Ecosystem engineers and coastal sedimentary communities

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Sedimentary bottoms encompass a vast majority of the marine realm. Yet, our understanding of the processes that shape their biodiversity and function remains fragmentary. In the past, most theory predicted that at the local scale predation and physical factors would play a paramount role regulating sedimentary communities. However, numerous subsequent studies have also showed that the establishment of habitat-forming species is as critical to shape diversity and function in these systems. These foundation species, more generically known as (autogenic) ecosystem engineers, have the ability to create or alter the properties of a habitat, promoting the development of new, more complex communities. The role of ecosystem engineers has been well studied in rocky shores, kelp forests, mangroves, coral reefs, and even saltmarsh systems. However, in unstructured sedimentary bottoms, in particular those in Atlantic Canada, much remain to be explored and tested. Mounting evidence suggests that ecosystem engineers may play key roles on community attributes and services in sedimentary settings, but not enough information is available on their role driving the species interactions occurring within and among different trophic levels. This is relevant at a time when we witness the ongoing spread of non-indigenous species that have the ability to exploit, consume or disrupt local ecosystem engineers, and opens relevant questions about their interactions and, ultimately, about the actual role of these engineers on sedimentary systems. This research program focuses on several prominent ecosystem engineers present and scattered along sedimentary shorelines of Atlantic Canada: blue mussels, eastern oysters, eelgrass, and rockweeds. The main goal of this program is testing the effects of these ecosystem engineers on the assembly and species interactions of surrounding sedimentary infauna and their potential alteration by non-indigenous species. Six hypotheses are addressed by working on three main research scenarios: Ecosystem engineers as drivers of infaunal structure and function, their role as mediators of top-down interactions, and their role as mediators of native-invader species interactions. A considerable amount of exploratory work already conducted in sedimentary areas in the Atlantic region, and coastal Prince Edward Island in particular, provides the basis to propose and test each of these hypotheses. The outcome of this research program will contribute to our knowledge on ecosystem engineers and their role driving biological interactions. Such outcome will also have implications for theory on community regulation, trophic complexity, and coastal conservation.