Submerged cave biofilms in the Dominican Republic. Manantial del Toro

Manantial del Toro is a submerged flank margin cave in the southeast Dominican Republic. Its water column is stratified, with oxic, nitrate-rich waters overlying a sharp halocline and a low-oxygen seawater mass below. This cave hosts strikingly large, rust-colored biofilms in its low-oxygen seawater layer, which include many Thaumarchaea and diverse Bacteria.