Abstract

Red swamp crayfish (Procambarus clarkii) may be very abundant and constitute the major part of the benthic biomass in many freshwaters of the Iberian Peninsula. Crayfish trophic behaviour has been related to several negative impacts, namely on fish, macrophyte and invertebrate communities with major changes in the food-web structures. In this study, crayfish impact on macrophytes and invertebrates was evaluated through in situ enclosure experiments. Trials were conducted in a small reservoir in the south of Portugal. Two crayfish densities were tested: moderate with 170 g m^-2 and high with 400 g m^-2. Crayfish reduced the macrophyte and invertebrate biomass in all the experiments. Crayfish caused an average decrease on the macrophyte biomass of approximately 54%. Invertebrate biomass declined 86%. In both, no significant differences were observed between the moderate and high density experiments. Chara was the vegetal species suffering major losses. Gastropoda biomass was highly correlated with this macroalgae and was also the invertebrate taxon more strongly reduced by P. clarkii. Our results show that crayfish may cause very high losses and great impact, particularly on macrophyte-associated invertebrates and invertebrates with low escape reactions.

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