A SUSTAINABLE SHRIMP MARICULTURE INDUSTRY FOR ECUADOR

Edjttd by Stephen Olsen and Luis Arrlaga Environmental fssues Impacts of Shrimp Mariculture Practiceson the Ecotogyof Coastal Ecosystemsin Ecuador

Andlisis del Ecosistemadel Estuario del Rio Guayasen el Ecuador: Implicacionespara el Manejo de Manglares y la Maricultura del Camar6n.

Robert R. Twilley

Resumen

La expansi6nde la consEuccidnde piscinas para el cultivodel camar6nen la zonaintermareal ha causadoel mayorcambio en el usodel sueloen el iireacostera. Este crecimiento, en su mayorparte, esl6 ubicadoen lasprovincias de Guayasy El Oro. El mayorrio y m6simportante sistema estuarino de la costa fluye-atravds de estasprovincias hacia el Golfo de Guayaquil.El Golfo y los estuariosadyacentes constituyenel ecosistemaestuarino mayor de la costaoccidental de Sudam6rica.La descargamedia del rio Guayases de 1.143,7m3/s, con ampliasvariaciones estacionales que van desde un promediode 200 m3lsen \a 6pocaseca hasta unosl.600 m/s, en la estaci6nlluviosa. El cultivodel camardnen esta6rea, se halla influenciado por algunasactividades tambi6n en expansi6n,como la agricultura,exploraci6n de petrdleo, desarrollo urbano y pesquerias. BaMndoseen la densidadde siembrade postlarvas (pls) por hertArea(ha),los m6todosde cultivoson clasificados (a) - en: extensivo(siembra de 10.000 20.000pls/ha; rendimienros de 100-400Kgha/aflo); O) semi-extensivo(50.000 - 60.000pls/ha con suplementoalimenticio; obtiene doble producci6n-a la del' m6todoextensivo); y, (c) semi-inlsnsivo(100.000 pls/ha; con suplementoalimenticio o fertilizacidn; rendimientos1.000 - 1.800Kglha). La existenciade la ampliazona de manglaresen la provinciadel Guayas(12L.4& ha) ha sido atribuidaaun gmnaporte de la Cuencadel Guayasy a lasaltas tasas de euapo-transpiraci6n.isto, asociadoa la frecuenciade maleas,ha creadolas condicionesfovarables para desarrollo del manglarcon densidadesde 185 rirboles/hay unadrea ba sal de 62,4^2, lo queindica mejores condiciones que en Venezuela,Colombia, Malasiay PuertoRico. En el estuariodel Guayas,la calidaddel aguaestii influenciada por las aportacionesprovenientes de 13Cuenca del Rio Guayas,el intercambiocon Ia zonaintermareal y los procesoioceanogrdfiiosfisicos del Golfo. El trabajorevisa la influenciade la industriade la mariculturadel camardnen la calidaddel agua, estimandoquela cantidadde aguaderecambio entre los esterosy laspiscinas, mediante bombeo, es de 20xl0omJ por dia, (30.000has de piscina,tasa de recambioSvoldia),volumen que es tan grandecomo la descargadel rio Guayasdurante el perfodode estiaje.Esto, asociado a la evaporaci6nen laipiscinas,indica unagran descarga de aguashipersalinas en el estuario. Sediscute el efecto_dela calidaddel aguaen el cultivodel camar6ny los factoresque influyen en la grod_uc9i61como son: perdidas de manglar;salinizaci6n del aguaen los esteros;futura operici6n deia presa Daule-Peripa;enriquesimiento excesivo de nuffientesy posterioranoxia; presencia de suitanciast6xicas comohidrocarbulos, pesticidas y metalespesados. Tambi6n, serealizaun anrilisis global, desde el puntode vistaecoldgico, de las interaccionesenfe la industriadel cultivo del camar6ny el eituariodel rio Guayas, especialmentereferidas a factoresasociados a la calidaddel agua,incluyendo lai descargasde aguasresiduales domdsticas e industriales,el incrementode bombeo de agua,la feraltiaci6nenlas pisJinas y ierturbaciones clim6ticoscomo las originadasen el eventode El Nifro. Lasrecomendaciones del autorcomprenden: efectuar el inventariode la pirdida demanglares; disnibuci6nactual del bosquede manglarpara identificar impactos actuales y futuros;restauracidn e integraci6ndel manglaren lasoperaciones de lascamaroneras, para control de la erosi6n,estabilizacidn de sedimentosy Eatamientode efluentesen lascamaroneras; estudios sobre balance hidrico en el estuariodel Guayas;desarrollar un modelosobre la calidaddel aguapara el ecosistemadel estuario;establecer un progama paravigilancia de la calidaddel agua.

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Citation:

Twilley, R. (1989) Impacts of Shrimp Mariculture Practices on the Ecology of Coastal Ecosystems in Ecuador. In: Olsen, S. and Arriaga, L., editors. A Sustainable Shrimp Mariculture Industry for Ecuador. Narragansett, RI: Coastal Resources Center, University of Rhode Island

Introduction

The Incaspracticed mariculture in Ecuador400 yearsago by closingoff lagoonswhich were temporarilyflooded with seawaterandpenaeid shrimp larvae. While the Indianshrimp farmers used ttreir harveststhemselves, ttre rapid growth of maricultureas an indusftyover the last decade in Ecuadorhas made it the leading farm shrimp producerin the world (McPadden,1985). The first commercialshrimp operationsdid not beginttrere until 1969(Siddall et al., 1985),and by 1979farming produced only 4,698 metrictons (m.t.) of shrimpcompared tD7,787 m.t. caughtat sea. Ecuadorianfarmed shrimp production rosedramatically from 1979to 1984;in 1983,the yearof the highestproduction on record,shrimp ponds produced29,100 m.t. while productionfrom the searemained at 7,500m.t. The exportvalue of the total tonnagein 1983,nearly triple the amount produced in 1979,was U.S. $183 million, ranking shrimp secondonly to petroleumas an exportcommodity for Ecuador. The expansionof the farmedshrimp industry resulting in the constructionof pondswithin the intertidal zonehas caused a major changein coastalland use. Initially shrimp pondswere constructedin moreinland, baren intertidalareas (salinas). Locating the pondscloser to the shorelowers costs associated with supplyingwater and larvae to ttreponds. From 1980to 1984nearly 10,000hgctares (ha) of ponds wereauthorizedfor construction annually, increasing the total to 60,000ha by 1983(Figure 1). A recent suvey by CLIRSEN(1984) shows that thereare currently 89,368 ha of shrimpponds along the coastof Ecuador(Table 1), manyoccupying former mangrove habitats. itris expansionof the farmedshrimp industry has been largely confined to the two southerncoastal provinces,Guayis andEl Oro (Table1). The largestriver andestuarine ecosystem of the-coastallowlands, ihe GoayasRiver basinand estuary, flows throughthese provinces and into the Gulf of Guayaquil.The Gdf of buayaquiland adjacent esiuaries are tle largestestuarine ecosystem on the westernPacific coast of SouthAmerica (Cucalon, 1984). This ecosystemhandles 95 percentof the country'simports and 50 percentof its exports,and its coastlineincludes the mostpopulated city in Ecuador,Guayaquil @ngineering iournal, 1972). Theshrimp farming indusry developedin an areaof the coastalzone that is influencedby severalother expanding industries including agliculture, oil exploration,utban development, and coastal fisheries.In addition,ihis regionmaintaini an extensivearea of intertidalcommunities including nearly 83 percentof all man$ovesin Ecuador(Table 1). Oneof the majorreasons that farmed shrimp production has not returnedto high levelsobserved in 1983is reducedavaitability of postlarvae(PL) for stockingponds. Total productionin shrimpwas down in 1984compared to the previousyear, not only becauseof low catchrates in the trawl fishery,but also becauseoi the lack of iarvaefor shrimpponds during the secondhalf of the year. It is estimatedthat during 1985,only half (30,000-40,000ha) of theshrimp ponds consftucted in theGuayas province were in operationbecause of the lack of postlarvae.The 4 billion postlarvaeprovided largely by the "laveros" (primarilypush net fishermen) representedan annualstocking rate of about133,000 postlarvae per ha of p-ondor abbut65,000 postlarvae per ha per season,based on two harvestsper year. This_isfairly intensive maricultureand produition rates per ha of pondseem to be decreasing.However, such calculations are tenuoussince iniormation on ttrequality of shrimpsold and tlre area of pondsactually in operationis somewhatconfusing. Severalfactors have been associated with the declineofpostlarvae in the estuariesalong the coast of Ecuador,including lower watertemperatures following an El Niflo eventin 1982-83,lossof mangrove habitat,decline in witer quality and overfishing. Poorerwater quality hascontributed to increasein disease andpoor maturation of postlarvae,and lower growthrates and higher mortality of wild shrimp,which affect the availabilityof wild postlarvaeas well as the survivalof larvaetransported to glowoutponds. Coasialresoruce management to sustainoptimum levels of productivityis complicatedby conflictinggoals of diverseuser groups. Changes in watershedland useand utilization of estuarinewaters traveprorn-pied concern ouer posiible negative impacts to theqlality of coastalresources and resultant damageto the shrimpindustry. Also, constructionand operation of the shrimpindustry itself haveraised concsrnsabout its negativeimpact on the coastalzone. This paperwitl showihe interactionsof variouseconomic enterprises and environmental resources, andwill recommendelements for an integrativemanagement scheme for fte coastalzone of Ecuador. Geography

