Freshwater Copepoda (Crustacea) from the Chihuahuan Desert with Comments on Biogeography (Report‪)‬

A series of surveys of the zooplankton fauna of freshwater systems of northern Mexico and the southwestern United States was developed over several years. These studies included the Chihuahuan Desert; this area is of high priority among hydrological basins of northern Mexico and southwestern Texas (Dinerstein et al., 2000). The Chihuahuan Desert comprises many arid and semi-arid areas with different hydrologic basins and a variety of aquatic habitats; some of these areas are protected to varying degrees (Gomez-Pompa and Dirzo, 1995). We obtained samples of plankton from limnetic and nearshore zones in aquatic habitats including springs, natural lakes, ephemeral pools, and reservoirs. Calanoid, cyclopoid, and harpacticoid copepods were studied taxonomically. The works by Zamudio-Valdez and Reid (1990) and Zamudio-Valdez (1991) in Cuatro Cienegas, Coahuila, which is part ofthe Chihuahuan Desert, were the first surveys of Copepoda in this system. Recently, Suarez-Morales and Walsh (2009) described two new, presumedly endemic, species of Eucylops from this arid region. Herein, we present a complete inventory and perform a general analysis of taxonomic composition and biogeographic affinities of the copepod fauna in the Chihuahuan Desert and compare it with adjacent areas of North America. MATERIALS AND METHODS--Samples of zooplankton were obtained from freshwater habitats in the Chihuahuan Desert. Biological samples were obtained from springs, ponds, natural lakes, reservoirs, and ephemeral waters during 2005-2008. Samples were taken throughout the year without a planned component for looking at seasonal efforts; 26% of samples were collected in winter, 16% in spring, 48% in summer, and 10% in autumn. Zooplankton was collected by using hand-towed plankton nets (0.64-mm mesh) at both open water (limnetic) and nearshore (littoral) zones of water bodies. Overall, we sampled 134 sites, 103 (77%) were natural and 31 (23%) artificial. Samples were fixed and preserved in 70% ethanol or 4% formalin for long-term storage. Copepods were sorted from the original samples and maintained in 70% ethanol with a drop of glycerine. Specimens were dissected and examined following techniques described by Williamson and Reid (2001) and Reid (2003). Dissected specimens were mounted in semi-permanent slides with glycerine sealed with Entellan (Merck, Darmstadt, Germany) or nail varnish. Specimens were deposited in the collection of zooplankton at El Colegio de la Frontera Sur in Chetumal, Quintana Roo, Mexico.