Structural and Geochemical Assessment of the Coralline Alga Tethysphytum antarcticum from Terra Nova Bay, Ross Sea, Antarctica

• Published in: Minerals
• Main Authors: Matthias López Correa, Sebastian Teichert, Federica Ragazzola, Salvador Cazorla Vázquez, Felix B. Engel, Katrin Hurle, Claudio Mazzoli, Piotr Kuklinski, Giancarlo Raiteri, Chiara Lombardi
• Format: Article in Journal/Newspaper
• Language: English
• Published: MDPI AG 2023
• Subjects: crustose coralline algae; Antarctica; taxonomy; phylogeny; thallus structure; biomineralization; Mineralogy; QE351-399.2; Ross Sea; Terra Nova Bay; Antarc*; antartic*
• Online Access: https://doi.org/10.3390/min13020215; https://doaj.org/article/5a9492be40f346ac912ebf5b7f60b67d

Crustose coralline algae (CCA) occur from the tropics to the poles in photic benthic environments. Here, we report on some of the world’s southernmost and coldest CCA sites in Terra Nova, Ross Sea, Antarctica at 74°41′ S. The recently described red alga Tethysphytum antarticum is investigated for its skeletal architecture, its mineralogical and geochemical composition, as well as for its taxonomic classification. A phylogenetic analysis based on molecular genetics and the sequencing of the photosystem II protein D1 (psbA) gave a perfect match with T. antarcticum . Histological sections and micro-CT-scans provide new diagnostic details for the conceptacles (the reproductive organs of the alga). X-ray diffractometry and electron-microprobe measurements yielded a clear high-Mg calcite (~8 mol%) composition of the skeletal parts. Detailed back-scattered electron imaging of polished petrographic thin sections revealed a two-layered thallus (vegetative plant tissue), comprising an organic-rich irregularly calcified basal layer with rectangular cells, overlain by the main thallus. Elemental maps show relatively increased sulphur in the basal layer, clearly tied to organic cell walls. MgCO 3 and SrCO 3 were targeted with semiquantitative elemental mappings and in an ontogenetic quantitative spot transect. Compared with temperature (−1.95 °C to +1.08 °C), the MgCO 3 (mol%) reflects this world’s coldest CCA site temperature with the lowest MgCO 3 content of 7.9 ± 1.6 mol%. The along transect variability, however, shows with ~6 mol% a larger MgCO 3 variability than expected for the 3 °C intra-annual temperature amplitude in Terra Nova Bay. This implies that in low amplitude settings the biomineralisation control on Mg/Ca ratios can outcompete its temperature sensitivity. Mark-recapture studies, next to the environmental logger station La Zecca are suggested, to perform a detailed growth rate and biomineralisation quantification.