The coastalzone of Ecuador(1oN to 3o20's)consists of four coastalprovinces @smeraldas, Manabi,Guayas, and El Oro) situatedin 284,000km2 of lowlandsbetween the pacific Oceanand the Andeanhighland @gure 2). Thereare thre€ climatic zones along the coast: a moderatelywet climatein the southwith abundantfresh water from runoff aroundGuayaquil; an arid centralprovince with very sparse vegetation;and, in the northnear Esmeraldas, a more humid, tropical zone with abundantrainfall and runoff. More than95 percentof the-annualprecipitation falls duringthe wet seasonfrom Januaryto May (Stevenson,198 1), andvaries from lessthan 500 mm in the centralprovinces and the coastof the southern provinces to over 3000mm at SantoDomingo de las Coloradosin the north @ngineer loumal, 1972; Schaeffer-Novelli,1983). .Annualmean temperatures (from 24.2ob 27o C) vary liule alonglhe coast, thuspotential evapotranspiration is about1300 mm per yeu. _ The two majorriver andestuarine ecosystems of tle coastare Rio Esmeraldasin the norttrand the Rio Guayaswhich flows into the Gulf of Guayaquilin lhe sourhEgore 2). TheGulf of Guayaquil receivesrunoff from some20 riverswith a watershedof 51,230 km2, equivalentto a watershed:water surfacearea ratio of 4.3. The GuayasRiver is the majorsource of freshwater to the Gulf, which forms60 km inlandat the confluenceof Rio Dauleand Rio Babahoyo.This freshwater enters the Rio Guayas estuary,and to a lesserextent the Estero Salado, around the city of Guayaquiland tl-ren flows 55 km to the Gulf of Grayaquil.The meandischarge of 1143.7m3/s for ttreGuayasriver is thehighest among the 30 riversin the coastalzone of Fcuador,iepresenting 39 percentof ttreiotal dischargerro? trrisiowUna region. Me-anprecipitation^in the GuayasRiver drainigesystem north of Guayaquilis BSimm/yr, which may rangefrom lessthan 400 mm to morethan 1800mm duringany oneyear (Figure3). Discliargeis strongly-seasonalranging from 200 m3/sduring the d.y season!o 1600r3/, in ur,-uueralewet season Gigure 3). Tidesare semi-diurnal and are of equala*ptituae (1.8m) in the Gulf of Guay"aquii,bur are amplifiedto 3-5 m in the Rio Guayasestuary near the city of buayaquil. Flushingtime of ttreGulf of Guayaquilis about21 days.

Shrimp Mariculture Management

The methodsof shrimpmariculture in the intertidalzone are grouped into threeclassifications based on the densitiesof iuvenileshrimp stocked in the ponds. Exteniivemariculture, using a stocking densityof 10'000-20,000iuveniles per heclare(ha), relies little on furthersupplements from"seawater exchange^via pu-mpingor from artificialfertilization. h._lrt9rl arepresent and annual yields are relatively low at.100-400kgftia' An increasein stockingrates to 50,000-60,b00*juveniles per trais a semi extensivesystem that requires some supplemental feeding and exchange of seawateito con6olwater quality problems suchas decreased levels of dissolvedoxygen. Production rites rno." thandouble with this program. The mosthighly managedsystem is semi-intensiveoperations that stockponds at 100,000* juvenilesper ha-andsupply food supplementsor fertilizethe ponds to increasesources of food. Water exchangewith the esfuaryis higherandannual production raies increase to 1,000-1,g00kgd. The dramaticexpansion of thefarmed shrimp industry and increased levels of pont *-ug.r.nt stimulated-the developmentofa new fisherytoprovide postlarvae and seed shrimp rotiro.llng mariculture polds' Industry sources_estimated that up to 90,000artisanal fishcrman were involved in the 19g3harvest andin 1984 numbersof fishermenyo+ing alongthe coast were even higher (N4cpadden, 19g5). Seed fishingis concentratedin areas-ofsignificant freJh water discharge along ttre ioastline, such as bt oro and Esmeraldas,with the highesteffort occurringin the Guayasp.oulnce. The catchesare non-selective, with smallfish, pena-eiOpostlarvae and juvenile shrimp including a mixtureofP.vannamei,P.stylirostris,P.occidentalisandP. ialiforniensis,aswellassomefreshwater Carid spe*ies'Since only the lorqer two speciessurvive best in maricultureponor, o*n.ir pay according to the proportion of the stockthat is P . vainamei andP. stylirostris(Mcpadden, r43sl. ser;ion is a post-harvest processand therefore less-valued species are lost from thi estuary.The peak of theseed fishing seasonis from Deccmberto March whenfisherm an maytake up to 40,000p.istr-uai a-oal iii sire rangingfrom 7-10mm.

* villalon et al. (thisvolume) report slightly higher stocking densities.

93 A majorfactor associated with the availabilityof immatureshrimp is temperatureof offshore water. Temperaturesare controlled by the mixtureof warmwater flowing southwardfrom thePanama Bight wittr cold watersflowing northwardfrom thePeruvian Humboldt Current. This mixing occurs beiweenManta and Punta Santo Elena along the coast of Ecuadorand gradually moves southward into the Gulf of Guayaquil.The southerlyflowing watercauses increase in seawatertemperature and initiates the onsetof therainy season (Cucalon, tttis volume; Cucalon, 1984; McPadden, 1985). Yearso1abnormally warm water temperatures and high rainfall areassociated with El Niflo events andhave resulted in the explosivepopulations of white shrimpoff the coastof Ecuador.The high availabilityofpostlarvae that supportedthe expansionofthe shrimpindustry in 1983and 1984has been associatedwith theseoffshore processes (Cucalon, this volume).

