The red coral ( <i>Corallium rubrum</i> ) population of the Portofino MPA (Ligurian Sea, Italy): a multi-decadal comparison

The Corallium rubrum population of the Portofino Marine Protected Area (MPA) has been monitored since 1964, when Marchetti conducted the first survey, establishing a baseline for long-term ecological analyses. That initial study recorded the presence of red coral at 40 sites, spaced approximately 150 m apart, and documented the minimum depth of occurrence. Subsequent quantitative surveys were conducted in 1990 and 2014. Sixty years after the first observations, the species remains present at all previously surveyed sites, with the average minimum depth of occurrence (26.5 m) remaining unchanged. In 10 of these sites, a standardized quantitative sampling was conducted in 2024, following Marchetti’s original protocol, by collecting all colonies within three 900 cm2 replicates per site. Comparative analysis revealed that average biomass increased from 300 to 1500 g m−2 between 1990 and 2014, but declined sharply in the last decade to 450 g m−2. This negative trend is attributed to a widespread reduction in colony density, size, and branching complexity. The recent history of the red coral population in Portofino appears to be shaped by the synergistic impacts of global warming, anthropogenic pressure (e.g. recreational diving, fishing), and the extreme storm event of November 2018, the most intense ever recorded in the region.