ShrimpBook Impacts Twilley

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

A SUSTAINABLE SHRIMP MARICULTURE
INDUSTRY FOR ECUADOR
Edjttd by Stephen Olsen and Luis Arrlaga

Environmental fssues

Impacts of Shrimp Mariculture Practiceson the Ecotogy of
Coastal Ecosystemsin Ecuador
Andlisis del Ecosistemadel Estuario del Rio Guayas en el
Ecuador: Implicacionespara el Manejo de Manglares y la
Maricultura del Camar6n.
Robert R. Twilley
Resumen
La expansi6nde la consEuccidn
depiscinasparael cultivodel camar6nen la zonaintermarealha
causadoel mayorcambioen el usodel sueloen el iireacostera.Estecrecimiento,en su mayorparte,esl6
ubicadoen lasprovinciasde Guayasy El Oro. El mayorrio y m6simportantesistemaestuarinode la costa

fluye-atravdsde estasprovinciashaciael Golfo de Guayaquil.El Golfo y los estuariosadyacentes
constituyenel ecosistema
estuarinomayorde la costaoccidentalde Sudam6rica.La descarga
mediadel rio
Guayasesde 1.143,7m3/s,con ampliasvariaciones
quevandesdeun promediode 200 m3lsen
estacionales
\a 6pocasecahastaunosl.600m/s, en la estaci6nlluviosa.
El cultivodel camardnen esta6rea,sehallainfluenciadopor algunasactividades
tambi6nen
expansi6n,comola agricultura,exploraci6ndepetrdleo,desarrollourbanoy pesquerias.
BaMndoseen la densidadde siembradepostlarvas
(pls)por hertArea(ha),
los m6todosde cultivoson
clasificadosen: (a) extensivo(siembrade 10.000- 20.000pls/ha;rendimienros
de 100-400Kgha/aflo); O)
(50.000- 60.000pls/hacon suplemento
semi-extensivo
alimenticio;obtienedobleproducci6n-a
la del'

m6todoextensivo);y, (c) semi-inlsnsivo(100.000pls/ha;con suplementoalimenticioo fertilizacidn;
rendimientos
1.000- 1.800Kglha).
La existenciade la ampliazonade manglares
en la provinciadel Guayas(12L.4& ha) ha sido
atribuidaaun gmnaportede la Cuencadel Guayasy a lasaltastasasde euapo-transpiraci6n.
isto, asociadoa
la frecuenciade maleas,ha creadolas condicionesfovarablesparadesarrollodel manglarcondensidades
de 185
y unadreabasalde 62,4^2, lo queindicamejorescondiciones
rirboles/ha
queen Venezuela,
Colombia,
Malasiay PuertoRico.
En el estuariodel Guayas,la calidaddel aguaestiiinfluenciada
por las aportaciones
provenientes
de
13Cuencadel Rio Guayas,el intercambiocon Ia zonaintermarealy los procesoioceanogrdfiios
fisicosdel

Golfo.
El trabajorevisala influenciade la industriade la mariculturadel camardnen la calidaddel agua,
estimandoquela cantidadde aguaderecambioentrelos esterosy laspiscinas,mediantebombeo,esde
20xl0omJ por dia, (30.000hasde piscina,tasade recambioSvoldia),volumen
queestangrandecomola
descarga
del rio Guayasduranteel perfodode estiaje.Esto,asociadoa la evaporaci6n
en laipiscinas,indica
unagrandescarga
de aguashipersalinas
enel estuario.
la calidaddel aguaen el cultivodel camar6ny los factoresqueinfluyenen la
Sediscuteel efecto_de
comoson:perdidasde manglar;salinizaci6ndel aguaen los esteros;futuraoperici6ndeia presa
grod_uc9i61
Daule-Peripa;
enriquesimiento
excesivode nuffientesy posterioranoxia;presencia
de suitanciast6xicas
comohidrocarbulos,

pesticidasy metalespesados.Tambi6n,serealizaunanrilisisglobal,desdeel puntode
vistaecoldgico,de las interacciones
enfe la industriadel cultivo del camar6ny el eituariodel rio Guayas,
especialmente
referidasa factoresasociados
a la calidaddel agua,incluyendolai descargas
de aguasresiduales
domdsticas
e industriales,el incrementodebombeode agua,la feraltiaci6nenlaspisJinasy ierturbaciones
clim6ticoscomolas originadasen el eventode El Nifro.
Lasrecomendaciones
del autorcomprenden:efectuarel inventariodela pirdida demanglares;
disnibuci6nactualdel bosquede manglarparaidentificarimpactosactualesy futuros;restauracidn
e
integraci6ndel manglaren lasoperaciones
paracontrolde la erosi6n,estabilizacidn
de lascamaroneras,
de
sedimentos
y Eatamientode efluentesen lascamaroneras;

estudiossobrebalancehidricoen el estuariodel
Guayas;desarrollarun modelosobrela calidaddel aguaparael ecosistema
del estuario;establecer
un
progama paravigilanciade la calidaddel agua.

9r

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Coastal Resources Center,
Graduate School of Oceanography,
University of Rhode Island
220 South Ferry Road
Narragansett, Rhode Island, USA 02882
Telephone: 401.874.6224
http://www.crc.uri.edu
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
TheIncaspracticedmariculturein Ecuador400 yearsagoby closingoff lagoonswhich were
andpenaeidshrimplarvae.While theIndianshrimpfarmersusedttreir
temporarilyfloodedwith seawater
ttrerapidgrowthof maricultureasan indusftyoverthelastdecadein Ecuadorhasmade
harveststhemselves,
it the leadingfarm shrimpproducerin the world (McPadden,1985). The first commercialshrimp

operationsdid not beginttrereuntil 1969(Siddallet al., 1985),andby 1979farmingproducedonly 4,698
metrictons(m.t.) of shrimpcomparedtD7,787m.t. caughtat sea. Ecuadorianfarmedshrimpproduction
rosedramaticallyfrom 1979to 1984;in 1983,the yearof the highestproductionon record,shrimpponds
produced29,100m.t. while productionfrom the searemainedat 7,500m.t. The exportvalueof the total
tonnagein 1983,nearlytripletheamountproducedin 1979,wasU.S.$183million,rankingshrimp
secondonly to petroleumasan exportcommodityfor Ecuador.
The expansionof the farmedshrimpindustryresultingin the constructionof pondswithin the
intertidal zonehascauseda major changein coastalland use. Initially shrimppondswere constructedin
moreinland,baren intertidalareas(salinas).Locatingthepondscloserto theshorelowerscostsassociated
with supplyingwaterandlarvaeto ttreponds. From 1980to 1984nearly 10,000hgctares(ha)of ponds
wereauthorizedforconstructionannually,increasingthe total to 60,000ha by 1983(Figure1). A recent
suvey by CLIRSEN(1984)showsthat therearecurrently89,368ha of shrimppondsalongthe coastof
Ecuador(Table1), manyoccupyingformermangrovehabitats.
itris expansionof the farmedshrimpindustryhasbeenlargelyconfinedto the two southerncoastal
lowlands,
of the-coastal
provinces,Guayis andEl Oro (Table1). The largestriver andestuarineecosystem
ihe GoayasRiver basinandestuary,flows throughtheseprovincesand into theGulf of Guayaquil.The
on thewesternPacificcoastof
Gdf of buayaquilandadjacentesiuariesaretle largestestuarineecosystem

