Reconstructing salinity changes and environmental influence on dinoflagellate cysts in the central Baltic Sea since the late 19th century

Abstract

We present a record of dinoflagellate cyst assemblage composition, abundance, and morphology from the central Baltic Sea, spanning from the late 19th to the early 21st century. Environmental time-series were analyzed in relation to changes in community structure and diversity as inferred from the sediment record, and average summer sea surface salinity (SSS) was reconstructed based on the average process length of Protoceratium reticulatum resting cysts. The reconstructed summer SSS was compared to instrumental data for a critical evaluation of this approach. The most abundant species in this record were P. reticulatum and Biecheleria baltica, and on average ten taxa were identified per sample. The cyst record of B. baltica indicated that although this species has been present in the Gotland Basin at least since the 1880s, its concentrations have increased significantly since the 1980s, possibly linked to eutrophication. Variations in assemblage composition and P. reticulatum cyst morphology reflected patterns of major, instrumentally recorded hydrographic and environmental changes in the Baltic Sea during the past century. The variability in microfossil relative abundances was best explained by the average spring SSS as well as by the average NO 3 concentrations during spring and by the combined effects of average summer SSS and NAO index variability. Reconstructed summer SSS and instrumental SSS showed notable differences, depending on the year and function applied for reconstruction. Although roughly reflecting the same patterns, the reconstructed values are offset when compared to instrumental measurements. We put forward suggestions for improvement of the process-length method and recommend using the reconstructed values as an indication of relative changes in past summer sea surface salinity, preferably as part of a multiproxy approach. Highlights ► Dinoflagellate cyst assemblage analysis from 19th century to present. ► Statistical analysis on the influence of environmental parameters to microfossils. ► Average summer sea surface salinity reconstructions based on cyst morphology. ► Most abundant species were Protoceratium reticulatum and Biecheleria baltica. ► Spring SSS, N0 3 , summer SSS, NAO best explained variability in microfossil abundances. ► Cyst assemblages and morphology reflected major environmental changes.

Diversity and geographical distribution of resting stages of eukaryotic algae in the surface sediments from the southern Chinese coastline based on metabarcoding partial 18S rDNA sequences

“…The small thin-wall dinoflagellate Biecheleria cincta was present in all sites (Figure 5b). Both cysts and motile cells of Biecheleria were detected many coastal sea areas such as the Baltic Sea (Sildever et al, 2017(Sildever et al, , 2019, New Zealand (Rhodes, Smith, MacKenzie, & Moisan, 2019), the Korean coast (Kang et al, 2011), and the Japanese coast (Takahashi, Sarai, & Iwataki, 2014). It is also the dominated sequence in sediments from the Black Sea (Dzhembekova et al, 2018) and occurred abundantly in the germinated phytoplankton after incubating surface sediments from the Guangxi and Hainan coasts (Liang, 2018).…”

Glimpse of past dynamics: A new set of phytoplankton primers for sedaDNA

“…This may decrease the detection of dinoflagellate diversity with eukaryotic primers because they contribute to only a small fraction of the total amplifiable DNA (Govender et al., 2022; Thomas et al., 2020). Analyses of dinoflagellate cyst stratigraphy (Kremp et al., 2018; Sildever et al., 2019) highlight the importance of them as climate‐sensitive proxies and their contribution to harmful algal blooms (Karlson et al., 2020; Telesh & Skarlato, 2022) and emphasize the need for dinoflagellate‐specific and short primer pairs suitable for sedaDNA studies.…”

Single‐cell DNA from West Greenland marine sediments suggests presence of Protoperidinium tricingulatum in the Arctic

“…Organic‐walled dinoflagellate cysts are commonly used as a proxy for reconstructing past sea‐surface conditions, such as temperature, salinity, primary production, and sea‐ice cover (e.g., Allan et al., 2021; Brice et al., 2020; de Vernal et al., 1994, 1997, 2005, 2008; Marret & Zonneveld, 2003; Ouellet‐Bernier et al., 2014; Pospelova et al., 2008; Radi & de Vernal, 2008; Ribeiro et al., 2012; Rochon et al., 1999; Sildever et al., 2019). Certain dinoflagellate cysts have a distinct, spherical brown central body with processes and are therefore informally named “round brown spiny cysts” (RBSCs; Radi et al., 2013).…”