Coastal Wetlunds of the Noytherrn Gua of Califurnia

Home , Brackish marsh, Distichlis palmeri, Jouvea, Pacific Coast of Mexico

AQUATIC CONSERVATION:MARINE AND FRESHWATERECOSYSTEMS

Aquatic Conseru:Mar. Freshv. Ecosyst. l6: 5 28 (2006) Publishedonline in Wiley InterScience (www.interscience.wiley.com).DOI: 10.1002/aqc.68l

Coastal wetlundsof the noytherrnGuA of Califurnia: inventory flnd conservutionstatus

EDWARD P. GLENNO'*, PAMELA L. NAGLERU, RICHARD C. BRUSCAb and OSVEL HINOJOSA-HUERTA' " EnvironntentalResearch Laborator!-,2601 East Airport Drive, Tucson,AZ 85706, USA bAritora Sonora Desert Museum,2021 North Kinney RoacJ,Tucson, AZ 85743,USA 'Pronatura lVoroeste,Ave. Jalisco 903, Colonia Sonora, San Luis Rio Colorado, Sonora 83440. Meric'o

ABSTRACT 1. Above 28"N, the coastlineof the northern Gulf of California is indented at frequent intervals by negative or inverseestuaries that are saltier at their backs than at their mouths due to the lack of freshwater inflow. These 'esteros'total over l32,ogo ha in area and encompassmangrove marshes below 29"N and saltgrass(Drsrichlis palmeri) marshes north of 29"N. An additional 6000 ha of freshwaterand brackish wetlandsare found in the Colorado River delta where fresh water entersthe intertidal zone. 2. The mangrove marshesin the Gulf of California have been afforded some degreeof protected statusin Mexico, but the northern saltgrassesteros do not have priority conservationstatus and are increasinglybecoming developmenttargets for resorts,vacation homes and aquaculture sites. 3. We conducted an inventory of the marshesusing aerial photography and satelliteimages, and evaluatedthe extent and type of developmenton eachmarsh. We reviewedthe availableliterature on the marshesto document their vegetationtypes and ecologicalfunctions in the adjacentmarine and terrestrial ecosystems. 4. Over 95"h of the mangrove marshes have been developed for shrimp farming. However, the larms are built adjacent to, rather than in, the marshes, and the mangrove stands are still mostly intact. 5. The majority of saltgrassmarshes above the mangrove line are still relatively unspoiled. However, resort and vacation home developmentis taking place on land surrounding them. 6. We recommend a systemof protected reservesincorporating the pristine wetlands, along with water quality managementand buffer zonesfor the more developedesteros. The saltgrassmarshes should be consideredfor conservation protection" similar to the protection given to the southern mangrove marsheswhose value has already been recognized. Copyright O 2006 John Wiley & Sons, Ltd.

KEYwoRDS: estero:estuarv: wetland: Distichlis palmeri'. saltsrass: mansrove

*Correspondenceto: E. P. Glenn, Environmental ResearchLaboratory,260l East Airport Drive, Tucson, A285706, USA. E-mail: eglenn','ag.arizona.edu

INTRODUCTION

The northern Gulf of California is a unique marine biome in the heart of the Sonoran Desert,with over 1200km of desertcoastline in the statesof Sonora and Baja California in Mexico (Figure l) (Alvarez- Borrego,1983; Alvarez-Borrego and Lara-Lara,l99l Felgerand Broyles,1997; Brusca, 2004. Brusca et crl.. in press).The northern Gulf of California supportsimportant commercialfisheries (e.g. Morales-Bojo rquez and Lopez-Martinez,1999; Sala er al., 2004:),as well as endemicand endangeredspecies such as the vaquita porpoise (Phocoenasinus; Nava and Findley, 1994.Barlow et al., lggl), the corvina-like totoaba fish (Totoaba ntac:clonaldi;Cisneros-Mata et al., 1995; D'Agrosa et al., 2000), sea turtles (Alvarado and Figueroa, 1992,Seminoff et a\.,2003a,b;Felger et a\.,2004), sealions (Le Boeuf et ctl., 1983;Garcia- Rodriquez and Aurioles-Bambosa,2004), whales (Breeseand Tershy, 1993),and numerous speciesof waterbirds(Anderson, 1983; Evertt and Anderson,l99l;Palaciosand Mellink, 1996,2000;Mellink,200l; Hinojosa-Huerta et al., 2004).It is a key migration route for birds on the Pacific Flyway, providing a corridor of aquatic habitat across nearly 600km of desert for speciesmoving from South American

*'ffi,I**- ' Colorado River Detra"WHlft 32N

L ?#,l:0.-+TnqkBahlaAdalr

-San .il SanJorge w"- %""-ilffi

30 1{

28N

,BajaCalilornia

Figure I Locator ' map for the major esterosand other coastalwetl:rnds in the northern Gulf of California. The background imase rs a 1990Thematic Mapper satelliteirnage.

