Lat. Am. J. Aquat. Res., 41(4): 685-695, Freswather2013 crabs of Río Grande de Térrraba, Costa Rica 685 “Studies on Freshwater Decapods in Latin America” Ingo S. Wehrtmann & Raymond T. Bauer (Guest Editors) DOI: 103856/vol41-issue4-fulltext-5 Research Article Species diversity and distribution of freshwater crabs (Decapoda: Pseudothelphusidae) inhabiting the basin of the Rio Grande de Térraba, Pacific slope of Costa Rica Luis Rólier Lara 1,2, Ingo S. Wehrtmann3,4, Célio Magalhães5 & Fernando L. Mantelatto6 1Instituto Costarricense de Electricidad, Proyecto Hidroeléctrico El Diquís, Puntarenas, Costa Rica 2Present address: Compañía Nacional de Fuerza y Luz, S.A., San José, Costa Rica 3Museo de Zoología, Escuela de Biología, Universidad de Costa Rica, 2060 San José, Costa Rica 4Unidad de Investigación Pesquera y Acuicultura (UNIP), Centro de Investigación en Ciencias del Mar y Limnología (CIMAR), Universidad de Costa Rica, 2060 San José, Costa Rica 5Instituto Nacional de Pesquisas da Amazônia, Caixa Postal 478, 69011-970 Manaus, AM, Brazil 6Laboratory of Bioecology and Crustacean Systematics (LBSC), Department of Biology Faculty of Philosophy, Sciences and Letters of Ribeirão Preto (FFCLRP) University of São Paulo (USP), Postgraduate Program in Comparative Biology, Avenida Bandeirantes 3900 CEP 14040-901, Ribeirão Preto, SP, Brazil ABSTRACT. During the last decades, knowledge on biodiversity of freshwater decapods has increased considerably; however, information about ecology of these crustaceans is scarce. Currently, the freshwater decapod fauna of Costa Rica is comprised by representatives of three families (Caridea: Palaemonidae and Atyidae; Brachyura: Pseudothelphusidae). The present study aims to describe the species diversity and distribution of freshwater crabs inhabiting the basin of the Rio Grande de Térraba, Pacific slope of Costa Rica, where the Instituto Costarricense de Electricidad (ICE) plans to implement one of the largest damming projects in the region. Samples were collected in 39 locations at an altitude ranging from 20 to 1,225 m. Sampling was carried out during several months in 2007, 2009 and 2010. We collected a total of 661 crabs, comprising eight species of Pseudothelphusidae of three genera, representing 53% of the 15 pseudothelphusid crab species currently recorded from Costa Rica. The most common species was Ptychophallus paraxanthusi followed by P. tristani. Freshwater crabs were more frequently encountered in the middle-low region of the basin (between 311 and 600 m) and less frequently in the medium-high basin (between 601 and 1,225 m). Ptychophallus paraxanthusi showed the widest distribution and was collected in altitudes ranging from 20 to 700 m. The Rio Grande de Térraba region can be considered as a relatively small, but highly diverse system. Therefore, any alteration of the basin of Rio Grande de Térraba, and especially the possible construction of a hydroelectric power plant, needs to be carefully analyzed to mitigate the damaging effects of this project on the freshwater crabs. More ecological information about freshwater crabs from Costa Rica and the Central American region are needed to reach a first reasonable overview on the ecological role of these decapods in freshwater systems. Keywords: Crustacea, river crabs, faunal survey, species diversity, Central America. Diversidad de especies y distribución de cangrejos de agua dulce (Decapoda: Pseudothelphusidae) de la cuenca del Río Grande de Térraba, vertiente Pacífica de Costa Rica RESUMEN. El conocimiento de la biodiversidad de decápodos de agua dulce ha aumentado conside- rablemente durante las últimas décadas. Sin embargo, información sobre la ecología de estos crustáceos es limitada. Actualmente, la fauna de los decápodos de agua dulce está compuesta por representantes de tres familias (Caridea: Palaemonidae y Atyidae; Brachyura: Pseudothelphusidae). El presente estudio describe la diversidad de especies y la distribución de cangrejos de agua dulce de la cuenca del Río Grande de Térraba, vertiente Pacífica de Costa Rica, donde el Instituto Costarricense de Electricidad (ICE) está planeando construir una de las plantas hidroeléctricas más grandes de la región. Las muestras fueron recolectadas en 39 686 Latin American Journal of Aquatic Research localidades a una altitud entre 20 y 1.225 m. El muestreo se efectuó durante varios meses de los años 2007, 2009 y 2010. Se colectó un total de 661 cangrejos de ocho especies de Pseudothelphusidae de tres géneros, lo que representa un 53% de las 15 especies de Pseudothelphusidae actualmente reportado para Costa Rica. La especie más frecuentes fue Ptychophallus paraxanthusi, seguida por P. tristani. Los cangrejos de agua dulce fueron más frecuentes en la región medio-baja de la