Reclamation of Mangroves

Eight speciesof mangrovesare distributedalong a rurrow band of the outer intertidal zoneof Ecuador*it=h a non-negetated-areacalled "salinas"(salt flats) in more inland intertidal areasClable 2). The oiii.nr. of 121,4& hi of mangrovein the Guayasprovince has been attributed to extensiveriver flow iro* tft" GuayasRiverbasin ani high ratesof evapotranspiration(Schaeffer-Novelli, 1983). Theieaward intertidal ron6 is colonized6y specilsof mangrovesin theRhizophoraceae family, withRhizophora harisonii on the perimeterof the ihorelineand mixtures of the otherspecies inland of this andAuicennia zonelgintron et a1.,1981). More inlandof this fringe is a mixed zoneof Rhizophora gir*inort. Still fartherinland lies a monospecificsiand of Avicennia,which yieldseventually to shrub frequencyand ri-ver discharge create ii*s * Salinaswith extremehypersaline soil conditions.High tidal ionOitlon, suitablefor mangroveioreststructures in the northernprovinces with treedensity of 185/haand a basal arcaof 62.4,&ha. This densityis greaterthan for mangrovesin Venezuela,Columbia, Malaysia (CinEon' andpuerto Rico (Cintron,1981). Mangroveforests are less dense in tle southernprovinces 1981),particularly surrounding shrimp ponds (Snedaker et al., 1986)' The mostobvious exfloitation of mangrovesalong the coastalzone of Ecuadoris the construction of pondsfor the productionof shrimpand fish. This land usepattern in the intertidalzone first involved wholesaledestruction of mangrovesin Machalaand in the southernprovince of El Oro. Following this period of total mangrovedestl"uction, pond constructionwas authorizedmainly in the Salinasand inland less i"ung1ou.,ones. Ilo*euer, as the arei of pondconstruction increased dramatically in the early 1980s, the of tflir unu"getatedintertidal areawas avaiiableand mangroves wg_rg again heavily impactedby mariculturelndustry.Recently, there has been a decreeihat prohibitsnew authorizationof pondsin **g.ou"r. Severalthousandtechres of pondshave already Ueen authorized in the intertidalzone, though constructionin manyinstances has not yet begun. provinceof The exactnu*U.r -e of mangroveslostio the constructionof pondsal-o1g {e coastal percentof the Ecuador is uncerrain. t"..nt iufr"y from CLIRSEN(1984) shows that 79,396ha or 88.8 provincesof Guayas total areaof shrimpponds along the coast of Ecuadoris locatedin tle two southern proportionof ponds unagt Oro (Iable-li. A Aiagrai"representing the potential_loss of mangrovesbased on constructedin mangrove3r.lus ir shbwnin Ffuure+. ffris diagramdemonstrates that if all 52,9l2haof areawould .trrintpponds in Guiyasprovince(fable 1) wLe built in mangroue-areas,Ihe originalmangrove rateof 10 havebeen 174,375na, arid mangrove loss would be 30.3percint of the resource.At a utilization mangro-ve would be 4'2percenI' f.t".ni of pondsbuiliin mangr6ues,the lossof !a!i1at Historicalrecords of-the southern coast of tlie Gulf of Guayaquilin the provinceof€l Oro at ponds(fable Machalagive someindication as to the proportionof mangroveslsedfor the constructionof gi. F LgiT rherewere 834.ih;of pondsconsructed and, based on theloss of mangroves is probably Ouringrhis"*1qO6bperiod, 55 percentof theseponds w-ere built in mangrovehabitats. This estimate rince urba'nareas also apparently increased at the expenseof mangroves'If urban,expansion in this period *^"Jq"uUv"*ugg"out"d divided between salinaiand mangroves, then 45 percentof theponds constructed would havebeen in mangroves. From 19??to 1-982,an additional1496.5 ha of pondswere built, however,there was no wasobserved, conespondingloss of salinasand mangroves. Rather, decreased land use for agriculture thatall which couldaccount f* tnr additionalpondconsEuction and urban expansion. However, assuming pondswereconstructed in of the mangroveloss was from pondconstruction, then 63 p-ercentof the habitatin El *ungro"" f;abitats.gased on ttii, ,ung" of 45-63percent of pondconsEuction in mangrove

94 Oro, an estimated16-21 percent+ of the mangrovein theGuayas province may havebeen lost to shrimp farming. Recentestimates by CLIRSENindicate that mangroveloss in the GuayasProvince is muchless, at about4 percent+of the originallnangrove cover. This would meanthat about 10 percent. of the shrimp pondsconstructed in this provincewere built in mangrove(Figure 4).

Factors Influencing Water Quality

Waterquality of the GuayasRiver estuaryis influencedby inputsfrom the watershed,exchanges with the intertidalzone, and physical oceanographic processes in the Gulf of Guayaquil.Activities in the watershedinclude a damproject that will influencefresh water input, expanding agriculture with associated dischargeof chemicalsincluding nutrients and pesticides, sewage from increasedurbanizatton,and toxic substancesfrom industrialactivities (Arriaga, this volume). Exchangeof estuarinewater with the intertidal zonevia tideshas been replaced wittr dieselpumps ttrat pump water to improvethe productivity of grow-out ponds.Natural resources within the intertidalzone, including mangrove, may alsoinfluence water quality, thoughthe functionof thesecommunities is still uncertain.Offshore waters influence the temperatueand salinityof the GuayasRiver estuary,most notably during El Niffo eventsand during presence of red tidesin coastalwaters. These diverse natural and anthropogenic influences on waterquality in the estuary complicatewater quality management in this coastalecosystem.

Daule-Peripa River Dam Project

A damis proposedat the confluenceof the Dauleand Peripa rivers for watersupplies, conEol of river flow, andhydroelectric power. Waterwill be divertedwith an aqueductfrom theRio Dauleto the SantaElena peninsula for potablewater, irrigation for agricultureand industriat use. The damwill also increasethe flow of freshwater to the GuayasRiver estuaryduring ttre dry seasonto preventsalt water intrusionin fhe lowerDaule River andenhance agriculture in this area. The Rio Dauledrains one-third of the GuayasRiver basinand hasa meancapacity flow of 11.5km3/yr or 365r3/r. Thr total river basinof both the Dauleand Peripa Rivers is 420,000ha andit receivesa meanprecipilation of 1800mm per year. A thoroughdescription of thesoil characteristicsand land use of this watershedare provided in a reportby the GuayasRiver BasinCommission (CEDEGE, 1970). The damwill createan impoundmentwitfi a storagecapacity of 6.0 km3 of waterwiti a surface area,of 2'70km2, meandepth of 21 m andvolume of 5.4 tL3. fne impoundmentwill supplypotable waterfor 300,000people at 400 litersper personper day,irrigation waierfor 42,000ha of tandand 20 Titlign cubicmeters per yearfor industry. Projectedindusrial useincludes apetroleum refinery, nirrogen fertilizercomplex, petrochemical complex, and a perochemicalport facility at-Monteverde The damwill influencethe amountof waterfrom the Dauleand Peripa Rivers that normaly dischargeinto theGuayas River. Presenl.lythe proposed operation of the damcalls for an averageannual flow of from 100to 175mr/s (Jenkins,1979; Arriaga,this volume). This flow will vary from a high of 321m3/s during the wet seasonin April, to a low oi nq *3/s in August. Comparedto the normalflow of theDaule and Peripa Rivers @gure 5), this modifiedflow is muchlower thanthe freshwater discharge of up to t000 m3/sthat usuallyoccurs during the wet season.During the dry season,to controlsalt water intrusion,the damwill providewater above the avengedischargeof about50 m3ls from suppliesstore.d in the impoundment.Based on averagemonthly flows, the normaldischarge of 343m3/s for thesetwo rivers will be restrictedto 175m3ls, a reductionof about49 pe,rcent(Figure 5). This reductionrepresents a loss of 15percent of the freshwater to the GuayasRiver and 13percent from the GuayasRiver estuary.The lossof freshwater from an estuaryin a semiaridzone such as the Guayasprovince may influencettre patternsof salinityin the ecosystem.

+ Alvarezet al. (this volume)report slightly differentpercentages of mangroveloss for 1986-1984.

95 Nutrient Loading

Sourcesof nuEientsfrom watershedsto aquaticecosystems may be describedas either diffuse or from somespecific point of effluent. Diffuse nutrientinputs include runoff from naturalvegetation or from managedlandscapes such as agriculture or forestryareas. Much researchhas gone into developingnutrient loading ratesfor different typesof native vegetationand for specifictypes of cropsin watershedsin various geographicareas. Most of theseloading rates have been developed for watershedslocated in temperate climates.Less is known aboutthe lossof nutrientsfrom tropicalwatersheds. The five principlecrops raised along the coastofEcuador are bananas, rice, sugarcane, cacao, and coffeefilho, 1983). Theseagricultural products come primarily from the Guayaslowlands, situated north andeast of the city of Guayaquil,and along the eastemshore of the Gulf of Guayaquil(Table 4). Statistics for the Guayasand Ins Rios provinceshave been combined to representagricultural activity in the Guayas River basin. Over 50 percentof ttreagricultural activity described in Table4 for the coastalzone of Ecuador occursin the GuayasRiver basin. The GuayasRiver basinis a majorproducer of rice, witfr neady95 percentof the totalrice productionalong the coastoccurring in the Guayasand Los Rios provinces.Rice in the GuayasRiver basinis of particularsignificance to the nutrienteconomy of the GuayasRiver estuarybecause of the large areaof production(Iable 5), the potential expansionof this crop in the watershedonce the Daule-Peripa damis completed(projected at 17,000ha duringthe initial phaseof the project),and its proximity to waterways.