Copyright .r) 2006John Wiley & Sons,Ltd. Arlutttic Consert':Mttr. Fre,slnr.Et.o.st,st.l6: 5 2B (2006) WETLANDS OF THE GULF OF CALIFORNIA wintering grounds to North American nesting areas(Anderson, 1983;Garcia-Hernandez et ttl,, 2001a, Hinojosa-Huerta et al., 2004). Brusca et al. (2004) report 2802 marine speciesfrom the northern Gulf of California, including2258invertebrates, 367 fish, 146sea birds, 24 martnemammals (cetaceans, pinnipeds, fishing bats),and sevenreptiles (sea turtles, sea snakes). Up to the 1940s the region was still nearly pristine (Steinbeck and Ricketts, I94l). Since then, however, the coastal zone has undergone increasingly rapid development and population growth (Almada-Bay, 2000), which in Sonora increasedfrom 550000 in 1950 to 2.3 million in 2000. Most of the coastalsettlements are now linked to the major inland citiesby paved roads and receiveelectricity from the national grid. Shrimp farms, salt ponds, electricity generatingplants and resorts have also beenbuilt along the coast,and villageshave expanded into smallcities (Moreno, 1992;Almada-Bay,2000). Guaymas, San Felipe, Puerto Pefrascoand El Golfo now each support fleets of commercial trawlers and/or small-boat, artisanal fisheries,as well as extensiveand growing resort developments.Much of the beach-frontresort and residentialdevelopment caters to US citizenswho holiday or retire in Mexico. Some 10 million peoplenow live within a few hundred kilometresof the head of the gulf in the USA and Mexico. In the face of this rapid development,the health of the marine ecosystemis in question,the degradation of coastalhabitats is alreadysevere, and the esterosof the northern Gulf of California are undergoingrapid development(Brusca et al., rn press).Efforts are under way to protect the most important parts of the marine ecosystemand to regulate the fisheriesso that they are sustainableover time. The value of the coastal rocky 'reef habitat for marine life has been recognized,and a string of marine sanctuarieshas been proposed(Sala et a|.,2002). The delta of the Colorado River, although much alteredby upstreamwater diversions,is now protectedin the Upper Gulf of California and Colorado River Delta BiosphereReserve (Morales-Abril, 1994). but lishing restrictionsare only weakly applied in the core and buffer zones (Cudney-Buenoand Turk-Boyer,1998). Although much of the shoreline is rocky or sandy, at frequent intervals the coast is indented with 'negative estuaries'(esteros) that tend to be saltier at their heads than at their mouths due to lack of freshwaterinflow (Lavin et al., 1998;Lavin and S6nchez,1999; Brusca et al., rn press).These esteros are extensive in area due to the extreme tidal range of the northern Gulf of California (5-10m amplitude) (Alvarez-Borrego, 1983). Most of the esteros are above the mangrove line (28 29'N) and are dominatedby a low-growing saltgrassand herbaceousand shrubby halophytes(Felger, 2001;Brusca et u\.,2004,in press).Other coastalwetlands form wheregroundwater surfaces in springsnear the coast or where agricultural drainagewater is dischargedinto the intertidal zone (Glenn et al., 1996, 200l ). Except for the Colorado River estuary (Glenn et al.. 2001), the wetlands of the northern Gulf of California have been little studied and have not becomeconservation targets. To the contrary, they have becomeprimary sitesfor human developmentas resorts,marinas, salt works and shrimp farms. Although much of the estero land is federally owned (Steenblik, 1997). the government can grant concessionsfor developmentactivities, such as aquaculture,in the esteros.Furthermore, some of the intertidal land was deededin the past to individual ejidos(communal rural enterprises)for developmentof small-scaleaquaculture. With passageof the 1992landreforms in Mexico (Jonesand Ward, 1998),the ejido lands have been privatrzed and can now be sold for private development of the land as resorts, vacation homes and marinas.Thus, the northern Gulf of California wetlandsare under considerabledevelopment pressure. This paper inventories this unique string of wetlands for the flrst time, documents the types of land conversion they are undergoing, and discussestheir ecologicalroles in the adjacent marine and terrestrial ecosystems.It also makes recommendationsfor their conservationand management.The goal is to synthesizethe availableknowledge about thesewetlands so that their potential conservationvalue can be recognized.

P. GLENN ET AL.

MATERIALS AND METHODS

Overview of methods The study area includesthe esterosand other coastal wetlandsof the Gulf of california from Sonora (28"N)' to the head of the gulf Guaymas, on th. so,ora coast (32'N), and to Bahia california (29"N) on de Los Angeles,Baja the Baja caliiornia coast (Figure t,). riris mangrove encompassesthe northern rimits of the zone on both coasts (Turner et ctl', toos; and the saltgrass-dominatedesteros mangrovezone (Brusca et al., in press). above the Aerial surveyswere usedto document around the wetlands' human developmentin and together with recent and archival Thematic determine Mapper (TM) satelliie images aerial coverageand changeswithin ro each wetland system over time. we reviewed topographicmaps and the scientific iiH:[1ffJ:Til:Tfi::::: localknowledge to derermine the composition and

Vegetationsurveys

checklists of species were compiled at 16 wetlands during ground 1983-2003(Yensen surveysconducted over the period et ctl', 1983; zengelet al., 1995; Grennlr" ar., 1996;R.c. Brusca,pers. additional specieswere added based comm.), and on the literature and data from the Macrolauna project et al'' in press)'Tidal wetlands Golfo (Brusca were divided into four zoneswith respect high and supralittoral' to tidal inundation: low, middle, Taxonomic designationsand notes on distribution of specieswere based ;:dyi;rtliffii:ffi:::'"?',7'i;;;olLfio;,wiggins (re80), Yensen etat (1e83),rurner etat (ree5),

Aerial photographyand satelliteimagery The coastlinefrom Puerto LibertadJo San Felipewas flown at approximately three flights 500m to 1000m altitude on in June and July 2003'The flight line was automatically recordei with a geographical system(GPS)' The aircraft was positionedjust position offthe coastand a continuousrecord and estuarieswas recorded of the coastalwetlands with a hand-heldvideo camera.The video note positions had a sound track that was usedto of each marsh and features of interest, including the extent of human Simultaneously'a photographicrecord development. of eachwetland was acquiredwith a high-resolution Following the flight, a DVDwith film camera. commentarywas prepared,to uic in assembling digitized the final list of wetrands. then mosaickedio produce a high-resolution :?t:H]],|;'offi: i-ag! or each wetrand and its TM 5 satelliteimages taken in 1990(30m resolution)were mosaicked northern to form a singleTM image of Gulf of california (Figure 1). Each the wetland was located on the TM and information systemoverlay of a geographical the perimeter was createdand used to of the wetland' determine the size and exact location For most marshes,the perimeterswere drawn to encompassthe intertidal zoneand within the marsh, including thickly lagoon vlgetated areas and the sparselyvegetated However' for the delta region salt flats at the backs. of the coLrado River, the vegetated the mainland _only parts of the extensivetide flats on and islandswere included within the wetland perimelers.The vast areasof bare flats were excluded'Names of wetlands intertidalmud and other areasof interestwere taken seriesfor Mexico (GETENAL, from the 1975topographic lg75)' Some wetlandswere not named names' then on those maps; if- they had rocal thesewere included in our tables.Locations of wetlandsin tables are given in coordinates'A geospatialdatabase was Lat./Long. constructed,containing rM-i-uges, meta and current aerial photographs d,ata,publishedliterature, of each wetland (Nagler et al., in press). checklistsof vascular This databasealso contains plants and invertebratesin the marshes.

Copyright i\:,2006 John Wiley & Sons.Ltd. Aquutic Con,sarr,; Mar. Fre.shtr.Eco,s.t,,st.l6: 5_2g (2006) WETLANDS OF THE GULF OF CALIFORNIA

Other satelliteimages were used for changedetection. The coastlinearound Guaymaswas viewedon TM imagesfrom 1913.1983, 1990and 2003.The delta of the Colorado River and associatedwetlands were available on 1993-2002annual images.Bahia Kino was covered on 1973, l9B3 and 1990 TM images. Archival satellite images were acquired from the Arizona Regional lmage Archive (Office of Arid Lands Studies,University of Arizona, Tucson,USA). Other imageswere obtained lrom EarthSat,Inc. (Rockville, MD, USA).

