THE FRESHWATER MUSSEL Margaritifera margaritifera (L.) IN GALICIA (NW OF SPAIN). PRELIMINARY STUDY IN THE RIVERS EO AND MASMA Fernández, C.1; Outeiro, A.2, Ondina, P.2, Amaro, R.1 & San Miguel, E.1 (1) Dpto. Xenética. Fac. de Veterinaria. USC. 27002 Lugo. Spain. (2): Dpto. Bioloxía Animal. Fac. de Veterinaria. USC. 27002 Lugo. Spain.
[email protected] INTRODUCTION Throughout the last century, the populations of the freshwater bivalve Margaritifera Masma river Eo river Cantabric Sea margaritifera have suffered drastic decreases in all their geographical extension (Young et al., 2001). Many populations have disappeared and others are unable to reproduce successfully. The eutrophication of the rivers is considered the main cause, which is Foz r M1 determinant for the establishment and survival of young mussels (Bauer, 1986). This e eutrophication is caused mainly by intensive agriculture and anthropogenic activities from v Ribadeo i the growing urban areas. r a M3 Seasonally punctual measures of water quality were used to evaluate the degree of m s eutrophication. Besides, maps and satellite images were used to evaluate the degree of a alteration of the environment (Fig.1), specially of the riparian forests (Fig. 2). Both M M4 technologies were used to measure possible impacts on the populations of M. margaritifera. M2 In this context we study several populations of M. margaritifera located in two close rivers (Masma and Eo). Both rivers present different hydrological and environment Lourenzá characteristics. Fig. 4.- Frequency distribution of shell lengths in Masma and Eo M5 We analyze here the density and structure of the populations of M.