The impact of the Messinian Salinity Crisis on marine biota

Abstract

<p>The Messinian Salinity Crisis (MSC) was the greatest paleoenvironmental perturbation the Mediterranean has ever seen. The literature is abundant in hypotheses on the repercussions of the MSC on organisms. However, all these are based on incomplete and still uncertain scenarios about the MSC evolution, as well as on the assumption that such a paleoenvironmental perturbation must have completely reset marine biota. Having prevailed for many decades now, this assumption has leaked from paleontology and geosciences to biological sciences, with numerous studies taking this scenario for granted instead of using it as a starting hypothesis to be tested. Here, we review and revise the marine fossil record across the Mediterranean from the Tortonian until the Zanclean to follow the current rules of nomenclature, correct misidentifications, and control for stratigraphic misplacements. We examine the composition of marine faunas, both taxonomically and considering the function of each group in the marine ecosystem and the transfer of energy through the marine food web. Specifically, we investigate the following functional groups: 1) primary producers, 2) secondary producers, 3) primary consumers, 4) secondary consumers, and 5) top predators. Our study includes sea grasses, phytoplankton, corals, benthic and planktonic foraminifera, bivalves, gastropods, brachiopods, echinoids, bryozoans, fishes, ostracods, and marine mammals. We calculate biodiversity indexes to provide independent evidence quantifying to what degree the marine fauna underwent:</p><ol><li>A drop of overall regional biodiversity of the Mediterranean due to environmental stress during the Messinian.</li> <li>A taxonomic and functional change between the Tortonian, Messinian, and the Zanclean, that is before and after the MSC, as well as during the precursor events to that actual crisis taking place after the Tortonian/Messinian boundary.</li> <li>The onset of the present-day west-to-east decreasing gradient in species richness, which has been related to the sea temperature and productivity gradients and the distance from the Gibraltar connection to the Atlantic.</li> </ol>

Late Miocene transformation of Mediterranean Sea biodiversity

“…In contrast, other apparent faunal changes among carnivore gastropods such as the sharp increase in number of species of the families Mangeliidae and Raphitomidae (Neogastropoda), Eulimidae (Caenogastrpopoda) and the parasitic family Pyramidellidae (Heterobranchia) in the Zanclean may be attributed to the biases of the record (see Limitations section in the main text)few occurrences of these taxa in the Late Miocene, probably due to preservation and sampling bias. Moreover, the biodiversity results are driven by changes in the PoA region, because the fossil record (26) does not contain sufficient occurrences from all stages in all three regions to conduct the analysis.…”

“…The Mediterranean fossil record for the Zanclean is limited to a few localities (26). The most abundant and diverse order of bryozoans, the Cheilostomes, is the best studied and represented in the Neogene Mediterranean deposits, corresponding to about 80% of the analyzed faunas.…”

“…1 and 2) is highly uneven both geographically and in terms of sedimentary facies representation, leading to sampling bias (52,53). First, the fossil record analyzed here (26) was derived from paleontological studies conducted since the 19 th and beginning of the 20 th century, but these were constrained by the socio-economic and political conditions, favoring sampling in the European Mediterranean countries. Secondly, biodiversity estimated from the paleontological record depends on the volume and area of the sedimentary rocks exposed and potentially accessible for studies of their fossil content (54).…”

“…The dataset that was used contains 22988 fossil occurrences of 4959 species, including some occurrences which have been considered reworked (26). We excluded these from the present analysis.…”

“…Otolith and skeletal findings were combined to obtain the Tortonian-Zanclean fossil record of bony fishes (26), which collectively represent both the shallow and deep environments before and after the MSC within the Mediterranean and the three regions. The Tortonian and preevaporitic Messinian bony fish record of the Mediterranean (26) comprised species of Mediterranean-Atlantic distribution (110) and several with Paratethyan-affinity (111,112).…”