An integrative perspective to understand the impact of co-occurring ecosystem engineers on macroinvertebrates

Invasion of habitat-modifying nonnative species and alteration of ecosystem engineer by exploitation are two of the dominant human impacts on natural ecosystem functioning. The effects of these co-occurring ecosystem engineers may act simultaneously and vary independently depending on ambient environmental conditions they modify. Using a saltmarsh ecosystem with continuing invasion of nonnative cordgrass and aggregation of native bivalve shells, we tested whether the ecosystem engineering effects of shell aggregation on macroinvertebrates depended on the plants due to their ability to trap shell debris. We found habitats covered with shell aggregation and vegetated cordgrass significantly increase the biodiversity but decrease the biomass of macroinvertebrates comparing to the tidal bare flats, whereas no differences were detected among shell covered, cordgrass vegetated and their coexistent habitats. Our study highlights the importance of considering multiple, potentially conflicting management goals, which may require flexibility and trade-offs to integrate nonnative and native resources into ecosystem management.