The loss and modification of coastal habitats due to urbanization is a global issue gaining mometum, due to the need for improved coastal defences in consequence of climatic changes. Marine artificial structures such as breakwaters, seawalls and pilings, are replacing natural structures and are, therefore, often associated with habitat and diversity loss. They also support novel ecosystems unlike any that exist in natural structures. In order to design artificial structures with increased contributions to ecosystem services, we need to understand how these novel systems function. We have, therefore, evaluated the functioning properties of the kelp Ecklonia radiata, an important habitat-forming species in temperate Australia, in artificial and natural habitats in Sydney Harbour. Pilings and rocky shores were surveyed two locations in the inner Harbour and two locations in the outer part of Sydney Harbour. We measured the growth and erosion rates of E. radiata, as well as their photosynthetic efficiency, using the traditional hole-punch method and a diving PAM, respectively. Abundance of kelp and the major herbivores present in the area (e.g. sea urchins), as well as the structure of epifaunal assemblages, were also measured. We also surveyed the abundance and composition of fish in each type of habitat at each location, using unbaited GoPro cameras. We found no significant differences in the photosynthetic efficiency or the growth-rates of kelps between habitats, but erosion was greater on natural rocky shores than on pilings. These results have important implications in the productivity of these systems, given that kelp detritus, generated mainly by erosion and dislodgement, is likely to support different types of consumers and is considered a key vector of trophic connectivity in many coastal systems. Results of this work can be used as baseline on how to ecologically engineer artificial structures so they minimise adverse ecological impacts and incorporate other functions, e.g. maintenance and/or restoration of local and regional diversity, water quality improvement, food production, educational and recreational opportunities.