percent
of
the
country'simportsand50
handles
95
This
ecosystem
SouthAmerica(Cucalon,1984).
percentof its exports,andits coastlineincludesthemostpopulatedcity in Ecuador,Guayaquil@ngineering
iournal, 1972). Theshrimpfarmingindusry developedin an areaof the coastalzonethatis influencedby
andcoastal
severalotherexpandingindustriesincludingagliculture,oil exploration,utbandevelopment,
nearly83
including
communities
intertidal
of
extensive
area

maintaini
an
region
fisheries.In addition,ihis
percentof all man$ovesin Ecuador(Table1).
Oneof themajorreasonsthatfarmedshrimpproductionhasnot returnedto high levelsobservedin
1983is reducedavaitabilityof postlarvae(PL) for stockingponds. Total productionin shrimpwasdown in
1984comparedto thepreviousyear,not only becauseof low catchratesin thetrawl fishery,but also
becauseoi the lack of iarvaefor shrimppondsduringthe secondhalf of theyear. It is estimatedthatduring
in theGuayasprovincewerein
ha)of theshrimppondsconsftucted
1985,only half (30,000-40,000
providedlargelyby the "laveros"
postlarvae
postlarvae.
4
The billion
operationbecauseof thelack of
an annualstockingrateof about133,000postlarvaeper ha of
(primarilypushnet fishermen) represented

p-ondor abbut65,000postlarvaeper ha per season,basedon two harvestsper year. This_isfairly intensive
maricultureandproduitionratesper ha of pondseemto be decreasing.However,suchcalculationsare
tenuoussinceiniormationon ttrequality of shrimpsoldandtlreareaof pondsactuallyin operationis
somewhatconfusing.
alongthecoast
with thedeclineofpostlarvaein the estuaries
Severalfactorshavebeenassociated
following an El Niflo eventin 1982-83,lossof mangrove
of Ecuador,includinglower watertemperatures
habitat,declinein witer quality andoverfishing. Poorerwaterquality hascontributedto increasein disease
andpoormaturationof postlarvae,andlower growthratesandhighermortalityof wild shrimp,which affect
to glowoutponds.
theavailabilityof wild postlarvaeaswell asthe survivalof larvaetransported
productivity
is complicatedby
to sustainoptimumlevelsof
Coasialresorucemanagement
of estuarinewaters
utilization
land

use
and
groups.
in
watershed
Changes
goals
of diverseuser
conflicting
andresultant
concernouerposiiblenegativeimpactsto theqlality of coastalresources
traveprorn-pied
damageto the shrimpindustry. Also, constructionandoperationof the shrimpindustryitself haveraised
concsrnsaboutits negativeimpacton thecoastalzone.
resources,
andenvironmental
This paperwitl showihe interactionsof variouseconomicenterprises
schemefor fte coastalzoneof Ecuador.
andwill recommendelementsfor an integrativemanagement

Geography
The coastalzoneof Ecuador(1oN to 3o20's)consistsof four coastalprovinces@smeraldas,
Manabi,Guayas,andEl Oro) situatedin 284,000km2 of lowlandsbetweenthepacific Oceanandthe
Andeanhighland@gure 2). Therearethre€climaticzonesalongthecoast:a moderatelywet climatein
thesouthwith abundantfreshwaterfrom runoff aroundGuayaquil;an arid centralprovincewith very sparse
vegetation;and,in the northnearEsmeraldas,
a morehumid,tropicalzonewith abundantrainfall and
runoff. More than95 percentof the-annual
precipitationfalls duringthe wet seasonfrom Januaryto May
(Stevenson,
1981), andvariesfrom lessthan500mm in the centralprovincesandthe coastof the southern
provincesto over 3000mm at SantoDomingode las Coloradosin the north
@ngineerloumal, 1972;
Schaeffer-Novelli,1983).
(from 24.2ob 27o C) vary liule alonglhe coast,
.Annualmeantemperatures
thuspotentialevapotranspiration
is about1300mm per yeu.
The
two
major
river
and
estuarineecosystems
of tle coastareRio Esmeraldas
in thenorttrandthe
_
Rio Guayaswhich flows into the Gulf of Guayaquilin lhe sourh
2).
The
Gulf
of
Guayaquil
Egore
receivesrunoff from some20 riverswith a watershed
of 51,230km2, equivalentto a watershed:
water
surfacearearatio of 4.3. The GuayasRiver is themajorsourceof freshwaterto the Gulf, which forms60
km inlandat theconfluenceof Rio DauleandRio Babahoyo.This freshwaterenterstheRio Guayas
estuary,and to a lesserextenttheEsteroSalado,aroundthecity of Guayaquilandtl-renflows 55 km to the
Gulf of Grayaquil.Themeandischargeof 1143.7m3/sfor ttreGuayasriver is thehighestamongthe30
riversin the coastalzoneof Fcuador,iepresenting
39 percentof ttreiotal dischargerro? trrisiowUna
region. Me-anprecipitation^in
the GuayasRiver drainigesystemnorthof Guayaquilis BSimm/yr, which
may rangefrom lessthan400 mm to morethan 1800mm duringany oneyear (Figure3). Discliargeis
strongly-seasonal
rangingfrom 200 m3/sduringthe d.y season!o 1600r3/, in ur,-uueralewet season
Gigure 3). Tidesaresemi-diurnalandareof equala*ptituae (1.8m) in theGulf of Guay"aquii,
bur are
amplifiedto 3-5 m in theRio Guayasestuarynearthe city of buayaquil. Flushingtime of ttreGulf of
Guayaquilis about21 days.

