Temporal changes in marine benthic communities in the Gulf of Venice: an ARMS (Autonomous Reef Monitoring Structures) approach

Subtidal hard-bottom benthic communities are crucial components and important indicators on the health of marine ecosystems, therefore monitoring such environments for prolonged periods becomes indispensable in an effort of conservation. In this thesis, Autonomous Reef Monitoring Structures (ARMS), multi-layered PVC structures that mimic natural substrate and offer a standardized method to assess benthic biodiversity have been deployed at a Long Term Ecological Research site in the North Adriatic Sea, underneath the oceanographic CNR platform “Acqua Alta”, located 8 miles off the cost of Venice; North Adriatic Sea. An integrated approach combining morphological identification and photo analysis has been used to evaluate temporal changes in benthic communities over four years of from 2022 to 2025, based on the use of ARMS. Observations yielded 194 taxa in total, predominantly Arthropoda, Annelida and Bryozoa. Statistical analysis on diversity indices found no differences between years, yet multivariate tests reported significant differences in communities’ structure especially between the first and last two-year period of sampling. Analysis on motile fraction community structure reported significant differences only between 2022 and 2024, whereas for the sessile fraction no temporal differences were detected. These results may indicate that community is founded on the same recruiting species, but abundances vary in certain groups and on a replicate spatial scale. Metabarcoding data on sessile fraction (SF40) from 2022 and 2023 obtained from another study on 18S and COI markers in the same period present discrepancies little overlap with morphological findings, suggesting further integration of morphological and molecular data. An increase in the number of ARMS in the surrounding area is also advocated for, to better understand the origin of the species found.