Point Source Inputs

Point sourceeffluents are associated witl urbanareas and industry. However,nutrient waste from urbancenters can also be diffuseload.ings via groundwatertransport from septicsystems. Loading rates of nutrientsfrom citiesare dependent on populationdensity and degree of wastetreatment prior to discharge into aquaticsystems. In the GuayasRiver basin,there is very little treatmentof domesticwaste. Sewage is eitherreleased directly to therivers or estuariesvia ditches(refened to as "treated"),or is divertedto septic ponds. Thusnurient loadingfrom point sourcesin this watershedis largelyrelated to populationdensity andper capilarafes of nutrientinput from untreatedsewage. The populationin the coaslalprovinces of Ecuadorhas increased over the past 35 years,most dramaticallyin the Guayasprovince (Figure 6). From 1962to 1982the populationof this provincemore thandoubled to over 2,000,000persons. In the last severalyears, the gowth ratehas been even geater with a presentpopulation of over 2,568,452(Figure 6). Togetherwith the populationof Los Rios, there ue 3.14million peoptein the GuayasRiver basin@gure 6), of which 84 percentis consideredurban, with 53 percentof the basinpopulation located in the vicinity of Guayaquil.Cunently, only 18percent of the 34i00 ha city is servicedLy sewers.The city'scontaminated waters are emptied, untreated, into the GuayasRivei @l Guasmopumping sfation), Daule River @l Progresopumping station), and Estero Salado. Initial estimatesof the impactof urbanwaste on the qualityof waterin therivers andestuaries of the southerncoastal zone of Ecuadorare listed in Table6. Theseestimates are for the majorpopulation centersalong the waterwaysof the GuayasRiver basin(including the Guayasand Los Riosprovinces), and includea total populationof 1.7million people,or 54 percentof the watershedpopulation. Treatediewage here refers to sewagewhich is transporteddirectly to therivers and estuaries, whereasuntreated sewage is transportedto septicponds. From the availablestatistics, waste from 62 percentof thepopulation is pumpedto septicponds (untreated), however, 86 percentof the 54.83(10)6m3 ;f wastegenerated annuallyis discharged directly to aquaticecosy-stems. Based on thesepoprlation statisticsind per capitaratesfor eachtreatment, the loadingrates for oxygendemand (biological and chemical),soilas (totat and dissolved), and nutrients (total nirogen andphosphorus) have b-een calculated. This preliminaryanalysis indicates that the city of Guayaquildischarges over 90 percentof all domestic wastesthat enter the river, andan evengreater percentage of thenutrients that enter the GuayasRiver estuary.Solorzano (this volume) claimi that domesticand industrial waste has lowered water quality in the Dauleand Guayas Rivers by contributingto a high level of bacterialcontamination, decreasing dissolved oxygencontent and increasing concentration of nutrients. River Discharge

Ratesof nutrientinput from riversdischarging into the GuayasRiver estuaryand Estero Salado may be estimatedfrom informationon seasonalconcentrations relative to periodsof high andlow river flow (Figure7). Ammoniumconcenftations above 15 ug-at/L occur in threeof the four riverssurveyed and concentrationsas high as4A ug-atloccurred in theRio Milagro. Thesehigh concenfrationsoccurred during the low flow season,and thus do not necessarilyindicate high input to the GuayasRiver estuary.However, peaknitrite andnitrate concentrations with valuesgreater than 2.0 and50.0 ug-av, respectively, occurred in all the riversfrom Februaryto Juneduring periods of high river flow (seeFigure 3 foi seasonalriver flow in the GuayasRiver basin). Thepattern for nitratewas common among lhe river systemsinvestigated, indicatingthat this may representa high input of nitrogento the estuaryfigure 7). Concenrationsof nitrite above2.0 ug-atlue indicativeof ninification,which is usuallyaccompanied by decreasesin dissolvedoxygen concenfiations (dissolved oxygen is requiredfor the oxidationof ammoniumto nitrate; nitrite is an intermediaryion of this process).Low dissolvedoxygen concentrations were observed in lhe Rio Coloradoduring the wet season,but the otherrivers were nearly saturated with dissolvedoxygen throughoutthe year. High concenEationsof silicateand phosphate were also associated with the wet season,but the otherrivers were nearly saturated with dissolvedoxygen throughout the year. High concentrationsof silicateand phosphate were also associated with the wet season,indicating that the deliveryof thesenutrients may be substantialto thedownstream estuaries. This typeof information,along with dischargedata for eachriver system,is importantfor the developmentof nurient loadingrates to the GuayasRiver estuary.

Toxic Substances

Pesticides

Agriculturemay alsocontribute toxic substancessuch as pesticides to riversand estuaries of the Guayasbasin (Table 7). Table7 is basedon thearea of rice andsoy beans under cultivation in the Guayas andLos Rios provinces,an^d_the specific application rate for eachcrop. This analysisis only an approximationof the useof thesechemicals in the watershedand doei not indicatetheir actualtransport to aquaticsystems. Dr. Solorzano(personal communication) has expressed concern about the concendadons of pesticidesin the estuary,bur only tracesof pesticideshave been detected at thebeginning of therainy seasonin the DauleRiver (Solorzano,this volume). A CEDEGEriver basinstudy sho*ed'that DDT levels in the rivers flowing into the estuarywere low, but little documentationwas availlble.

Petroleum Hydrocarbons

Petroleumis the primarysource of foreignincome for Ecuador.The impactof oil on coastal provinceswas documented (Cintron et al., 1981),and one publication refers specifically to the coastalzone of Ecuador@lho, 1983). Concenfationsof oil hydrocarbbnsin the Guayasniuer estuaryand Ester Salado rangefrom 0.10 to 2.80 ug/L (Solorzano,*ris volume). Concenrationsare generally leis than2 ug& exceptnear oil spills or centersof commercialoil vesselactivitv.

Heavy Metals

Thereis somemining activity in the GuayasRiver basin,and several metals have been found concentratedin riverineand estuarine sediments. Solorzano (this volume) gives recent measurements of copper,iron, cadmiumin the watercolumns of the Babahoyo,Daule and Guayas Rivers, and mercury in the sedimentof the Guayas. The readeris referredto that repori.

97 Shrimp Farming

Pumping of Estuarine Water

More intenseshrimp farming techniques involve stockingponds at higherdensities of juveniles, which necessitatesadditional fertilization and supplementalfeeding to assurean adequatefood supplyfor secondaryproductivity. This level of pond management.requires sfiict control of water quality since phytoplanktonblooms resulting from nuftientadditions may depletedissolved oxygen concentrations to levels that will causeshrimp mortality. Oneof the solutionsto this potentialwater quality problem is to increasethe exchangeof seawater throughthe pondsby pumpingwater from the estuary.This exchangerate varies from 3 percentto 8 percentof th-evolume of the shrimppond per dayunder semi-extensive madculture, and may increase wifi moreintense farming practices. The total volumeof waterpumped from the GuayasRiver estuaryto shrimpponds depends on pondmanagement practices and the totalarea of pondsunder oper,ation. Figure 8 showi the volumi of estuarinewater exchanged with ponds(using a meanpond depth of 1.5m) basedon variousexchange rates (percent of pondvolume per day), and areas of pondsin operation.These exchange volumesare coinpared t-o the low andhigh flow dischargeof the GuayasRiver. At a presentoperation of 30,000ha of pondsunder semi-extensive management (5 percentpumping rate), the volumeof water exchangeddaily with the estuaryis approximately20 (10)6m3 €rgur9 8). This volumeis greaterthan freshwater discharge ftom the GuayasRiver duringlow flow periods.With intensivepond management (10 percentpumping rate), the samearea of pondswould exchangenearly 36 percentofthe riverine Os.i'rrg" Airindtrigtr flow periods. Thesetlpes of reasonablescenarios underscore the importanceof the impact' of shrimpponds on the waterflow patternin this estuary. Most oi'ihe waterthat is pumpedinto theponds replaces losses associated with seepageand evaporation.Although there are no dan on waterbudgets for semi-extensivemariculture, observations suggestthat lessthan half of the waterremoved from the estuaryis returnedin a flow-throughdesign @. ponds probably l,tiigle, personalcommunication). The amountof waterloss due to evaporatiolin 4q is highlr thanin the estuary,since shallowness decreases the heat absorption capacity of the watercolumn. Oien watergenerally loses more water per areato evapotranspfuationthan wetlands. For example, *'ungrou"t i-nsouth iforida areknown to havelower actualrates of evapotranspirationthan potential mtes mangrovesto shrimp ltwiiley, 1982). Therefore,the conversionof intertidalareas originally vegetated by pondscould intrease rhe loss of freshwater from the GuayasRiver Estuary. This_increas^ein water loss iould resultin the dischargeof hypersalinewaters to theestuary. Snedaker, et al (1986)found that water in 22 of 30 pondssurveyed had higher salinities ttran the sourcewater.

