Origin, evolution and decline of European mangroves: the Cenozoic paleobotanical record

This paper reviews available paleobotanical evidence (pollen and macrofossils) from 114 European sites to infer Cenozoic mangrove dynamics. European mangroves originated at the Paleocene/Eocene boundary in western Europe as relatively diverse communities comprising seven true-mangrove taxa, including the major mangrove-forming elements Rhizophoraceae, Avicennia and Nypa. Some taxa arrived from the Indo-West Pacific (IWP) via the Tethyan seaway, while others evolved locally. The occurrence of Pelliciera, the only element from the Atlantic–East Pacific (AEP) region, remains questioned. Maximum expansion and diversity occurred during the Early–Middle Eocene (Ypresian–Bartonian), coinciding with Cenozoic thermal and eustatic maxima. The European mangrove flora was completed following the arrival of seven additional true-mangrove and associate elements; however, four of these, including Rhizophoraceae, disappeared by the Lutetian. A first diversity crisis occurred during the Priabonian, when Nypa became the sole European mangrove component. This coincided with the cooling trend preceding the abrupt Eocene/Oligocene cooling and its associated eustatic drop, which restricted mangroves to southern refugia in Anatolia and Iberia. Following the definitive disappearance of Nypa during the Aquitanian, a mangrove recovery—in terms of geographical range but not diversity—culminated during the Middle Miocene Climatic Optimum. During this Langhian maximum, Avicennia-only mangroves formed an extensive arc across the northern proto-Mediterranean and Paratethys. A second crisis during the Messinian Salinity Crisis almost eradicated European mangroves, forcing Avicennia into a Black Sea refugium before its final disappearance during the Pliocene. Finally, pending uncertainties and knowledge gaps are identified, and further studies are proposed to address them.