Assessmentof human impact Human impact was assessedon the basisof visual effectsof developmentin and around the wetland area. Three primary types of human developmentwere seen.First, many esterossupport resortsand vacation homes,or local settlements(small towns, fishingcamps). Second, some of the esteroshave beendeveloped for shrimp farming. Third, some of the esterosformerly had significant freshwater inflows that have now been diverted for agricultural development.These factors were consideredin rating the wetlands on a scale of 0 to 3, where0 representsno apparenthuman impacts,I representssome signs of human impact on the margins,2 representssigns of moderateto heavyimpact on the marginsbut the marsh systemappears to be basically intact, and 3 representsgreater than 50oh of the wetland has been converted to alternate uses (ponds,marinas, resort development).

RESULTS

Inventory of wetlands trorty-threemajor wetlandswere identified in the study area(Figure l, Tables I and 2), rangingin sizefrom 5 ha to nearly 100000ha (the interconnectedesteros of Bahia San Jorge).Numerous smallerwetland areas were observedand photographed,but theseare not includedin the tables.Total wetland areawas >\X?foo ha, of which 50000 ha were mangrove marshes,165 000 ha were saltgrassmarshes, and 6000 ha were freshwateror brackish wetlands.Wetlands were much more extensiveon the Sonoran coast (ttqo-o ha) than on the Baja coast (rlg,ooaha). Baja California is a steep,narrow peninsulawith a predominantly rocky shoreline,whereas the Sonorancoast is lesssteep and has a predominantlysandy coastline that lendsitself to the formation of salt marshes.The largestmarshes are at the northern end of the study area,where the tidal amplitude is most extremeand where the shorelinehas the shallowestslope, due to the depositionof sedimentby the Colorado River. Most of the esterosare of marine origin, formed by the action of tidesand currentson coastallandforms. Small esterosform behind rocky headlandsor sandspits, whereas very largeesteros, such as thosein Bahia San Jorge(Figure 2) and BahiaAdair, form at the backsof shallowbays. The backsof thesetidal marshes are vast salt flats (salinas)created by the evaporationof seawater.Some of the marshesare of deltaicorigin, formed at mouths of now-ephemeralrivers, including the Rio Sonoyta(forming Estero Morua and Estero Pinta in Bahia San Jorge)and the Rio Sonora(forming EsteroSanta Cruz in Bahia Kino). The delta of the Rio Asuncion (an extensionof the Rio San Miguel) ends behind a high strand of coastaldunes without forming a large delta, but groundwater comes to the surfacebehind the dunes, thus creating wetlands (Figure3). The only true estuarytoday is the intertidal zone of the Colorado River (Figure 4), sincethis is the only marsh that has a perennialinflow of river water (now made up mainly of agriculturaldrainage water except during flood years) (Glenn et al., 1996).Since silt is now trapped in upstream reservoirs,the delta is diminishing in area rather than accreting (Carriquiry and Sanchez, 1999). Large slices of shoreline frequentlycalve into the currentsin the final, intertidal part of the river as it approachesthe north side of Isla Montague (Carriquiry and S6nchez,1999). Hence, the marine zone is moving upstream.However, the

Copyright rt'.2006 John Wiley & Sons.Ltd. Arltrrrtir'('onserv: Mur. Frc.slrr.Ecosl'st.16: 5 28 (2006) l0 E.P. GLENN ET AL.

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Copyright it) 2006 John Wiley & Sons, Ltd. Arluntic Con.servMctr. Fresltt,.Ec:osyst.l6: 5_2g (2006) WETLANDS OF THE GULF OF CALIFORNIA ll

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Table 2. Coastal estuariesof the Baia California coast in the Gulf of California. from the delta of the Colorado River to Bahia de Los Anseles

No. Name Latitude Longitude Area Vegetation Human (''"N) ("'"W) (ha) impact"

36 Salinasde Ometepec tr4 s8t2 31 36 39 1616 Halophytemarsh (0) a- -)l Esterosde la Bolsa 11453 35 31 1659 15660 Halophyte marsh (2) SF, R 38 San Felipe n4 4947 3102 13 0 Halophyte marsh (3) C, R 39 EsterosPercebu and Aztecu tt4 420s 3045 53 738 Halophyte marsh (l) R 40 Estero Bahia San tt4 24t8 2948 3l 189 Haloohvte marsh (l) R Luis Gonzaga 4l Bahia de Los Angeles I 1329 18 28 53 18 145 Halophyte marsh with (l) R some black mangroves 42 EsteroLa Mona n3 2916 28 53 19 110 Halophyte marsh with (0) mangroves (?) 43 E,steroLos Animas l13 l8 47 2848 02 55 Halophyte r-narshwith (0) some black mangroves

Total area 18513

"The extent of human impact on eachwetland was rzrtedfrom 0 to 3: 0 is no apparent impact; I is somehutlzrn impact evident but the wetland appearsintact; 2 is the wetland has beenaltered by reducedfreshwater flows, extensiveresort developmentor aquaculture,but appearsmostly intact; 3 is > 50% of the wetland has been convertedto other uses.Codes for types of development:shrirnp farms on margins of the marsh (SF); resort and vacation homes on margins (R); local settlementson margins (S): diversion of freshwaterflows from rivers (D): and clearins of marsh area for development(C).

Figure 2. Estero Almejas, one of the large interconnectedesteros in Bahia San Jorge in the northern Gulf of California. The darker vegetation on the sand bars at the mouth of the estero are beds of the grass Distichli.spulmeri. The lighter vegetation is the mixed halophyte community in the mid zone. The back of the esterois covered with salt flats.

