RESPONSE OF THE FISH COMMUNITY TO DREDGE OF COASTAL RIVERS IN THE BIOBIO REGION (CHILE)

The freshwater fish communities present degrees of resistance and resilience to human activities, which have a positive relationship with species diversity, and a negative relation with levels of previous intervention. The costal rivers in the Central-Southern zone of Chile are characterized by a diverse icthyofauna, principally in the low zones. Particularly, the potamon areas of the Andalien and Nonguen rivers, both running through the city of Concepcion, have a high conservation value of biodiversity. In these areas, the reoccurring flooding in residential zones constructed over the floodplain has caused both channels to be dredged and semi-canalized. The fish community's response to this type of interventions has not been studied yet in Chile. We propose, given its high diversity and low level of previous intervention, that the fish community of the Andalien and Nonguen rivers is resilient to the effects of the dredge. To understand the community response in both rivers, we first analyzed the changes in the structure in situations before the dredge, with dredge actions, as well as after the dredge. Second, we analyzed the species-specific response to explain the Community changes and be able to understand the sensibility of the different species to this intervention. Immediately after the dredge, a decrease of the species diversity Occurred, generating the dominance of a single species, Cheirodon galusdae. Later, a partial recovery of the community parameters was noted. Based on species-specific responses of this type of perturbation, we identified 3 resistant species, 3 resilient species and 8 sensitive species. Among these last species, Nematogenys inermis has the highest relevance in conservation terms.