Sabrina van de Velde defended her PhD-thesis

We are super proud of Naturalis PRIDE researcher Sabrina van de Velde who succesfully defended her PhD-thesis on 2 October 2020 at Utrecht University. Promotor: Prof. Luc Lourens, co-promotors: Dr. Frank Wesselingh, Dr. Thomas Neubaur.

Congratulations, Sabrina!!


Title of the PhD-thesis: Mollusc species response to drivers in space and time. Rise and demise of the unique Pontocaspian fauna.

A major centre of continental aquatic biodiversity today is the Pontocaspian region. The Caspian Sea basin and parts of the Black Sea basin are home to unique species of which the majority are endemic to these specific waters. There are indications that human activities, like poaching, pollution and invasive species are now threatening the endemic species’ survival. To find out if there is a species downfall and how big the decline is, we need information about the communities before anthropogenic impact.

The research presented in this thesis examines the diversity of fossil Pontocaspian shells to understand what the communities looked like in the past 100,000 years and how they are different from the shelly assemblages nowadays in the same area and habitats.

The results show that there is most likely a species crisis going on. Before human impact the shells in the Caspian Sea were 100% Pontocaspian while right now the majority consist of invasive species introduced by humans. Fossil time snapshots of Pontocaspian molluscs in the Black Sea do not show much difference with current species assemblages, yet today the size of their habitat is under threat of human actions. It is possible that species found refuge in deeper areas of the Caspian Sea, but there is a data deficiency on the species’ identities, distributions and ecologies. More knowledge on the current situation of living Pontocaspian species and more historical data on ancient communities are necessary to assess the nature of the Pontocaspian biodiversity crisis more comprehensively and plan conservation actions accordingly.