Benthic communities across recent and historical volcanic lava flows of an oceanic island

Volcanic eruptions create new marine substrates that serve as natural laboratories for examining benthic ecological succession over time. Benthic community assembly was examined across three lava flows of different ages (<1 year, 73 years, 473 years) at Playa del Arco (28.609141° N, 17.923526° W), La Bombilla (28.592422° N, 17.919193° W) and Puerto Naos (28.584996° N, 17.910301° W), and on La Palma Island (Spain). Fieldwork was conducted in August 2022. Using underwater photoquadrats, microinvertebrate settlement collectors, and microinvertebrate sampling from rocks at two depths (10 and 20 m), distinct successional trajectories were identified for macroalgae, early microinvertebrate settlers, and benthic microinvertebrates. Macroalgal richness was lowest in the youngest flow, peaked in the 73-year-old flow dominated by Lophocladia trichoclados and Canistrocarpus cervicornis and slightly declined in the oldest substrate. Early settlers increased in richness from the youngest to the 73-year flow, with families such as Caprellidae, Cerithiidae, and Alpheidae driving community differentiation, and later stabilized at 473 years. Benthic microinvertebrates showed the strongest successional shift, with peak richness and taxonomic uniqueness at 73 years, followed by dominance of specialized or predatory taxa such as some, Cirratulids, and Alpheus macrocheles in the oldest flow. The ratio of larval arrivals to successfully settled species decreased with substrate age, indicating intensified post-settlement filtering. These findings demonstrate a unimodal diversity peak at intermediate successional stages and underscore the role of substrate stability, macroalgal structure, and biotic filtering in shaping benthic community assembly on volcanic coasts.