Coastal marine ecosystems and the services they provide are increasingly threatened by climate change. The Mediterranean basin, recognized as a climate change hotspot, is experiencing a rise in the frequency and intensity of heat extremes. Among coastal ecosystems, intertidal communities are particularly exposed to temperature fluctuations. Although they are adapted to such variability through physiological plasticity, the intensification of extreme thermal stress may negatively affect their metabolism and adaptative capacity.  

 A key intertidal habitat in the Mediterranean Sea is the vermetid reef, a bioconstruction formed by the coralline red alga Neogoniolithon brassica-florida and the gastropod Dendropoma cristatum. These bioconstructions provide essential ecosystem services, including coastal protection and biodiversity support, but are endangered throughout the basin, have already collapse in the western Mediterranean, and remain among the most poorly studied marine habitats.   

This study investigates the metabolic response of the vermetid reef habitat to thermal stress, considering varying levels of community complexity: vermetid reefs naturally covered by brown macroalgae, reefs naturally free of macroalgae and reefs where macroalgae were experimentally removed. Oxygen fluxes were measured as a proxy for community metabolism, using ad-hoc developed intertidal benthic chambers. The experiment was carried out on reefs located in northern Sicily and repeated different times throughout 2025, to obtain measurements before, during, and after the warmest period of the year for this area.   

We hypothesized that warming affects the metabolism of the vermetid reef, but that this effect is buffered by the associated biodiversity, particularly the presence of canopy-forming brown algae. This experiment defines a non-destructive method to measure the metabolism of intertidal communities directly in the field, addressing the lack of field-based marine climate change studies, especially on vermetid reefs. Understanding how different levels of structural complexity mediated the response to thermal stress is crucial for developing conservation strategies targeting this endangered ecosystem.