WETLANDSOF THE GULF OF CALIFORNIA t3

Figure 3. The delta of the fuo Asunci6n in the northern Gulf of California. Owing to upstreamdiversions for agriculture there is no surfaceflow in the river as it approachesthe sea.However, groundwater surfacesnear the coast, creating a vegetatedzone behrnd the dune line. Vesetation consistsof haloohvtesand mesouite trees. estuary is still turbid due to resuspensionof sedimentsby the tides (Carriquiry and S6nchez.1999) and is not consideredto be nutrient limited (Hernandez-Ayonet al., 1993).The delta supports the greatest diversity of wetland types found in the northern Gulf of California, including saltgrassmarshes, cattail marshes,pozos and a riparian corridor containing native Populus.fi'emontii (cottonwood) and Salir gooddingii(willow) trees(Glenn et a|.,2001). Although they have beencalled negative or inverseestuaries, or esteros(Lavin et al.. 1998),many of the salt marsheshave somefreshwater influence. This is an important considerationin assessingtheir ability to support plants, becausethe range of plants that can grow in perpetuallyundiluted seawateris limited (Felger, 2000). Many are set in sand dunes that rapidly infiltrate rain water. The infiltrated water forms an aquifer that can be perchedabove seawaterat the foot of the duneswhere they encroachon the back of the marsh. Deeply rooted shrubs can root into this groundwater. For this reason, the high zone and supralittoral are often the most thickly vegetatedparts of the marsh and may conrain less-salt-tolerant plants that do not penetrateinto the open marsh. Marshesat the mouths of ephemeralrivers usually have fresh or brackish aquifers that surfacewhere the river approachesthe coast or back of the marsh system. The Rio Asuncion is thickly vegetatedbehind the foredunes on the coast, and Estero Morua and Estero Pinta support brackish vegetationwhere the Rio Sonoyta riverbed reachesthe coast betweenthe mouths of the two esteros.Since the filling of Lake Powellin 1981,the Colorado River has carriedsubstantial flows of fresh water to the Gulf of California in half the years,totalling about 20"/, of total river flows (Glenn et al., 1996,2001). Non-tidal coastal wetlands are created around freshwater springs where subsurfacewater discharges near, or into, the intertidal zone,especially along the easternescarpment of the delta region and near Bahia

Cierregade SarrtaClala

F*z** Granfresiertn

Estero El firlfn tlnr#t*psf

FigLrre4. Major wetland areasof the Colorado River delta. shown on a 1990Ther-natic Mapper satelliteimage.

Adair (Felger, 1980,2000; Zengelet nl., 1995;Brusca, 2002,Brusca et a\.,2004). These 'pozos' (natural wells) are apparentlyled by water that collectsunder the dunesof the Gran Desiertoas run-off from the Pinacate,and flows towards the sea (Figure 5), or perhaps from even further away, north of the US Mexican border (Brusca et al.. 2004).Most of thesepozos emergeonto salt flats as lreshwatersprings. Along the delta's easternescarpment, between the intertidal zone and the Gran Desierto,the El Doctor pozosdischarge into sand and form freshwater,pocket wetlands.The largestnon-tidal wetland is Ci6nega de Santa Clara (seeFigure 4), an anthropogenicbrackish marsh formed by the dischargeof agricultural drainagewater (3000ppm total dissolvedsolids) from the USA into the easternpart of the Colorado River delta (Glenn et al.. 1992,1996;Zengel et al., 1995;Zengel and Glenn, 1996).Although they occupy only 6000ha, the lreshwaterand brackishemergent marshes provide critical habitat for residentand migratory terrestrialbirds and waterfowl (Garcia-Hernandezet ul.,200la).

Vegetationdistribution

Lists of plant speciesare in Tables3 5, divided into intertidal salt marsh species,species from the supralittoralzone of salt marshes,and speciesfrom non-tidal, fresh or brackishwater marshesand pozos.

WETLANDS OF THE GULF OF CALIF'ORNIA l5

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Figurc 5. Pozos (sprin-es),formin-q an interconnectedstrand of wetlands along the easternescarpl-ncnt ol- the Gran Desicrto where it intersectsthe intertidalzoneof the Colorado River delta.Plants include cmcrgeut species. shrubs (c.g. saltcec'lar)and trecs (rnesquites).

l6 E.P,GLENN ET AL.

Table 3. List of vascularplants of the intertidal zone in northern Gulf of California esteros. The table indicateszonation within the marsh. Status of the plant as native or endemic is rndicated

Mangroves Avicenniaceae Avic'enniagerminuns (black mangrove), native, mid zone Rhizophoraceae Rhizophoramangle (red mangrove), native, low zone Combretaceae Lagtrnculariuracemosa (white mangrove), native, high zone Conocarpuserecta (button mangrove), native, high zone or supralittoral

Halophyte salt marsh community Aizoaceae SesuviumverrLtcossum (western sea purslane),native, mid zone Sessuvitrmportulacastrum (sea purslane). native, mid zone Batidaeceae Batis ntaritinta (saltwort), native, low and mid zones Convolvulaceae Cre.g.gatruxillensis (alkali weed), native, mid zone and surpralittoral Frankeniaceae Frankenia salina (alkali heath), native, mid zone Poaceae(grasses) Distic'hlispalmeri (Palmer grass),endemic, low and mid zones Monanthot'hloelittoralz^r (shore grass),native, mid zone Sporobolusvirginicus (beach grass),native, high zone and supralittoral Chenopodiaceae Allenrolfia ot'cidentalis(iodine bush), native, high zone Atripler barc'layana(coast saltbush),endemic, high and mid zones Atriplex canescensvar. linearis (narrow-leaf saltbush),endemic, high zone Salicorniasuhterminall;r, native, high and mid zones Salicornia virginica,native, mid zone Salicorniabigelovii (pickleweed),native, low and mid zones Suaedamoquinii (desertseepweed), native, high zone and supralittoral Suaedaesteroa. native. mid zone Suaedapuertopenascoa, endemic, mid zone

Mangrove swamps form below 29'N, and saltgrass(Dtslichlis palmeri) marshesform above 29'N on both coasts(Turner et nl., 1995)(Table 6). All of the 20 intertidal plant speciesin the northern Gulf of California esterosare natives,and four species are endemic to the Sonoran Desert. The endemicsinclude D. palmeri, a saltgrassthat is only found in northern Gulf of California esteros.It produces a large grain that was harvestedas a staple food by the Cucupa peoplein the delta of the Colorado River in the pre-damera (Felger,2000).Other endemicsinclude a salt marsh succulent,Suaeda puertopenescoe, only found in the vicinity of Puerto Peflasco(Sonora, Mexico), and severalendemic Atriplex spp. or varieties.In contrast to theseesteros, nearby Pacific coast, southern California salt marsheshave been extensivelycolonized by non-native species(Kuhn and Zedler, 1997). On the other hand, the brackish wetlandsin the delta of the Colorado River have been extensively colonized by introduced species.The salt-tolerant shrub Tamorix ramo,sis,cima.introduced to the southwesternUSA in the 1900s,now dominatesapproximately 60000 ha in the Colorado River delta (Glenn et a|.,2001).In the deltaregion it extendsfrom the freshwater,riparian corridor downriver nearlyto the intertidal zone. It has spreadsouth along the coastto Guaymas,occupying brackish niches in riparian

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.. , .J+* ? t.i; "

,'"|, or, +m;; T. *,* - "- o*to

@* - kfr** h:@tr.{.@. T**"?t''m-

,*p,,a +$tu -* -%-;"qb.-$ 'ik{fl**f ffiffi"* -T .&- *ggqr*" M& -.: ry, @i t- * $r.- 4ft" ., ,.

