REEFCAP: eight open, parametric prototypes of epifauna-focused retrofit habitat modules for subsea cable protection, derived from a systematic scoping review

Offshore wind farms are connected to the grid by subsea power cables. Where these cables cannot be buried, or where they cross other cables and pipelines, they are covered with rock, concrete mattresses or protective shells. Over time, this protection becomes a new kind of hard seabed in areas that are otherwise mostly sand. Marine life settles on it anyway, but nobody designs it for that purpose: its only job is to keep the cable safe. Studies of harbours, breakwaters and artificial reefs show that small design choices, such as surface texture, holes and crevices, or the way surfaces face, can change how many organisms settle and which ones. This knowledge has never been applied to cable protection. Cable protection is also a difficult place for habitat: it is long and low, it must not overheat the cable or press on it, it must stay accessible for inspection and repair, and in some places fishing gear must be able to pass over it. As a result, no add-on habitat module for existing cable protection has been described, built or tested. This gap matters in the southern Baltic Sea, where new export cables for offshore wind are being planned near Łeba and Choczewo. This study first reviewed the published evidence in a scoping review that followed the PRISMA-ScR reporting guidelines. Of the 69 studies included, none compared a purpose-built habitat unit on cable protection with standard protection. The shape and surface of a structure had more consistent support than the material it was made of. These findings were turned into 20 design constraints, and eight open, parametric prototypes (C1–C8) were designed from them. Each prototype offers 4.4–6.5 times more surface than the seabed area it covers, and all of them met the constraints that can be checked from geometry alone. The prototypes are a shared, testable starting point, not proof of ecological benefit. The CAD files and scripts are openly available so that others can build, test and improve them, and the next steps are engineering checks with a cable owner and a controlled field trial in the Baltic.