The tropical history and future of the Mediterranean biota and the West African enigma

Abstract

Aim Since the opening of the Suez Canal in 1869, many tropical taxa from the Indo‐West Pacific (IWP) realm have entered the Mediterranean Sea, which is experiencing rising temperatures. My aims are: (1) to compare biogeographically this tropical transformation of the Mediterranean biota with the tropical faunas of the Mediterranean and adjacent southern European and West African seas during the Late Oligocene to Pliocene interval; (2) to infer the relative contributions of the tropical eastern Atlantic and IWP to the tropical component of the marine biota in southern Europe; and (3) to understand why West Africa is not now a major source of warm‐water species. Location Southern Europe, including the Mediterranean Sea, and the coast of tropical West Africa. Methods I surveyed the literature on fossil and living shell‐bearing molluscs to infer the sources and fates of tropical subgenus‐level taxa living in southern Europe and West Africa during the Late Oligocene to Pliocene interval. Results Ninety‐four taxa disappeared from the tropical eastern Atlantic (including the Mediterranean) but persisted elsewhere in the tropics, mainly in the IWP (81 taxa, 86%) and to a lesser extent in tropical America (36 taxa, 38%). Nine taxa inferred to have arrived in the tropical eastern Atlantic from the west after the Pliocene did not enter the Mediterranean. The modern West African fauna is today isolated from that of other parts of the marine tropics. Main conclusions Taxa now entering the Mediterranean through the Suez Canal are re‐establishing a link with the IWP that last existed 16 million years ago. This IWP element, which evolved under oligotrophic conditions and under a regime of intense anti‐predatory selection, will continue to expand in the increasingly warm and increasingly oligotrophic Mediterranean. The IWP source fauna contrasts with the tropical West African biota, which evolved under productive conditions and in a regime of less anti‐predatory specialization. Until now, the post‐Pliocene West African source area has been isolated from the Mediterranean by cold upwelling. If further warming should reduce this barrier, as occurred during the productive and warm Early Pliocene, the Mediterranean could become a meeting place for two tropical faunas of contrasting source conditions.

New and rare sponges from the deep shelf of the Alboran Island (Alboran Sea, Western Mediterranean)

“…It remains unclear whether the common occurrence of "North-Atlantic" deep-shelf immigrants that has been detected in this and previous sponge studies at the Alboran Island reflects only vestiges of ancestral faunal expansions during the Quaternary interglacial periods or it is also partially derived from recent northward expansions favored by man-driven global warming. While the former mechanism is more likely the main cause, our results contribute to reinforce the idea that the Alboran shelf provides a privileged natural laboratory from where to document past, present, and future biotic exchange between the Atlantic and the Mediterranean Vermeij 2012). From this notion, two major actions would be advisable for the immediate future: 1) to complete timely an exhaustive, global characterization of the benthic assemblages of the deep shelf of the Alboran Island, establishing a crucial baseline for further monitoring steps; 2) to extend the environmental protection currently given to the shallow-shelf communities of the Alboran Island to the singular and ecologically valuable deep-shelf bottoms, taking the opportunity of the currently developing frame of the Nature 2000 Network.…”

“…Additionally, some studies have suggested a continued input of sponge species from the Lusitanian region into the Alboran Sea over the Quaternary (Maldonado & Uriz 1995), despite sponges being sessile organisms with short-living planktonic larvae lacking recognizable strategies for long-distance dispersal (Maldonado 2006). Since global warming enhances northward migration of subtropical marine species (Coll et al 2010), it is urgent to improve our knowledge of these deep-shelf Alboranian communities before the immigrants get integrated in them and further complicate both discrimination of the pre-warming original fauna and the understanding of future Mediterranean faunal shifts (Vermeij 2012).…”

Biogeographical homogeneity in the eastern Mediterranean Sea - I: the opisthobranchs (Mollusca: Gastropoda) from Lebanon

“…Finally, the short-and medium-term fate of the marine molluscan fauna of the Mediterranean Sea depends on the species pools from which alien spreading taxa are drawn (mainly from Red Sea and West African coasts), as well as on the food resources in the recipient regions and on the anti-predatory strategies of the invaders (Vermeij, 2012). The current lack of evidence on species extinction in relation to the establishment of alien species is seemingly leading to increased species richness for global Mediterranean molluscan fauna (Briggs, 2006(Briggs, , 2010, and in turn the biodiversity increase may be perceived as a positive consequence of alien arrival and establishment, especially in the eastern basin (Galil, 2007).…”

Out of the tropics, but how? Fossils, bridge species, and thermal ranges in the dynamics of the marine latitudinal diversity gradient

“…2 surely underestimate tropical/extratropical differences in origination, owing to the undersampling of the tropical fossil record, particularly in and around the Indo-West Pacific diversity maximum; this sampling bias makes rigorous per-taxon calculations difficult. However, except for the East Atlantic, where the late Cenozoic tropical fossil record is "woefully meager" (29), each major coastline in the world ocean exhibits preferential tropical origination (Fig. S2).…”