Bioerosion ichnodiversity in barnacles from the Ross Sea, Antarctica

Breakdown of skeletal and lithic hard substrates by organisms, a process referred to as bioerosion, is part of the global carbon cycle and receives increased attention, but little is known about bioerosion in polar environments. Here, we study bioerosion traces (addressed by their respective ichnotaxa) recorded in the barnacle Bathylasma corolliforme from the Ross Sea, Antarctica. Traces were visualized via scanning electron microscopy of epoxy casts prepared with the vacuum cast-embedding technique. In 50 samples from shallow 37 m to bathyal 1680 m water depths, 16 different bioerosion traces were found, classified into microborings presumably produced by cyanobacteria (1), chlorophytes (1), fungi (9), foraminifera (1), unknown organotrophs (5), and macroborings produced by cirripeds (1). Statistical ichnodiversity analysis resulted in a significant (p = 0.001) ANOSIM with moderate differences (R = 0.5) between microbioerosion trace assemblages at different water depths and revealed two main clusters (NMDS, SIMPROF) corresponding to the photic and aphotic stations. A comparison between this study and a corresponding study from the Svalbard archipelago, Arctic Ocean, shows that the ichnodiversity in calcareous barnacle skeletons is similar in polar waters of both hemispheres. This includes several ichnotaxa that are indicative for cool-to cold-water environments, such as Flagrichnus baiulus and Saccomorpha guttulata. Nine of the investigated ichnotaxa occur in both polar regions and seven ichnotaxa show an extensive bathymetrical range down to the deep sea at bathyal 1680 m water depth.