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Análisis del proceso de recolonización del tramo afectado del Guadiamar in Europe and in the USA (e.g. Ensign and Leftwich, 1997; Meade, 2004; Kennedy et al., 2012) also mention a time lapse of 1 year to overall assemblage recovery; 2-3 years or longer were needed for certain species or specific age structures to reach previous conditions. Nevertheless, two recent studies showed a recolonization process similar to our case. First, colonization experiments in Virginia (USA) concluded that most fish populations recovered 2 years after defaunation and only species with low movement rates took longer (Albanese et al., 2009). Second, a study investigating the effects of an oil spill in South Carolina (USA) placed the time of recovery in fish assemblage structure at 4.3 years after the spill (Kubach et al., 2011). Interestingly, from 2005 onwards, fish assemblage structure in the affected reach diverged from that of the reference site again (Fig. 6 and 7). This year was the driest in the sampling period (SAIH, 2012) and native species, better adapted than exotics to drought (Ribeiro and Collares-Pereira, 2010), were favored in those upstream reaches where flow was mightily reduced (E1 and E2, Fig. 5). However, exotic species thrived in the affected reach because flood shortage enhanced the lentic nature and stable flow of this area (Clavero and Hermoso, 2011). In subsequent years, native species decreased in the upstream sites (E1 and E2) because of both downstream displacement by floods and recovery of interactions with exotics (Ribeiro and Leunda, 2012). Nevertheless, at the end of the sampling period, native species abundance returned to average values for each sampling site. On the other hand, exotic species abundance recovered in upstream sites (E1 and E2) and both floods that displaced individual downstream and upstream migration from Doñana marshland, increased the abundance of exotics in the affected reach at the end of the sampling period (Fig. 5). Regarding recolonization sources, the unaffected upstream and downstream Guadiamar River main stem seemed to be the most relevant fish source (Fig. 9). Areas upstream from the spill provided mainly native species from a low disturbance area where natural conditions still remain. Introduced centrarchids present upstream, were occasionally displaced with floods. Potential colonists from downstream sources may be mainly migratory native and exotic species present in the highly human-modified marshland. Lateral sources from tributaries contributed to recolonization to a lesser extent because of accumulation of urban sewage, water collection and diffuse agricultural pollution, that largely reduced water quality (Fernández-Delgado and Drake, 2008) and caused fish assemblage to become poorer or absent as the tributaries go downstream. Nevertheless, floods enhance fish drift (Harvey, 1987) and dilute 97
Las comunidades de peces del río Guadiamar y el accidente minero de Aznalcóllar pollution (Cánovas et al., 2010), so upstream fish may be able to reach the tributary mouth and swim into the Guadiamar River main stem. After such pulse events, Ardachón stream could be considered as the third main fish source due to the highest richness species value among the tributaries (Table 1, Fig. 9). Alcarayón and Majaberraque streams may have only a slight contribution to recolonization, but in a monospecific and antagonistic way. The first could be the source of a native species (C. paludica) while the second of an exotic one (G. holbrooki) (Fig. 9). When considering the relevance of barriers, mining leachates in the Agrio River were likely the most harmful for recolonization. Although the Agrio reservoir may be restraining downstream fish displacement from the upstream tributaries to the affected reach, fish from Los Frailes stream, that connects onto the Agrio River downstream from the dam, were also absent near the confluence with the Guadiamar River (E2) (Fig. 9). This fish absence may be because the Agrio River crosses the mining area in this stretch, and becomes contaminated by acid mine drainage (Olías et al., 2006). This mining pollution is previous to the April 1998 spill (Cabrera et al., 1984, 1987; Arambarri et al., 1996) and it has not been adequately addressed yet. A second considerable chemical barrier was urban sewage that fills the De la Cigüeña stream, which may have stopped upstream fish from reaching the affected reach (Fernández- Delgado and Drake, 2008). On the contrary, the two mills in the main stem lower section did not represent a significant enough obstacle to prevent upstream fish recolonization because catadromous species (L. ramada and M. cephalus), whose only source could be the downstream marshland, were present upstream from the mills (E4, Table 1) during the study period (Fig. 9). Most species underwent an initial rise in abundance because a continuous flow was restored after the cessation of the main cleaning works. However, most of these species maintained a low abundance in the affected reach during the sampling period. Only L. sclateri, P. willkommmii and L. gibbosus maintained stable populations through the entire sampling period. These three species together with A. alburnus were identified by the PRC as the species with greater weight on assemblage structure (Fig. 6). Consequently, the overall fish assemblage recovery process in the affected reach must be addressed taking into account the dynamics of these four species that stood out in the fish assemblage patterns. The southern Iberian barbel, L. sclateri, was the dominant species in both the affected and non-affected reaches of the Guadiamar River. This native species 98
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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 60 and 61: Condición somática de L. sclateri
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Appendix 1. Environmental variables
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