Completing forty years of investigation on macroalgal distributions in Calvi Bay (Corsica, France).

During 1978-1979 and 1991-1992 periods, STARESO and Liège University initiated an early systematic monitoring of seaweed communities along 24 transects (0-15 m) in Calvi Bay (Corsica), considered as a reference site in the North Occidental Mediterranean Sea ecosystem. These 2 studies established basic knowledge on composition and distribution of macroalgae communities and highlighted certain effects of tourism activity in the Mediterranean Sea. About thirty-five years later, new records were collected on the inpulse of STARE-CAPMED project (STAtion of Reference and rEsearch on Change of local and global Anthropogenic Pressures on Mediterranean Ecosystems Drifts) in order to further investigate their long term spatio-temporal dynamics. During 2013-2018 period, first efforts were devoted to re-evaluate community composition along the historical 0-15 m transects. Further, complementary survey approaches were performed, including 0-3 m CARLIT index, additional 0-40 m scubadiving transects and Remotely Operated Vehicle (ROV) imagery transects. Macroalgae distribution data had different structures : historical early coding choices, refined SACFOR scales, cover rate in percent from direct observation and seabed image annotation with COVER software. They were compiled in common format to produce an improved synthesis and vision on statistics associated to distribution profiles and long-term temporal changes, from average profiles at bay-scale to remarkable sub-areas. This refined distribution information is mainly illustrated for Cystoseira brachycarpa, Dictyota dichotoma and Stypocaulon scoparium, species considered by other studies which evaluates macroalgae primary production in Calvi Bay by combining locally measured production with estimated distribution. The global data set compiled and associated tools, including R codes, will also facilitate the exploration of some of the future questions that might arise about any recorded species or communities (impact of massive benthic blooms on underlying macroalgal communities, change trends in depth distribution ranges, invasive trends, localisation of species of interest for new biochemical properties, biomass evaluations, remarkable macroalgal habitats).