Spatial and temporal patterns of macroboring within Mesozoic and Cenozoic coral reef systems

1 Department of Environmental and Geographical Sciences, Manchester Metropolitan University, John Dalton Building, Chester Street, Manchester, M1 5GD, UK c.t.perry{at}mmu.ac.uk 2 Geologisch-Paläontologisches Institut und Museum, Pferdegasse 3, D-48143 Münster, Germany Macroboring of coral reefs has varied significantly through time, with the modern intensity and producer composition (usually dominated by sponges) as a rather recent phenomenon. Given the outstanding role and influence of bioerosion on framework morphology, community composition and sediment production, Modern conditions are therefore poor analogues for the structure and function of pre-Neogene reef systems. Modern and Neogene reef borer associations are mostly dominated by sponges, although marked spatial variations in the abundance of borer groups are evident within individual reef systems. Highest diversity typically characterizes low energy, shallow water back-reef or lagoon sites. This condition evolved gradually from the Late Triassic onwards, when scleractinians first built reefs. Sponges appear to have played a subordinate role in Mesozoic coral-dominated buildups. Worms and barnacles dominate in the early Mesozoic (Triassic and Lower Jurassic), with a progressive increase in bivalve borers through the Jurassic. The paucity of data collected to date makes determination of the causes of temporal change in macroboring community composition difficult to constrain. Macroboring groups seem to have withstood biotic crises much better than their coral substrate and thus reef ecological evolutionary units are not applicable. There is some indication that macroborers may have radiated to colonize new ecological niches during the early stages of coral reef diversification. The development was nonetheless influenced by biotic changes in the marine realm, the strongest effects potentially resulting from switches in nutrient status and the origin or diversification of reef grazers.