscoincides with the latter period. Highestbiomassvalue (61.7 g organic matter/m2)was obtained in tropical eelgrasshaving a net production of 1.4 g C/m2/day,and an averageleaf growth rate of 1.1 cm/day. The recordedmean total turnover time in tropical eelgrassis 115 days, which meansthat the whole leaf biomassis producedevery 16 weeks,forming two to four leaf crops annually. For managementpU1]JOses, thesedata suggesta year-round supply of organic matter by the seagrass.Total dry leaf biomassof selectedseagrasscommunities in the Philippinesrangedfrom 8 to 132 g/m2,73 Few ecological data on seagrasses from Indonesiaare available. At Pari Island, meanleaf growth rates of 0.8 cm/day for old leavesof tropical eelgrass and 0.6 cm/dayfor young leaveswere observed.7Meanleaf productionratewas 3.37g/m2/day, with a biomassof 96.11 g/m2 and 3.48% per day meanturnover rate. Dugong grassshowed mean growth rates of 0.24 cm/day for new leaves and 0.2 cm/day for old leaves.Mean leaf productionwas J.8 g/m2/day, with a 3.74% per day turnoverrate,S

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.Unit area measuresof biomassand leaf growth are a function not only of plant size but of shootdensity. All these'measuresof the plant com:munityare mediatedby environmentalconditions. In the Philippines, shoot density in seagrassesis directly associatedwith water temperature.31Dugong grass has the widestrange of temperaturetolerance.In terms of biomass,however, daylength appearsto be the mostinfluential factor, while the numberof extreme low tides during daytime creates a negative effect on seagrassabundance,biomass, growth rate andproduction. Generally,salinity andrainfall are ineffective in directly controlling the abovefeaturesin local seagrasses.31 Fig. 4 showsthe setof recurringbiological eventsor phenologicalindices, plotted againstthe gradientsin the environmentalfactors at Puerto Galera. It is probable that daylength,temperatureand rainfall, interacting independentlyor

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Seagrasses in Philippine

Coastal Food Chains

Under the conditions in Southeast Asia, the trophic hierarchy involved the processing and transport of organic detritus from seagrass ~osystems

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consumers appear rather intricate. Actwil observations and simpl~ experiments indicate that detritivores, herbivores, carnivores and omnivores are all well-represented. The primary source of organic material comes from production by the seagrasses themselves. This is followed by contributions from the associated epiphytes and macrobenthicalgae,29,3l and phytoplankton and terrestrial plants. The organic materials are utilized by the fauna either through grazing of the

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living plant tissues or consumption of the detritus. Fig. 5 shows the generalized relationships among the major components identified from seagrass systems in the Philippines. The food and energy pathways are simplified, and the different trophic levels are represented only by species more commonly encountered in the beds. Fig. 5 also incorporates the functions and probable uses of the plants as these relate directly to past and ongoing activities on seagrass ecosystems in the country. Our understanding of seagrass ecology and their relationships is based largely on qualitative data. Many linkages within the trophic structure remain vague, unquantified or 1arge 1y u nknown.

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Among the diverse plant and animal life associatedwith SoutheastAsian seagrasses, many are commercially important Studieshave identified epiphytes (organismsattachedto plant surfaces),epibenthos(those on sedimentsurfaces), infauna(thoseliving buried in sediments),nekton(thosethatlive in or abovethe plant canopy), birds, reptiles and mammals,as componentsof the seagrass ecosystem. Fish some and shrimp probably most important among these groups,although coastalare villages in thethe region derive a significant portion of their sustenancefrom other componentsof the grassbeds.

