Different colonization patterns of various natural substrata in the harbour environment.

Bedrock lithological properties shape the structure and dynamics of benthic communities across spatial and time scales. This study investigates how mineral composition, grain size, and colour influence early colonization of benthic communities in Genoa harbour during summer 2024. Panels of marbles, travertines, quartzite, siltite and granitoids (10 × 10 cm) were used to monitor settlement of fouling species like the barnacle Amphibalanus amphitrite, the serpulid Hydroides elegans, and the bryozoan Schizoporella errata. Results showed the highest settlement on dark siltite and the lowest on light marbles and travertines. No significant effect of mineral composition or grain size was detected, including the expected inhibitory effect of quartz. Larval preference for darker substrata, confirmed by comparisons between marble and granitoids with varying grey levels, suggests colour as a key driver of settlement. Post-settlement survival was mainly influenced by substratum stability. These findings highlight the complex interactions between physical properties and colonization patterns.