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Methods and materials

A total of 19 samples were selected for the study of microbioerosion in order to allow for the detection of trends along the deglacial succession from the LGM to the final drowning of the drilled coral reefs (16,000–8,000 y BP) (Camoin et al., 2007). Seven samples were taken close to the base of the deglacial (post-LGM) reef succession from Faaa, Maraa, and Tiarei; eight samples represent the middle part of the post-LGM reef from Maraa and Tiarei, and four samples represent the upper deglacial succession from Maraa and Tiarei (Table T2).

For taxonomic description of the bioerosion traces, the samples were impregnated with epoxy resin and subsequently dissolved, producing so-called casts of the bioerosion patterns inside the carbonate. For a detailed description of the vacuum-embedding technique after Golubic et al. (1970, 1983), see Beuck and Freiwald (2005) and Wisshak (2006). Determination of the bioerosion traces down to ichnospecies level was attempted where possible.

Two different methods of cast preparation were used. For the first method, selected samples were cut vertical to growth direction to cover the complete growth succession from corals to coralline algal crusts to microbialite crusts. Organic matter was eliminated with hydrogen peroxide followed by carbonate cleaning in the ultrasonic bath. After impregnating and curing the resin, the impregnated samples were etched shortly in hydrochloric acid (5%) in order to remove only the uppermost ~100 µm of carbonate substrate (coral, coralline algae, and microbialite). These casts were analyzed with respect to the vertical extension of microborings in the substrate, potential changes in the composition of the microbioeroder communities with progressive penetration depths, and substrate dependence of the microborer communities. For the second cast preparation method, other samples were taken from upper, not further encrusted surfaces of the substrate (coral and microbialite). The impregnated sample was completely dissolved in order to study superficial microbioerosion patterns and the horizontal extension of microbioerosion patterns. The casts of all samples were sputter-coated with gold for scanning electron microscopy (SEM) analysis. SEM images (Figs. F3, F4, F5, F6, F7, F8, F9, F10, F11, F12, F13, F14, F15) show resin casts of boreholes—“negatives” of the actual traces, which are boreholes inside the carbonate.