Holocene fish assemblages provide baseline data for the rapidly changing eastern Mediterranean

Abstract

The eastern Mediterranean marine ecosystem is undergoing massive modification due to biological invasions, overfishing, habitat deterioration, and climate warming. Our ability to quantify these changes is severely hindered by the lack of an appropriate baseline; most ecological datasets date back a few decades only and show already strong signatures of impact. Surficial death assemblages (DAs) offer an alternative data source that provides baseline information on community structure and composition. In this study, we reconstruct the marine fish fauna of the southern shallow Israeli shelf before the opening of the Suez Canal based on fish otoliths. We quantify the age of the otolith DAs by radiocarbon dating, and describe its taxonomic composition, geographic affinity, and trophic structure. Additionally, we test by radiocarbon dating the hypothesis that Bregmaceros, a presumed Lessepsian invader with continuous presence in the Mediterranean throughout the late Cenozoic, is a relict species. The otolith DA dates back to the mid-Holocene because 75% of the dated otoliths of the native species are older than the opening of the Suez Canal in 1869, suggesting that the DA is a proper baseline for quantifying modern impacts. Consistently, 97% of the otoliths and 88% of the species we collected belong to native Mediterranean species. The native anchovy Engraulis encrasicolus dominates the DAs, although gobiids are the most diverse group (14 species, 28%). The DAs show similar trophic structure to present-day pristine Mediterranean coastal fish assemblages. Two non-indigenous species are recorded here for the first time in the Mediterranean Sea, Amblygobius albimaculatus and Callogobius sp., highlighting the importance of DAs for detecting non-indigenous species. Finally, Bregmaceros otoliths are modern, not supporting the previous hypothesis that the taxon is a Pleistocene relict.

At the crossroads: early Miocene marine fishes of the proto-Mediterranean Sea

“…In contrast to the specimen figured by Nolf and Brzobohaty (2004), the otolith found in Felli shows a more regular rectangular shape. Our specimen is quite similar to the modern species Arnoglossus rueppellii (Cocco), but its inner and outer face have the same convexity, whereas A. rueppellii has a flatter inner face (Agiadi and Albano, 2020…”

“…This specimen is significantly shorter than those assigned to Apogon vigneauxi (Steurbaut, 1984), and it shows the same dorsal depression and relative size of the ostium to the cauda (OSL : CaL = 1.128) as A. moyesi from the Oligocene-Miocene of Aquitaine Basin (Steurbaut, 1982(Steurbaut, , 1984. Compared to the modern species Apogon imberbis from the Pliocene-Holocene of the eastern Mediterranean Sea (Agiadi et al, 2019(Agiadi et al, , 2020Agiadi and Albano, 2020), this specimen is shorter (OL : OH = 1.33 compared to a mean of 1.42 in A. imberbis).…”

“…They have a straight sulcus and a triangular ostium, which is characteristic of all Spicara spp., but these specimens are particularly angular in shape and have a strongly delineated sulcus. The rostrum is more robust in these specimens than in the modern species Spicara flexuosa, S. smaris, and S. maena (Agiadi and Albano, 2020), and S. gossei from the Oligocene-lower Miocene of France (Steurbaut, 1984). In addition, the posterior end of the cauda is very pointed in the examined specimens.…”

“…These otoliths have a more elongated sulcus than Ariosoma balearicum otoliths, which almost reaches the posterior edge (Fig. 3E-F; Agiadi and Albano, 2020). Moreover, the dorsal extension is located more frontally, as it is in Ariosoma Zelilidis et al, 2002, andThivaiou et al, 2019).…”

Numerous new records of tropical non-indigenous species in the Eastern Mediterranean highlight the challenges of their recognition and identification

“…The main limitation of this approach is that it is applicable only to organisms with hard skeletal parts like foraminiferans, ostracods and fishes (e.g. Agiadi and Albano 2020 ).…”