Abstract
Stable isotope analysis was used to determine the relative proportions of terrestrial and marine subsidies of carbon to invertebrates along a tidal gradient (low-intertidal, mid-intertidal, high-intertidal, supralittoral) and to determine the relative importance of terrestrial carbon in food web pathways leading to chum salmon fry Oncorhynchus keta (Walbaum) in Howe Sound, British Columbia. We found a clear gradient in the proportion of terrestrially derived carbon along the tidal gradient ranging from 68% across all invertebrate taxa in the supralittoral to 25% in the high-intertidal, 20% in the mid-intertidal, and 12% in the low-intertidal. Stable isotope values of chum salmon fry indicated carbon contributions from both terrestrial and marine sources, with terrestrially derived carbon ranging from 12.8 to 61.5% in the muscle tissue of chum salmon fry (mean 30%). Our results provide evidence for reciprocal subsidies of marine and terrestrially derived carbon on beaches in the estuary and suggest that the vegetated supralittoral is an important trophic link in supplying terrestrial carbon to nearshore food webs.
Highlights
Subsidies of prey and detritus across ecotones have been shown to affect food webs in both aquatic and terrestrial habitats [1,2,3]
In this study we report the results of stable isotope analysis of carbon and nitrogen for a collection of marine, intertidal, and terrestrial organisms collected in the intertidal and supralittoral in Howe Sound, British Columbia, Canada
Our results suggest the importance of reciprocal subsidies in the terrestrial-marine ecotone in the Howe Sound estuary
Summary
Subsidies of prey and detritus across ecotones have been shown to affect food webs in both aquatic and terrestrial habitats [1,2,3]. Nearshore marine habitats commonly receive prey and detritus from adjacent terrestrial habitats [2]. In small watersheds with dense surrounding forests much of the stream organic matter originates in the surrounding forest [5] and in freshwater riparian and stream food webs terrestrial invertebrates can comprise more than 50% of energy intake by stream fishes and are often a preferred prey of salmonids [6]. In marine coastal habitats, supralittoral vegetation may provide an important source of terrigenous input in the form of leaf litter to intertidal areas [7,8] and terrestrial and intertidal invertebrates have been shown to comprise a proportion of their diets of salmon fry caught in nearshore habitats [9,10,11,12,14,15]
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