The foraminiferal response to methane emissions in shallow water environments from the Scoglio d’Africa (Tuscan Archipelago, Northern Tyrrhenian Sea)

In this research benthic foraminiferal response to shallow water methane (CH4) emissions located in the area around Scoglio d’Africa (Tuscan Archipelago, Northern Tyrrhenian Sea) was investigated. Methane (CH4) is an important greenhouse gas, with a global warming potential about 20 times as large as carbon dioxide (CO2) on a 100-year horizon. In the marine environment, coastal areas represent methane hotspots highly exceeding emissions from the open ocean. In this view, Scoglio d’Africa may represent a much-promising study site for multidisciplinary marine research (carbon capture and storage, geochemistry of hydrothermal fluids and ocean acidification vs. benthic and pelagic organisms). The study area is located in the southernmost part of the Elba-Pianosa Ridge, a mainly submarine, north-south elongated morpho-structural high separating the Tuscany Shelf to the east from the Corsica Basin to the west. In the study area, submarine methane emissions have been studied since the 1960s and they are linked to the combined action of two processes: biogenic (microbial process called methanogenesis) and thermogenic origin. The gas emissions affect an area characterized by widespread Posidonia oceanica meadows occurring primarily between 10 and 40 m water depth. Two sampling surveys were conducted during 2021 and 2022: in the first (2021) thirteen sample grabs were collected while in the second, sediments and Posidonia samples were collected around two main mounds by scuba. The microfaunal analyses were carried out from samples coming from 11-16 m depth. The Posidonia were sampled 5-10 m from the emission points while sediment samples (grab and 50 ml syringe samples) were collected both at the Posidonia and no plant covering sites. The preliminary results of this research highlighted a very patch distribution and variability in density and biodiversity probably linked to the irregular distribution of the venting activity on the ground floor. The complexity of the interaction of the ecological factors characterizing extreme environments such as shallow hydrothermal vents did not allow us to carry out a real pattern of biota responses in situ. Around the muddy mounds, a strong loss of biodiversity and collapse in faunal density are recorded due to the combined effect by the CH4 emissions and the mud flow setting. The rare living specimens are represented by agglutinated species like Lepidodeuterammina ochracea and Ammodiscus sp. Contrarily to sediment samples, the epiphytic foraminiferal assemblages (living on Posidonia leaves and rizhomes) are abundant, mainly dominated by rosalinids (Neocorbina posidonicola and Rosalina spp.). EDS microanalysis and isotopic analyses will be conducted both on the foraminiferal test and Posidonia leaves to highlight the isotopic signatures of living benthic foraminifera from methane rich environments. The aim of the research is to increase the knowledge on the of microfaunal response in this extreme environment as a proxy to improve reconstructions of methane release in the past and better predict the impact of future climate warming on methane seepage.