Morphometry of the diatom Fragilariopsis kerguelensis from Southern Ocean sediment: High-throughput measurements show second morphotype occurring during glacials

Biogeographic differentiation between two morphotypes of the Southern Ocean diatom Fragilariopsis kerguelensis

“…A threshold value of rectangularity to differentiate between both morphotypes was estimated as the intersection location between the density functions of the two inferred component distributions, at 0.761. This was slightly higher than the corresponding value of 0.753 obtained by Kloster et al (2018) from the fossil record. The location of this intersection depends not only on the mean and spread but also on the relative contributions of both component distributions.…”

“…Rectangularity values of individual valves ranged from 0.676 to 0.836. Rectangularity distribution for all samples pooled showed two distinct modes, albeit with slightly shifted locations and differing relative contributions when compared to previous observations from the sediment record (Kloster et al 2018) (Fig. 2).…”

“…The location of this intersection depends not only on the mean and spread but also on the relative contributions of both component distributions. In the recent samples, the high rectangularity class contributed stronger and both rectangularity classes had slightly higher means compared to the sediment core data of Kloster et al (2018), together explaining the difference in these threshold estimates.…”

“…This extensive body of research of patterns of intraspecific morphological variation in F. kerguelensis was recently extended by the differentiation of two valve outline shape morphological variants in a sediment core (Kloster et al 2018). This study used semi-automated microscopic and image analysis methods for a precise morphometric characterization of F. kerguelensis assemblages across two glacialinterglacial transitions in the Polar Frontal Zone sediment core PS1768-8 (Zielinski et al 1998;Gersonde et al 2003).…”

Polares Plankton

“…Somit kann man die Biogeografie einzelner Diatomeenarten anhand von georeferenzierten Präparaten aus der Sammlung untersuchen, diese mit ozeanografischen Daten verknüpfen und dadurch die Verbreitung einzelner Arten kartografieren. Modellrechnungen sagen voraus, dass sich das Verbreitungsgebiet der im Südozean endemischen Diatomeenart Fragilariopsis kerguelensis (Abbildung ) in den kommenden Jahrzehnten Richtung Süden verlagern wird . Auch die bereits erwähnten Labor‐ und Felduntersuchungen zeigen, dass der Klimawandel noch drastischere Konsequenzen für das Vorkommen von antarktischen Diatomeen haben könnte .…”