Salmon act as an ecological process vector, important in the transport of energy and nutrients between the ocean, estuaries, and freshwater environments. The flow of nutrients back upstream via spawning salmon and the ability of watersheds to retain them plays a vital role in determining the overall productivity of salmon runs.
Salmon runs function as enormous pumps that push vast amounts of marine nutrients from the ocean to the headwaters of otherwise low productivity rivers. For example, sockeye salmon runs in southwest Alaska contribute up to 170 tons of phosphorous per year to Lake Illiamna.
A common question we ran across in our research was “How do salmon affect the nutrient cycle?”.
One answer is that salmon heavily affect the nutrient cycle in coastal ecosystems because they carry nutrients to other animals and bring MDN to the ecosystem .
Why are salmon so important to the food pyramid?
They bring Marine Derived Nutrients (MDN) to fresh water. These MDN promote the growth of both the plants and animals in the ecosystem. Without it the amounts of both the plants and animals will drop. Salmon are also a major part of the food pyramid.
How do salmon help trees?
The remains of the salmon contain vast quantities of nitrogen that plants need to grow. Eighty percent of the nitrogen in the forest’s trees comes from the salmon. In other words, these ocean dwellers are crucial for the forest’s long-term survival.
Although trees do not eat salmon, salmon do turn into food for trees. Shortly after salmon spawn and contribute to the next generation, they die. With such a large influx of dead fish, a large amount of decomposition occurs, turning the bodies into available nutrients for trees.
In southeastern Alaska, spawning salmon contribute up to 25% of the nitrogen in the foliage of trees, resulting in tree growth rates nearly three-times higher than in areas without salmon spawning .
What can we do to help restore salmon habitat?
We can also help re-naturalize salmon spawning habitats by reintroducing native vegetation and cleaning up litter from the river corridor. Planting native trees and plants in river corridors will reduce stream temperature, improve water quality, and enhance nutrient cycling in rivers.