Salmon return from the sea to the freshwater breeding grounds of their
birth to spawn and die. In doing so, they import ocean-derived mineral
nutrients that fertilize the riparian ecosystem. The effect of this mineral
import has been quantified by Helfield and Naiman for a site in southeast
Alaska. Using isotopic analysis, which can identify marine-derived
elements, they find that at least one-fifth of the nitrogen (N) in the
needles of Sitka spruce trees and other plants near spawning sites comes
from the ocean via Pacific salmon carcasses. Growth rates of trees near
spawning sites were significantly higher than in reference sites. These
marine subsidies to inland ecosystems are likely to decline as Pacific
salmon become increasingly rare. - AMS

Ecology 82, 2403 (2001).