Temporal changes of a fouling community: Colonization patterns of the benthic epifauna in the shallow northern Adriatic Sea

Abstract Sessile benthic communities are an important element of marine ecosystems, yet their temporal patterns remain poorly understood. For this reason, the temporal changes of the fouling community on brick plates in Piran Bay, Gulf of Trieste (northern Adriatic Sea), were studied for two calendar years. The aim of this study was to identify the settlement of dominant native and alien species on artificial substrates and their temporal occurrence, both in terms of season and duration of submersion. In addition, we tried to assess the impact of the placement period on developing communities. The dominant taxonomic groups were bryozoans, which accounted for almost half of the total coverage (46%), serpulid polychaetes (25%) and bivalves (11%). Most of the species belonging to the dominant taxa occurred throughout the year, with the peak of occurrence in summer. The first settlers included serpulids and bivalves, which were constantly found on the plates together with bryozoans. Alien and cryptogenic species represented about 13% of all taxa found during the study. This highlights the importance of bare artificial structures erected outside typical hotspots for alien species; they serve as a springboard for the spread of alien fouling species. The communities that formed on plates placed in different seasons showed significant differences between them. High bryozoan coverage characterized the communities placed in winter and spring, while the plates placed in summer and autumn were dominated by serpulid polychaetes. These differences are the result of species seasonality as well as the interaction between them. The study demonstrates the importance of timing for initial colonization. It can be linked to the placement of the bare substrate for the development of the community, and provides a baseline for research and projects involving underwater constructions and the detection of alien species.