Figure 5. Pozos(springs). forming au interconnectedstrand of wetlandsalon-q the eastemcscarpnent of the Gran Desiertowhere it intersectsthe intcrtidalzone olthe Colorado River delta.Plants include elnergent specics, shrubs (e.g. saltcedar) and trees(mesquites).

Table 3. List of vascularplants of the intertidal zone in northern Gulf of California esteros. The table indicateszonation within the marsh. Status of the plant as native or endetnicis rndicated

Mangroves Avicenniaceae Avicenniagerntinans (black mangrove), native, mid zone Rhizophoraceae Rhizophnramangle (red mangrove), native, low zone Combretaceae Lugtrnculariaracemosa (white mangrove), native, high zone Conocarpusere('tu (button mangrove), native, high zone or supralittoral

Halophyte salt marsh community Aizoaceae Sestnium verrLtcossum(western sea purslane),native. mid zone Sessuviumportulacustrum (sea purslane), native, mid zone Batidaeceae Batis maritima (saltwort), native, low and mid zones Convolvulaceae Cressatruxillensis (alkali weed), native, mid zone and surpralittoral Frankeniaceae Frankenia salina (alkali heath), native, mid zone Poaceae(grasses) Distichlispalmeri (Palmer grass),endemic, low and mid zones Monanthochloelittoralis (shore grass),native, mid zone Sporobolu,svirginicus (beach grass),native, high zone and supralittoral Chenopodiaceae Allenrolfia occidentalis(iodine bush), native, high zone Atriplex barc'layana(coast saltbush),endemic, high and mid zones Atriplex canescensvar. linearis (narrow-leaf saltbush),endemic, high zone Sctlicorniasubterminalis, native, high and mid zones Salicornia virginica,native, mid zone Salic'orniabigelovii (pickleweed),native, low and mid zones Suaedamctqttinii (desert seepweed), native, high zone and supralittoral Suaedaesteroa. native. mid zone Suaedapuertopenascoa, endemic, mid zone

Mangrove swampsform below 29'N, and saltgrass(D/s/ichlis palmeri) marshes form above 29'N on both coasts(Turner et al., 1995)(Table 6). All of the 20 intertidal plant speciesin the northern Gulf of California esterosare natives,and four species are endemic to the Sonoran Desert. The endemicsinclude D. palmeri, a saltgrassthat is only found in northern Gulf of California esteros.It producesa large grain that was harvestedas a staple food by the Cucupa peoplein the delta of the Colorado River in the pre-damera (Felger,2000).Other endemicsinclude a salt marsh succulent,Sucteda puertopenascoa, only found in the vicinity of Puerto Pefrasco(Sonora, Mexico), and severalendemic Atriplex spp. or varieties.In contrast to theseesteros, nearby Pacific coast, southern California salt marsheshave been extensivelycolonized by non-native species(Kuhn and Zedler. 1997). On the other hand, the brackish wetlands in the delta of the Colorado River have been extensively colonized by introduced species.The salt-tolerant shrub Tamarix ramosissima,introduced to the southwesternUSA in the 1900s,now dominatesapproximately 60000 ha in the Colorado River delta (Glenn et a|.,2001).In the delta regionit extendsfrom the freshwater,riparian corridor downriver nearlyto the intertidal zone.It has spreadsouth along the coastto Guaymas,occupying brackish niches in riparian

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Table 4. Plants from the supralittoral zone, backs of esterosand adjacentdunes in the northern Gulf of California esteros.These are mostly halophytesor salt-tolerant glycophytesthat grow above the high-tide line in freshwateror brackish soils. Some of them are also found within the marsh. occurrenceand form of each .The -urowth speclesls glven

Nyctaginaceae Abronia maritima (coastal sand verbena),native Asteraceae Amhrosia dumosa(white bursage),native Bat: c ltar is entory i, native Chenopodiaceae Atripler bu'clayana (coast saltbush),endemic A tr ip ler ('anescens var. grandidentatum (fourwing saltbush),endemic Atriplex lentiforntis(quailbush), native Poaceae Distichli.cspicata (saltgrass),native Jouveapilosa (tropical beach grass),native Frankeniaceae Fr ankeniapalnteri, native Boraginaceae Heliotropium curassovicunt(alkali heliotrope), native Lycium L1:ciumandersonii (desert wolfberry), native L)'ciunt hrari pa.s - native Celastraceae Maytensus phyllanthoides (.mangledulce), native Cactaceae Opuntia bigelovii var. bigelolii (teddybearcholla), native Prosopis Prosopi,sglanduloscr var. torret-una(western honey mesquite),native Prosopispubescens (screwbean mesquite), native Tamarix Tantarix ramo,si,ssinta(saltcedar), introduced Typhaceae Ty"phaclontengensrs (southern cattail), native

zonesand at the backs of esteros(Glenn and Nagler, in press).Other invasive,introduced species include Rumex clentatus(dock) and the annual grass Polypogonmon,\peliensi,\.

Human influences The mangrovemarshes and the saltgrassmarshes are distinctlydifferent in their degreesof human impact, as well as in the types of developmentpressure they face (Table 7).

Mangrove esteros Over 95oh of the mangrove marshesin the study area have been developedfor shrimp aquaculture.As of May 2004, 115 shrimp farms had beenbuilt on the coast of Sonora alone,covering an area of 24 000 ha (Meling-Lopezet a|.,2004).Inspection of 1973,1983, 1990 and 2003TM imagesshows that nearly all the developmenthas taken place after 1990 (Table B). Some destruction of mangroveshas been reported (Meling-Lopezet a1.,2004).However, in nearly all casesthe shrimp farms have beenlocated adjacent to, rather than within, the mangrovestands (Figure 6), and therehas beenlittle net lossof mangrovestands so far (Table B; also seeP6ez-Osuna (2001) and Gonzalezet al. (2003)).This is due to federallegal restrictions

Copyright 't'. 2006 John Wiley & Sons, Ltd. Aqutttit' Conserv:Mur. Freslttr.Ec'o.s1'.st.16: 5 28 (2006) l8 E.P.GLENN ET AL.

