A six thousand-year record of climate and land-use change from Mediterranean seagrass mats

Abstract

1. The Mediterranean seagrass Posidonia oceanica maintains a biodiverse ecosystem and it is aworld-wide important carbon sink. It grows for millennia, accumulating organic-rich soils (mats)beneath the meadows. This marine habitat is protected by the European Union; however, it is declin-ing rapidly due to coastal development. Understanding its response to dist urbances could informhabitat restoration, but many environmental impacts predate monitoring programs (<50 years).2. This research explores the palaeoecological potential of Posidonia mats to reconstruct six thou-sand years of environmental change that could have affected Posidonia meadows and, in turn, leftan imprint on the mats.3. Palynological, microcharcoal, magnetic susceptibility and glomalin-related soil protein (GRSP)analyses on Posidonia mats enabled us to detect climate- and human-induced environmentalprocesses impacting on the seagrass during the Late Holocene.4. The poll en and microcharcoal records reconstructed anthropogenic disturbances attributed to agri-culture. The record of GRSP shows that agrarian activities affected continental soil quality. Changesin magnetic susceptibility reveal that enhanced soil erosion was caused by both climate (major flood-ing events in the NW Mediterranean) and humans (cultivation) which impacted on the Posidoniamat. Finally, increased human impact is linked to eutrophication of coastal waters since Roman-Medieval times.5. Synthesis. This study shows that climate and land-use changes in the western Mediterraneanresulted in enhanced loadings of terrigenous material to the coastal zone since the Late Holocene,likely disturbing the Posidonia meadows and their mat carbon accumulation dynamics. Under thecurrent global change scenario in which CO2emissions are projected to increase, restoring carbonsinks is a priority. Seagrass habitat rest oration should consi der not only the coastal perturbations,but also the continenta l ones at a catchment scale to preserve the socio-economic ecosystem servicesprovided by seagrasses