title: 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.
authors.affiliation: Senckenberg am Meer, Abteilung Meeresforschung, Südstrand 40, 26382 Wilhelmshaven, Germany.
authors.forename: Claudia
authors.initials: C
authors.lastname: Färber
authors.affiliation: Senckenberg am Meer, Abteilung Meeresforschung, Südstrand 40, 26382 Wilhelmshaven, Germany.
authors.forename: Max
authors.initials: M
authors.lastname: Wisshak
authors.affiliation: GeoZentrum Nordbayern, Fachgruppe Paläoumwelt, Universität Erlangen-Nürnberg, Loewenichstraße 28, 91054 Erlangen, Germany.
authors.forename: Ines
authors.initials: I
authors.lastname: Pyko
authors.affiliation: Hellenic Centre for Marine Research, Institute of Oceanography, 46.7 km Athens Sounio, 19003 Anavyssos, Greece.
authors.forename: Nikoleta
authors.initials: N
authors.lastname: Bellou
authors.affiliation: Senckenberg am Meer, Abteilung Meeresforschung, Südstrand 40, 26382 Wilhelmshaven, Germany.
authors.forename: André
authors.initials: A
authors.lastname: Freiwald
mesh_terms: D000818:Animals; D002119:Calcium Carbonate / Q000737:chemistry; D055669:Ecological and Environmental Phenomena; D008522:Mediterranean Sea; D012621:Seasons; D012623:Seawater / Q000737:chemistry; D062211:Spatio-Temporal Analysis; D013696:Temperature; D014871:Water Microbiology
chemical_list: D002119:Calcium Carbonate