Integrating short- and long-term bioerosion processes in the Eastern Mediterranean Sea

Bioerosion, the degradation of hard substrate by living organisms, is an integral process of the marine carbonate cycle, contributing to the recycling of carbonate substrates and helping to maintain the balance between construction and destruction in reef environments. Experimental studies on bioerosion are an important tool for carbonate budget calculations and palaeoenvironmental reconstruction. Most previous bioerosion experiments were conducted over a period of 1 to 2 years giving a detailed picture on microbioerosion in different geographical settings. Experimental studies on the long-term succession of macrobioeroders were previously limited to tropical coral reef systems. Aim of this thesis was the integration of short- and long-term bioerosion processes in the Eastern Mediterranean Sea. Research on bioerosion in the Mediterranean Sea has a long tradition, but experimental studies are scarce and were previously restricted to the Western Mediterranean Sea. The Eastern Mediterranean Sea is an extreme environment, characterised by an ultra-oligotrophic nutrient regime and exceptionally high temperature and salinity conditions. Experimental data on Mediterranean bioerosion, hence, contributes important information for evaluating global patterns of bioerosion and for modelling the future impact of bioerosion. This is particularly relevant since bioerosion is considered to increase with ongoing ocean acidification, with potentially detrimental effects on carbonate-dominated ecosystems. The main objectives were (1) to analyse the spatio-temporal variability of bioerosion in the Eastern Mediterranean Sea and its effect on the carbonate budget, (2) to assess the usability of the observed bioerosion traces for palaeoenvironmental reconstruction, and (3) to set the results in latitudinal and longitudinal context to previous bioerosion experiments. This was based on three experimental studies: (1) a carbonate cycling experiment with experimental platforms deployed for a summer, a winter, and one year along a bathymetric transect from 15 to 250 m water depth south-west off the Peloponnese Peninsula in the Ionian Sea, (2) a coastal bioerosion experiment with limestone substrates mounted for 1 and 2 years in the inter- to supratidal zone at the island of Rhodes, and (3) a long-term experiment with experimental blocks deployed for 1 to 14 years in 3 to 17 m water depth around Rhodes. Short-term bioerosion rates and traces were analysed by gravimetrical measurements and scanning electron microscopy, respectively. For the analysis of long-term bioerosion rates and traces micro-computed tomographic (micro-CT) analysis was chosen in a novel approach.