Table5. Plantsof Cienegade SantaClara and the El Doctor and BahiaAdair pozos. Thesemarshes occur wherebrackish water or fresh water entersthe intertidalor supralittoralzones. The soils become more saline away from thewater source. The plants grow in lreshwater, brackish water or highlysaline water, depending on theirposition aroundthe water source.(Plants of the Cienegaand pozosthat are alreadyiirt.d in tablesfbr the intertidalor supralittorerlzones are: Scs.sayruznlt)erucos5lrnt, Bat,hari.s entorfi, Heliotroptuttt'ura,ssavictutt, Allenrolt'ia occidenlulis, Atriple.r (,(me.\(en5, Atripler lenti/ttrntis, Salic:orniasubterminalis, Salicomia virginica, Suaeclantoquinii. Cie,ssa trtr-rillensi.t,Prctsopis glandulosa, Prosopi,s ptrbe.sc'en.s, Di,stichli;; ltahneri, Diitichtis spigata) Apiaceae H y'drocolylevert ir:ullata (water pennywort), native Asteraceae Plucheasericea (arrowweed), native Plucheaodorata (alkali camphorweed),native Chenopodiaceae Nitrophila occidentalis(alkali weed), native Cyperaceae Cvperttsluevigatus (flat sedge),native Eleochari,sgeniculata (spike rush), native Eleot'harisrostellata (travelling spike rush), native Scirpus anterit' anus (bulrush), native Sc'irpusntaritintus (saltmarsh bulrush), native Juncaceae Juncust'ooperi (spiny rush), native Poaceae Leptoc:ltloauninervict (Mexican sprangletop),native Phragmites austroli:i (common reed), native Polypogonmonspelienrzs (rabbitfoot grass),introduced Sporobolusairoides (alkali sacaton),native Polygonaceae Rumex dentatus(dock, sorrel), introduced Saururaceae Anintopsiscalif ornica (yerba mansa), native

Table 6. Plants lbund mainly north or south of 29.N alone the coasts of the northern Gulf of California Mainly north of 29"N Frankeniu .galina Di,stichlispalmeri M onuntho t' h loe lit t orali s Atripler canescen.tvar. linearis Straeclamoquinii Suaeda plter t openasco a Ambrosia dumosct At rip lex canescensvar. grandidentatum Frankenia polmeri Atriplex lentifbrmis Tant ar i-r r anto s i,s s i mu Mainly south of 29'N Avicenniagerntinans Rhizophora ntangle Lagttnc'ularia r acemo s a Conocurpuserecttt Se s suy ium p or t uI at' as t r unt M a v-t e n,str s p hy Ilan t h oide s

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Table 7. Degree of human disturbance in mangrove and non-mangrove wetlands of the northern Gulf of California

Disturbance Mangrove Non-mangrove esteros category" esteros(%) and other wetlands(%o) 0 3.9 17.8 I 0.8 62.4 L 94.8 t9.7 3 0.5 0.1

Total area (ha) 49311 112204

"The extent of human irnpact on each wetland was rated from 0 to 3: 0 is no apparent impact; I is some human impact evident but the wetland appears intact; 2 is the wetland has beenaltered by reducedfreshwater flows, extensive resort developmentor aquaculture,but appearsmostly intact; 3 is > 50% of the wetland has been converted to other uses.

Figure 6. Tastiota estero in the northern Gulf of California in 2003, showing shrimp farm development.The inset is from a 1990 Thematic Mapper satelliteimage and it shows that the shrimp farms were placed on a former dry arm of the esterorather than in the vegetatedportion of the estero. on the clearing of mangrove forests,and also becausepond construction and managementare easieron the flats than in the mangrove marshesthemselves. A similar development pattern has taken place in the mangrove esterosof southern Sonora, Sinoloa, and Nyarit (P6ez-Osunaet al., 1997. 1998, 1999,2002;

P6ez-Osuna,2001). The only significantmangrove esteros in the study areathat have escapeddevelopment so far are in the Canal del Infiernillo betweenthe Sonora mainland and Tiburon Island (nos 8-15 in Table l), which is a protectedhomeland area for the SeriIndians. Near Guaymas,Estero Soldado also has a limited protectedstatus through ongoing efforts of Conservationlnternational, Mexico. Mangrove esteroswith shrimp ponds nearby have been damaged by severalindirect impacts, including alteredhydrological patterns, hypersalinity, and eutrophication(Paez-Osuna, 2001). The systemof ponds, roads and leveesat the back of the esterosreduces the ability of freshwater flows (rainfall, streams and springs)to penetrateto the intertidal zone. Furthermore,the seawater in aquacultureponds inducessea water intrusion that raisesthe salinity at the backs of the marshes.As a result, the marsh may become hypersaline,reducing the vigour of the mangrove forestsand in some casesleading to die-offsof white mangroves,which require some fresh water influence.In addition, eutrophication can occur through the dischargeof shrimp pond effiuentinto the estero,or along the adjacentcoastline. Eutrophication may not directly affectthe mangroves,but it affectsthe periphyton and prop root communitiesat the baseof the food chain, and the excessnutrients (and added chemicalsand exotic pathogens)are dischargedto the open sea(Pd,ez-Osuna et al., 1998,1999,2003). Esteros with shrimp farms, such as thoseat Guaymas and Kino Bay, have reportedly experiencedincreased incidences of red tide blooms and fish die-offs (Cort6s- Altamirano et al., 1996;Alonso-Rodriquez and P6ez-Osuna,2003). Hence, studies are needed on the ecosystemeffects of shrimp farming on mangrove marshesand adjacent coasts. Agricultural and municipal developmenthave also impacted the mangrove marshes(P6ez-Osuna, 2001). Upstreamdams and water diversionsfor agriculturemean that the esterosof the Yaqui River delta (nos I and 2 in Table 1) no longer receivefreshwater inflow. On the other hand, they do receiveagricultural drainage water that is collectedthroughout the inland irrigation districts and dischargedinto the esterosvia canals. They also receivemunicipal sewagedischarge. These highly polluted waterscontribute to eutrophicationand introduce pesticidesand industrial chemicalssuch as polychlorinated biphenyls (PCBs) and heavy metals (Paez-Osunaet al., 2002). Mangrove esteroshave been directly impacted where land has been cleared of mangrovesfor agricultural development(P6ez-Osuna, 2001). Roads cut into the area around many esteros also destroy archaeologicalsites, such as shell middens and pre-Hispanic(aboriginal) camp sites.

