Aquatic Invasions (2009) Volume 4, Issue 3: 435-450 DOI 10.3391/ai.2009.4.3.2 © 2009 The Author(s) Journal compilation © 2009 REABIC (http://www.reabic.net) This is an Open Access article Research article Invasive mollusks Tarebia granifera Lamarck, 1822 and Corbicula fluminea Müller, 1774 in the Tuxpam and Tecolutla rivers, Mexico: spatial and seasonal distribution patterns Eugenia López-López1*, J. Elías Sedeño-Díaz2, Perla Tapia Vega1 and Eloiza Oliveros1 1Laboratorio de Ictiología y Limnología, Escuela Nacional de Ciencias Biológicas. IPN. Prol. de Carpio y Plan de Ayala, Col. Sto. Tomás, 11340, México D.F. 2Coordinación del Programa Ambiental.IPN Edificio CFIE, Planta Baja, Av. Wilfrido Massieu esq. Av. Luis Enrique Erro, Unidad Profesional Adolfo López Mateos, Col. Zacatenco, 07738, México D.F. E-mail: [email protected] (ELL), [email protected] (JESD) *Corresponding author Received 16 April 2009; accepted in revised form 24 July 2009; published online 13 August 2009 Abstract The Tuxpam and Tecolutla rivers in the Gulf of Mexico, are located in the Mesoamerican biodiversity hotspot and support different human activities: crude oil extraction, agriculture and livestock, that provoke environmental disturbances. Aquatic mollusks, physicochemical water characteristics and substrate type were examined along the main watercourse of these rivers during three periods of one year: the wet season, dry season, and during the northern winds season, when hurricanes are more frequent. In both rivers, physicochemical water characteristics, types of substratum and mollusk fauna demonstrated environmental gradients and differentiate two river zones: freshwater and estuarine. Differences were also found between the dry season, with higher inorganic salts content, and the wet and northern winds and hurricane seasons, when inorganic and organic nutrient inputs occurred. The mollusk fauna is composed of nine and eleven taxa in the Tecolutla and Tuxpam rivers, respectively. In both rivers, the introduced gastropod Tarebia granifera is the dominant species in the freshwater zone with regard to population density and the area it covers within the ecosystem, followed by the introduced bivalve Corbicula fluminea. Native mollusk species were confined to point-locations and attained very low densities. The gastropod Neritina virginea and the bivalve Brachidontes exustus were dominant in the estuarine zone of both rivers. Mollusk population densities declined during the wet, northern winds and hurricane seasons, while in the dry season both alien species reached higher densities, which could indicate that alien mollusks are removed by effect of climatic events. T. granifera and C. fluminea exhibit traits characteristic of invasive species and pose a risk to native mollusk biodiversity in these rivers. Key words: invasive aquatic mollusks, tropical Mexican rivers, environmental degradation, biodiversity loss Introduction Other human activities including aquaculture, recreation, transport, and trade globalization The Mexican rivers Tecolutla and Tuxpam drain intentionally or accidentally also contribute to into the Gulf of Mexico within the Meso- the spread of invasive aquatic species (Cohen american biodiversity hotspot (Myers et al. and Carlton 1998; Carlton and Geller 1993) that 2000). Throughout much of the Mexican Gulf can use such available spaces. Invasive species coast region human activities such as crude oil are considered the second major cause of bio- extraction, intensive agriculture, water extraction diversity loss in the world (Vitousek et al. 1996; and inputs of untreated wastewater have Leung et al. 2002) and their spread is one of the degraded various aquatic ecosystems (Ortíz- major problems in ecosystem conservation (Ruiz Lozano et al. 2005). Lake (2000), states that et al. 2000). Adverse effects of invasive species several environmental disturbances have a may take different forms: once they have negative impact on native species, through achieved a wide distribution, these species eradication or removal of sensitive species, and produce global homogenization of the patterns of can create spaces available for colonization. distribution, altering the once distinctive 435 E. López-López et al. regional biota, and they may affect aquatic the distribution of species catalogued as invasive ecosystems through competitive exclusion of by CONABIO (2008). It is therefore essential for indigenous biota (Rahel 2000; Sousa et al. 2008). studies to focus on the impact of invasive species Some invasive species displace native species on the native biota and invaded habitats. This through direct competition, predation, intro- paper contributes to the understanding of duction of diseases, changes in biological and patterns of distribution