Shrimp Mariculture Management
The methodsof shrimpmariculturein theintertidalzonearegroupedinto threeclassifications
basedon the densitiesof iuvenileshrimpstockedin theponds. Exteniivemariculture,using
a stocking
densityof 10'000-20,000
iuvenilesper heclare(ha),relieslittle on furthersupplements
from"seawater
exchange^via
pu-mping
or from artificialfertilization.h._lrt9rl arepresentandannualyieldsarerelatively
low at.100-400kgftia' An increasein stockingratesto 50,000-60,b00*
juvenilesper trais a semi
extensivesystemthatrequiressomesupplemental
feedingandexchange
of seawateito con6olwaterquality
problemssuchasdecreased
levelsof dissolvedoxygen.Productionrites rno." thandoublewith this
program. The mosthighly managedsystemis semi-intensive
operationsthat stockpondsat 100,000*
juvenilesperha-andsupplyfood supplements
or fertilizethepondsto increasesourcesof food. Water
exchangewith theesfuaryis higherandannualproductionraiesincreaseto 1,000-1,g00
kgd.
The dramaticexpansionof thefarmedshrimpindustryandincreased
levelsof pont *-ug.r.nt
stimulated-the
developmentofa new fisherytoprovidepostlarvaeandseedshrimprotiro.llng mariculture
polds' Industrysources
thatup to 90,000artisanalfishcrmanwereinvolvedin the 19g3harvest
_estimated
andin 1984numbersof fishermenyo+ing alongthecoastwereevenhigher(N4cpadden,
19g5). Seed
fishingis concentrated
in areas-ofsignificantfreJhwaterdischargealongttreioastline,suchasbt oro and
Esmeraldas,
with the highesteffort occurringin theGuayasp.oulnce.
The catchesarenon-selective,
with smallfish, pena-eiO
postlarvaeandjuvenileshrimpincludinga
mixtureofP.vannamei,P.stylirostris,P.occidentalis
andP.ialiforniensis,aswellassomefreshwater
Carid spe*ies'Sinceonly the
lorqer two speciessurvivebestin maricultureponor,o*n.ir pay according
to theproportionof the stockthat is P . vainamei andP. stylirostris(Mcpadden,r43sl. ser;ion is
a
post-harvest
processandthereforeless-valued
speciesarelost from thi estuary.Thepeakof theseedfishing
seasonis from Deccmberto Marchwhenfisherman maytakeup to 40,000p.istr-uai a-oal iii sire
rangingfrom 7-10mm.
*

villalon et al. (thisvolume)reportslightlyhigherstockingdensities.

93

of offshore
with theavailabilityof immatureshrimpis temperature
A majorfactorassociated
arecontrolledby themixtureof warmwaterflowing southwardfrom thePanama
water. Temperatures
Bight wittr cold watersflowing northwardfrom thePeruvianHumboldtCurrent. This mixing occurs
beiweenMantaandPuntaSantoElenaalongthecoastof Ecuadorandgraduallymovessouthwardinto the
andinitiatesthe
temperature
Gulf of Guayaquil.Thesoutherlyflowing watercausesincreasein seawater
1985).
McPadden,
onsetof therainy season(Cucalon,tttisvolume;Cucalon,1984;
with El Niflo events
andhighrainfall areassociated
Yearso1abnormallywarmwatertemperatures
andhaveresultedin the explosivepopulationsof white shrimpoff the coastof Ecuador.The high
availabilityofpostlarvaethat supportedtheexpansionofthe shrimpindustryin 1983and 1984hasbeen
(Cucalon,this volume).
with theseoffshoreprocesses
associated

Reclamation of Mangroves
Eight speciesof mangrovesare distributedalonga rurrow bandof the outerintertidal zoneof
called"salinas"(saltflats) in moreinland intertidal areasClable2). The
Ecuador*it=ha non-negetated-area
in the Guayasprovincehasbeenattributedto extensiveriver flow
mangrove
hi
oiii.nr. of 121,4& of
1983).
(Schaeffer-Novelli,
iro* tft" GuayasRiverbasinani highratesof evapotranspiration
family,
the
Rhizophoraceae
in
mangroves
Theieawardintertidalron6 is colonized6y specilsof
of this
inland
species
other
of
the
mixtures
and
perimeter
ihoreline
of
the
withRhizophoraharisoniion the
Auicennia
and
Rhizophora
zone
of
is
mixed
fringe
a
inland
of
this
1981).
More
et
a1.,
zonelgintron
gir*inort. Still fartherinlandlies a monospecificsiandof Avicennia,which yieldseventuallyto shrub
frequencyandri-verdischargecreate
ii*s * Salinaswith extremehypersalinesoil conditions.High tidal
provinces
with treedensityof 185/haand
northern
in
the
structures
ionOitlon, suitablefor mangroveiorest
Columbia,Malaysia
in
Venezuela,
mangroves
greater
for
than
a basal arcaof 62.4,&ha. This densityis
(CinEon'
provinces
in
southern
tle
puerto
less
dense
forests
are
Mangrove
(Cintron,
1981).
Rico
and
1986)'
(Snedaker
al.,
ponds
et
shrimp
surrounding
particularly
1981),
The mostobviousexfloitationof mangrovesalongthecoastalzoneof Ecuadoris the construction
of pondsfor theproductionof shrimpandfish. This land usepatternin the intertidalzonefirst involved
wholesaledestructionof mangrovesin Machalaandin the southernprovinceof El Oro. Followingthis
pond constructionwas authorizedmainly in the Salinasand inland
period of total mangrovedestl"uction,
less
i"ung1ou.,ones. Ilo*euer, asthearei of pondconstructionincreaseddramaticallyin the early 1980s,
the
by
impacted
heavily
again
wg_rg
mangroves
and
was
avaiiable
of tflir unu"getatedintertidal area
mariculturelndustry.Recently,therehasbeena decreeihat prohibitsnew authorizationof pondsin
**g.ou"r. Severalthousandtechresof pondshavealreadyUeenauthorizedin theintertidalzone,though
constructionin manyinstanceshasnot yet begun.
-e of mangroveslostio the constructionof pondsal-o1g{e coastalprovinceof
The exactnu*U.r
percentof the
Ecuador is uncerrain. t"..nt iufr"y from CLIRSEN(1984)showsthat 79,396ha or 88.8
provinces
of Guayas
total areaof shrimppondsalongthecoastof Ecuadoris locatedin tle two southern
proportion
of ponds
on
based
mangroves
potential_loss
of
gt
the
una Oro (Iable-li. A Aiagrai"representing
if
all
52,9l2haof
that
demonstrates
ffris
diagram
+.
Ffuure
in
ir
shbwn
constructedin mangrove3r.lus
Iheoriginalmangroveareawould
.trrintppondsin Guiyasprovince(fable 1) wLe built in mangroue-areas,
At a utilizationrateof 10
resource.
percint
of
the
havebeen 174,375na,aridmangrovelosswould be 30.3
4'2percenI'
be
would
mangro-ve
loss
of
the
!a!i1at
f.t".ni of pondsbuiliin mangr6ues,
Historicalrecordsof-thesoutherncoastof tlie Gulf of Guayaquilin theprovinceof€l Oro at
ponds(fable
Machalagive someindicationasto the proportionof mangroveslsedfor the constructionof
mangroves
loss
of
on
the
based
gi. F
LgiT rherewere 834.ih;of pondsconsructedand,
"*1qO6b
period,55 percentof thesepondsw-erebuilt in mangrovehabitats.This estimateis probably
Ouringrhis
at theexpenseof mangroves'If urban,expansion
rince urba'nareasalsoapparentlyincreased
in thisperiod
45 percentof thepondsconstructed
"*ugg"out"d
then
mangroves,
salinaiand
between
divided
*^"Jq"uUv
would havebeenin mangroves.
From 19??to 1-982,an additional1496.5ha of pondswerebuilt, however,therewasno
landusefor agriculturewasobserved,
lossof salinasandmangroves.Rather,decreased
conesponding
andurbanexpansion.However,assumingthatall
which couldaccountf* tnr additionalpondconsEuction
in
p-ercent
of thepondswereconstructed
63
then
of the mangrovelosswasfrom pondconstruction,
in El
habitat
mangrove
in
pond
gased
percent
consEuction
of
45-63
,ung"
of
ttii,
on
*ungro"" f;abitats.

