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Census-based approaches to reefal carbonate budgets are increasingly being used to project the near-future fate of tropical coral reefs. Some of the census parameters are difficult to achieve in fossil reef systems, which may be the reason why no census-based estimates of fossil reef carbonate production have been published until now. Here, we apply a census-based estimate of gross carbonate production in two reef systems from southeastern Italy to (1) test if reasonable estimates are possible and (2) assess the variability of carbonate production rates over time and reef environment. We confirm that estimates of late Oligocene and late Miocene reef gross carbonate production are within the range of modern coral reefs with the late Oligocene reef front showing the greatest carbonate production (6.1 ± 1.3 kg CaCO3 m−2 year−1) and the late Miocene reef front exhibiting the lowest production (1.7 ± 0.5 kg CaCO3 m−2 year−1). The decline of reef carbonate production from the Oligocene to the Miocene is accompanied by a decline of reef builder biodiversity but driven by the lower coral cover and coral growth rates in the Miocene. The decline of reefal carbonate production may be related to late Cenozoic cooling. [ABSTRACT FROM AUTHOR]

Hard substrate communities can impact coral reef growth by adding or removing calcium carbonate when they act as encrusters or bioeroders, respectively. Although such sclerobiont communities are known across the Phanerozoic, the Triassic saw a substantial increase in reef macrobioerosion. This study provides the first quantitative assessment of sclerobionts in a Late Triassic (Norian) reef coral community (from the Nayband Formation in central Iran) and establishes some post-Paleozoic trends in reef bioerosion. Sclerobionts were common on the dominant coral Pamiroseris rectilamellosa and covered between 0 and 26.4% of total coral surface area among the 145 colonies investigated. Encrustation was significantly more prevalent (1.78% of total area) than bioerosion (0.36% of total area). The underside of corals was 3.5 times more affected by sclerobionts than the upper surfaces. This suggests that the sclerobionts preferentially colonized dead parts of the corals. The main encrusting taxa were polychaete worms (76.2%), followed by bivalves (11.9%). The main bioeroders were Polychaeta (51.4%), Porifera (22.2%), and Bivalvia (20.7%). The lack of a correlation between encrustation and bioerosion intensity suggests that the number of sclerobionts is not simply a function of exposure time before final burial. Our review of the published literature suggests a declining trend in the relative importance of bivalves, polychaetes and cirripeds in reefs, whereas sponges increased in importance from the Triassic until today. [ABSTRACT FROM AUTHOR]