Abstract
Microorganisms play a crucial role in all the environments they inhabit, including coastal areas. These ecosystems are facing increasing pressures due to climate change, rising sea levels, and mitigation measures. One such measure in the Venice lagoon is the MOSE system, a large-scale infrastructure designed to protect the city of Venice from tidal events by regulating water inflow from the sea. To understand the ecological consequences on microorganisms of this regulated seawater exchange, the present study analyzes benthic and pelagic prokaryotic communities of the Venice Lagoon before the systematic activation of the MOSE barriers. Water and sediment sampling was conducted every three months at five stations over a thirty-month period, and microbial communities were investigated using 16S rRNA metabarcoding. The samples were analyzed to describe microbial abundances and variation across different sites and seasons. The results revealed a significant difference between benthic and pelagic communities, although a considerable amount of species were shared among them. While pelagic communities showed strong seasonal variations, benthic communities were more temporally stable, but exhibited strong variability across sites. These results provide a detailed characterization of the prokaryotic communities associated with surface water and sediment, offering a valuable baseline for future studies assessing the impact of highly regulated coastal environments.