From Artificial Structures to Biogenic Habitats: Two-Year Ecological Responses to Eco-Engineered Reefs in a Tourism-Dominated Adriatic Sandy Coast

Sandy coastal ecosystems are among the most widespread yet ecologically simplified marine habitats, particularly where anthropogenic pressures and the scarcity of structurally complex habitats limit biodiversity. This study evaluated the ecological effects of eco-engineered submerged reefs deployed in 2021 along the sandy coast of Lido degli Scacchi (northern Adriatic Sea, Italy). Twenty-one fully submerged eco-engineered Tecnoreef® modules were installed within the gaps between existing detached breakwaters, introducing a highly porous and architecturally complex habitat into a shallow sedimentary environment. Benthic communities were monitored over two years through the assessment of soft-bottom infaunal and hard-substrate epifaunal assemblages. Community development on Tecnoreef modules was compared with that occurring on adjacent limestone breakwaters under both windward and leeward exposure conditions. Infaunal assemblages were primarily influenced by hydrodynamic exposure and showed limited differentiation between habitat types, although abundance and diversity increased around the submerged structures over time. In contrast, epifaunal communities exhibited marked temporal changes and developed compositions distinct from those observed on breakwaters. Among the taxa contributing most strongly to community differentiation was the reef-building polychaete Sabellaria spinulosa. The progressive establishment of this ecosystem-engineering species suggests that the eco-engineered modules provided favorable conditions for the early stages of secondary biogenic habitat development, although longer-term monitoring will be required to determine whether these developing habitats persist and evolve into stable ecological systems. Our results provide encouraging evidence that structurally complex submerged reefs can increase habitat heterogeneity and support the development of diverse benthic assemblages in highly modified sandy coastal environments. Although longer-term monitoring is required to assess habitat persistence and ecosystem-level effects, these findings highlight the potential of eco-engineered reefs as nature-based tools for supporting biodiversity enhancement and habitat development in tourism-dominated coastal landscapes.