Diversity and long-term dynamics of coccolithophores in the Gulf of Trieste (Adriatic Sea) with insights into the in vitro growth of "Syracosphaera pulchra"

Coccolithophores are key marine calcifying phytoplankton that play an important role in biogeochemical cycling and carbon export in open-ocean as well as in coastal systems. This study investigates the long-term community structure and environmental drivers of coccolithophores in the Gulf of Trieste (Northern Adriatic Sea) over a 33-year time series (1990–2023). In parallel, a short-term laboratory experiment on Syracosphaera pulchra gave us insights into its thermal response under simulated marine heatwave (MHW) conditions. Our time-series analysis revealed clear seasonal patterns, with winter dominance of Gephyrocapsa huxleyi and autumn for Syracosphaera pulchra, and a marked interannual variability linked to environmental factors. Generalized linear models identified seawater temperature as a major negative factor, while nitrate and ammonium were positively associated with coccolithophore abundance. Although coccolithophores contributed modestly to total biomass, their ecological role remains significant. Our laboratory experiment highlighted the life-phase-specific thermal responses of S. pulchra, with the haploid (HOL) phase exhibiting a significant growth increase under MHW conditions. In contrast, the diploid (HET) phase showed a weaker, non-significant trend. Both phases displayed short-term recovery after peak thermal stress, suggesting some resilience. Together, these findings emphasize the importance of long-term monitoring and experimental validation to understand coccolithophore ecology in a warming ocean, and highlight the need to account for life-cycle phase when assessing species vulnerability to climate extremes.

Mentor: Prof. Dr. Patricija Mozetič
Co-mentor: Prof. Edward Mitchell
Co-worker: Petra Slavinec

2024/2025