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At low tide, the reef flats are constantlybeingpicked oyer by coastalfamilies who gathera major portion of their daily nutrition from the seagrassand seaweedflats, and patches of coral.53The harvest from this "gleaning," an activity predicatedon a healthygrassbed,includesedible seagrassfruits, algae, molluscs, seaurchins, seacucumbers,crustaceans,eelsand small fISh. In Pamilacan Island (Bohol, southern Philippines), gleaning of seagrassbeds contributed7.1 t/kri12or 40% of the total reef yield in the area.76In addition, shell industrieshave developedfrom the gleaningactivities in many shorevillages in the Philippines. Unfortunately, the actual contribution of this practice to coastal revenuesand nutrition in the country is unknown. In the following portion, only the major componentsof seagrassbeds which contribute substantially to the coastal economy of the countries in the region, as well as those related to conservationwill beemphasized.

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BenthicSeaweeds I

Although there are few seaweedspeciesin the ASEAN region, theseexhibit great seasonalabundance.In summer,for instance,biomassof the associated greenseavegetables,suchas the pond seaweedand the sealettuce,exceeds that of the seagrasses themselves.Seaweedsare harvestedfrom the bedsas food, as a rich source of chemicals for many industries and as mulch fertilizer for crops. Caulerpa. a high-priced seaweed,grows profusely in muddy pond bottoms amongthe commonseagrasses, and the agar-bearingGracilaria and Gelidiella both dominatein bedsfound on openreefs in the Philippines and indonesia. Sargassum,a brown seaweedusedas a feedstuffand fertilizer, as well as a \

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i sourceof alginates,commonlycolonizesbare rocky patcheswithin reefs dominated by seagrasses.In Calatagan,north-centralPhilippines,a successfulfarm of the red seaweed,Euchema,is located in a lagoon domiI:latedby tropical eelgrassand dugonggrass. It is interesting to note that the three seaweed-producing countries in the ASEAN region (philippines, Indonesia and Thailand) produce at least 100,000 t of dried raw seaweedsworth aboutUS$30 million annually.71.The main species

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harvestedare farmed Euchemaand wild Graci/aria, Caulerpaand Sargassum. In the Philippinesalone, the averageyearly net income per hectarefrom farmed Caulerpais P29,750(US$1,430),and from Euchema,P20,675.(US$994).

Epibenthic Invertebrates , Most of the large and conspicuousepibenthicanimals in seagrassbeds are commercially important in their adult or juvenile stages.Hence, common in ASEAN countriesare shrimp, seacucumbers,sea urchins,crabs,scallops,mussels and snails. The ASEAN countries had the following shrimp production, some of which may be attributed to healthy seagrassbeds:Thailand, 174,000t (the highest); Indonesia, 130,000t; Malaysia, 76,500 t; Philippines, 55,700 1; and Brunei Darussalam,500 t.26In 1977alone, the shrimp fisheries industry in Malaysiaproduced50,000 1,contributing 12% of the total marinecatch.14The high-priced banana shrimp feeds mainly on other crustaceansand on macrophytes;The latter comprisesthe highestpercentage(64.4%) in the gut contents of nurserypopulations of the species.at the 1,491 taxa trawled from seagrass beds, fish accountedfor 28.6%, while shrimp, 71.4%.33At three sites in northern Philippines, eight commercial shrimp specieshave been collected at an average 171 individuaIs/2-minute Tropical eelgrasses were found to of support the greatestnumbertrawl/month.32 of shrimp followed by the round-tipped

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seagrass,dugonggrass,syringegrass,spoon-grassand fiber-strandgrass. \.

A survey of edible molluscs harvestedby local fIShermenin Bai$ Bay, southernPhilippines, included 27 species of bivalves and univalves.4These were found in areaswith either pure or mixed growth of the tropical eelgrass and the spoon-grass.In two seagrass areasin the bay, they estimated69 kgjha of molluscs. About 1,000-2,000kg of the eggsof sea hare,valued at US$226-456, are gatheredfrom the bay yearly.2The eggs are a marketableitem, and interestingly, this mollusc has beena potential and low-cost source of anti-cancer agents.66All the other invertebratesobserved in seagrassbeds in Central Visayas,Philippines,are listc