94

Oro, an estimated16-21percent+of themangrovein theGuayasprovincemay havebeenlost to shrimp
farming. Recentestimatesby CLIRSENindicatethat mangrovelossin the GuayasProvinceis muchless,
at about4 percent+of the originallnangrovecover. This would meanthatabout10percent.of the shrimp
pondsconstructed
in this provincewerebuilt in mangrove(Figure4).

Factors Influencing Water Quality
Waterqualityof theGuayasRiver estuaryis influencedby inputsfrom thewatershed,
exchanges
with the intertidalzone,andphysicaloceanographic
processes
in theGulf of Guayaquil.Activitiesin the
watershed
includea damprojectthatwill influencefreshwaterinput,expandingagriculturewith associated
dischargeof chemicalsincludingnutrientsandpesticides,
sewagefrom increasedurbanizatton,and
toxic
substances
from industrialactivities(Arriaga,this volume).Exchangeof estuarinewaterwith theintertidal
zonevia tideshasbeenreplacedwittr dieselpumpsttratpumpwaterto improvetheproductivityof grow-out
ponds.Naturalresources
within theintertidalzone,includingmangrove,may alsoinfluencewaterquality,
thoughthe functionof thesecommunitiesis still uncertain.Offshorewatersinfluencethe temperatueand
salinityof the GuayasRiver estuary,mostnotablyduringEl Niffo eventsandduringpresenceof red tidesin
coastalwaters.Thesediversenaturalandanthropogenic
influenceson waterqualityin theestuary
complicatewaterqualitymanagement
in this coastalecosystem.
Daule-Peripa River Dam Project
A damis proposedat theconfluenceof theDauleandPeripariversfor watersupplies,conEolof
river flow, andhydroelectricpower. Waterwill be divertedwith an aqueductfrom theRio Dauleto the
SantaElenapeninsulafor potablewater,irrigationfor agricultureandindustriatuse. Thedamwill also
increasethe flow of freshwaterto the GuayasRiver estuaryduringttredry seasonto preventsaltwater
intrusionin fhe lowerDauleRiver andenhanceagriculturein this area.TheRio Dauledrainsone-thirdof
the GuayasRiver basinand hasa meancapacityflow of 11.5km3/yr or 365r3/r. Thr total river basinof
both theDauleandPeripaRiversis 420,000ha andit receivesa meanprecipilationof 1800mm per year.
A thoroughdescriptionof thesoil characteristics
andlanduseof this watershed
areprovidedin a reportby
the GuayasRiver BasinCommission(CEDEGE,1970).
The damwill createan impoundmentwitfi a storagecapacityof 6.0km3 of waterwiti a surface
area,
of 2'70km2, meandepthof 21 m andvolumeof 5.4tL3. fne impoundmentwill supplypotable
waterfor 300,000peopleat 400 litersper personper day,irrigation waierfor 42,000ha of tandand20
Titlign cubicmetersper yearfor industry. Projectedindusrial useincludesapetroleumrefinery,nirrogen
fertilizercomplex,petrochemical
complex,anda perochemicalport facility at-Monteverde
The damwill influencethe amountof waterfrom the DauleandPeripaRiversthatnormaly
dischargeinto theGuayasRiver. Presenl.ly
theproposedoperationof thedamcallsfor an averageannual
flow of from 100to 175mr/s (Jenkins,1979; Arriaga,this volume). This flow will vary from a high of
321m3/sduringthe wet seasonin April, to a low oi nq *3/s in August. Comparedto the normalflow
of theDauleandPeripaRivers@gure 5), thismodifiedflow is muchlower thanthefreshwaterdischarge
of up to t000 m3/sthat usuallyoccursduringthe wet season.During the dry season,to controlsaltwater
intrusion,the damwill providewaterabovethe avengedischarge
of about50 m3ls from suppliesstore.d
in
the impoundment.Basedon averagemonthlyflows, the normaldischargeof 343m3/sfor thesetwo rivers
will be restrictedto 175m3ls,a reductionof about49 pe,rcent
(Figure5). This reductionrepresents
a loss
of 15percentof the freshwaterto the GuayasRiver and 13percentfrom theGuayasRiver estuary.The
lossof freshwaterfrom an estuaryin a semiaridzonesuchasthe Guayasprovincemay influencettre
patternsof salinityin the ecosystem.

+ Alvarezet al. (this volume)reportslightly differentpercentages
of mangrovelossfor 1986-1984.

95

Nutrient Loading
maybe describedaseitherdiffuseor
Sourcesof nuEientsfrom watersheds
to aquaticecosystems
from somespecificpoint of effluent. Diffuse nutrientinputsincluderunoff from naturalvegetationor from
managedlandscapes
suchasagricultureor forestryareas.Muchresearchhasgoneinto developingnutrient
loadingratesfor different typesof nativevegetationandfor specifictypesof cropsin watershedsin various
geographic
for watersheds
locatedin temperate
areas.Most of theseloadingrateshavebeendeveloped
climates.Lessis known aboutthe lossof nutrientsfrom tropicalwatersheds.
rice, sugarcane,cacao,and
Thefive principlecropsraisedalongthecoastofEcuadorarebananas,
coffeefilho, 1983). Theseagriculturalproductscomeprimarily from theGuayaslowlands,situatednorth
andeastof the city of Guayaquil,andalongtheeastemshoreof the Gulf of Guayaquil(Table4). Statistics
for the Guayasand Ins Rios provinceshavebeencombinedto representagriculturalactivity in the Guayas
River basin. Over 50 percentof ttreagriculturalactivitydescribedin Table4 for the coastalzoneof Ecuador
occursin the GuayasRiver basin.
The GuayasRiver basinis a majorproducerof rice, witfr neady95 percentof the totalrice
productionalongthecoastoccurringin the GuayasandLos Rios provinces.Rice in the GuayasRiver
basinis of particularsignificanceto thenutrienteconomyof theGuayasRiver estuarybecauseof thelarge
areaof production(Iable 5), the potentialexpansionof this crop in the watershedoncethe Daule-Peripa
damis completed(projectedat 17,000ha duringthe initial phaseof the project),andits proximity to
waterways.
Point Source Inputs
witl urbanareasandindustry. However,nutrientwastefrom
Pointsourceeffluentsareassociated
via groundwater
transportfrom septicsystems.Loadingratesof
urbancenterscanalsobe diffuseload.ings
population
and
degreeof wastetreatmentprior to discharge
density
on
are
dependent
nutrientsfrom cities
into aquaticsystems.In the GuayasRiver basin,thereis very little treatmentof domesticwaste. Sewage
via ditches(refenedto as "treated"),or is divertedto septic
is eitherreleaseddirectlyto theriversor estuaries
point
in this watershedis largelyrelatedto populationdensity
from
sources
ponds. Thusnurient loading
from
sewage.
nutrient
input
untreated
per
rafes
of
capila
and
Thepopulationin the coaslalprovincesof Ecuadorhasincreasedoverthepast35 years,most
dramaticallyin the Guayasprovince(Figure6). From 1962to 1982the populationof this provincemore
thandoubledto over 2,000,000persons.In thelastseveralyears,thegowth ratehasbeenevengeater
with a presentpopulationof over 2,568,452(Figure6). Togetherwith the populationof Los Rios, there
ue 3.14million peoptein the GuayasRiver basin@gure 6), of which 84 percentis consideredurban,with
53 percentof the basinpopulationlocatedin the vicinity of Guayaquil.Cunently,only 18percentof the
watersareemptied,untreated,into the
34i00 ha city is servicedLy sewers.The city'scontaminated
pumpingstation),andEstero
Progreso
River
pumping
Daule
sfation),
Rivei
Guasmo
@l
Guayas
@l
Salado.
Initial estimatesof theimpactof urbanwasteon the qualityof waterin theriversandestuariesof
the southerncoastalzoneof Ecuadorarelistedin Table6. Theseestimatesarefor themajorpopulation
centersalongthe waterwaysof the GuayasRiver basin(includingtheGuayasandLos Riosprovinces),and
includea total populationof 1.7million people,or 54 percentof the watershedpopulation.
directlyto theriversandestuaries,
Treatediewagehererefersto sewagewhichis transported
ponds.
availablestatistics,wastefrom 62
From
the
to
septic
whereasuntreatedsewageis transported
(untreated),
86 percentof the 54.83(10)6m3
ponds
however,
percentof thepopulationis pumpedto septic
Based
on thesepoprlation
ecosy-stems.
to
directly
aquatic
generated
discharged
annuallyis
;f waste
statisticsind per capitaratesfor eachtreatment,the loadingratesfor oxygendemand(biological and
calculated.
haveb-een
chemical),soilas(totatanddissolved),andnutrients(totalnirogen andphosphorus)
percent
domestic
of
all
90
over
discharges
This preliminaryanalysisindicatesthatthecity of Guayaquil
River
Guayas
enter
the
that
percentage
nutrients
greater
the
of
even
wastesthatentertheriver, andan
quality
in the
water
has
lowered
waste
industrial
and
(this
domestic
claimi
that
volume)
Solorzano
estuary.
dissolved
decreasing
DauleandGuayasRiversby contributingto a high level of bacterialcontamination,
of nutrients.
oxygencontentandincreasingconcentration

