A global analysis of complexity-biodiversity relationships on marine artificial structures

3D printed habitat panels enhance biodiversity on seawalls in global harbours.


The world’s coastlines and harbours are increasingly being covered in human built structures which lack the complexity of natural habitats, resulting in a major loss of associated wildlife and ecosystem functions. In some urban harbours, more than 50% of natural intertidal habitats have been replaced with coastal defence structures such as seawalls and breakwaters.


The World Harbour Project (WHP), initiated by the Sydney Institute of Marine Science, is a global research program and network of 36 partner cities across 6 continents aimed at enhancing the sustainability of urban harbours.  A flagship program of the WHP is the “Green engineering” group, which aims to enhance the biodiversity of artificial structures. SIMS’ Living Seawalls Project is a part of this group.

A paper just published in the journal Global Ecology and Biogeography by the Green Engineering Group of the WHP tested how the physical complexity of habitats affects biodiversity and how this relationship varied across harbours. The experiment was done by 3D printing habitat panels with differing physical complexities (ridges, crevices) and attaching them to coastal defence structures (seawalls) at 27 sites in 14 harbours across the globe.


Panels with greater complexity generally had positive effects on the diversity of invertebrates such as barnacles or snails. However, the effects of adding complexity to coastal defence structures was surprisingly variable among harbours and among different groups of organisms.


The effect of panel complexity was strongly influenced by tidal elevation and latitude. Complex habitats had greater diversity and abundances of invertebrates at low to mid tidal elevations, likely due to greater levels of predation. The effects of complexity on species diversity were also greater at tropical or subtropical sites, due to complex surfaces providing protection from higher temperatures and desiccation.


The paper highlights how the effects of complexity on biodiversity are themselves complex, and construction of new eco-engineered structures such as seawalls and breakwaters must take local conditions into account in their design.  This means developers and ecologists must work together to design complex habitats to enhance the biodiversity of coastal defence structures. Such collaborations are now emerging in a number of urban harbours across the world, including Sydney.


The paper further shows the benefits of global research collaborations, where best practice for sustainable urban harbours can be assessed across the diversity of harbours and conditions found across the world.