Alvania acida sp. nov., a new late Quaternary gastropod adapted to the shallow-marine CO2 seep of Vulcano Island

Submarine CO2 emissions are a recent (probably younger than about 5 ka) expression of volcanism at Vulcano Island (off NE Sicily), a Mediterranean natural laboratory for the study of ocean acidification. An impoverished molluskan association is known from the naturally acidified waters of Vulcano, at Levante Bay, where pH drops to 5.64. Here we describe a new gastropod, Alvania acida sp. nov., living in the bay, and found at the nearby site of Capo Milazzo (NE coast of Sicily) within a Late Pleistocene paleocommunity related to vegetated bottoms. The study species underwent a habitat change during its short evolutionary history, resulting in the recent adaptation to the CO2 seep at Vulcano. Similarly to the gastropods Tritia corniculum and T. neritea from the same seep, A. acida was up to 24% smaller than fossil shells from Milazzo, showing a further probable case of adaptation to high-CO2 waters through dwarfing. The new species shows distinctive features: an inflated shell; very convex, axially ribbed whorls; weak spiral cords. Because of its current distribution, limited to Levante Bay, and anthropogenic pressure from tourism affecting the site, A. acida deserves protection.