River Discharge
Ratesof nutrientinput from riversdischarginginto the GuayasRiver estuaryandEsteroSalado
may be estimatedfrom informationon seasonal
concentrations
relativeto periodsof high andlow river flow
(Figure7). Ammoniumconcenftations
above15ug-at/Loccurin threeof thefour riverssurveyedand
concentrations
ashigh as4Aug-atloccurredin theRio Milagro. Thesehigh concenfrations
occurredduring
the low flow season,andthusdo not necessarily
indicatehigh input to the GuayasRiver estuary.However,
peaknitrite andnitrateconcentrations
with valuesgreaterthan2.0 and50.0ug-av,respectively,occurredin
all theriversfrom Februaryto Juneduringperiodsof highriver flow (seeFigure3 foi seasonal
river flow
in the GuayasRiver basin). Thepatternfor nitratewascommonamonglhe 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 decreases
in
dissolvedoxygenconcenfiations
(dissolvedoxygenis requiredfor theoxidationof ammoniumto nitrate;
nitrite is an intermediaryion of thisprocess).Low dissolvedoxygenconcentrations
wereobservedin lhe
Rio Coloradoduringthewet season,
but the otherriverswerenearlysaturated
with dissolvedoxygen
throughouttheyear. High concenEations
of silicateandphosphate
werealsoassociated
with thewet
season,but the otherriverswerenearlysaturated
with dissolvedoxygenthroughoutthe year. High
concentrations
of silicateandphosphate
werealsoassociated
with thewet season,
indicatingthatthe
deliveryof thesenutrientsmaybe substantialto thedownstreamestuaries.This typeof information,along
with dischargedatafor eachriver system,is importantfor the development
of nurient loadingratesto the
GuayasRiver estuary.

Toxic Substances
Pesticides
Agriculturemay alsocontributetoxic substances
suchaspesticidesto riversandestuaries
of the
Guayasbasin(Table7). Table7 is basedon theareaof rice andsoybeansundercultivationin the Guayas
andLos Rios provinces,an^d_the
specificapplicationratefor eachcrop. This analysisis only an
approximationof theuseof thesechemicalsin thewatershed
anddoei not indicatetheir actualtransportto
aquaticsystems.Dr. Solorzano(personalcommunication)
hasexpressed
concernabouttheconcendadons
of pesticidesin theestuary,bur only tracesof pesticideshavebeendetectedat thebeginningof therainy
seasonin the DauleRiver (Solorzano,this volume). A CEDEGEriver basinstudysho*ed'thatDDT levels
in the riversflowing into the estuarywerelow, but little documentation
wasavaillble.
Petroleum Hydrocarbons
Petroleumis theprimarysourceof foreignincomefor Ecuador.The impactof oil on coastal
provinceswasdocumented
(Cintronet al., 1981),andonepublicationrefersspecificallyto thecoastalzone
of Ecuador@lho, 1983). Concenfationsof oil hydrocarbbns
in theGuayasniuer estuaryandEsterSalado
rangefrom 0.10 to 2.80 ug/L (Solorzano,*ris volume). Concenrationsaregenerallyleis than2 ug&
exceptnearoil spills or centersof commercialoil vesselactivitv.
Heavy Metals
Thereis somemining activity in the GuayasRiver basin,andseveralmetalshavebeenfound
concentrated
in riverineandestuarinesediments.Solorzano(thisvolume)givesrecentmeasurements
of
copper,iron, cadmiumin the watercolumnsof theBabahoyo,DauleandGuayasRivers,andmercuryin the
sedimentof the Guayas.The readeris referredto that repori.