of native and introduced geochemical cycles, and alteration of the trophic mollusk species in the Tuxpam and Tecolutla web, thus causing adverse effects in the invaded rivers, in the Mexican subtropics. The different habitats (Davis et al. 2000; Mack and Lonsdale forms taken by the invasion of two alien species 2001; Sax et al. 2002). in each of these rivers are explained and the risks In Mexico, the National System on Invasive these species pose are evaluated. Species established by the National Commission for the Understanding and Use of Biodiversity (CONABIO 2008) has preliminarily identified at Study area least 1000 invasive species of plants, mollusks, crustaceans, insects, fishes, amphibians, reptiles, Tuxpam and Tecolutla rivers cross the Gulf of birds and mammals. These include 13 species of Mexico coastal plain in the northern part of the invading mollusks: 11 bivalves (four freshwater) state of Veracruz (Figure 1). Both are perennial and two gastropods (one freshwater). CONABIO rivers with high discharges arising in the Eastern (2008) states that these species affect the natural Sierra Madre (more specifically the Sierra Norte wealth of Mexico, deteriorate environmental de Puebla) and flowing through a region of hot conditions in ecosystems and may have negative humid and sub-humid climate with abundant consequences on human health, production and rainfall throughout the year, particularly in the economy and recognizes the urgent need for summer. Discharges of both rivers are affected additional knowledge of the distribution of these by the impact of northern winds and hurricanes. species and their impact on native biota, and the The Tecolutla drainage includes the major need to identify high-risk biodiversity areas. tributaries Necaxa, Tenango, Laxaxalpan, Zem- Mexico has been ranked as one of the five poala, Apulco and Chichicatzapa rivers within its megadiversity countries in the world (Bezaury et total drainage area of 7,903 km2 to discharge a al. 2000), however, knowledge of the diversity of mean of 6,885 million m3, into the Gulf of certain groups within its territory is limited Mexico at Barra de Tecolutla (CONAGUA because large areas remain unstudied, especially 2007). The mean air annual temperature is 21- in the case of freshwater mollusks (Naranjo 26°C, total annual rainfall ranges from 1,200 to 2003). Based on worldwide diversity estimates, over 4,000 mm, and the rate of evaporation is Strong et al. (2008) recognize Mollusca with as 1,064-1,420 mm (Sanchez and De la Lanza many as 80,000-100,000 described species, as an 1996). The vegetation cover is semi-deciduous extraordinarily diverse phylum, second in tropical forest, mangrove, halophytic vegetation diversity only to arthropods. In Mexico, 16 and palm grove (Arriaga et al. 2002). Tecolutla families of freshwater mollusks have been River is listed by CONABIO (Arriaga et al. recorded, representing five orders, four 2002) as a priority hydrologic region since it subclasses (Naranjo 2003) and 211 species flows through an area of high biodiversity, and is (Contreras-Arquieta 2000). Furthermore, in a catalogued as threatened because it supports study of the continental gastropods of Mexico diverse land uses (agriculture, livestock, fishing and Central America, Thompson (2008) found and tourism). 168 aquatic operculate and 84 aquatic pulmonate Tuxpam River watershed covers a surface area species and emphasized that the mollusk fauna of of 5,899 km2 and has a mean annual flow of Mexico is poorly studied. Thus, the number of 2,580 million m3 (CONAGUA 2007). Its princi- continental mollusk species may exceed current pal headwater known as Río Pantepec is joined records, particularly since two zoogeographic by several tributaries before reaching the coastal regions, Nearctic and Neotropical, each with its plain named Tuxpam to discharge into the Gulf own characteristic fauna, converge in Mexican of Mexico at Barra de Tuxpam. Human activities territory sharing a broad transition zone in this basin include livestock, agriculture, (Morrone and Márquez 2001). To the paucity of fishing and industry. There is a power plant in knowledge on the native freshwater mollusks of Barra de Tuxpan, and a shipyard and the seaport Mexico must be added the lack of information on of Tuxpam are located near the river’s mouth. 436 Invasive mollusks in rivers of the Gulf of Mexico Figure 1. Location of study sites in the Tecolutla and Tuxpam rivers. Tx followed by a number indicates the number of the study site in the Tuxpam river. Tc followed by a number indicates the number of the study site in the Tecolutla river. Geographic coordinates are in Annex 1 within 1-m2 quadrats, sieving of sediments, 1 m2- Material and Methods base Surber net, and collection among roots,