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 sources after the spill. In these non-affected sources, fish were sampled twice, in 2003 and 2006, and only information about species richness was obtained. Electrofishing following the CEN standard protocol (CEN, 2003) was the sampling gear used in the tributaries and the same passive methods used in the sites of the longitudinal sampling design was the method used in the river-marsh site. Data analyses Following the spill, the riparian habitat of the affected reach was physically altered because of both toxic sludge dragging and the subsequent cleaning works. So, although we use the term fish assemblage recovery, we expected significant assemblage structure changes, in comparison to the pre-disturbance data (Doadrio, 1996). Jaccard’s similarity index was applied to identify patterns in an initial comparison between the pre-disturbance species composition in the affected reach (1996) and the annual sampling data from the four affected sampling sites (E2, E3, E4 and E5). This index is used as a measure of similarity based on presence/absence data, and quantifies fish assemblage similarity between all possible site pairs within each time period (Gillette et al., 2012). In surveys carried out from 1999 onwards, species richness (S) and diversity (H’, Shannon’s diversity index; Shannon and Weaver, 1949) were calculated. Fish abundance was estimated using catch per unit effort (CPUE), standardizing total species catch with both passive sampling methods to 24 hours. Sampling site E1 (reference site) was considered representative of non-affected fish assemblage conditions, so a principal response curve (PRC) was used to test differences between the affected sites and the reference site through time. The PRC approach constitutes a multivariate method, based on redundancy analyses, which describes changes in assemblage response over time in relation to a control (Van den Brink et al., 2003; Silva et al., 2010). The principal component is plotted against time, giving a PRC of the fish assemblage for each sampling site. A quantitative interpretation of the effects at species level is possible by scoring the species weight, according to each species accounting for the deviances (Van den Brink et al., 2003). PRC were performed considering fish abundance at the species level. Monte Carlo permutations tests commonly carried out to test the significance of the axis (Van den Brink et al., 2003; Silva et al., 2010) could not be performed because of lack of sampling replicates in the same year. 83
Las comunidades de peces del río Guadiamar y el accidente minero de Aznalcóllar Non-metric multidimensional scaling (NMDS) ordination was used, after CPUE log(x+10) transformation, to extract spatio-temporal patterns in fish assemblage structure (Kruskal, 1964a,b; Mather, 1976; Kruskal and Wish, 1978). NMDS is a general ordination procedure recommended for non-normal or questionably distributed data and calculates ranked ecological distances (Clarke, 1993; McCune and Grace, 2002), providing a relative measure of proportional similarity in fish assemblage structure (Kubach et al., 2011). NMDS estimates distances between samples out of a derived “sample by sample” matrix. This matrix is obtained by transforming the original matrix using a dissimilarity measure. NMDS is not restricted to Euclidean distance measure but any dissimilarity measure can be used, which can also relax the requirement of normality of data (Van den Brink et al., 2003). We used the Bray–Curtis dissimilarity distance to compute the resemblance matrix among sites. In this study, distances between reference site data and those from the affected reach were used to detect fish community recovery trends. The statistical significance of differences in fish assemblages between years was tested using a semi-parametric permutational multivariate analysis of variance using the Bray-Curtis distance matrices (henceforth PERMANOVA). One PERMANOVA was performed per site, species abundances acted as the dependent variables, and both axes (time and site) were factors, so axes weight in each case was also assessed. Abundance values from E4 in 2005 were not included because during this year the sampling site was confined to an isolated pool where fish abundance (mainly Luciobarbus sclateri) was overestimated. All statistical analyses were performed using R version 2.12.1 (R Development Core Team, 2012) and its package 'vegan' (Oksanen et al., 2011). 84
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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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Appendix 1. Environmental variables
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