Fertilization

Supplementalfeeding and fertilization arerequired to *ryt the demandfor food at higherstocking densitiesof'postlarvae in pon-cls.A main sourceof nutritionfor shrimpin growoutponds is phytoplankton bloomsthat iesult from uria andsuperphosphates added prior to stocking.Supplemental feeding is carried out towardthe endof the growthcycle, usually in the last four weeks. The impactof rhese^chemicalson tt r *ut r qualityof the GriayasRiver esruary depcnds on their fatewithin thepond an{ on effluentdischarge rates.Muc^h of ihe nitrogenind phosphateapplied !o pondsare absorbed by phytoplanktonand are thus returnedto the estuaryi-n organii form. fnesi organii nutrientsrepresent biologic.al oxygen demand with ida;;*posirion of ttrispl-ankton biomass. Nutrients released during decomposition may thenbe availablefor Uiotogicalupiak" andcontribute to thered tidesrecently observed in theestuary. Therefore, nutrient effluent fr-ompondr *uy contributeeithcr directly or indirectly to the balanceof dissolvedoxygen in the estuary.

98 Mangroves

Sincethe Guayasestuary is tightly coupledto ttreintertidal zone via 3-5 metertides, mangroves may influencethese waters in severalways. Sedimentssuspended in the watercolumn are deposited in mangrovesduring flooding, enriching these forests. The extensiveroot systemof mangrovesenhances the sedimentationprocess and retards the forcesof erosionalong the shoreline(Scoffin, 1970). Nixon (1984) observedthat total suspendedsediment load of an estuaryin Malaysia,in which mangroveshad been reclaimedfor agriculture,was an orderof magnitudehigher than in an adjacentmangrove-dominated system. Somepreliminary evidence indicates that mangroves may alsobe a sinkfor nutrientsin coastal waters.This may seemto contradictthe theorythat mangroves act asa sourceof detritusto estuarine ecosystems(Odum and Heald, 1972;Twilley, 1985;Twilley et al., 1986). One explanationis that net nu,trientuptake may be a balancebetween inorganic nutrient input andorganic nutrient export. Walsh (1967)noticed a decreasein inorganicnutrient concentrations in watersmoving through a mangrovein Hawaii. Nedwell(1975) used enclosures to measurenufient uptakeby mangrovesediments and noticed theyhad a greatcapaciry to removenitrates, particularly in areasof nuhientenrichment from sewage discharge.The useof mangrovesfor treatmentof nutrient-enrichedeffluent has received some preliminary investigation(Sell, 1977),but this functionis still poorly understood.The lossof mangrovesmay be a contributingfactor to changesin waterquality, particularly nutrient levels, in the GuayaiRiver esruary.

Impact of Water Quality on Shrimp Mariculture

Fxisting informationsuggests that the production in shrimpponds has decreased from 1600to 250 kg of shrimpTha/yrover the last severalyears, though stocking rateJ 6ave been mainLained at about65,000 PL/haper harvest.Mortality ratesin shrimpponds are estimtted at greaterthan 50 percent(p. Maugle, personalcommunication), and evidence suggests that maturation rates are also lower-. In addition,there has beena declinein the availabilityof wild PL to the shrimpfarming industry, restricting ttre acreage of ponds in operation'Decrease of wild PL hasincreased demand for PL fiom hatciieries.Curiently, there are some 68 hatcheriesunder construction. Twenfy hatcheries still in initial phasesof operationproduced about 500 million postlarvaein 1985. _. 9ood waterquality is critical to theproductivity of hatcheriesbecause larvae are susceptible to disease.no$t_ eI, supplyand shrimpgrowth and mortality in pondsdetermine the productivity of tnis indusEy;and both depend on thequaliry of waterin rheeituary.

Mangroves and Fisheries

The lossof mangrovesfrom tropicalestuaries may have direct consequence to economically importantfisheries through loss of habitatand food. Zimmermanand Minello (this volume)have found lhatP. vannameiand P . stylirostrisinhabit areas in the mangroves,buf it is noi known whetherthese habitatsenhance the survivalor growthof theseand other marine organisms in theEstero Salado. Associationsdo existbetween the productionrate of shrimpand the txFnt of mangrovearea (Macnae, 1974;Tumer,1977: Jottry, 1984) because one hectare of mangrovescan yield rnoi" thanOOO tgyr of shrimpand 100 !S/:r of .fistrwithout management(Turner, tOzll. naseaon an approximatelJsi of 10,500 ha of mangrove(Figure 4), thereduction in shrimpproduction from the estuaryroutO Ueequivalent to 5,300_m.t./yr.Although these statistics do not shbwcausal relationships, they do polnrou?ihat wheneuer a?roductivepostlarvae fishery exist, there is thepresence of themangrove habitat as observed in Ecuador (Turner,this volume). Withoutfurther information on possibledepeidance of shrimplarvae and other marinefauna on mangrovesfor part of their life cycles,the effectof mangroueclearing on natural populationsin theGuayasRiver estuary will remainunknown. Mangrovedestruction-may also have an indirecteffect on fisheriesby changingwater quality

99 Salinization

The Daule-Peripadam and the pumpingof waterinto shrimpponds, may influencethe disnibution andincrease the concenfrationof salinityin the GuayasRiver estuary.Mangroves that exist in arid environmentssuch as the coastof Ecuadorwhere evapotranspiration is greater than precipitation are very susceptibleto slight changesin hydrology. For mangroveforests in arid life zones,small shiftsin precipitationresult in increasedsoil salinity followed by an increasein tree moftality and a shift in vegetationfrom foreststo tannesor Salinas(Davis and Hilsenbeck, L974: Cintron et al.,1978). In Ecuador the diversionof freshwater from the GuayasRiver estuarymust be managedwith awarenessof possible negativeeffects on mangrovessince they existin a relativelyarid environment.Margalef and Crespo (1979)suggested that the lossof freshwater from ttredam will probablynot affectmangroves, though the researchersdid not takeinto accountthe climaticinfluence of mangrovedistribution in the southern provinces. Increasesin salinitydue to changesin freshwater supply to the GuayasRiver estuarymay also impacteconomically important. fisheries in this estuarineecosystem. The EsteroSalado, which harbors mostof thefishery resoruces of theinner Gulf of Guayaquil,does not receivefresh water discharges directly from the GuayasRiver. Therefore,the flushingrate of this sectionof the innergulf is lessthan the more southemsections that are linked directlyto dischargefrom theriver. As a consequenceof lessdischarge, the EsteroSalado may be moresusceptible to increasesin the concenftationof materialsdissolved in the water column. Salinityis a conservativeelement in the watercolumn and indicates the concentratingnature of this bodyof waier. Precipitationduring 1985was relatively low, andthe Estero Salado was hlpersaline with valuesup -other to 30 parti per thousand(Zimmerman and Minello, this volume). This increasein salinity suggeststhat miterials,such as toxic chemicalsand nutrients may alsobe concentrated(assuming that their betravioris conservative).Organisms, such as shrimp,that inhabitthe EsteroSalado are very susceptibleto changesin waterquality, especially salinity and toxicity which may increasemortality and growth rates. retard" Changesin freshwater supply may alsoinfluence seasonal movement or recruitmentof organisms into the Guayi River estuary.The recruitmentof shrimpinto an estuaryis importantto their life cycle becausethe estuaryprovides optimal conditions, such a low predation,during critical stagesof maturation. Seasonaltiming oi recruitrneniis thoughtto be dependenton fluctuationsin salinityalong with influx of offshorewater masses. Since the Daule-Peripadam is designedfor a nearconstant flow of waterto the EsteroSalado, the potential impact of this projectshould be evaluatedrelative to disturbingseasonal fluctuationsoi saliirityin the eituary. Sincethe maricultureindustry relies on shrimppostlarvae thaf seasonallyutilize thelstuary, managementplans should strongly consider those factors that influence recruitmentof fisheriesin the estuarineecosystem.

