Upgrades of coastal protective infrastructure affect benthic communities

Abstract

Sea-level rise, storm surges, ageing and wear are forcing upgrades to breakwaters and sea walls to protect coastal areas from erosion and inundation. Such upgrades involve the introduction of new material which may consequently act as an ecological disturbance that can alter established marine communities and ecosystem function. Mitigating ecological impacts requires an understanding of how species assemblages are affected by such works. Here, we use the major upgrade of a regularly wave-overtopped breakwater as a case study to evaluate the impacts of upgrades to hard coastal protective infrastructure on benthic rocky reef communities. An asymmetrical Before-After Control-Impact (BACI) experimental design was used to test interactive effects of the infrastructure upgrades on benthic communities. While benthic assemblages were not significantly different from controls prior to the upgrade, improving the defensive capacity of the breakwater significantly changed community structure. Notably, most taxonomic groups showed higher cover at the control sites than at the impacted site post-upgrade, with articulated calcareous algae (e.g. Corallina officinalis and Amphiroa anceps) showing an opposite trend. Synthesis and applications. Ecological implications and structural limitations make regular upgrading of existing infrastructure unsuitable as a long-term management strategy. More sustainable alternatives need to be considered, such as decommissioning of structures and retreat from flood-prone areas. This transition, however, will take time and requires a change of mindset and policies. Where upgrades are urgent, eco-engineering techniques can mitigate impacts to habitats and associated taxa.