97

Shrimp Farming
Pumping of Estuarine Water
More intenseshrimpfarmingtechniquesinvolve stockingpondsat higherdensitiesof juveniles,
additionalfertilization andsupplementalfeedingto assurean adequatefood supplyfor
which necessitates
requiressfiict control of waterquality since
secondaryproductivity. This level of pond management.
to
phytoplanktonbloomsresultingfrom nuftientadditionsmay depletedissolvedoxygenconcentrations
levels that will causeshrimp mortality.
Oneof the solutionsto thispotentialwaterqualityproblemis to increasethe exchangeof seawater
throughthe pondsby pumpingwaterfrom the estuary.This exchangeratevariesfrom 3 percentto 8
madculture,andmayincreasewifi
percentof th-evolumeof the shrimppondper dayundersemi-extensive
pumped
from
theGuayasRiver estuaryto
volume
of
water
practices.
The
total
moreintensefarming
practicesandthe totalareaof pondsunderoper,ation.Figure8
shrimppondsdependson pondmanagement
with ponds(usinga meanponddepthof 1.5m) basedon
showi thevolumi of estuarinewaterexchanged
per
rates(percentof pondvolume day),andareasof pondsin operation.Theseexchange
variousexchange
volumesarecoinparedt-othe low andhigh flow dischargeof theGuayasRiver. At a presentoperationof
(5 percentpumpingrate),thevolumeof water
management
30,000ha of pondsundersemi-extensive
(10)6
m3 €rgur9 8). This volumeis greaterthan
20
is
approximately
estuary
the
with
exchangeddaily
freshwaterdischargeftom theGuayasRiver duringlow flow periods.With intensivepondmanagement
nearly36 percentoftheriverine
(10 percentpumpingrate),thesameareaof pondswould exchange
underscorethe importanceof the
reasonable
scenarios
of
periods.
These
tlpes
Os.i'rrg" Airindtrigtr flow
pattern
in
this
estuary.
flow
ponds
water
on
the
of
shrimp
impact
'
and
with seepage
Most oi'ihe waterthatis pumpedinto thepondsreplaceslossesassociated
mariculture,observations
evaporation.Althoughthereareno dan on waterbudgetsfor semi-extensive
suggestthat lessthanhalf of thewaterremovedfrom the estuaryis returnedin a flow-throughdesign@.
l,tiigle, personalcommunication).The amountof waterlossdueto evaporatiolin 4q pondsis probably
theheatabsorptioncapacityof thewatercolumn.
decreases
highlr thanin the estuary,sinceshallowness
thanwetlands.For example,
Oien watergenerallylosesmorewaterper areato evapotranspfuation
thanpotentialmtes
rates
of
evapotranspiration
lower
to
have
actual
*'ungrou"t i-nsouthiforida areknown
mangrovesto shrimp
by
vegetated
originally
intertidal
areas
of
the
conversion
Therefore,
1982).
ltwiiley,
in waterloss
pondscouldintreaserhelossof freshwaterfrom the GuayasRiver Estuary.This_increas^e
(1986)
thatwaterin
found
et
al
watersto theestuary.Snedaker,
iould resultin the dischargeof hypersaline
water.
source
ttran
the
22 of 30 pondssurveyedhadhighersalinities
Fertilization
feedingandfertilizationarerequiredto *ryt thedemandfor food at higherstocking
Supplemental
densitiesof'postlarvaein pon-cls.A main sourceof nutritionfor shrimpin growoutpondsis phytoplankton
feedingis carried
addedprior to stocking.Supplemental
bloomsthatiesult from uria andsuperphosphates
on
impact
of
rhese^chemicals
The
last
four
weeks.
the
in
growth
usually
cycle,
out towardthe endof the
discharge
pond
effluent
on
an{
within
the
fate
on
their
depcnds
River
esruary
quality
the
Griayas
r
of
tt r *ut
applied!o pondsareabsorbedby phytoplanktonandarethus
rates.Muc^hof ihe nitrogenind phosphate
biologic.aloxygendemandwith
returnedto the estuaryi-norganii form. fnesi organii nutrientsrepresent
may thenbe
decomposition
during
released
Nutrients
pl-ankton
biomass.
of ttris
ida;;*posirion
Therefore,
estuary.
in
the
observed
recently
red
tides
to
the
contribute
and
upiak"
Uiotogical
for
available
nutrient effluent fr-ompondr *uy contributeeithcr directly or indirectly to thebalanceof dissolvedoxygen
in the estuary.

98

Mangroves
Sincethe Guayasestuaryis tightly coupledto ttreintertidalzonevia 3-5 metertides,mangroves
may influencethesewatersin severalways. Sediments
suspended
in thewatercolumnaredepositedin
mangrovesduringflooding,enrichingtheseforests.The extensiveroot systemof mangrovesenhances
the
processandretardsthe forcesof erosionalongthe shoreline(Scoffin,1970). Nixon (1984)
sedimentation
observedthattotal suspended
sedimentloadof an estuaryin Malaysia,in which mangroves
hadbeen
reclaimedfor agriculture,wasan orderof magnitudehigherthanin an adjacentmangrove-dominated
system.
Somepreliminaryevidenceindicatesthatmangroves
may alsobe a sinkfor nutrientsin coastal
waters.This may seemto contradictthe theorythatmangroves
act asa sourceof detritusto estuarine
(OdumandHeald, 1972;Twilley, 1985;Twilley et al., 1986). One explanationis that net
ecosystems
nu,trientuptakemaybe a balancebetweeninorganicnutrientinput andorganicnutrientexport. Walsh
(1967)noticeda decrease
in inorganicnutrientconcentrations
in watersmovingthrougha mangrovein
Hawaii. Nedwell(1975)usedenclosures
to measurenufient uptakeby mangrovesediments
andnoticed
theyhad a greatcapaciryto removenitrates,particularlyin areasof nuhientenrichmentfrom sewage
discharge.The useof mangroves
for treatmentof nutrient-enriched
effluenthasreceivedsomepreliminary
investigation(Sell, 1977),but this functionis still poorly understood.The lossof mangrovesmay be a
contributingfactorto changesin waterquality,particularlynutrientlevels,in the GuayaiRiver esruary.

Impact of Water Quality on Shrimp Mariculture
Fxisting informationsuggests
thattheproductionin shrimppondshasdecreased
from 1600to 250
kg of shrimpTha/yr
over the lastseveralyears,thoughstockingrateJ6avebeenmainLained
at about65,000
PL/haper harvest.Mortality ratesin shrimppondsareestimttedat greaterthan50 percent(p. Maugle,
personalcommunication),
andevidencesuggests
thatmaturationratesarealsolower-.In addition,therehas
beena declinein theavailabilityof wild PL to theshrimpfarmingindustry,restrictingttreacreageof ponds
in operation'Decrease
of wild PL hasincreased
demandfor PL fiom hatciieries.Curiently,therearesome
68 hatcheriesunderconstruction.Twenfyhatcheries
still in initial phasesof operationproducedabout500
million postlarvae
in 1985.
becauselarvaearesusceptible
to
_.
9ood waterqualityis critical to theproductivityof hatcheries
disease.no$t_eI, supplyand shrimpgrowthandmortalityin pondsdeterminetheproductivityof tnis
indusEy;andbothdependon thequaliryof waterin rheeituary.
Mangroves and Fisheries
Thelossof mangroves
from tropicalestuaries
mayhavedirectconsequence
to economically
importantfisheriesthroughlossof habitatandfood. ZimmermanandMinello (this volume)havefound
lhatP. vannameiandP . stylirostrisinhabitareasin the mangroves,
buf it is noi known whetherthese
habitatsenhancethe survivalor growthof theseandothermarineorganismsin theEsteroSalado.
Associations
do existbetweenthe productionrateof shrimpandthetxFnt of mangrovearea(Macnae,
1974;Tumer,1977:Jottry,1984)because
onehectareof mangroves
canyieldrnoi" thanOOO
tgyr of
shrimpand 100!S/:r of
without
management
(Turner,
tOzll.
nasea
on
an
approximate
lJsi of 10,500
.fistr
ha of mangrove(Figure4), thereductionin shrimpproductionfrom the estuaryroutO Ueequivalentto
5,300_m.t./yr.
Althoughthesestatistics
do not shbwcausalrelationships,
theydo polnrou?ihat wheneuer
a?roductivepostlarvaefisheryexist,thereis thepresence
of themangrovehabitatasobservedin Ecuador
(Turner,this volume). Withoutfurtherinformationon possibledepeidanceof shrimplarvaeandother
marinefaunaon mangrovesfor part of their life cycles,theeffectof mangroueclearingon natural
populationsin theGuayasRiverestuarywill remainunknown. Mangrovedestruction-may
alsohavean
indirecteffecton fisheriesby changingwaterquality

