MICROBIAL MAT CONTROLS ON INFAUNAL ABUNDANCE AND DIVERSITY IN MODERN MARINE MICROBIALITES

Microbialites are the most abundant macrofossils of the Precambrian. Decline in microbialite abundance and diversity during the terminal Proterozoic and early Phanerozoic is commonly attributed to the concurrent radiation of burrowing and grazing metazoans (e.g. Awramik, 1971). Similarly, the apparent resurgence of microbialites in the wake of Paleozoic and Mesozoic mass extinctions (e.g. Sheehan and Harris, 2004) is frequently linked to drastic declines in the diversity and abundance of metazoan reefal communities. However, it has become increasing clear that microbialites are relatively common in modern shallow, normal marine carbonate environments—foremost the Bahamas. For the first time, we present data, collected from the Exuma Cays, the Bahamas, systematically characterizing the relationship between framework-building cyanobacteria, microbialite fabrics, and microbialite-associated metazoan abundance and diversity. We document the coexistence of mutually thriving microbialite and infaunal metazoan communities and demonstrate that the predominant control upon both microbialite fabric and metazoan community structure is microbial mat type; i.e. the community of cyanobacterial framework-builders. The manner in which metazoan diversity and abundance influence the formation, early diagenesis and preservation of modern microbialite fabrics holds important implications for our understanding of both modern and ancient microbialites. Moreover, these findings necessitate that we rethink prevalent interpretations attributing end-Proterozoic declines and Phanerozoic fluctuations of microbialites to metazoan-mediated exclusion.