Nutrient Enrichment and Anoxia

Nutrients that increasethe productivity of agricultureand are the by-products.ofhuman nutrition alsostimulate the primaryproductivity of aquaticecosyst€ms. Changes in waterquality in responseto nu6ientenrichment is caiteOeurophiiation.- Dissolved oxygen is a popularindex of waterquality; oxygen concentrationsbelow 4 mgl ueconsideredstressful to manyfisheries. The negativeeffects of low dissolved oxygento fisheriescan alil be indirectby disturbingbasic foodchains. The dischargeof organicmaterials ttrat"consumeoxygen during decomposition (biological oxygen demand, BOD) andof someinorganic nu6ients(chemicil o*yg.n?"ranO, COO),can cause a decreasein concentrationsof dissolvedoxygen in the estuary.A balance5f pto""r.es thatcontribute (photosynthesis and diffusion) and remove BOD and COD dissblvedoxygen is necessaryfor a healthyenvironment for economicallyimportant fisheries. Anoxia or low dissolvedo*yg"n -Bay conditionshave been observed historically in somestratified estuaries,such as in the Chesapeake whereanoxia of bottomwaters was observed in the 1930s may be relevantto many Q.{ewcombeand Horne, 1938). A concernregarding the ChesapegkeBay that irturtin" is'therecent increase inlnoxia in greatervolumes of waterand the persistenceof tttis condition".oryrt"*,in the water column. The linkagebetween incieased nutrient loading, enhanced production of phytoplanktonbiomass, and the consumftion of oxygen during decompositionof this organic material in itt" ryrt". eitherin the watercolumn oiin the surfacesediments may contributeto anoxiain the in 6tt rlup"ut" Bay (Officeret al., 1984).Therefore, nutrient abatement and control becomes a centralissue dealingwith simiiarwater quality problems in estuarineecosystems such as the GuayasRiver estuary. Redtides, phytoplankton blooms that discolor the water,are a commonoccurrence in the Gulf of Guayaquiland in the inlandwaters of the GuayasRiver estuary@eArcos, 1982; Jimenez,1980; Jimenez, this volume). Theseblooms vary in speciescomposition, density of cells,and duration. The mostdirect influenceon the estuaryis fish kills causedby thepresence of toxic organismssuch as Gonyaulaxcatenella and Gymnodiumbreve. Gonyaulexmonilata occurred in the upperportion of the Gulf of Guayaquilin April 1980,and in March 1986along the coastof Manglaralro.The 1980bloom resultedin high fish mortality (Jimenez,1980), while the 1986bloom causedsignificant mortality of shrimppostlaryae in eight hatcheries,interrupting operations for 3045 days(Jimenez,1986). Otherred tidesin ilre GuayasRiver estuaryinclude Gyrodinium stratum in September1982, Mesodiniumrubrum in August 1984,Prorocentrum maximum from February1985 to February1986, and a recentbloom of Nitzschiasp. (Jimenez,this volume). Theseblooms caused high mortalityin shrimp pondswhen phytoplankton contaminated waters were pumped from the estuary. Anoxic watersare apparendy uncommon in the GuayasRiver estuary,occurring only in areasnear sewageoutfalls (Arriaga, this volume). A surveyof five stationsin EsteroSatado found that dissolved oxygenconcentrations at 1 m depthranged from 3.5 to 5.3 mV (Solorzano,this volume). Concenfations arenormally lower nearthe bottom; for instance,Solorzano and Viteri (1981)measured concenEations of 1.5 ml/ at 1 m depthcompared to 2.0-2.5ml/ nearthe bottomat two stationsadjacent to the city of Guayaquil.The strongtides with amplitudesfrom 3 to 5 m in the GuayasRiveiestuary are responsible for the well-mixedaerated water column. Evenduring presence of red tidei in the estuary,inoxic pioblemsin pondsare not causedby pumpinganoxic water from the estuary;rather, anoxia in pondwater d^evelops when waterthat containsmaterials that may promotelow oxygenconditions is pumpedinto the lesswell-mixed shrimpponds.

Toxic Substances

Hydrocarbons

Hydrocarbonscan be lethalto fish at relativelylow concentrations(Table 8). However,cturent informationsuggests that the concentrationsof hydrocarbonsin EsteroSalado are less ni z ig/,an' order of magnitudeless than concentrations that may ai'fectthe naturalresources of this ecosysi...

Pesticides

Crustaceans,especially larvae, are usually more sensitive to 1owconcentrations ofpesticides ttran areother marine organisms (Costlow, 1982). Theextensive use of thesechemicals in the eituarine watershed createsa potentialhazard to the shrimpmariculture industry in Ecuador.Table 9 showsthe amount pesticides of importedinto Ecuadorin 1979and 1980.For eiample,Endrin, which is appliedat an approximaterate of 145m.t. per yearin therice paddiesof the GuayasRiver'basin significantly reduced growth_rates of rapidly growingjuvenile Mysidipsis bahia (McKenney, 1986), ar coicentationsof 60 *gF: Jn addition,physiological measurements of metabolicdysfunciio n in iysids ruurethallyro pesticides in laboratoryand field conditionsshowed lower growth and reproductlu" "r,for"Jin trese organismsduring later stages of theirlife cycle(McKenney, 1986). Daugherty (1975j "upuiitynodd ftar decreased yields !!.ifp in El Salvadorprobably resulted from the heavyuse or peJticidesin cottonfarming during the 1960s andearly 1970s.Pestiiides have a tendencyto becomemore concentrated along the food chainand thusmay stresspredators and higher trophic leveis such as fish. Beforethis problemian be solved,more information is neededon the ambientconcentration of thesechemicals that are toxic to certainfisheries, and on their fatein the aquaticenvironment.

Metals

High concentrationsof heavymetals in certainareas of the estuarineecosystem demons6ate the affectsof urbandevelopment and industry. Solorzano(1986) expressed particular ion.e.n for the concenftationof copper,cadmium and mercuryin the water column and sedimen8of the GuayasRiver estuary.Copper concentrations are higher than 10ug/ which is consideredinnocuous to aquaticspecies (Ketchum,1975), although these concentrations could be dueto naturalprocesses. Cadmium is also presentin concentrationsthat could impact aquatic organisms (etchum, 1975),and sediments showed significantmercury contamination (Solorzano, 1 986).

