Understanding environmental and anthropogenic factors affecting dinoflagellate communities in the Black and Caspian seas

Abstract

Biodiversity loss worldwide is linked to human activities and climate change, this trend is threatening the function and health of ecosystems globally. In aquatic ecosystems, studying the biodiversity of key trophic groups at regional and local scales and including coastal and estuarine areas is essential for understanding how such ecosystems respond to perturbations. The Black Sea and the Caspian Sea both have highly variable environmental conditions with steep salinity gradients and are experiencing strong anthropogenic activities in places. These basins are part of the Pontocaspian region which, as a consequence of its geological and climatic history, hosts unique biological assemblages adapted to variable environmental conditions.
Dinoflagellates are a key component of aquatic systems and an ideal group for biodiversity studies on short and longer timescales, e.g. from current monitoring to millions of years. They respond to and are therefore used as proxies for changing water conditions including pollution, and provide a rich fossil record based on their resting cysts (dinocysts). Previous studies on dinoflagellates in the Pontocaspian region are fragmented by geographically uneven sampling efforts. They are also, almost exclusively, based on traditional taxonomic observations under light microscopy. This methodology is time-consuming, requires considerable expertise to undertake and may not be suitable for identifying cryptogenic and parasite species.
This study targeted both dinocysts and dinoflagellates, adding substantial new data to previously poorly studied areas of the Pontocaspian, using both traditional morphological identification and new genetic methods to infer the biodiversity and biogeography of the group.
Statistical analyses of new dinocyst data generated from this project confirm that temperature, salinity and primary productivity are the main drivers of dinocyst distribution and assemblages in the Pontocaspian basins. This conclusion was also achieved by analysing water samples from the different Black Sea environments. The results demonstrate that the main factor affecting the diversity of dinoflagellates and limiting their distribution is salinity, followed by temperature, rather than spatial factors; indicating that dinoflagellate communities in the Black Sea are mostly dependent on niche-based processes. This new dinoflagellate diversity and distribution data were obtained by applying Next Generation Sequencing (NGS) and DNA barcoding methods. These techniques recovered a high diversity of dinoflagellates including taxa recorded for the first time for this region and those known to be hard to identify by light microscopy. Dinocyst assemblages analysed in this thesis also reflect nutrient-enriched conditions in the north Caspian Sea and the western Black Sea. Moreover, there is a significant correlation between shipping activities and dinocyst assembles in the Caspian Sea. In addition, new dinoflagellate cultures isolated from the Pontocaspian region were established to test the effect of dominant environmental factors on dinoflagellates under controlled conditions. Culture experiments with Gymnodinium aureolum suggest that this species is adapted to Black Sea water conditions, indicating that it is probably a long-established population, which has the potential of developing harmful blooms.
This study is the first to test statistically the impact of shipping activities on dinocyst assemblages, and the first work to implement NGS and ITS barcoding to study diversity and biogeography of dinoflagellates in the Pontocaspian region. In addition, new cultures of HAB species of dinoflagellate were established expanding the knowledge of these species in the region. This work also complements and confirms the findings from previous studies in the region and provides new data and information to support further ecological, diversity and monitoring studies.

Date of Award	24 Jun 2021
Original language	English
Awarding Institution	University of Bristol
Supervisor	Rachel M Flecker (Supervisor) & Dan Lunt (Supervisor)