99

Salinization
The Daule-Peripadamandthe pumpingof waterinto shrimpponds,may influencethe disnibution
of salinityin the GuayasRiver estuary.Mangrovesthatexistin arid
andincreasethe concenfration
is greaterthanprecipitationarevery
suchasthecoastof Ecuadorwhereevapotranspiration
environments
For
mangrove
forests
in
in
hydrology.
arid life zones,small shiftsin
slight
changes
susceptibleto
precipitationresult in increasedsoil salinity followed by an increasein treemoftality and a shift in
vegetationfrom foreststo tannesor Salinas(DavisandHilsenbeck,L974:Cintronet al.,1978). In Ecuador
of possible
the diversionof freshwaterfrom theGuayasRiver estuarymustbe managedwith awareness
negativeeffectson mangrovessincetheyexistin a relativelyarid environment.MargalefandCrespo
(1979)suggested
thatthe lossof freshwaterfrom ttredamwill probablynot affectmangroves,thoughthe
researchers
did not takeinto accounttheclimaticinfluenceof mangrovedistributionin the southern
provinces.
Increasesin salinitydueto changesin freshwatersupplyto the GuayasRiver estuarymay also
impacteconomicallyimportant.fisheriesin this estuarineecosystem.TheEsteroSalado,which harbors
directly
of theinnerGulf of Guayaquil,doesnot receivefreshwaterdischarges
mostof thefisheryresoruces
the
more
gulf
less
is
than
inner
of
the
rate
this
section
the
flushing
of
Therefore,
from the GuayasRiver.
of lessdischarge,the
southemsectionsthatarelinked directlyto dischargefrom theriver. As a consequence
of materialsdissolvedin the water
in theconcenftation
to increases
EsteroSaladomaybe moresusceptible
natureof
indicates
the concentrating
elementin thewatercolumnand
column. Salinityis a conservative
hlpersaline
was
Estero
Salado
low,
the
1985
relatively
and
was
during
Precipitation
this bodyof waier.
to 30 parti per thousand(ZimmermanandMinello, this volume). This increasein salinity
with valuesup
-other
(assumingthat
miterials,suchastoxic chemicalsandnutrientsmay alsobe concentrated
suggeststhat
very
are
Estero
Salado
their betravioris conservative).Organisms,suchasshrimp,that inhabitthe
and
mortality
increase
may
which
toxicity
quality,
salinity
and
especially
to changesin water
susceptible
growth
rates.
retard"
movementor recruitmentof organisms
Changesin freshwatersupplymay alsoinfluenceseasonal
into the Guayi River estuary.The recruitmentof shrimpinto an estuaryis importantto their life cycle
becausetheestuaryprovidesoptimalconditions,sucha low predation,duringcritical stagesof maturation.
on fluctuationsin salinityalongwith influx of
Seasonaltiming oi recruitrneniis thoughtto be dependent
damis designedfor a nearconstantflow of waterto the
offshorewatermasses.SincetheDaule-Peripa
EsteroSalado,thepotentialimpactof this projectshouldbe evaluatedrelativeto disturbingseasonal
fluctuationsoi saliirityin the eituary. Sincethe maricultureindustryrelieson shrimppostlarvaethaf
plansshouldstronglyconsiderthosefactorsthatinfluence
utilize thelstuary, management
seasonally
recruitmentof fisheriesin theestuarineecosystem.
Nutrient Enrichment and Anoxia
Nutrientsthat increasethe productivity of agricultureandarethe by-products.ofhumannutrition
alsostimulatethe primaryproductivityof aquaticecosyst€ms.Changesin waterqualityin responseto
nu6ientenrichmentis caiteOeurophiiation.-Dissolvedoxygenis a popularindexof waterquality;oxygen
below4 mgl ueconsideredstressfulto manyfisheries.The negativeeffectsof low dissolved
concentrations
oxygento fisheriescanalil be indirectby disturbingbasicfoodchains.Thedischargeof organicmaterials
(biologicaloxygendemand,BOD) andof someinorganic
oxygenduringdecomposition
ttrat"consume
of dissolvedoxygenin
in concentrations
can
causea decrease
COO),
(chemicil
o*yg.n?"ranO,
nu6ients
anddiffusion)andremoveBOD and
the estuary.A balance5f pto""r.es thatcontribute(photosynthesis
for a healthyenvironmentfor economicallyimportantfisheries.
COD dissblvedoxygenis necessary
Anoxia or low dissolvedo*yg"n
-Bay conditionshavebeenobservedhistoricallyin somestratified
whereanoxiaof bottomwaterswasobservedin the 1930s
in
Chesapeake
the
as
such
estuaries,
Bay that may be relevantto many
regardingthe Chesapegke
1938).
A
concern
Horne,
and
Q.{ewcombe
of tttis
greater
volumes
of waterandthepersistence
in
is'therecentincreaseinlnoxia
irturtin"
production
of
enhanced
".oryrt"*,
loading,
nutrient
incieased
between
linkage
The
conditionin thewatercolumn.
phytoplanktonbiomass,and the consumftion of oxygenduring decompositionof this organic materialin
itt" ryrt". eitherin the watercolumnoiin the surfacesedimentsmay contributeto anoxiain the
andcontrolbecomesa centralissuein
6tt rlup"ut"Bay (Officeret al., 1984).Therefore,nutrientabatement
astheGuayasRiver estuary.
such
ecosystems
problems
in
quality
estuarine
water
simiiar
dealingwith

Redtides,phytoplanktonbloomsthatdiscolorthe water,area commonoccurrencein the Gulf of
Guayaquilandin the inlandwatersof theGuayasRiver estuary@eArcos,1982;Jimenez,1980;Jimenez,
this volume). Thesebloomsvary in speciescomposition,densityof cells,andduration. The mostdirect
influenceon theestuaryis fish kills causedby thepresence
of toxic organismssuchas Gonyaulaxcatenella
and Gymnodiumbreve. Gonyaulexmonilataoccurredin theupperportionof the Gulf of Guayaquilin
April 1980,andin March 1986alongthe coastof Manglaralro.The 1980bloom resultedin high fish
mortality (Jimenez,1980),while the 1986bloom causedsignificantmortalityof shrimppostlaryaein eight
hatcheries,
interruptingoperationsfor 3045 days(Jimenez,1986).
Otherred tidesin ilre GuayasRiver estuaryincludeGyrodiniumstratumin September1982,
Mesodiniumrubrumin August 1984,Prorocentrummaximumfrom February1985to February1986,and
a recentbloom of Nitzschiasp. (Jimenez,this volume). Thesebloomscausedhigh mortalityin shrimp
pondswhenphytoplanktoncontaminated
waterswerepumpedfrom the estuary.
Anoxic watersareapparendyuncommonin theGuayasRiver estuary,occurringonly in areasnear
sewageoutfalls(Arriaga,this volume). A surveyof five stationsin EsteroSatadofoundthatdissolved
oxygenconcentrations
at 1 m depthrangedfrom 3.5 to 5.3 mV (Solorzano,this volume). Concenfations
arenormallylower nearthebottom;for instance,SolorzanoandViteri (1981)measured
concenEations
of
1.5 ml/ at 1 m depthcomparedto 2.0-2.5ml/ nearthe bottomat two stationsadjacentto the city of
Guayaquil.The strongtideswith amplitudesfrom 3 to 5 m in the GuayasRiveiestuaryareresponsible
for
thewell-mixedaeratedwatercolumn. Evenduringpresence
of red tidei in the estuary,inoxic pioblemsin
pondsarenot causedby pumpinganoxicwaterfrom theestuary;rather,anoxiain pondwaterd^evelops
when
waterthat containsmaterialsthatmay promotelow oxygenconditionsis pumpedinto the lesswell-mixed
shrimpponds.

