Does Stream Current Influence Crayfish Impacts on Macroinvertebrate Communities?

Abstract

Crayfish are considered "ecosystem engineers" because they manipulate environments and can profoundly affect the aquatic ecosystems in which they live (Creed & Reed 2004). Crayfish also affect the composition of benthic stream communities by altering habitats (Hansen 2013) and modifying trophic relationships and food web structure (Bobeldyk & Lamberti 2010, Larsen 2013). They can directly affect benthic macroinvertebrates through predation (Keller & Ruman 1998) and indirectly through resource competition (Jackson 2014). The extent to which crayfish impact macroinvertebrates may be dependent on environmental factors in the stream, such as current velocity (Creed 2004). Current velocity is a particularly important factor as it defines stream ecosystems and many benthic organisms respond to its influence. For example, Clark et al. (2008) found decreasing crayfish activity with higher current velocity. Although the impact of current velocity on crayfish has been investigated, no studies have examined how stream current influences crayfish effects on benthic macroinvertebrates. If fast current velocity limits crayfish activity, we predict they will consume fewer macroinvertebrates. In addition, predators have less impact on prey in areas where exchange rates are higher (Cooper et al. 1990), such as those experiencing fast current. Thus, we would expect crayfish in fast current to have less impact on macroinvertebrate communities than in slow current.