The biodiversity and abundance of benthic foraminifera tend to increase with distance within a transect from the Rainbow hydrothermal vent field. Miliolids dominate closer to the vents and may be better adapted to the potentially hydrothermal conditions than hyaline and agglutinated species. The reason for this remains unclear, but there are indications that elevated trace-metal concentrations in the porewater and intrusion of acidic hydrothermal fluids could have an influence on the foraminifera.