Signals of loss, part two: A phytal community collapsing under extreme-climate conditions on a Mediterranean vermetid reef.

Climate change is increasing the frequency and intensity of transient extreme climate events that can be catastrophic for ecological communities. We studied the 2014-2022 period along the northern coasts of Sicily (Western Mediterranean Sea), evaluating the ecological impacts on three macroalgae (Ericaria amentacea, Jania rubens, and Padina pavonica) and one complex of species (Laurencia complex) inhabiting the vermetid bioconstructions. All climatological metrics indicate that desiccation conditions occurred in the intertidal zones for many consecutive days during 2022, compared to previous years. These extreme conditions have led to a drastic algal biomass reduction, especially for E. amentacea, P. pavonica, and Laurencia complex species. Consistently, the analysis of mollusc communities associated with macroalgae highlighted a sharp collapse, with a general inverse relationship between community composition and structure versus air temperature values. This worrying evidence indicates that anomalous desiccation conditions could have serious short-term impacts on the fragile and neglected vermetid ecosystem.