A bush, not a tree: The extraordinary diversity of cold-water basal foraminiferans extends to warm-water environments

Foraminiferal species distribution and richness have traditionally been assessed through examination of the shells (tests) built by most of the described species, but molecular surveys indicate that this approach likely underestimates true foraminiferal diversity. We use a series of targeted DNA-based surveys and focused morphological searches to document the diversity of allogromiid foraminiferans, which have less distinctive tests, at selected locations along the U.S. eastern seaboard. These sites, although well studied by previous foraminiferal researchers, have not been reported to host large numbers or diverse assemblages of allogromiids. Both survey methods revealed the presence of many new allogromiid taxa and documented striking differences in the allogromiid assemblages between the three locations. The assemblage at a given site as determined by morphological criteria also differed substantially from that determined by molecular surveys. Combined with information from other locales, our data strongly suggest that allogromiid diversity is underestimated; indeed, allogromiids may actually dominate many benthic foraminiferal assemblages. This finding has significant implications for benthic trophodynamics and for the reconstruction of paleoenvironments because the morphological inconspicuousness and taphonomic fragility of allogromiid foraminiferans may lead to underestimates of total foraminiferal diversity and abundance.