Cuenca (entre 311 y 600 m) y menos frecuentes en la región medio-alta (entre 601 y 1.225 m). Ptychophallus paraxanthusi demostró la distribución más amplia y fue colectado en altitudes entre 20 y 700 m. Se puede considerar el Río Grande de Térraba un sistema pequeño, pero altamente diverso. Por lo tanto, cualquier alteración de la Cuenca del Rio Grande de Térraba, y especialmente la posible construcción de la planta hidroeléctrica, requiere un análisis cuidadoso para mitigar efectos dañinos de este proyecto sobre los cangrejos de agua dulce. Se requiere más información ecológica sobre los cangrejos de agua dulce de Costa Rica y la región de Centro América para obtener una primera visión razonable del rol ecológico de estos decápodos en los sistemas dulceacuícolas. Palabras clave: Crustacea, cangrejos de agua dulce, inventario faunístico, diversidad de especies, América Central. ___________________ Corresponding author: Ingo S. Wehrtmann ([email protected]) INTRODUCTION rivers San Carlos and Sarapiquí, northern Costa Rica (Villalobos & Burgos, 1975), and one report on the Knowledge and literature about the taxonomic offspring production and juvenile occurrence of diversity of decapod crustaceans has increased Potamocarcinus magnus in the Costa Rican territory considerably during the last decades (Ng et al., 2008). (Wehrtmann et al., 2010). Most of these publications focused on decapods Detailed information about species diversity and inhabiting marine ecosystems; however, there has ecological features of the freshwater decapods fauna is been also a significant increase in studies concerning of special importance when evaluating the possible freshwater decapods, including representatives of the environmental impacts, which may be caused by the two families of Brachyura from the neotropical region construction of dams for hydroelectric plants (Holmquist (among others, Magalhães, 2003a, 2003b; Rodríguez et al., 1998; Benstead et al., 1999; March et al., 2003; & Magalhães, 2005; Magalhães & Türkay, 2008a, Greathouse et al., 2006). The Instituto Costarricense 2008b; Yeo et al., 2008; Cumberlidge et al., 2009; de Electricidad (ICE) is planning to construct, in the Pereira et al., 2009; Villalobos & Alvarez, 2010). southern Pacific lowlands, one of the largest Currently, there are approximately 6,800 valid species hydroelectric plants in Central America (ICE, 2009). of brachyuran crabs and about 1,300 (19.4%) of these Lara & Wehrtmann (2011) already analyzed the have been reported from freshwater habitats (Ng et al., species composition of river shrimps in this area and 2008; Yeo et al., 2008). recommended the incorporation of structures permi- The taxonomic composition of the freshwater tting the passage of the migrating shrimps to mitigate decapod fauna of Costa Rica is fairly well known and negative effects of the construction of the hydro- is composed by three families: Palaemonidae and electric power plant. Therefore, the present study Atyidae (Caridea), and Pseudothelphusidae (Brachyura). aimed to amplify the existing information about the The latter includes the freshwater crabs, a very diverse freshwater fauna in the study area and to provide basic group, which is currently comprised by 40 genera and information on the species diversity and distribution of roughly 255 species and subspecies in the neotropics freshwater crabs inhabiting the area (basin of the Rio (Rodríguez & Magalhães, 2005). Of these, a total of Grande de Térraba), where the ICE plans to imple- 15 species of four genera can be found in Costa Rica ment one of the largest damming projects in the (C. Magalhães et al., unpublished data.). The vast region. majority of the studies on freshwater crabs in Costa Rica concerns taxonomic aspects (Rathbun, 1893, MATERIALS AND METHODS 1896, 1898, 1905; Smalley, 1964; Bott, 1968; Pretzmann, 1965, 1972, 1978, 1980; Villalobos, 1974; Rodríguez, 1982, 1994, 2001; Rodríguez & Hedström, Study area 2000; Hobbs III, 1991; Magalhães et al., 2010). Apart The study was carried out in the Rio Grande de from these, there are just two publications concerning Térraba basin, provinces of San José and Puntarenas, their ecology: one study on the distribution of Pacific slope of Costa Rica (Fig. 1). The basin is the 2 Potamocarcinus nicaraguensis in the basins of the largest in the country and covers an area of 5,085 km ; Freswather crabs of Río Grande de Térrraba, Costa Rica 687 Figure 1. Location of sampling sites in the Rio Grande de Térraba basin, provinces of San José and Puntarenas, Pacific slope of Costa Rica, between April 2007 and April 2010. its rivers have a total length of 4,997 km (TNC, 2009). (Umaña-Villalobos & Springer, 2006), which is also The principal tributaries are the Rio General and the critical for the