Toxic Substances
Hydrocarbons
Hydrocarbons
canbe lethalto fish at relativelylow concentrations
(Table8). However,cturent
informationsuggeststhat theconcentrations
of hydrocarbons
in EsteroSaladoarelessni z ig/,an
order
'
of magnitudelessthanconcentrations
thatmay ai'fectthe naturalresources
of this ecosysi...
Pesticides
Crustaceans,
especiallylarvae,areusuallymoresensitiveto 1owconcentrations
ofpesticidesttran
areothermarineorganisms(Costlow,1982). Theextensiveuseof thesechemicalsin theeituarine
watershedcreatesa potentialhazardto the shrimpmaricultureindustryin Ecuador.Table9 shows
the
amountof pesticidesimportedinto Ecuadorin 1979and 1980.For eiample,Endrin,which is applied
at an
approximate
rateof 145m.t. per yearin therice paddiesof theGuayasRiver'basinsignificantlyreduced
growth_rates
of rapidly growingjuvenileMysidipsisbahia(McKenney,1986),ar coicentationsof 60
*gF:
of metabolicdysfunciion in iysids
ruurethallyro
Jn addition,physiologicalmeasurements
pesticidesin laboratoryandfield conditionsshowedlowergrowthandreproductlu" "r,for"Jin
trese
organismsduringlaterstagesof theirlife cycle(McKenney,1986).Daugherty(1975j
"upuiity
nodd ftar decreased
!!.ifp yieldsin El Salvadorprobablyresultedfrom the heavyuseor peJticidesin cottonfarmingduringthe
1960sandearly 1970s.Pestiiideshavea tendencyto becomemoreconcentrated
alongthefood chainand
thusmay stresspredatorsandhighertrophicleveissuchasfish. Beforethisproblemian be solved,more
informationis neededon theambientconcentration
of thesechemicalsthataretoxic to certainfisheries,and
on their fatein theaquaticenvironment.
Metals
High concentrations
of heavymetalsin certainareasof theestuarineecosystem
demons6ate
the
affectsof urbandevelopment
andindustry. Solorzano(1986)expressed
particularion.e.n for the

concenftationof copper,cadmiumandmercuryin the watercolumn and sedimen8of the GuayasRiver
innocuousto aquaticspecies
arehigherthan 10ug/ which is considered
estuary.Copperconcentrations
(Ketchum,1975),althoughtheseconcentrations
couldbe dueto naturalprocesses.Cadmiumis also
presentin concentrations
thatcouldimpactaquaticorganisms(etchum, 1975),andsedimentsshowed
significantmercurycontamination(Solorzano,1986).

The Ecosystemand Shrimp Mariculture
are
The interactionsof the shrimpfarmingindustrywith theGuayasRiver estuarineecosystem
summarizedin Figure9. Waterquaiityinfluencesthe supplyof wild PL aswell asthe successful
the swvival andgrowthratesof PL once
productionof PL by hatcheries.Waterqualityalsodetermines
quality
ponds
dependsprincipallyon the typeof
of
ponds.
growout
Alttrough
water
in
stocked
theyate
managementused,characteristicsof the waterpumpedfrom the estuarycan alsodeterminethe numberof
shrimpproducedin theponds. Activitiesin the GuayasRiver basinaffectthe qualityof waterin the
estuaryand,therefore,the shrimpindustrythroughchemicalssuchasnutrientsandpesticidesfrom
agdculture,sewagefrom the largepopulationcentersaroundthe estuary,andheavymetals_fromindustry.
Tiredisnibutionandtumoverraie of inesepollulantsandsalinityin the estuarinewatercolumnof the
estuaryareinfluencedby thedischargeof fieshwaterfrom thewatershed.Thusa damon theDaule-Peripa
Riveri mustbe evaluatedin termsof its potentialimpactto waterquality in this estuary,giventhe strong
seasonalnatureof its freshwaterinputs.
thatinfluencewaterqualityandthe shrimpindustryin this
Therearealsomanynaturaloccurrences
the Gulf of Guayaquillnay be a
ecosystem
@igure9). For example,elevatedwatertemperatures-in
estuariesduringclimatic
the
inner
into
of
shrimp
recruitment
in thetremendous
dominating'fadtor
in
from
Gulf
of Guayaquilto theestuaries,
the
recruited
are
also
Red
tides
ElNiflo.
known
as
disturbancis
nurseriesfor
areconsidered
additionto thebloomsthatoccurin situ. Theextensiveareasof mangroves
economicallyimportantshrimplarvaeaswell aspossiblyinfluencingnutrientand sedimentdynamicsin
this turbid .ituury. Tidesaffectwaterqualityin theestuaryby mixing the watercolumnandpreventing
stratificationthaicould leadto problernswith low levelsof dissolvedoxygen' Consideringthehuge
into this system,therearefew accountsof anoxiawith in
amountsof untreatedsewagettrratis discharged
tidal currentswithin the system.
to
the estuary,a patternthat his beenattributed thepresenceof stron-g
underscore
estuarineecosystem
of
this
natural
resources
and
human
the
of
interactions
*-y
1'tr"
in
thecomplexityinherentin questionsregardingttrefluctuationsof PL supplyandtheapparentdecrease
in
changes
bV
affectg$
not
is
only_
indusfiy
ponOptoOo"tionof shrimpin thepastseveralyears. The shrimp
nufrients
problem
loading
by
to
the
but
it
also
connibutes
itt" qriatityof waterpump.Otro* ttreestuary,
€tgure
waterloss(pumping),anddesroyingmangroveforests(construction)
ifertiiization),increaslng'fresh
ql. Td G".iits of ponf,management
invotvingthesepraclicesmustalsobe evaluatedin the contextof
their 'possiblenegativeeffectson waterqualityandthe shrimpindusry iself.
ThereiJ now a generalfeelingin Ecuadorthatttrelossof mangrovehabitathascontributedto the
declineof witd postlarvaE,particularlyturing periodso