COS 265-5 - CANCELLED - Experimental addition of marine-derived nutrients affects wildflower traits in a coastal meta-ecosystem

Background/Question/Methods

Organismal movement can bring individuals, resources, and novel interactions across ecosystem boundaries and into recipient habitats, thereby forming meta-ecosystems. Synchronous life cycle migrations, such as those undertaken by anadromous fishes that die after mating, can supply subsidies to both aquatic and terrestrial habitats with predictable and annual pulses of marine-derived nutrients such as nitrogen. For example, Pacific salmon ecosystems receive enormous inputs of marine-derived nitrogen annually, which can have a wide range of effects on aquatic and terrestrial plant species and communities. In this study, we aimed to test the effects of cross-ecosystem nutrient subsidies on terrestrial plant growth, reproduction, and pollination ecology. To accomplish this, we conducted a multi-year, large-scale field experiment using a blocked factorial design with four different treatments: an addition of a pink salmon (O. gorbuscha) carcass, an addition of the drift seaweed rockweed (Fucus distichus), an addition of both salmon + rockweed, and a control with no additions. Specifically, we examined whether these treatments affected leaf nitrogen content and fitness-associated floral traits in four different wildflower species: yarrow (Achillea millefolium), Douglas’ aster (Symphyotrichum subspicatum), common red paintbrush (Castilleja miniata), and silverweed (Potentilla anserina). We also examined plot-level patterns in pollinator visits.

Results/Conclusions

First, we found elevated leaf δ¹⁵N in all plant species across sampling years in both treatments with salmon carcass additions, whereas there were no differences in leaf percent nitrogen across sampling years or treatments. Second, we observed a larger leaf area in response to both salmon carcass treatments in yarrow and paintbrush plants in all sampling years. Third, there was a year-dependent increase in floral display area in paintbrush and Douglas’ aster in both salmon carcass treatments. Fourth, we observed a limited response in seed production to both salmon carcass treatments in yarrow plants in the third sampling year. Lastly, we found preliminary evidence indicating that visit patterns of pollinating insects were different among treatments and sampling years. Our findings provide an experimental account of whether and how meta-ecosystem-level processes—such as nutrient subsidies via organismal mortality—alter primary producer growth and reproduction. Salmon ecosystems face ecological threats that are not unique. Globally, the current capacity of meta-ecosystem level processes to transport nutrients is estimated to be a fraction of historical capacity. Empirically understanding meta-ecosystem processes allows for a more unified approach to ecosystem-based management, and a deeper understanding of the consequences of anthropogenic change across scales.