Context dependence of marine ecosystem engineer invasion impacts on benthic ecosystem functioning

Abstract

Introduced ecosystem engineers can severely modify the functioning on invaded systems. Species-level effects on ecosystem functioning (EF) are context dependent, but the effects of introduced ecosystem engineers are frequently assessed through single-location studies. The present work aimed to identify sources of context-dependence that can regulate the impacts of invasive ecosystem engineers on ecosystem functioning. As model systems, four locations where the bivalve Ruditapes philippinarum (Adams and Reeve) has been introduced were investigated, providing variability in habitat characteristics and community composition. As a measure of ecosystem engineering, the relative contribution of this species to community bioturbation potential was quantified at each site. The relevance of bioturbation to the local establishment of the mixing depth of marine sediments (used as a proxy for EF) was quantified in order to determine the potential for impact of the introduced species at each site. We found that R. philippinarum is one of the most important bioturbators within analysed communities, but the relative importance of this contribution at the community level depended on local species composition. The net contribution of bioturbation to the establishment of sediment mixing depths varied across sites depending on the presence of structuring vegetation, sediment granulometry and compaction. The effects of vegetation on sediment mixing were previously unreported. These findings indicate that the species composition of invaded communities, and the habitat characteristics of invaded systems, are important modulators of the impacts of introduced species on ecosystem functioning. A framework that encompasses these aspects for the prediction of the functional impacts of invasive ecosystem engineers is suggested, supporting a multi-site approach to invasive ecology studies concerned with ecosystem functioning.