Detecting Marine Nutrient and Organic Matter Inputs into Multiple Trophic Levels in Streams of Atlantic Canada and France
Timothy D. Jardine, Jean-Marc Roussel, Sean C. Mitchell, and Richard A. Cunjak
Abstract.—We used stable isotope analysis in an attempt to detect marine subsidies from anadromous fish to freshwater benthos in four river systems draining to the Atlantic Ocean. Benthic invertebrates in the West River, Nova Scotia, Canada, had elevated δ13C, δ15N, and δ34S values in a downstream reach that suggested consumption of marine-derived organic matter from spawning blueback herring Alosa aestivalis. In Doctor’s Brook, Nova Scotia, the arrival of rainbow smelt Osmerus mordax to spawn led to rapid increases in the δ13C and δ15N of a predatory stonefly (Perlidae), but lower trophic levels (mayflies and biofilm) showed inconsistent responses. Sculpin Cottus sp. showed no evidence of predation on Atlantic salmon Salmo salar eggs in Catamaran Brook, New Brunswick, Canada or the Scorff River, Brittany, France. These analyses suggest that marine organic matter subsidies, in the form of direct consumption of eggs and/or carcasses, are important in streams with concentrated spawning activity such as by alosid and osmerid species, whereas carbon and nitrogen contributions from more sparse spawning species such as by Atlantic salmon may be minimal.