Ecological responses to eco-engineering from micro- to macro- scales and implications for ecosystem function in urban coastal areas

Urban areas have broad ecological footprints with complex impacts on natural systems. In coastal areas, growing populations are rapidly advancing their urban footprint into the ocean through the construction of built infrastructure. These artificial structures, such as seawalls, reduce the availability of natural habitat with negative impacts on coastal areas. Recent efforts to mitigate these impacts have focused on adding complexity to these structures to provide more habitat. However, we still need to quantify the effectiveness of these designs at different biological levels, from macro- to micro-, and understand the consequences of these interventions for ecosystem functioning. To do this, intertidal seawalls in Sydney Harbour, Australia were retrofitted by adding concrete tiles with 5cm deep crevices and seeded with a native local habitat-former oyster or coralline algae or both. From these tiles we surveyed biofilm communities after 6 weeks with DNA extractions from swabs and amplicon sequencing of the 16S and 18S rRNA gene and found differences in bacteria diversity among treatments. We also sampled the macrofouling communities through time as well as fish-habitat interactions and feeding rates. We found that physical complexity increased the amount of time cryptobenthic fish (such as blennies) interact with the substrate. Functional aspects of complex and control tiles, including primary productivity and nutrient cyclingwere also measured after 6 months of deployment. We found significant differences in ecosystem processes between treatments. Findings from this and other, ongoing, large-scale studies will inform targeted strategies for management of urban structures in the future.