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Análisis del proceso de recolonización del tramo afectado del Guadiamar maintained an abundant population in the study area since 2000, even though the sampling site close to the Doñana marshland (E5) took one year longer in harboring it (Fig 8a). This delay suggests that this species recolonized the affected reach mainly from both the non-affected upstream areas of the main stem and the Ardachón stream (Fig. 9). L. sclateri is a potadromous species well adapted to the unfavorable Mediterranean summer conditions (Rodríguez-Ruiz and Granado Lorencio, 1992; Encina et al., 2006), with high temperature in isolated pools in the upper section, and organic matter accumulation in the lower section (Herrera y Fernández-Delgado, 1992; Torralva et al. 1997; Doadrio et al., 2011). This intrinsic resistance to adverse conditions makes L. sclateri the most ubiquitous and abundant species in southern Iberian courses, withstanding the increasing pollution that other native species are not able to face (Oliva-Paterna et al., 2003a; Encina et al., 2006; Fernández-Delgado et al., 2007). Moreover, its fast growth rate and large size provide this species a wide mobility and high capacity for dispersal (Saldaña, 2006), including L. sclateri in the fast recolonist group (Scholosser, 1990; Detenbeck et al., 1992). Consequently, and in agreement with others studies on recolonization processes (e.g. Ensign and Leftwich, 1997; Lonzarich et al., 1998; Kubach, 2011), high abundance (Sheldon and Meffe, 1995) and large mobility (Albanese, 2009) identified L. sclateri as the best colonist of the affected reach. To a lesser extent, scarce rainfall in 2002 together with the last soil movements (Arenas et al., 2008) hampered the southern Iberian barbel population, especially in E3, but in the following years, the species reached stable levels (Fig. 8a). Southern straight-mouth nase, P. willkommii, was the co-dominant species in the upstream non-affected reach of the Guadiamar River, together with L. sclateri. However, it was almost absent in the affected area (Table 1, Fig 8b). This native fish is a potadromous species highly sensitive to pollution and habitat fragmentation (Rodríguez-Ruiz and Granado-Lorencio, 1992; Doadrio et al., 2011). Furthermore, the species’ feeding habits consist on scraping algae or macroinvertebrates fixed to the stony riverbed (Bellido et al., 1989). Since the affected reach lacks many of those macroinvertebrates (Solà et al., 2004; Ferreras-Romero et al., 2003) and both anthropic pollution and sediment accumulation are still increasing (Carrascal et al., 2008), P. willkommii will rarely recolonise the affected reach as long as this trend is not changed. Only the stretch nearest to the upstream non-affected reach of the Guadiamar River can currently harbor the species (Table 1). This is because upstream areas are hardly polluted, low in sediments and have clean waters that are a source of macroinvertebrates 99
Las comunidades de peces del río Guadiamar y el accidente minero de Aznalcóllar and algae for P. willkommii individuals that successfully establish in this reach. This species’ dynamics in the reach where it is confined seemed to be influenced by both rainfall and habitat fragmentation. Thus, rainy years enhanced P. willkommii drift towards the nearest affected reach, whereas the driest year (2005; SAIH, 2012) promoted an increase in this species’ larvae (personal observation) due to two events. First, floods shortage during the period when individuals are most vulnerable to be killed by dragging (Pérez-Alejandre, 2009); and second, regarding exotic species interactions, the L. gibbosus population that predate on P. willkommii larvae or compete for the same habitat (García-Berthou and Moreno-Amich, 2000), decline due to their poor adaption to drought (Ribeiro and Collares-Pereira, 2010). On the other hand, early soil movements were probably hampering the free displacement along the river needed for the P. willkommi life-cycle (Herrera and Fernández-Delgado, 1994; Encina and Granado-Lorencio, 1997), probably reducing upstream P. willkommii abundance year after year. Since the cessation of the cleaning works (2002; Arenas et al., 2008), this species increased its upstream population until a maximum was reached in the last sampling year. However, P. willkommii was confined to the upstream non-affected reach of the Guadiamar River (E1) and its adjacent area (E2, Fig. 8b). Regarding exotic species, L. gibbosus was one of the most abundant in the upstream non-affected reach of the Guadiamar River and its dynamics were considered as the third representative recovery pattern in the study area. This large population favored rapid recolonization by this species from the upstream non-affected reach of the Guadiamar River and, to a lesser extent, from the Ardachón stream (Fig. 9). After the removal of the polluted sediments, when several weirs were built (Solà, 2004), the first flood that connected the Guadiamar River main stem occurred in October 12, 1999 (SAIH, 2012). This flood discharged 90 mm in only a few hours, the second maximum discharge in the study period (SAIH, 2012). Consequently, the largest fish displacement was triggered. Among them, L. gibbosus < 10 mm (Total Length) should have been one of the most displaced downstream towards the affected reach (Harvey, 1987). The absence of centrarchid juveniles or adults in the defaunated stretch probably prevented intraspecific predation of larvae (Harvey, 1991), so most larvae of this species reached the next age-group (juveniles). These young-of-the-year, < 41 mm in males and < 62 mm in females (Gutierrez-Estrada et al., 2000; Ribeiro and Collares-Pereira, 2010), were probably able to grow successfully through the winter since at this early stage juveniles mainly feed on littoral microcrustaceans (García-Berthou and Moreno-Amich, 100
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DEPARTAMENTO DE ZOOLOGÍA UNIVERSID
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DEPARTAMENTO DE ZOOLOGÍA UNIVERSID
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TITULO DE LA TESIS: LAS COMUNIDADES
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A mi Madre,
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A mis antiguos compañeros del Grup
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Material and Methods 39 Results 45
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ABSTRACT This PhD Thesis analyzes t
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Las comunidades de peces del río G
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ÁREA DE ESTUDIO Cuenca del río Gu
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Área de estudio Figura 1. Cuenca d
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Área de estudio farallón del Alja
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Área de estudio Principales impact
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PARTE I: Ictiofauna de la cuenca de
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II.1- Habitat quality affects the c
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Condición somática de L. sclateri
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Table 1. Mean habitat variable valu
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Page 62 and 63: Condición somática de L. sclateri
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