Protecting (marine) subsidies – nutrient flows from ocean to land

Researchers at Raincoast aimed to determine if the nutrients that herring contribute to intertidal and subtidal ecosystems during spawning events are cycling through coastal food webs.

Each spring along the coast of British Columbia, the typically calm nearshore waters begin to churn with thousands of spawning fish, turning the deep blue water a milky turquoise.

Ranging from California to Alaska, Pacific Herring are a schooling forage fish that constitute the largest amount of vertebrate biomass in marine ecosystems. As intermediaries between the bottom and top of food webs, these forage fish fuel a diversity of coastal species and have significance for communities and ecosystems throughout the Pacific ocean.

The return of herring from the open ocean to BC’s coastal waters provides a large nutrient influx to intertidal and subtidal ecosystems, which boosts their productivity and biodiversity. However, similar to other important Pacific fish species like salmon, herring populations have been experiencing declines due to exploitation, disease and climate change over the past two centuries. This continued decline could affect larger organisms that rely on spawning herring as a primary food resource during an otherwise nutrient poor season.

While we know that herring play a pivotal ecological role role in nearshore ecosystems, from a scientific perspective little is known about the amount of energy and nutrients (spatial subsidies) they transfer from the ocean to the land. Therefore, researchers at Raincoast aimed to determine if the nutrients that herring contribute to intertidal and subtidal ecosystems during spawning events are cycling through coastal food webs.

To determine this, our scientists adopted techniques used in salmon research that identifies the amount of marine-derived nitrogen and carbon that are present in intertidal invertebrates before and after herring spawning events. The study found that in intertidal and subtidal ecosystem where spawning events occur, there was a positive influence of nitrogen in invertebrates, while there was no significant change in carbon enrichment. Our research was able to determine that herring nutrients enter the nearshore and intertidal ecosystem through many organisms, which helps support food web dynamics and productivity.

Combined with previous literature on the energy that spawning herring provide for terrestrial predators and scavengers, this research demonstrates that herring provide a broad ecological source of energy to a range of organisms, from subtidal invertebrates to species of conservation concern like coastal wolves.

Considering the results of this study and others, it is an opportunity for the Federal fisheries management of Pacific herring to improve. A shift towards co-management with First Nations could provide an ecosystem-based management regime that would benefit human and non-human species that rely on the marine subsidies that Herring provide each spring.

Kristen Walters working with a net in the stream bed.

Kristen Walters

Kristen Walters is the Lower Fraser River Salmon Conservation Program Coordinator. She has an M.Sc. from Simon Fraser University. She’s here for the rain, salmon, eagles, and the Lower Fraser.

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