Biogeological signatures of microboring cyanobacterial communities in marine carbonates from Cabo Rojo, Puerto Rico Elizabeth Chaco ´n a, * , Esther Berrendero a,b , Ferran Garcia Pichel a a School of Life Sciences, Arizona State University, Tempe, AZ 85287, United States b Biology Department, Faculty of Sciences, Autonomous University of Madrid, 28049, Madrid, Spain Abstract 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. D 2006 Elsevier B.V. All rights reserved. Keywords: Endoliths; Endolithic cyanobacteria; Carbonate bioerosion; Microboring; 16s RNA; Micrite envelopes; Microbial diversity 1. Introduction Since the middle of the 19th century (Carpenter, 1845), numerous works have reported on the presence of microbial endoliths on a variety of substrates. In shallow waters and in exposed rocks, cyanobacteria are among the most common endolithic microbes. As has been pointed out (Golubic et al., 1981), one must differentiate euendoliths (microborers that actively penetrate the rock substrate) from cryptoendoliths (op- portunistic, if well-adapted, microorganisms that dwell in rocks crevices or pores with no dissolution action) and chasmoendoliths (those invading preexisting holes and cracks). While not all cyanobacteria or microalgae are able to bore, Mastigocoleous , Hyella , Solentia, and Plectonema are among the most representative euendolithic morpho-genera. The record of endolithic cyanobacterial communities shows a markedly wide distribution in the Phanerozoic (Campbell, 1983; Golubic, 1969; Golubic et al., 1984, 2000), as well as in the pre-Cambrian, where microfossils of endo- 0037-0738/$ - see front matter D 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.sedgeo.2005.12.014 * Corresponding author. Sedimentary Geology 185 (2006) 215 – 228 www.elsevier.com/locate/sedgeo