Fjordic bryozoan community: (Admiralty Bay, King George Island, South Shetlands, West Antarctic) – biodiversity, distribution and geochemistry

Qualitative faunal analyses of the Recent Antarctic glacjal fjordic cold-water bryozoans from the Admiralty Bay show the dominant ascophoran umbonulomorphs, mostly represented by the endemic species and accompanied by lepraliomorphs, schizoporellids, phidoloporoids, flustrinids, hippothoomorphs and cellaroids. The majority of the studied fauna form large-sized erect robust zoaria either bilamellar folded sheets or erect rigid cylindrical branches (Hara et al., 2010).

Four bryozoan assemblages (37 species) of cheilostomes dominated by ascophoran umbunulomorphs and lepraliomorphs, 4 cyclostomes and 1 ctenostome were analysed from a depth range of 15 to 280 m. The species richness (27 species), biomass and diversity were the greatest is the third assemblage from 120-200 m, where the fauna settled on the muddy substrate in the central part of the fjord. Dominant colony form was the adeoniform represented by erect, bilamellar plates, frondose or folded sheets, branched or lobate zoaria accompanied by numerous erect bugulids attached by chitinous rhizoids covered by epibionts.

The spatial variability in the bryozoan community structure, species richness and biomass are strongly associated with the number of environmental factors such as substrate type, water depth, location within the basin, hydrodynamic regime, influence of the suspended matter inflow or glacial disturbance (Pabis et al. 2014).

Mineralogically, the bryozoan skeletons from the Admiralty Bay are cheilostomes composed of intermediate magnesian calcite (IMC) where the Mg content ranges from ca. 4.3 to 6.5 wt% MgCO₃. The bryozoans skeletons exhibit ẟ¹⁸O and ẟ¹³C values typical of cool marine waters (according to the aquition given by Friedman, O’Neil, 1977), see Hara, 2022. Their ẟ¹⁸O ranges from ca. 2.25 to 4.3% PBD, with most data clustering between 3 and 4 % PBD. The ẟ¹³C varies from ca. – 1 to + 1.5% PBD with most data plotted between + 0.5 and +1.5% PBD (Hara et al. 2010).

To add the Cenozoic evolution of the modern community structure occurred more recently, due to the factors such as further cooling and isolation of the continent leading to widespread glaciation, which resulted in a loss of shallow shelf habitats (see also Whittle et al., 2014).

Hara U. Jasinowski M. & Presler P. 2010. Geochemistry and mineralogy of bryozoan skeletons from Admiralty Bay (South Sheltland Islands, Antarctica: a preliminary account, p. 56. Terra Nostra, 15^th International Conference IBA.

Hara U., 2022 – Geochemistry of the fossil and Recent bryozoan faunas in the natural diagenetic environments and their significance for the reconstruction of the biota and climatic regimes in Cenozoic. Archive of the Polish Geological Institute-National Research Institute, nr. 5210/2022.

Pabis K, Hara U. Presler P. & Siciński J. 2014. Structure of the bryozoans communities in an Antarctic glacjal fjord (Admiralty Bay), Polar Biology 37: 737-751.

Whittle R.J, Quaglio F., Griffiths H.J., Linse K., Crame J.A., 2014 – The Early Miocene Cape Melville Formation fossil assemblage and the evolution of modern Antarctic marine communities. Naturwissenschaften DOI 10.1007/s00114-013-1128-0.