Self-cleaning slipways: Harnessing species interactions for sustainable management of coastal infrastructureEcosystem Services

Sally Henderson^1,2,3, John Griffin¹, Louise Firth⁴, Matthew Perkins⁵

¹Swansea University, UK - ²Natural Resources Wales, UK- ³Pembrokeshire County Council, UK - ⁴University College Cork, Ireland - ⁵University of Plymouth, UK

Ecological engineering is the development of infrastructure that supports ecological functions thus reducing environmental impacts. Boat slipways are vital infrastructure that enable access to the sea. Applying ecological engineering to slipways could provide a nature-based solution to the management of hazardous algae. Slipways must be periodically cleaned to remove algae and ensure user safety, but methods are expensive and environmentally damaging. Molluscan grazers naturally inhabit coastal infrastructure and rocky shores globally, yet harnessing grazing services on slipways is hampered by a lack of substrate complexity and vulnerability to slipway traffic. Ecologically engineering slipway surfaces with refuges could encourage targeted grazing, provide protection from traffic and sustainably shift slipways to safer bare-substrate states. We are developing solutions for self-cleaning slipways in the UK, where the common limpet (Patella vulgata) is a key grazer on rocky shores with a demonstrated ability to maintain algae-free patches. Surveys across six disused slipways indicate strong negative relationships between limpet density and algal cover, underlining limpet potential to shift slipways to safe bare-substrate states. Experiments using concrete tiles investigated the effects of surface features and roughness on limpet movement and grazing. Results show limpets are more active at night with slightly higher refuge use on rougher surfaces. Importantly, limpets comfortably prevented algal growth on all designs over the 12-month experiment. A scaled-up experiment (1m² units) is now in place to determine which designs facilitate grazing at a scale relevant for slipway use. Collectively, results indicate that providing refugia for key molluscan grazers is likely a crucial step in developing self-cleaning slipways and more broadly underlines the importance of integrating grazers into the field of marine ecological engineering.