Collaborative Research: The consequences of species loss for food web persistence and functioning in the Gulf of Maine rocky intertidal

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Species are going locally extinct in coastal ecosystems at an alarming rate, yet the ability to predict the consequences of these extinctions remains limited. In particular, the loss of one species may trigger additional, and potentially unexpected, losses of species, because species depend on each other for food or habitat. For example, the loss of a prey species might result in predator declines and the loss of important functions and services that the predator provides (e.g., food production). In the Gulf of Maine, rapid warming and overexploitation are thought to have contributed to the near local extinction of the intertidal blue mussel (Mytilus edulis), an important prey species whose loss could have cascading consequences for this ecosystem. The project explores the consequence of blue mussel declines to the food web and to the ecosystem (e.g., through water filtration that improves water quality, and secondary production that supports food for people). The investigators are using theoretical models of species loss from food webs in combination with long-term ecological data and field experiments to investigate the effects of local species extinctions on ecosystem function. This combined approach is generating and testing theoretical predictions of species loss on ecosystem biodiversity and food web structure. Insights from this project are contributing to a better understanding of dynamics of coastal ecosystems worldwide that face similar losses of prey species. The project is fostering a new collaboration between a small liberal arts college (Colby College) and a research-intensive university (University of Colorado Boulder), creating unique training, mentoring, and educational exchange opportunities for graduate and undergraduate students. This project is training a PhD student, a postdoctoral scholar, and undergraduate students, with a focus on engaging underrepresented groups and enhancing computational training for marine ecologists. This project is supporting the development of web-based teaching modules on complex ecological systems in combination with outreach and education efforts in Maine's coastal communities and in Colorado’s inland rural and urban communities. Worldwide changes in local biodiversity are altering the functioning of ecosystems and the ecosystem services on which humans depend. Predicting the consequences of such changes in biodiversity to coastal ecosystem function and structure is complicated by the multiplicity of species interactions that characterize complex food webs. Food web theory predicts that the loss of species like the blue mussel has cascading impacts on the community through secondary losses of consumers that depend on resource species. However, such predictions of food web collapse (termed "robustness") have rarely been empirically tested. Furthermore, previous studies have rarely considered how secondary losses of species might alter coastal ecosystem function. For example, the loss of the abundant filter-feeding M. edulis is likely to affect water filtration, however, M. edulis’ role as a key prey species could impact other ecosystem functions performed by species that consume M. edulis (e.g., secondary production). Thus, to estimate and predict the consequences of local extinctions on coastal ecosystem functioning, requires a research approach that moves beyond a focus on single species, and considers both direct and secondary species losses. This project is integrating food web modeling, field observations, data synthesis, and experimental species removals to quantify the impact of recent species losses on the structure and stability of the Gulf of Maine rocky intertidal food web. Historical and existing species interaction data and field observations are being synthesized to generate a detailed food web with ecosystem functions for the Gulf of Maine rocky intertidal. This food web model is used to predict the cascading impacts of species loss in this community, with particular attention to the impact on key ecosystem functions measured in situ. Finally, the predictions are tested in a multi-year factorial species removal experiment that quantifies how the diversity, structure, and function of the food web is affected by targeted species removal. This novel approach is providing much-needed empirical ground truthing to predictions of food web ecology. It is among the first of such experimental tests in marine systems. This research has the potential to transform the understanding of how marine ecosystem structure and function are altered by species losses, and the predictability of food web changes through empirical testing.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.