Influence of barrier beach dynamics on ecological indicator taxa in north-central Lake Ontario coastal wetlands

Adaptive management of protected coastal wetlands requires an understanding of barrier dynamics over long timescales as well as feedbacks with ecosystem processes. In this study, we examined diatom (siliceous algae) and Cladocera (crustacean zooplankton) subfossil remains preserved in sediments as (paleo)ecological indicators of barrier beach dynamics in coastal wetlands along the north-central shore of Lake Ontario. Sediments integrate information across seasons and habitats, accounting for spatiotemporal variability in ecological indicator taxa that is often missed in contemporary sampling efforts. Subfossil remains also allow for reconstruction of historical changes before contemporary monitoring began. We found that small benthic Fragilariaceae diatom taxa were most abundant in high-closure barrier beach wetlands, and were uncommon in drowned river mouth wetlands, while Cladocera assemblages did not reflect coastal wetland hydrogeomorphology. A high-resolution paleoecological study of McLaughlin Bay, a high-closure barrier beach wetland, showed that the abundance of small benthic Fragilariaceae decreased, and diatom diversity increased, when the barrier was breached in 2005 and 1954. Recent increases in small benthic Fragilariaceae were consistent with assessments by the local conservation authority that McLaughlin Bay has become less connected to Lake Ontario in recent years, lending support to artificial barrier beach manipulation as a strategy to improve water quality. Barrier beach dynamics create a natural disturbance regime that is important for maintaining biodiversity and water quality in protected coastal wetlands. Our study provides an approach to monitor and investigate coupled physical-ecological dynamics of barrier beach coastal wetlands over decadal to centennial timescales.