Saltgrassesteros In contrast to the mangroveesteros, over 800%of the esteroarea north of the mangroveline is still only lightly impacted by human development(Table 7). Shrimp farm developmenthas been concentratedon the coastline south of Guaymas becausethe climate is warm enough to support two shrimp crops per year, compared with only one per year north of Guaymas. However, as the southern coastlinehas become overdeveloped,disease problems have resultedin reducedyields, and shrimp farming has moved north. At least two commercial shrimp farms of severalhundred hectareseach have been establishedat the head of the gulf near the towns of El Golfo and San Felipe. Unlike the casewith mangrove marshes,shrimp farms can be placed directly in the saltgrassmarshes, as there is currently no protection for this marsh type. The main type of human impact on the saltgrassmarshes to date has beentourist-related development of marinas, resorts and vacation homes. As with shrimp farms, in most casesthe developmentoccurs around the esterosrather than directly within them. In some cases,however, the esterosthemselves have been converted.as at EsteroCholla north of Puerto Peflasco.Over 50ohof this esteroarea has beendrained and filled for resort development.In more lightly developedesteros, most of the developmentoccurs along the dune line that typically separatesthe esterosfrom the open sea (Figure 7). The majority of resort and vacation home development is for US citizens,who visit the northern Gulf of California from southern Californian cities,as well as from Tucson and Phoenix in Arrzona.The main issuesassociated with this type of development is pollution from sewageand grey-water discharge,and from off-road vehicle use. The beachcommunities are not connectedto municipal sewagesystems, hence, leakage of sewagethrough the

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Figure 7. Estero La Pinta in the northern Gulf of California in 2003,showing extensivedevelopment of vacation homes on the coastal dune line in front of the estero.

dunesand into the esterosand the seais likely. This effiuentmay presenta human health hazard, and it may encouragethe spreadof introduced species,as has occurredin southernCalifornian marshesaffected by freshwater inflow (Kuhn and Zedler, 1997).

Other v'etlands The Colorado River delta has sufferedfrom a historic reduction in lreshwaterflows due to upstream water- diversion projects. A brackish clam (Mulinia coloradoensis)that was once abundant in the delta is now nearly extinct (Kowalewski e/ al., 2000;Rodriquez et a|.,2001). From 1937to 1964,very little river water reachedthe sea,as upstreamimpoundments behind the major dams (Hoover and Glen Canyon) were lilling (Glenn et al., 1996).Since the impoundments first reachedcapacity in 198I , however, water has flowed to the seaduring each major El Nifro cycle, and thesepulse floods have regeneratednative treesin the riparian zone (Zamora-Arroyo et al., 2001) and stimulated the shrimp fishery in the upper gulf (Galindo-Bect e/ al., 2000). At the same time, discharge of agricultural drainage water has created new wetland areas,such as Cienegade SantaClara and similar anthropogenicmarshes. These wetlands support a rich diversity of birds (e.g.Hinojosa-Huerta et a|..2004) and fish species(e.9. Zengel and Glenn, 1996) and, so far, have not presentedwater quality problemsfor wildlife (Garcia-Hernandezet a|.,2000,2001b). ln general,the wetlandsof the Colorado River delta, although much diminishedcompared with pre-dam conditions,have improved over the past 20 yearsdue to maturation of the dam systemand to the discharge of agricultural drain water into the delta and intertidal zone (Glenn et al., 1996.2001;Hinojosa-Huerta et a|.,2004).

22 E.P. GLENN ET AL.

DISCUSSION

Ecological and economicimportance of the wetlands

Strong food-web linkages have been demonstrated between North American salt marsh vegetation nearshore fish consumers via detritus and production and consumption. These systems ctlternifloramarshes include spartina along the Atlantic ani Gulf of Mexico coastlines (e.g.Darnell, 1g61,Teal, 1962),thes. /ttlio'sumarshes of the Pacific Northwest (Naiman and Sibert, lgTg),and-california coastalwetlands and Zedler' 1997)' For example, (Kwak the highly productive Atlantic menhaden (Brevoortia direct use tyrannus) makes of cellulose from s. atterniflira (Peters and Schaaf, lggl). In addition to the detritus from ruelthe roodchain through production ;il1,',:'fi"1t:1t:riii,#iijl" or eelgrass,macroargae, No studies on primary productivity or food-chain dynamics have been Gulf reported for the esterosof the of california' However, similar marsh systems have been studied along the southern california coastline' Although the california marshes aie sometimesconsidered to ha-velow productivity minimal input into the marine with food chain, Kwak and,zedler (1997)demonstrut.al'r,"r"rr;;t,'-urrt- channel linkage for the Tijuana estuary and San Deiguito lagoon. vascular plant supporteda variety detritus and algae of nearshorefish populations,as well as .ndung..ed these birds and other biota. Basedon findings' they recommendedthat ihe estuary-nearshore channel habitats should be managed singleecosystem, and that restoration as a of intertidal marsheswas compatiblewith enhancement fish populations,whereas previously of coastal they were consideredto be competingobjectives. The extensivenorthern Gulf of california esteros are a nursery area for penaeidshrimp (Snyder-conn and Brusca' 1977;Brusca, 2002; calderon-Aguileraet a|.,2003;Bruscaet marshes a:..2004)similarto the mangrove to the south (Flores-verdugoet aI. 1993: Pdez-osuna et al.. l99B;whitmore et a..,2004). commercial shrimp speciesspawn The offshore and the post-larval stagesmigrate into into juveniles(calderon-Agurlera iir.-.;;.;;; ,-o?u.rop et ctt',2003).Although the northern shrimp hypersaline populationsare adaptedto conditions (calderon-Aguilera et at., zool1, Gallindo-Bect et crl. (2000) found a positive correlationbetween freshwater flows in the colorado River and the subsequentyear,s shrimp San Felipe' They concluded -colorado landingsat that freshwaterflows reduce the sarinity providing in the River esruary, larval shrimp and perhapssome fish species protection fiom euryhalinepredator fish. The coastalwetlands of the gulf also play a critlcal role in the conservationof the california and avifaunaof the Gulf of Sonoran Desert.These wetlands provide habitat for nearly 500 speciesof birds, many of them federally protected in Mexico, including ilupp.r rails (Rattu,slongirostrr,r), virginia limicola)' least terns (sterna rails (Raltus antillarunt), and"western snowy plovers (Charadrius (Russell alexcmclrinusnivosus) and Monson, 1988; Brusca and Bryner, in pressj These resident speciesdepend upon the ecologicalintegrity of thesewetlands to survive. However, availabreinformation on their and the effectsof human regional status activitieson their populationsis very limited. over 200 speciesof migratory bird have beendocumented along stopoversites in coastalSonora (Patten et al'' 2001), and alone large pulsesof thesebirds are commoily observed migration (Hinojosa-Huerta during the peak of spring et ai.,2004).It is likely that an important percentageof bird populationsthat breed in the westernusA and canada migrate through the coast of Sonora.The quality of stopover wintering sites in migration routes and has been identifled as one of the most critical parameters statusand population defining the trendsof migratory birds (Rappole, petit, population l9g5; 2000). declineshave been linked to habitat lossand degradationoi stopoveruit", in the USA, Mexico, and central America (Hutto, 2000)'Yet' there is almost no information on g..r.rul patternsof geographicdistribution, and avian use of habitat quality, stopoversites along the coast of westernMexico. At the northern end of the Gulf of california, the wetlandsof the delta variety of the colorado River provide a of habitatsthat support a rich diversityof waterbirds, incruding,by one survey,Tl speciesof divers.

