‘Eco-unit services’: Positive and negative ecological services provided by seawall enhancement units

The replacement of natural coastlines with artificial structures such as seawalls is accelerating globally. These hard engineered defences have negative impacts on ecosystem function. Eco-engineering techniques have the potential to mitigate some of these effects by increasing the range and quality of ecosystem services offered by coastal infrastructure. Implementation of retro-fitted enhancement units, or ‘eco-units’, is a common strategy used to improve the ecological performance of traditional seawalls. However, despite numerous studies reporting the positive effects of eco-units on biodiversity, relatively few have focused on the ecosystem services provided by these interventions. In this review, we synthesize the literature to determine the potential ecosystem services and negative consequences associated with eco-units. Our findings indicate that eco-units can deliver a diverse range of ecosystem services, particularly regulating services and cultural services. We also identified several drawbacks of eco-units, including ecosystem disservices as well as costs incurred from their implementation. This comprehensive examination of the benefits and costs of eco-units will facilitate informed decision-making and more strategic ecological management of coastal infrastructure.