Do native white-clawed crayfish impact macroinvertebrate assemblages in Mediterranean limestone headwaters?

Crayfish are among the largest aquatic macroinvertebrates in rivers and streams. Their trophic ecology is important for the understanding of the functioning of benthic communities. This is relevant in key areas, such as headwaters, as they partly condition the processes occurring downstream. To shed light on the effects of native white-clawed crayfish, Austropotamobius pallipes , on local macroinvertebrate assemblages from running headwaters, a three-month mesocosm-based field study was designed. Collection and subsequent analysis of benthic samples under different crayfish density levels yielded a set of metrics indicative of short-term impacts at general and taxonomic scales. Neither significant positive nor negative effects on the community were evident in terms of richness, diversity, dominance and biomass. A combination of highly patched distributions of macroinvertebrates along with a weak impact of crayfish foraging activity is considered to explain this lack of effects. Only temporal changes associated with particular biological cycles appeared for some of the main taxa. Based on the results, we are not able to determine whether the white-clawed crayfish perceptibly disturbs the structure and composition of the local macroinvertebrate assemblages in the short-term. Thus, its use in future restocking projects is supported.