New research proves that nutrients from the sea can increase terrestrial plant growth and reproduction

This is the first study that proves causal links between salmon and wildflower ecology.

The relationship between terrestrial and marine environments within an ecosystem is essential. Newly published research from Simon Fraser University shows that salmon and marine plants increase both growth and reproduction in terrestrial plants. The findings, “Experimental addition of marine-derived nutrients affects wildflower traits in a coastal meta-ecosystem,” published in Royal Society Open Science show that nutrients from salmon carcasses can change the way that plants grow and reproduce.

Researchers from Simon Fraser University were motivated to understand how life in the ocean is connected to life on land. They conducted a large-scale field experiment in Haíɫzaqv (Heiltsuk) territory, on the central coast of BC, where they placed salmon carcasses and marine algae in a wildflower meadow and observed changes over three successive years to the plants that live there. 

The scientists found that nutrients from salmon cause two species of wildflower, yarrow and common red paintbrush, to grow larger leaves. Additionally, the authors found that common red paintbrush and another wildflower species, Douglas’ aster, have larger flowers, which has the potential to attract beneficial pollinating insects.  

People have known for millennia that nutrients from salmon travel into forests and ecosystems. Western science conducted in the last two decades has often found a special isotope of nitrogen, known as the “salmon signature,” in a variety of terrestrial plants and animals. This research elaborates on this background understanding by showing a causal connection between salmon nutrients and the growth and health of terrestrial plants using an experimental and long-term approach.

This research is the first to make causal links between salmon and terrestrial ecosystems, which is a difficult task in the Great Bear Rainforest, an area with thousands of distinct salmon watersheds. Most studies examining nutrients from salmon in terrestrial ecosystems are necessarily observational and correlational, and conducting a field experiment allowed the researchers to prove the causes and consequences of this phenomenon much more clearly.   

Some areas on our coast are rapidly losing the ocean’s connection to life on land. This study comes on the heels of other research in the region that indicates that salmon are in trouble. In particular, chum salmon abundance in Haíɫzaqv Territory on the central coast of BC has declined by over 70% in the last 50 years, and almost 50% in just the last 15 years.

Citation

Dennert AM, Elle E, Reynolds JD. 2023 Experimental addition of marine-derived nutrients affects wildflower traits in a coastal meta-ecosystem. R. Soc. Open Sci. 10:221008. https://doi.org/10.1098/rsos.221008

Abstract

Organismal movement can bring individuals, resources and novel interactions across ecosystem boundaries and into recipient habitats, thereby forming meta-ecosystems. For example, Pacific salmon ecosystems receive large marine-derived nitrogen subsidies during annual spawning events, which can have a wide range of effects on aquatic and terrestrial plant species and communities. In this study, we evaluate the effects of cross-ecosystem nutrient subsidies on terrestrial plant growth and reproduction. We conducted a large-scale field experiment with four treatments: (i) addition of a pink salmon (Oncorhynchus gorbuscha) carcass, (ii) addition of the drift seaweed rockweed (Fucus distichus), (iii) addition of both salmon + rockweed, and (iv) a control. We examined treatment effects on leaf nitrogen and fitness-associated floral traits in four common estuarine wildflower species. We found elevated leaf ∂15N in all plant species and all sampling years in treatments with salmon carcass additions but did not observe any differences in leaf per cent nitrogen. We also observed larger leaf area in two species, a context-dependent increase in floral display area in two species, and a limited increase in plant seed set in response to both salmon carcass treatments. In sum, our study suggests that marine nutrients can affect terrestrial plant growth and reproduction.

Select figures

Photos of the four focal plant species: (a) yarrow (Achillea millefolium, Asteraceae), (b) Douglas’ aster (Symphyotrichum subspicatum, Asteraceae), (c) common red paintbrush (Castilleja miniata, Orobanchaceae) and (d) silverweed (Potentilla anserina, Rosaceae).
Figure 1. The four focal plant species: (a) yarrow (Achillea millefolium, Asteraceae), (b) Douglas’ aster (Symphyotrichum subspicatum, Asteraceae), (c) common red paintbrush (Castilleja miniata, Orobanchaceae) and (d) silverweed (Potentilla anserina, Rosaceae).
Figure 2. Leaf δ15N in relation to the four treatments in the four plant species. Points indicate the raw data overlaid by the modelled least-squares means with 95% confidence intervals in black, averaged across years (N = 629).
Figure 3. The logarithm of the estimated leaf area (mm2) in relation to the four treatments in the four plant species. Points indicate the raw data in link space overlaid by the modelled least-squares means with 95% confidence intervals in black, averaged across years (N = 2180).
Figure 4. The logarithm of the estimated floral display area (mm2) in relation to the four treatments in the four plant species. Points indicate the raw data in link space overlaid by the modelled least-squares means with 95% confidence intervals in black, averaged across years (N = 1337).
Figure 5. Estimated seed set in relation to the four treatments in the four plant species. Points indicate the raw data in link space overlaid by the modelled least-squares means with 95% confidence intervals in black, averaged across years (N = 1458).

Authors and affiliations 

Allison Dennert, Earth2Ocean Research Group, Department of Biological Sciences, Simon Fraser University AND Wild Salmon Program, Raincoast Conservation Foundation

Dr. Elizabeth Elle, Department of Biological Sciences, Simon Fraser University

Dr. John Reynolds, Earth2Ocean Research Group, Department of Biological Sciences, Simon Fraser University

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Research scientist, Adam Warner conducting genetics research in our genetics lab.
Photo by Alex Harris / Raincoast Conservation Foundation.