Jennifer N Harding

PhD in Biology – Nutrient subsidies, food web dynamics and conservation

Opposing forces – do Pacific salmon elicit a trophic cascade in coastal streams?

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Total spring (grey circles) and fall (black triangles) invertebrate biomass per unit area by salmon density. Each data point represents a single stream for a given season.

Total spring (grey circles) and fall (black triangles) invertebrate biomass per unit area by salmon density. Each data point represents a single stream for a given season.

Despite that all functional feeding groups of stream invertebrates incorporate salmon-derived nitrogen and carbon in the spring and fall, we found that likely through substrate disturbance, Pacific salmon (Oncorhynchus spp.) are the cause of invertebrate biomass decline in the fall during spawning and the following spring.  However, the decline in the spring may be due to the slow recovery of invertebrates from substrate disturbance the previous fall or salmon nutrients may be indirectly driving declines in spring invertebrate biomass by subsidizing other trophic levels and eliciting a trophic cascade.

See our paper entitled “Opposing forces: Evaluating multiple ecological roles of Pacific salmon in coastal stream ecosystems” for more details.


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Movers and shakers

Pink salmon return to their natal stream to spawn near Bella Bella, British Columbia.  Photo credit: Conor McCracken, CDM Images

Pink salmon return to their natal stream to spawn near Bella Bella, British Columbia.
Photo credit: Conor McCracken, CDM Images

 

Our paper, “Movers and shakers: nutrient subsidies and benthic disturbance predict biofilm biomass and stable isotope signatures in coast streams” got the cover of Freshwater Biology this month.

In a 16 stream study, we found that out of several variables considered to affect biofilm isotopes and biomass, salmon density and catchment size are among the most influential.