Benthic macroinvertebrate and fish metacommunity structure in temperate urban streams

Urbanization may disrupt dispersal of organisms, thereby influencing metacommunity function. We assessed stream benthic macroinvertebrate (families) and fish (species) metacommunity structure along seven urbanizing streams on the same island city. We assessed whether metacommunities were limited by dispersal or by environmental conditions associated with local water and habitat quality, as well as % impervious cover (IC). Drained land represented gradients from agricultural to industrial uses, which were related to IC (52–68%), as well as water quality and habitat variables. An aggregate index assessing local contribution to beta diversity (LCBD) of sites was best explained by variation in water quality (21%) for macroinvertebrates, and by water and habitat quality (12–13%) for fish. LCBD declined and remained low following 20% IC in stream riparian zones. Along the lengths of streams, environmental similarity decayed at unexpectedly high rates with geographic distance between sites (slope –0.034), although water quality was generally low and pollution tolerant taxa dominated. Macroinvertebrate communities showed evidence dispersal barriers for terrestrial, but not for aquatic passive dispersers, indicating that periodic high discharge could homogenize communities across degraded urban sites. There was a surprising signal of active dispersal and habitat selection by the few active terrestrial macroinvertebrate taxa. Fish communities appeared to be relatively isolated and species-poor likely owing to extinctions in sub-optimal habitats. We identify high LCBD sites that could be targets of stream restoration. The removal of physical barriers and regulation of flooding events are required to promote re-establishment of fish and macroinvertebrate communities in this region through dispersal.