Biogeological signatures of microboring cyanobacterial communities in marine carbonates from Cabo Rojo, Puerto Rico

The occurrence of carbonate-boring organisms in marine and continental environments is well known and accounts for substantial rates of sediment and sedimentary rock reworking at the geological scale. Many case studies have documented the importance of cyanobacteria in near-surface environments, but nearly all have relied upon morphological descriptions. In this study we applied a polyphasic approach to evaluate euendolithic cyanobacterial assemblages from a variety of carbonaceous marine substrates, using electron microscopy, cultivation, and molecular genetic techniques. The limitations and biases of the different methods became evident: none could be deemed optimal, and each failed to detect much or some of the extant diversity in the samples. In general, SEM tended to underestimate the diversity of morphologically simple community members, and cultivation yielded a very biased view of the community. All approaches, however, congruently detected differences in community structure between soft substrates and hard substrates, with the latter displaying communities of higher complexity. In spite of these differences, the geological and sedimentary imprints of the boring community, exemplified in the formation of well-structured micritic envelopes of re-worked carbonate, were uniform throughout the samples, implying that the mechanism of action is common and most likely universal. Our results speak for the merits of a multidisciplinary approach and provide cautionary implications for paleoenvironmental reconstructions.