The Ecosystemand Shrimp Mariculture

The interactionsof the shrimpfarming industry with the GuayasRiver estuarineecosystem are summarizedin Figure9. Waterquaiity influences the supplyof wild PL as well as the successful productionof PL by hatcheries.Water quality also determines the swvival andgrowth rates of PL once they ate stockedin growoutponds. Alttroughwater quality of pondsdepends principally on the typeof managementused, characteristics of the water pumpedfrom the estuarycan also determinethe numberof shrimpproduced in theponds. Activitiesin the GuayasRiver basinaffect the qualityof waterin the estuaryand, therefore, the shrimpindustry through chemicals such as nutrients and pesticides from agdculture,sewage from the large populationcenters around the estuary,and heavymetals_from industry. Tire disnibutionand tumover raie of inesepollulants and salinity in the estuarinewater column of the estuaryare influenced by the dischargeof fieshwater from the watershed.Thus a damon theDaule-Peripa Riveri mustbe evaluatedin termsof its potentialimpact to waterquality in this estuary,given the strong seasonalnature of its freshwater inputs. Thereare also many natural occurrences that influence water quality and the shrimpindustry in this ecosystem@igure 9). For example,elevated water temperatures-in the Gulf of Guayaquillnay be a dominating'fadtorin the tremendousrecruitment of shrimpinto theinner estuariesduring climatic disturbancisknown asElNiflo. Redtides are also recruited from the Gulf of Guayaquilto the estuaries,in additionto the bloomsthat occur in situ. The extensiveareas of mangrovesare considered nurseries for economicallyimportant shrimp larvae as well aspossibly influencing nutrient and sedimentdynamics in this turbid .ituury. Tidesaffect water quality in the estuaryby mixing the watercolumn and preventing stratificationthaicould leadto problernswith low levelsof dissolvedoxygen' Consideringthe huge amountsof untreatedsewage ttrrat is dischargedinto this system,there are few accountsof anoxiawith in the estuary,a patternthat his beenattributed to thepresence of stron-gtidal currentswithin the system. 1'tr"*-y interactionsof thehuman and natural resources of this estuarineecosystem underscore the complexityinherent in questionsregarding ttre fluctuations of PL supplyand the apparentdecrease in ponOptoOo"tion of shrimpin the pastseveral years. The shrimpindusfiy is not only_affectg$ bV changesin itt" qriatityof waterpump.O tro* ttreestuary, but it alsoconnibutes to the problemby loadingnufrients forests(construction) ifertiiization),increaslng'fresh water loss (pumping), and desroying mangrove €tgure ql. Td G".iits of ponf,management invotving these praclices must also be evaluatedin the contextof iself. their 'possible negative effects on waterquality and the shrimpindusry ThereiJ now a generalfeeling in Ecuadorthat ttre loss of mangrovehabitat has contributed to the declineof witd postlarvaE,particularlyturing periodsof normal recruitment. In fact, new authorizations forbid.onrt octionof ponOsin mangioves.In orderto accommodatethese laws and maintain or increase (Siddall the level of shrimpproduction in th6 existingponds, mariculture operations must be intensified et pond al., 1985). fnus ftr6supply of postlarvaeinlhe estuaryiasa stronginfluence on both the rateof pondswould .onrt u.iion andthe typ66f poiramanagement (prg*d 9). The intenseutilization of existing loading .i*ie in.reasedpumplig andferritizatio-n of estuarinewater which would, in tum,leadto increased quality estuary of nutrientsto the estua{. This managementalternative may adverselyaffect water of the from the euenthough the objectiveis to lessen-negativeimpacts by preventingthe lossof mangroves increasedpumping ..oryrp1nl The negativeimpacts of pondconstruction on tireecosystem are replaced by- issues una-i..tifirutionasjociated *ittr *ore intensiveshrimp pond management (Figure 9). These and, demonsgatethe importanceof consideringshrimp pond management in the contextof the ecosystem with waterquality control (Figure 9). 'prii.ufarfy, payingclose attenrion to thoJefactois associated Tirtshiftirom extensiveto intensivemariculture may not necessarilyimpact the estuarine of several ecosystemif mangrovescould be utilizedin theoperation of ponds. Mangrovesmay actas-sinks p;i-'21'y;"ftients-used in rhefertilization of ponfu,particularly phosphates and nitrogen. Mangrove pond that is sedimentsmay alsotraue itte the capacityto ibsorb someof the BOD associatedwith biomass high in ctrloropnyiland as an effluent,may impactthe balance of dissolvedoxygen in the estuary' prior to irjtu.nt, trom stfimp pondscould be oisfiiuutedin nearbymangrove forests for nutrientremoval would most the returnof pondwater Uact to the estuary.This useof mangrovesas a nutrientbuffer, which

r07 likelyenhancemangrove productivity, would serveas a meansof minimizingthe negativeimpact of intensiveaquaculture on th_eestuarine ecosystem. N{angroves could also Ue rititlzeO iir pondmatragement to preventor relarderosion along the shorelinesof ponds. Sedimentstabilization is an importantnatural functionof mangrovesalong the coastline,particularly because they minimizethe impactof stormsurges. , Eventhough ttrere is a law that deniesthe constructionof newly authorizedpbnds in mangrove areas,there are thousands of hectaresof pondsthat were previously authorized but nofconstructed,ind are exemptfrom this decree.It is only the lack of postlarvaeand capital that hascontrolled the constructionof pondsin mangrovehabitats. Thus, an increasein the supplyof postlarvaeby warmertemperatures of offshorewaters or increasedproduction from hatcheries,iepieseni a dangerro mangroves. Hatcherieshave been viewed as an operationthat would savemangrove f6rests from further desftuction.However, if hatcheriesand larveros become able to produceeriough postlarvae for 45,000- 50'000ha of pondsas predicted,_then pressure to ggiljle mangrovesites for po.-ndconsrucrion is likely to dgvglo.n(present postlarvae levels keep less than 30,000 - 45;000ha of pondssupptieO). ihus, ttregrbwth of thehatcheryindustry to supplypostlarvae will havesome influence on manag-ehenfdecisions to either intensify existingponds or to constructnew ones. If this meansmore intensiv"l*tning iaatrniques,then mangrovesshould be part of the operationalscheme to €nhancethe production of this iiOustry. Profit in shrimpfarming is incomegenerated from pondproduction less the costsasiociated with pond operationThe levelof shrimpproduction and operation costs including dredging, const uction, pumping, fertilization,and land (authorizations)dependlargely on ttrequali$ of w"atei*tatis from the estuaryinto fumpeo the ponds. Severalfactors have been ioentiiied in the estuaryand the waterstrfr ftat could influence waterquality and, thereby, determine the economyof the shrimpi"o".t y. ffiy ;i th" natural resources suchas mangrov_esand tides provide the shrimpindustry with cieanwater and important habitats that enhance wild PL supplyand shrimp production in ponds(Figure 9). The lossof these?reeservices increasesthe costof shrimpproduction, iuch asthe coit of proufring pL by operatingtlarcheries. Negative effectsfrom otherindus&ies andshrimp mariculture itself on waterqiality inonut*uir.;;;;;;; shouldhave someinfluence on the costsand profis of shrimpfarming, since it is so uitally tint

Recommendations

Document the lossof mangrovesfrom the coastalzone of Ecuador;since mangruves are the center of the controversyon impactsin the coastalzone, then all piernisesrelated to this impactwill requireinformation on the exlentof loss. Doclment the presentdisribution of mangroveforests to identifypresent and future impacts on this naturalresource. Restoreand-integrate existingmangrove forests into the operationof shrimpponds. Utilize mangrovesfor treatmentof effluentsfrom pondsin operadbn,and for erosioniontroland sedimentstabilization in areasof pondconitruction. Developa waterbudget.for G-uayasRiver estuary,including a synthesisof existing information {re andthe calibrationof cunentdata gathering, to incieasethe utility of this?ata base. Integrate an-analysis of nutrientsand toxic substancesinto thewater budget to develop quality a water modelfor this ecosystem.Include in this modelthe fateof chem]cabin trreestoary,-- andthe modeof impactof thesechemicals economically important fisheries.

103 Institutea waterquality monitoring program design to determinethe cunentlevels of nutrients,dissolved oxygen (including BOD andCOD), pesticides, heavy metals, -. . petrochemicalhydrocar6ons and physical characteristics (temperature, Ug!! Td salinity)in the iresh and estuarinewaters of the GuayasRiver estuary. This progfamcould alsobe expanded to aid shrimppond and hatchery operators with decisionsconcerning water quality management. Evaluatethe relative contribution of cold/warm water intrusionsin the Gulf of Guayaquil,loss of mangrovehabitat, nu6ient loading and water quality on the maricultureindustry of Ecuador. Table 1. Land usepattems along the coast of Ecuador(areas in ha)

LandUse Guayas El Oro Manabi Esmeraldas TOTAL Mangroves 121463.5 24489.3 7973.4 21293.2 175219.4 69.4 24.0 4.4 12.2 100.0

Shrimpponds 52911.8 26483.9 8376.6 ?

Mangroveqpecies tffJf""?'tt'e coasrofEcuador Rhizophoraceae Rhizop lnr a harrisonii (eachm) Rhizoplnra racemosa(GFM Mayer) Rhizophoramangle Q) Rhizophorasamoensis Pellicieraceae Pelliciera rhizophorae@lanchon and Triana) Avicenniaseae Avi ce nni a ge r minan s Q_.) Combretaceae Lagunculariaracentosol.) Gaertn f. ConacarpuserectusL)

Historicalrecords t#lrtJ;.*s (areasin hectares) showingthe declinein mangroves"f 19arCuayaquil (CI-fB5q(19g3y. (Arealocared in hovince El Oro,iriloto Machala) LandUse 1966 1977 1982 It4angrove 4962.9 423t.7 3294.7 Camaroneas 0.0 834.2 Salinas 2330.7 1087.7 478.5 162.6 Agriculture 615.2 730.2 Vegetation 634.7 466.3 332.2 139.4 Urban 256.7 434.7 Rivers 588.5 1437-5 1514.5 1465.7 TOTAL 8556.3 8556.0 8616.3

105 Table 4. Cultivation areasin hectaresfor different cropsin the coastalprovinces of Ecuador (datataken from Solorzano1981)

GuaYas Oro T0TAL Crop Guayas l,os Rios RiverBasin Manabi Fsmeraldas El

75,688 Rice 35,280 37,058 72,338 1,304 1918 128 6,196 Cotton 540 540 5,656 90 34,800 Soya 10,038 24,470 34,508 165 5t 196,810 Cacao 12,134 I 16,115 t28,249 40,077 12,367 t6,117 t5,L76 238,308 Coffee 31,681 42,020 73,701 138,431 11,000 31,511 551,802 TOTAL 89,133 220,203 309,336 185,633 25,322

Source;Solorzano, 1981.

