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

Relaciones peces/hábitat
en el Guadiamar
Almodóvar, 2001). These stable conditions can be found in reservoirs and their
regulated downstream tailwaters, but reaches immediately upstream suffer large
fluctuations with strong flows during rainy periods and drought during summer, so they
are inappropriate environments for these exotic species (Moyle, 1986; Maghalaes et al.,
2002 and 2007).
Unfortunately, the attempt to discern between spill and reservoir effects did not
yield a clear result, but suggests a combination of events. The observed native species
richness and diversity depletion caused by reservoirs in other river basins, similar to
Guadiamar, provides a range of values, and those observed in the Guadiamar River fit
within that range. Therefore, the current potential effects of spill remnants are not strong
enough to cause abnormal fish species richness and diversity values. The analysis
performed with exotic species yields the same result, which suggests that the set of
factors that promote exotic species richness in the Guadiamar River basin are equal to
those found in other similar river basins, not affected by the spill. This conclusion
suggests that eight years after the accident, the habitat recovery works have minimized
the spill effect and the reach originally affected is now exposed to the same impacts that
it suffered before this event.
Finally, with respect to the main aspects of the Guadiamar River basin fish
community, results agree with several studies carried out for other Mediterranean
watersheds (Godinho and Ferreira, 1998 and 2000, Moran-López et al., 2006) that
report a pivotal point with the highest species richness and diversity in the area just
upstream from a reservoir. In this study, there is a steady increase from the source in
parallel to river order and suddenly, downstream from the reservoir, the trend is
interrupted. Thus, the highest values are observed at the last sampling site upstream
from the reservoir. This could be because the reservoir may also acts as a refuge from
drought for several native species during the dry season (Schlosser, 1987; Rodríguez-
Ruiz and Granado-Lorencio, 1992; Poff et al., 2007) and although the exotic species
found in the reservoir have a limited ability to swim large distances against the main
current, they may be attracted to a nearby area upstream, rich in nutritional resources
(mainly native species juveniles). In consequence, both native and exotic fish coincide
in a complicated equilibrium that results in maximum in richness and diversity at a
specific place.
In summary, the native species of the Guadiamar River basin are favoured by
environments with low human influence, locations far away from reservoirs, a large
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