las comunidades de peces del río guadiamar y el accidente minero ...

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Análisis del proceso de recolonización del tramo afectado del Guadiamar Figure 9. Diagram of the main potential sources of fish colonists for the affected reach of the Guadiamar River after the April 1998 spill. Physical and chemical barriers (crosses denote insuperable conditions and arrows those permeable for fish) and fish species caught in each source are shown (Ala: A. alburnus, Gh: G. holbrooki, Cg: C. gibelio, Ab: A. boyeri, Cc: C. carpio, Cp: C. paludica, Ms: M. salmoides, Sa: S. alburnoides, Ls: L. sclateri, Lg: L. gibbosus, Pw: P. willkommii, Aa: A. anguilla, Mc: M. cephalus, Lr: L. ramada, Il: I. lemmingii, Sp: S. pyrenaicus). 95
Las comunidades de peces del río Guadiamar y el accidente minero de Aznalcóllar Discussion Guadiamar River fish assemblages at the different sampling sites evolved in different ways throughout the 13 years following the spill. Several barriers hampered recolonization from tributaries; however, this process was carried out and is still underway. The fish assemblage after the spill event almost disappeared, and was therefore, highly dissimilar to that found in the previously undisturbed Guadiamar River main stem (Doadrio, 1996 and 2001). Different trajectories at each sampling site reduced or increased this similarity through time, but no clear patterns were found. Available prespill information was limited, so only species presence could be used as reference data. Species richness commonly ranged from 1 to 3 every year for both native and exotic species. Therefore, species presence was a weak changing variable for pre- and postspill similarity comparisons. Although fish diversity allowed us to draw a general outline of assemblage dynamics, this approach did not help us identify the dynamics of fish assemblage structure through time. The PRC and NMDS analyses, based on abundance, offered both overall and specific approaches to explain the observed patterns. First, the early spill effect and subsequent cleaning works, especially the withdrawal of vast amounts of soil in the summer of 1999 that cut and dried several main stem reaches (Arenas et al., 2008), impeded fish establishment in the affected reach (E2-E5) until 2000 - Fernández and Drake (2008) caught some individuals before but were scarce and probably reduced during these soil movements (personal observation) -. From that year, fish assemblage structure in affected sites tended towards that of the reference site (E1), where native species were dominant and exotics were scarce (Table 1, Fig. 6 and 7). The increase in assemblage similarity was especially relevant in E2, which was the nearest sampling site to the reference. Thus, between 2002 and 2004 (four-six years after the spill), fish assemblage structure in affected sites stabilized, with slight increases or decreases in similarity, depending on the sampling year, to that of the reference site (Fig. 5). These first signs of recovery were considerably belated compared with those of other studies where a defaunated river stretch, experimentally or by accident, was considered. In Illinois (USA), a fish assemblage took between 3 and 10 days to reach background levels in a river without barriers and drained by many tributaries (Peterson and Bayley, 1993). In another case, in South Carolina (USA), several downstream pools recovered in 1 month, while upstream sites took longer to recover (Sheldon and Meffe, 1995). Several studies both 96
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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 58 and 59: Condición somática de L. sclateri
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Appendix 1. Environmental variables
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