Spatiotemporal separation of New Zealand mudsnails from predatory fish

AbstractThe use of subsurface sediments by benthic prey as spatial refugia from predators can potentially influence predator consumption, and hence density-dependent relationships. We studied how predatory fish affect subsurface sediment use by spiny- and smooth-shelled morphs of the mudsnail, Potamopyrgus antipodarum, on New Zealand’s South Island. Spines reduce consumption risk by small benthic fishes (e.g., bullies [Gobiomorphus spp.]). Thus, we predicted that spiny morphs would be more likely to use sediment surfaces with relatively high algal food supplies than the more vulnerable smooth morphs when exposed to fish predators. Epi- and endobenthic samples from 5 streams with fish showed that ∼80% of snails typically were retrieved from subsurface sediments, whereas only 33% of snails from fishless Jackson’s Creek occurred in subsurface sediments. A laboratory experiment revealed that significantly more snails used subsurface sediments when with common bullies (G. cotidianus) than when without. Subsurf...