Mollusc species from the Pontocaspian region – an expert opinion list

Abstract

Defining and recording the loss of species diversity is a daunting task, especially if identities of species under threat are not fully resolved. An example is the Pontocaspian biota. The mostly endemic invertebrate faunas that evolved in the Black Sea – Caspian Sea – Aral Sea region and live under variable salinity conditions are undergoing strong change, yet within several groups species boundaries are not well established. Collection efforts in the past decade have failed to produce living material of various species groups whose taxonomic status is unclear. This lack of data precludes an integrated taxonomic assessment to clarify species identities and estimate species richness of Pontocaspian biota combining morphological, ecological, genetic, and distribution data. In this paper, we present an expert-working list of Pontocaspian and invasive mollusc species associated to Pontocaspian habitats. This list is based on published and unpublished data on morphology, ecology, anatomy, and molecular biology. It allows us to (1) document Pontocaspian mollusc species, (2) make species richness estimates, and (3) identify and discuss taxonomic uncertainties. The endemic Pontocaspian mollusc species richness is estimated between 55 and 99 species, but there are several groups that may harbour cryptic species. Even though the conservation status of most of the species is not assessed or data deficient, our observations point to deterioration for many of the Pontocaspian species.

A revision of the extant species of Theodoxus (Gastropoda, Neritidae) in Asia, with the description of three new species

“…It is possible that the specimens used in that study may have been misidentified, as Sands et al (2019a), using mtDNA and nDNA of material conforming to T. anatolicus from near İzmir, found an independent monophyletic clade. Their clade shares a close sister relationship with T. altenai and is distinct from both T. jordani and T. baeticus (Sands et al 2019; also see Fig. 2).…”

Differential impact of anthropogenic pressures on Caspian Sea ecoregions

“…Some of the respective compounds might be biologically magnified along the food chain, causing physiological impairments (Bickham et al, 1998;Moore et al, 2003;Wilson et al, 2014). Thus, chemical pollution may be of particular concern for endemic species in the deeper parts of the Caspian Sea (Parr et al, 2007;Tait et al, 2016) and could, for example, explain the strong decline of mollusks species in the profundal zone (Wesselingh et al, 2019).…”

“…However, over the last decades, many of its unique species assemblages have increasingly suffered from environmental (e.g., water-level fluctuations, salinity changes) and anthropogenic pressures (e.g., oil extraction, overfishing, introduction of invasive species). As a consequence, the overall ecosystem health has deteriorated and many endemic species have become regionally or globally extinct (Dumont, 1995;Karpinsky, 2005;Zonn, 2005;Zarbaliyeva et al, 2016;Mammadov et al, 2016;Wesselingh et al, 2019).…”

Historical faunal exchange between the Pontocaspian Basin and North America

“…In the western part of its range, Ecrobia likely occurs from the Hudson Bay in Canada (Layton, Martel, & Hebert, ) to the Chesapeake Bay in the United States (Davis, McKee, & Lopez, ). The eastern distribution border ranges from brackish water bodies in the Lake Issyk‐Kul area (Wilke & Delicado, ) via the Caspian Sea (Starobogatov, ; Wesselingh et al, ) to southern Iraq (Haase et al, ) and potentially to areas just north of the Arabian (Persian) Gulf (Glöer & Pešić, ). The highest species richness of Ecrobia can be found in the Mediterranean Basin (Wilke & Delicado, ).…”