Patterns and Pace of Polar Bioerosion
Final Report Abstract
In the understanding of biosedimentary processes, research on bioerosion is gaining momentum, acknowledging the important role of this process in carbonate (re)cycling and the significant impact of the present global change (ocean acidification, ocean warming, eutrophication) on this process. While investigations of bioerosion in tropical coral reefs and in temperate coastal waters are far advanced, reports on bioerosion of polar carbonates are anecdotal and merely descriptive – despite of prominent centres of cold-water carbonate production in the polar biogeographic realm. This very gap in research was the subject of this project, its objectives having been directed towards a better understanding of the qualitative and quantitative role of bioerosion in polar carbonate factories and depositional environments. The primary study site was the Svalbard archipelago that, prior to the project, was target of two research cruises with RV Maria S. Merian. During these expeditions, 10-year settlement and bioerosion experiments were successfully deployed in Mosselbukta in a rhodolith bed as well as adjacent aphotic waters and diverse samples of marine epibenthic calcifiers were taken along bathymetrical transects. This material provided the basis for elucidating the ichnodiversity and to study the bathymetrical distribution of bioerosion traces as a function of the photic zonation. A total of 30 different bioerosion traces were identified from the experimental substrates, 28 at the 46-m-station and 24 at the 127-m-station. The majority of these are microborings (19), followed by attachment traces (9) and traces of grazing activity (2). In addition, life sampled acorn barnacles were chosen as a model substrate, as they occur in abundance in all water depths and are sessile, i.e. they faithfully record the bioerosion trace assemblage of the water depth at which they were sampled. This analysis, performed on samples from the intertidal to aphotic 125 m water depth, added another 8 microborings to the inventory, resulting in a total of 38 different bioerosion traces now recorded from arctic Svalbard. For a more comprehensive picture on polar bioerosion, additional barnacles were studied from another Svalbard site and from the Canadian Arctic, as well as from the Ross Sea in the Southern Ocean of Antarctica. Samples from the latter site extended the bathymetrical range of the study down to bathyal 1680 m water depth. In total, 28 different microendolithic traces formed by cyanobacteria (4), chlorophytes (2), rhodophytes (1), sponges (1), fungi (12), foraminiferans (3), bacteria (1), and unknown microorganisms (4) were recorded in more than 200 epoxy-resin casts studied with SEM. While some of these traces were restricted to certain study sites, there were also traces that were found in both polar regions, suggesting some degree of former or present interconnectivity. The inferred trace-makers are mainly organotrophs and dominated by marine fungi, identifying them as robust under harsh environmental conditions imposed by the cold temperatures, months of sea ice cover, and the cycle of polar day and night. The latter is reflected in a general impoverishment in phototrophic bioeroders, with only traces formed by low-light specialists found present. Among the recorded microbioerosion traces, several are new to science and one was established as a new ichnospecies (based on corresponding fossil type material). This trace, Saccomorpha guttulata, may now serve as indicator for cold-water (palaeo)environments. Surprisingly, there was an almost complete lack of macrobioerosion traces ubiquitous at lower latitudes, with only one such trace (by an acrothoracid barnacle) recorded from the Ross Sea. Our 10-year settlement experiment allowed, for the first time, to assess gravimetrically determined carbonate accretion and bioerosion rates from a polar environment. Rates of carbonate accretion and bioerosion were very low and varied markedly with water depth and substrate orientation. The highest accretion rates (24.6 ± 18.3 g m2 yr^-1 ) were recorded for up-facing PVC substrates at the 46-m-station, driven by the colonization of the crustose coralline alga Lithothamnion glaciale, the local ecosystem engineer supporting the formation of the rhodolith beds. Rates on the limestone tiles were somewhat lower as a result of intense grazing activity. Accordingly, these substrates also show the highest recordedbioerosion rates (-35.1 ± 2.8 g m2 yr^-1 ). Rates at all the down-facing substrates and at the 127-m-station were considerably lower (< 10 g m2 yr^-1 ) and less variable. Overall, carbonate accretion was found similar on PVC versus limestone substrates and in the same range than the inverse bioerosion rates, suggesting that epilithic carbonate production and bioerosion in Mosselbukta are nearly in balance.
Publications
- (2018) Saccomorpha guttulata – a new marine fungal microbioerosion trace fossil from cool- to cold-water settings. Paläontologische Zeitschrift 92:525-533
Wisshak M, Meyer N, Radtke G, Golubic S
(See online at https://doi.org/10.1007/s12542-018-0407-7) - (2019) Epibenthos dynamics and environmental fluctuations in two contrasting polar carbonate factories (Mosselbukta and Bjørnøy-Banken, Svalbard). Frontiers in Marine Science 6: article 667, 31 pp.
Wisshak M, Neumann H, Rüggeberg A, Büscher JV, Linke P, Raddatz J
(See online at https://doi.org/10.3389/fmars.2019.00667) - (2020) Ichnodiversity and bathymetric range of microbioerosion traces in polar barnacles of Svalbard. Polar Research 39: article 3766
Meyer N, Wisshak M, Freiwald A
(See online at https://dx.doi.org/10.33265/polar.v39.3766) - (2021) Bioerosion ichnodiversity in barnacles from the Ross Sea, Antarctica. Polar Biology
Meyer N, Wisshak M, Freiwald A
(See online at https://doi.org/10.1007/s00300-021-02825-4)