Table 5 of Ecuador Arealcultivation of rice associatedwith the riversin the coastalregion (fromSolorzano 1981)

Rivers Area

GUAYAS 35,280 1,600 Guayaquil 7J4s Daule 4,198 Sanrborandon 3,038 Balzar 8,003 Yaguachi 1,106 Milagro 5,164 El Triumfo 4A26 Naranjal 37,058 R10S 19A09 Babahoyo 3,033 Baba 3,000 Vinces r2r4 Urdanea 2,160 Puebloviejo 860 Ventanas 7,382 Quevedo r,304 MANABI 565 SantaAna AA' Portoviejo 29'.7 Rocafuerte 1,918 ESMERALDAS 293 Esmeraldas r,625 Quininde t28 ELORO 128 SantaRosa

r06 Table 6. Estimatesof ttredischarge of domesticwaste from the Guayaswatershed basedon thepopulation of the majorcities of the Guayasand Los Rios provinces

City Treatnent Population Volume BCD TSS TDS ]N GUAYAS Guayaquil sewer 634,720 46.335 r2,5M 27,927 t2,694 23,t67 2094.5 253,8 unfeated 876,520 6.399 6,049 t4,024 t4,024 TOTAL 1,511,240 52.734 19,552 4l,g5t 26,7L9 23,t67 2094.5 253.8 Salinas sewer untreated 22,360 .163 154 357 358 TOTAL 22,360 .163 t54 357 358 0.0 0.0 I-alibertad sewer unrea@d 65,45A .478 452 1,447 l,M7 TOTAL 65,450 .478 452 l,M1 7,047 0 0.0 0.0 Naranjal sewer 4,580 .335 90 202 92 r6'l 15.0 2.0 unfeated 7,480 .055 52 329 329 TOTAL 12,060 .390 r4z 531 42r r67 15.0 2.0 Manglaralto sewer unrearcd 12,300 .090 85 r97 197 TOTAL L2,3OO .090 85 t97 r97 0.0 0.0 Playas sewer unteated 18,550 .208 r97 457 451 TOTAL 28,550 .208 r97 457 457 0 0.0 0.0 SantaElena sewer unneated 15,670 .tI4 108 25r 25r TOTAL 15,670 .114 108 25L 251 0.0 0.0 LOS RIOS SantaRosa sewer 6,040 .44r 119 266 r2r 220 20.0 2.0 untreated 27,530 .20r 9A 444 440 TOTAL 33,570 .&2 309 706 s6l 220 20.0 2.0 TOTAL sewer ss34a 47.111 t2,713 28,395 12,907 23,554 unEeated 2129.5 257.8 1,055,960 7.709 7,286 17,102 17,103 0 TOTAL 1,701,200 0 0 54.819 19,999 45,497 30,010 23,554 2129.5 257.8 EngineeringI oarnal,I97 2.

107 Table 7. Applicationrate and input of pesticidesused in the cultivationof rice and soybeans basedon thearea of eachcrop in theprovinces Guayasand Los Rios,the watershedof the Gulf of Guayaquil

Rice SoyBeans

Pesticide Treatrnent Input Pesticide Treatrnent Input

Ronstar25 2.00 Llha r44,676 Bravo 3.00 Lftla t03,524 Ronstar12 4.00 289,3s2 Daconil 2.50 Kg/ha 86,270 Machete 4.00 289,3s2 Afalon 3.00 r03,524 Saturno 3.00 217,0r4 Preforan 15.00 Llha 5r7,620 Propanil 8.00 578,704 Hormonales 2.00 144,676 Fuxadan 15.00 Kdha 1,085,070 Curater5-lA7o 0 Diazinon 1.00 72,338 Ozad:r;, 0.50 36,169 Lorshan 0.50 36,169 Endrin 2.00 144,6'16 Lannate 2.00 r44,6'76 Diprerex957o 1.00 72,338 Bin 75 300.00 gllha 21,701,400 Benlate 250.00 glha 18,084,500 Kasumin 0.75 Llha 54,253.5 Inosin 0.75 54,253.5

Solorzano,1981

Table 8. fuel oil Comparativetoxicity of the watersoluble fraction of No' 2 to different life stagesof four marinecnrstaceans Concentrationsare ppm of total hydrocarbon 1981) 6en ei a- 1976,cited fi6m Neff andAnderson' LC-50 CI(95Vo) Species 6.6 6.1 6.9 Penoeusaztecus postlarvae ).t 3.0 5.1 (brownshrimP) earlyjuveniles latejuveniles 2.9 2.2 3.8

postlarvae t.4 0.9 2.1 Penaeussetiferus 0.8 r.2 (white shrimP) juveniles 1.0 - larvae 1.2 1.0 1.5 PalaemonetesPugio 2.4 2.r - 2.8 (grassshrimP) postlarvae - adults 3.5 2.4 4.9 1.8 MysidopsisalmYra postlarvae(1 daYold) (opossumshrimP) postlarvae(7 daYsold) 1.8 adults .7 Figure I Areas of ponds authorized by the Ecuadorian govemment for the construction of shrimp ponds.

o 9so

0 cLrRsEN fr 3sn

L

=10

8so

U N

l

?ro U

76 77 '6 79 a0 YEAR

Figure Thecoastal provinces ofEcuador

80 Figure- 3 A) Forty yearrecord of annualprecipitation in Guayaquil. B) Averagemonthly dischargeof theRiverGuayas from 1962to I9&. (Bothfigures from Stevenson1981).

RIO GUAYAS 1962 - '196.1

6 c E (9

z I'J I F

ts 7 g o o a t! o

RiosDaule_-tj'Ii oj: 7.

JJ

YEAFS MON]HS

Guayasprovince' Figure4 Hypotheticalloss of mangrovesin the giventhat a percentageof pondsare constructedin (53'000ha) -rngrin. forest.fbr examp'te,if all pondsasof 1984 tr"adUeen constructed inmangroves, then 307oof Guayas mangroveswould havebeen cut' (Seetable 1)'

o9

f. FA.l. at 0 0a (lt6 ';h c)=

a0trL OQ

=q, (! tr> q a=

25Vo 50Vo 75Vo Hypotheticalarea of pondsconstructed in Mangroves hs io of tolal area of shrimPfarms) Figure5 No-rmaldischarge at theconfluence of tlte Dauleand PeripaRivers (solid line) comparedto the restrictedflow controlledby the proposeddam (dottedline). Slantedlines represent dischargelost from theestuary during the wet season,and the stipuledarea is discharge providedby the impoundmentduring the dry season(From Jenkins 1979).

rt o

:c 500 o o

.IFMAMJJASOND

MONTHS

Figure 6 Population duringttre past 35 yearsin the coastalprovinces of Ecuador(data from Gomez 1986).

@ o r ,.s ; F J:) 3 r.o c MANABI -.t' 't":,r;$H'::

1970 YEAR.

111 Figure7 Concentrationsof nuffientsfor differentrivers in the GuayasRiver basin(data from Rendon et al., 1983).

E 3

a a Figure 8 Volumesof waterexchanged with shrimpponds per dayat differentpumping rates (percentageof the volumeof a shrimppond per day)based on the areaof ponds(ha) with a meandepth of 1.5m (seetext).

(o 200 x c) E t {En o o [rJ o z T 100 () x uJ UJ

J o

50,000 100,ooo AREA OF PONDS,hA

ll3 Figure 9 Interactionsbetween shrimp farming and GuayasRiver estuarineecosystem. References

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