Copyright .t' 2006John Wiley & Sons.Lrd. Atlttrttit, Con.yert,.-Mar. Freslur..Ec,ct.st.gt.l6: 5_28 (2006) WETLANDS OF THE GULF OF CALIFORNIA z)^a waders,gulls, terns, skimmers,pelicans, cormorants, marshbirds, shorebirdsand waterfowl (Hinojosa- Huerta et al., 2004).Montague Island alone supportsbreeding populations of l2 speciesof waterbirdsin the D. palmeri beds.Over 160000shorebirds and tensof thousandsof waterfowl usethe delta as wintering grounds, making it one of the critical sites for migratory waterbirds on the Pacific Flyway (Hinojosa- Huerta et al,, 2004). The delta appears to play an equally important role for migratory neotropical terrestrialbirds, including threatenedand endangeredspecies (Garcia-Hernandez et al.,200la). Very large numbers of thesebirds arrive at the delta during the spring migration seasonon their way to northern nestingareas.

Current conservationstatus

The wetlands at the head of the Gulf of California, including the large esterosof Bahia Adair and the Colorado River delta wetlands, are part of the Biosphere Reserveof the Upper Gulf of California and Delta of the Rio Colorado (Morales-Abri1,1994. Brusca and Bryner, in press).This affords them some protection from development, although aquaculture and artinesial fisheries are still permitted. The mangrove marsheshave some degreeof protected status,as all four mangroveshave been listed as rare and endangeredspecies (P6ez-Osuna, 2001). The remaining wetlands are, for the most part, unprotected. In particular,the saltgrassmarshes do not havethe samedegree of protectionas the mangrovemarshes, and it is legally possibleto clear the vegetationin thesemarshes for aquacultureor other uses.In the Gulf of California, rocky headlandsand the southern mangrove esteroshave beenproposed for protection because of their demonstratedimportance to the fisheriesand to non-commercial speciesin the marine zone (Sala et a1.,2002).By contrast,there have beenfew studieson the importanceof the saltgrassesteros and they have not beenproposed for specialprotection. In Mexico, severalfederal agencieshave responsibilityfor designatingprotected areas. These agencies include the National Institute of Ecology (Instituto Nacional de Ecologia),the National Commissionon Natural Protected Areas (Comision Nacional de Areas Naturales Protegidas), and the National Commissionfor the Use and Study of Biodiversity(Comision Nacional para el Uso y Conocimiento de la Biodiversidad(CONABIO)). Priority conservationstatus for an areais awardedby CONABIO basedon scientificstudies documenting the importance of that habitat type in preservingand enhancingbiodiversity, an important national goal.CONABIO actsas an information clearing-housefor completedenvironmental studies.Hence, the northern gulf wetlands will not be consideredfor protection until their value in supportingbiodiversity is documented.The presentstudy is an attempt to beginthe documentationprocess and to encourageresearch on the ecologicalvalues of thesewetlands. Our working hypothesis,based on the observationsreported here, is that theseesteros might have great, if unrecognrzed,importance to the marine food chain and to the movement of waterbirds and terrestrial neotropical birds along the desertcoastline in the northern gulf. Basedon our initial observations,the human impact on the esteros at current levels appear to be manageable.Aquaculture and tourism developmenthas, for the most part, not taken placedirectly within the esteros,but adjacentto them.

Recommendations

As has beenproposed for the southernGulf of California rocky headlandsand esteros(Sala et a|.,2002),a systemof protected reservesincorporating the pristine wetlands,along with water quality managementand buffer zones for the more developedesteros, could preservethese wetlands for the future. The still-pristinemangrove marshes along the Canal del Infiernillo betweenthe Sonora mainland and Tiburon Island should becomeprimary targetsfor protection in coastalreserves. This area also supports seagrassbeds that are the baseof a rich marine food chain (Meling-Lopez and Ibarra-Obando, 1999),and it is the homeland of the Seri Indians, who have so lar not permitted aquaculture developmentin the esteros (Felgerand Moser, 1985;Burckhalter, 2000).

Most of the remaining mangrove esteroshave already been developedfor shrimp aquaculture, but the mangrove standsare still largely intact. Theseesteros require initial water quality assessment,establishment of water quality standardsfor effiuent discharge,establishment of operating standards to meet the water quality goals,and then monitoring to assurecompliance (Paez-Osuna et al., 199S). The saltgrassesteros of the northern gulf are not yet heavily influencedby human development.Hence, conservation efforts at this time could have profound and far-reaching positive impacts on the marine ecosystemof that region.Still-pristine or lightly impactedsaltgrass esteros on the Sonorancoast include the esterocomplexes of Bahia San Jorge and Bahia Adair, covering 130000 ha. Theseesteros, as well as the estuary of the Colorado River, appear to play important roles as feeding stations and nursery areasin the marine zone. They should be primary targets for protection within coastal reserves. Many of the remaining saltgrassesteros have been moderately impacted by adjacent residential and resort developments.These esterosshould be protected by prohibiting dredging or building within the intertidal zone,restricting off-road vehicleactivities, and controlling the dischargeof domestic sewageinto the esteros.Of specialconcern are the developmentsbuilt along the foredunesof theseesteros. These typically rely on septic tanks to treat domestic sewage.These tanks dischargepartially treated freshwater effiuent into the dunes that presumably leaks into the esteros,introducing the possibility of eutrophication and the creation of areas of diluted salinity where introduced speciescan establish, as in Pacific coast marshes(Kuhn and Zedler, 1997).Golf courses,proposed for land adjacentto some of the esteros,would be another source of fresh water and nutrient runoff. The water quality problems associatedwith these esteros need to be identified, standards for discharge established,and monitoring programmes implemented.The Gulf of California saltgrassesteros may be especiallysusceptible to pollution because they currently receive little if any freshwater inflow, and have much less vegetation and, therefore, less capacityfor absorbingnutrients than other coastalsalt marshes. The northern saltgrass marshes also need protection from development directly within the marsh. Unlike the mangrove marshes, it is still permissibleto convert saltgrassmarshes to shrimp ponds and marinas, or to fill them in for resort development.The saltgrassmarshes should be given the same degreeof protection as the mangrove marshes,as they fulfil many of the sameecological functions. Given the rapid population growth and economic developmentin the northern Gulf of California, an effective conservationpolicy must incorporatehuman aspirationsinto the planning process(Palmer et a\.,2004). Researchis neededto demonstratethe value of intact esterosto the commercial fisheriesand tourist-related industries.

ACKNOWLEDGEMENTS

Funding was provided by the National Aeronautics and SpaceAdministration Earth ScienceProgram and the David and Lucile Packard Foundation.

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