No abstract

This first comprehensive investigation of microbioerosion traces in polar barnacles addresses two bathymetrical transects from the intertidal down to subtidal water depths in two different carbonate factories in the Svalbard Archipelago: the bay Mosselbukta and the ocean bank Bjørnøy-Banken. Scanning electron microscopy of epoxy resin casts of barnacle shells yielded 20 different microendolithic bioerosion traces, probably produced by cyanobacteria (three), chlorophytes (two), rhodophytes (one), sponges (one), foraminifera (three), fungi (nine) and bacteria (one). The lowest ichnodiversity in both locations was observed in the shallow euphotic zone and is likely a result of strong temperature fluctuations, extreme seasonality of light levels and episodic sea-ice cover. At 25–150 m water depth, the ichnodiversity remains relatively constant (9–13 ichnospecies), albeit with differing ichnospecies composition, generally dominated by borings from chlorophytes and fungi. Ichnotaxa at Mosselbukta and Bjørnøy-Banken were similar in numbers but differed in abundance and slightly also in ichnospecies composition. Statistical tests indicate that water depth (affecting the availability of light) is the most significant driver for the development of different microbioerosion trace assemblages across the bathymetrical transects. In contrast, no significant differences in ichnodisparity were found, indicating a comparable suite of architectural designs of the micro-borings throughout bathymetry and location. The comparison of our results with literature data confirms a decrease in ichnodiversity from lower to higher latitudes, although targeted bioerosion analyses from other polar environments are needed to gain a more complete picture of the role of bioerosion in polar carbonate factories.

No abstract

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.