The Asian clam Corbicula fluminea ( Müller , 1774 ) in the Guadiana River Basin ( southwestern Iberian Peninsula ) : Setting the record straight

This paper aims to set the record straight regarding the first observations of Corbicula fluminea (Müller, 1775) in the Guadiana River Basin. According to the available data, C. fluminea was first observed in 1988 and not in 2006 as suggested by Pérez-Bote and Fernandéz (2008). The first observations of C. fluminea in the Guadiana estuary were reported in 2000. In 2003, C. fluminea was already well established in the estuary and in many rivers and streams. C. fluminea is likely to expand its current biogeographic distribution in Portugal, since suitable lentic habitats for colonization will be crea ted by the implementation of the “National program of dams with high hydraulic potential”, which should be concluded by 2016.

The Asian clam Corbicula fluminea (Müller, 1774) is one of the 100 worst invasive species in Europe (DAISIE 2009).It was first noticed in the Iberian Peninsula in 1980, in the Tagus estuary (Mouthon 1981).Pérez-Bote and Fernández (2008) stated that C. fluminea was first recorded in the Guadiana River Basin (southwestern Iberian Peninsula, Figure 1) in June 2006, more precisely in the rivers Lacarón and Lobón and in the Montijo reservoir.However, Pérez-Quintero (1990) had already registered the presence of C. fluminea in Rivera Grande de la Golondrina (Lower Guadiana River basin) in 1988.In March 2000, the first observations of C. fluminea in the Guadiana estuary were registered in Guerreiros do Rio (37º23'52"N, 7º26'45"W), during a survey to identify the bivalves occurring along the first 40 kilometers of the estuary (Chícharo et al. 2000).More specimens of C. fluminea were collected from subtidal areas of the upper estuary (Figure 2), from Foz de Odeleite (station 3) to Alcoutim (station 8).
C. fluminea is currently known to be present in several tributaries of the River Guadiana and estuary, namely in the following rivers: Alvacar, Beliche, Carreiras, Cobres, Degebe, Foupana, Limas, Odeleite, Oeiras, Terges and Vascão and in Lake Mina de São Domingos (Reis 2006).In the river Guadiana, the distribution range of C. fluminea seems to have increased downstream of the Alqueva dam (Figure 1), since the closure of its gates in February 8 th , 2002.
In Portugal, C. fluminea is also present in Minho, Lima, Douro, Vouga, Mondego, Lizandro, Tagus and Sado river basins (Reis 2006).The "national program of dams with high hydraulic potential" has the potential to cause a greater proliferation of C. fluminea in Portugal, increasing its biogeographic distribution and local abundances.Eleven new dams are scheduled to be built under this program until 2016, so that non-used hydraulic potential decreases from 54% to 33% (Garcia 2009).This will certainly create suitable lentic habitats for colonization of C. fluminea (Pérez-Quintero 2008) and other non-indigenous freshwater aquatic species (Johnson et al. 2008).It is important to emphasize that the population dynamics of aquatic invasive species are better understood if the timing of introductions is known as accurately as possible.Moreover, biological invasions can only be eradicated if they are detected on time, but the best policy is still to prevent them.Thus, we urge for the creation of monitoring projects aiming both to evaluate the conservation status of native bivalves and to detect, as soon as possible, the introduction of non-native species.

Figure 1 .
Figure 1.Geographical context of the Guadiana river basin in the Iberian Peninsula (Europe).Map modified from http://www.maps-for-free.com

Figure 2 .
Figure 2. Specific diversity of freshwater bivalves along the Portuguese Guadiana river basin in the summer of 2003 Legend for Station: numbers-locations with bivalves; capital letters -locations only with empty shells; lowercase letters -locations without bivalves