The infuence of shallow-water methane emissions on foraminiferal assemblages. The case of Scoglio d’Affrica (Northern Tyrrhenian Sea, Mediterranean Sea)

Microfaunal analyses were conducted near Scoglio d’Affrica in the Tuscan Archipelago (Northern Tyrrhenian Sea), to study the response of benthic foraminifera to methane (CH4) venting activity that occurs in this shallow water environment. Our data show that sedimentary processes linked to the CH4 emissions exert a strong in- uence on foraminiferal assemblages, resulting in a very patchy spatial distribution linked to complex abiotic and biotic interactions. Methane emissions and mud represent the two main stressor factors for the benthic foraminiferal assemblages, although at present it is not possible to determine which impact dominates. Five different morphological settings, controlled by venting activity, were de ned on and off the mud vol- canoes (MVs). Each of these settings has distinct assemblages: 1) areas with strong emission activity at the top of the MVs, locally associated with gryphons and mud ows, where the environmental conditions are clearly pro- hibitive for foraminiferal life; 2) mud ows along the MV anks, where overlapping mud ows likely limit foraminiferal colonization; 3) muddy sediments associated with weak emissions where the development of foraminiferal community is favored, although with differences in terms of density, diversity and compositional features linked to the timing of colonization by each species; 4) intermatte zones with scarce or absent emissions, characterized by typical shallow water taxa indicative of well-oxygenated and highly hydrodynamic conditions; and 5) Posidonia oceanica substrates, characterized by higher foraminiferal content on the leaves compared to the rhizomes and surrounding sediments; indeed, sediments and rhizomes were more impacted by emissions, whereas Posidonia leaves offer “refugia” and a more mitigated environment. Although it is dif cult to de ne a pattern of biota response and to identify seep-exclusive taxa, foraminifera can represent good environmental proxies for both monitoring the variability of recent venting activity and detecting stressed conditions occurring in the geological record. The sea oor around Scoglio d’Affrica represents a very promising study site for multidisciplinary marine research regarding venting activity, geochemistry of cold seep uids and their effects on benthic organisms.