Abstract
Coastal infrastructure has reduced habitat complexity and altered light regimes compared to natural habitats, altering ecological communities and reducing overall biodiversity. Although, many studies have assessed effects of infrastructure on the overall biodiversity, these were often restricted in scope, by assessing only a particular type of infrastructure, such as coastal defence structures, or by focusing solely on diversity metrics. Therefore, we still have little knowledge on the functional impacts of infrastructure, in general, on coastal habitats. To address this knowledge gap, we conducted a systematic review and meta-analysis comparing the functional composition of natural and artificial marine habitats. We analysed a total of 68 publications from 26 countries, with data collected between 1995–2019. We found up to 60% more habitat-forming algae on natural habitats than on infrastructure at most tidal heights, but no differences were found when looking at all species of macro-algal, i.e. including non-habitat-formers. In contrast, we found more habitat-forming filter feeders, such as oysters and mussels, on subtidal vertical and floating structures, such as pylons and pontoons, respectively, than on natural habitats. Differences on the abundance of grazers varied with tidal height and/or the type of infrastructure. For example, in the subtidal, grazers were significantly more abundant on natural boulders than on infrastructure, while at low tidal heights, we found significantly less grazers on artificial floating structures and on vertical structures than on natural habitats. With coastal development on the rise, these differences have significant implications for productivity, energy and nutrient flow in coastal systems. Our findings highlight the importance of adopting a functional approach to have a more holistic understanding on the environmental impacts associated to marine urbanisation and thus better inform management and restoration efforts.