Effects of Water Depth, Seasonal Exposure, and Substrate Orientation on Microbial Bioerosion in the Ionian Sea (Eastern Mediterranean)

Abstract

The effects of water depth, seasonal exposure, and substrate orientation on microbioerosion were studied by means of a settlement experiment deployed in 15, 50, 100, and 250 m water depth south-west of the Peloponnese Peninsula (Greece). At each depth, an experimental platform was exposed for a summer period, a winter period, and about an entire year. On the up- and down-facing side of each platform, substrates were fixed to document the succession of bioerosion traces, and to measure variations in bioerosion and accretion rates. In total, 29 different bioerosion traces were recorded revealing a dominance of microborings produced by phototrophic and organotrophic microendoliths, complemented by few macroborings, attachment scars, and grazing traces. The highest bioerosion activity was recorded in 15 m up-facing substrates in the shallow euphotic zone, largely driven by phototrophic cyanobacteria. Towards the chlorophyte-dominated deep euphotic to dysphotic zones and the organotroph-dominated aphotic zone the intensity of bioerosion and the diversity of bioerosion traces strongly decreased. During summer the activity of phototrophs was higher than during winter, which was likely stimulated by enhanced light availability due to more hours of daylight and increased irradiance angles. Stable water column stratification and a resulting nutrient depletion in shallow water led to lower turbidity levels and caused a shift in the photic zonation that was reflected by more phototrophs being active at greater depth. With respect to the subordinate bioerosion activity of organotrophs, fluctuations in temperature and the trophic regime were assumed to be the main seasonal controls. The observed patterns in overall bioeroder distribution and abundance were mirrored by the calculated carbonate budget with bioerosion rates exceeding carbonate accretion rates in shallow water and distinctly higher bioerosion rates at all depths during summer. These findings highlight the relevance of bioerosion and accretion for the carbonate budget of the Ionian Sea.

Limited Carbonate Dissolution by Boring Microflora at Two Volcanically Acidified Temperate Sites: Ischia (Italy, Mediterranean Sea) and Faial (Azores, NE Atlantic Ocean)

“…Measured depths of penetration in all substrates at the CO 2 venting areas in Ischia and Faial were particularly low (<30 μm after 6 months at Faial) and always lower than those found at ambient pH. Those depths, due mainly to Phaeophila sp., were similar to those reported by several authors for various carbonate substrates in warm temperate (Färber et al, 2015) and shallow tropical settings (Carreiro-Silva et al, 2009Enochs et al, 2016;Kiene et al, 1995;Mao Che et al, 1996). Phaeophila sp.…”

Cyanobacteria of Greece: an annotated checklist

“…Gloeocapsa polydermatica Kützing found in Nigrita hot springs (Anagnostidis 1961) is currently regarded as a taxonomic synonym of the chlorophyte Sporotetras polydermatica (Kützing) I.Kostikov, T.Darienko, A.Lukesová, & L.Hoffmann (Guiry and Guiry 2016). The taxon Scolecia filosa found in microbial bioerosion at an underwater marine site in Peloponnese (Färber et al 2015) belongs to ichnotaxa produced by unknown heterotrophic organisms (Heindel et al 2009), not cyanobacteria. The remaining 17 species belong to the family Pelonemataceae; this family, consisting of the genera Achroonema , Pelonema , Peloploca , and Desmanthos , was created to accommodate some colorless bacteria with multicellular filaments (trichomes), which were observed in hypolimnia of lakes and ponds or in sulfur springs (Hirsch 1981).…”

Ichnodiversity and bathymetric range of microbioerosion traces in polar barnacles of Svalbard

“…Orthogonum-form 1 was until now also only described from the Kosterfjord and is therefore also restricted to cold-temperate and polar regions (Wisshak 2006). Saccomorpha clava is usually a ubiquitous fungal ichnotaxon (e.g., Wisshak 2006;Wisshak et al 2011;Färber et al 2015), but only one single colony was observed in Mosselbukta, whilst we commonly found S. guttulata as a substitute of this trace. Fascichnus isp.…”