Diverse Ecological Pathways of Salmon Nutrients Through an Intact Marine-terrestrial Interface

Abstract

Based on five years of field studies (1992, 1993, 1994, 1998, 2000), I quantified bi-directional movement of salmon nutrients through an estuary, stream, and old growth forest in a large protected reserve on Haida Gwaii, British Columbia. In 1993, when most data were collected, about 6000 Chum Salmon (Oncorhynchus keta) entered the river of which 22% of the total biomass of senescent carcasses were swept downstream into the estuary and were scavenged by gulls (n = 350) and subtidal invertebrates. Of the 3700 salmon (10 000 kg) transferred by American Black Bear (Ursus americanus) to the riparian zone and partially consumed along the 800 m of stream channel, 5070 kg of salmon tissues abandoned by the bears were scavenged by Northwestern Crows (Corvus caurinus; n = 200) but mostly (4100 kg) by calliphorid blowfly larvae resulting in larval densities averaging 240/m2 throughout the riparian zone. Total nitrogen input to the soils from the combined effects of bear and scavenger activity as well as carcass input was 18 g/m2 within 10 m of the stream channel. δ15N of foliar tissues of Lanky Moss (Rhytidiadelphus loreus), Red Huckleberry (Vaccinium parvifolium), Salal (Gaultheria shallon), and Western Hemlock (Tsuga heterophylla) ranged about 15‰ to 20‰ among adjacent microsites in each species, with higher values occurring in salmon carcass zones. Total nitrogen in foliar tissues ranged from 1% to 2.4% among microsites and was best predicted by positive correlations with foliar 15N values and secondarily by presence/absence of salmon carcasses. This is the first study to integrate estuarine to riparian ecological processes in the cycling of salmonid nutrients and identifies a range of ecological baselines that can inform the multiple restoration programs underway in degraded watersheds in the North Pacific.