A ribosomal sequence-based oil sensitivity index for phytoplankton groups.

Species-level variability has made it difficult to determine the relative sensitivity of phytoplankton to oil and mixtures of oil and dispersant. Here we develop a phytoplankton group sensitivity index using ribosome sequence data that we apply to a mesocosm experiment in which a natural microbial community was exposed to oil and two oil-dispersant mixtures. The relative sensitivity of four phytoplankton taxonomic groups, diatoms, dinoflagellates, green algae, and Chrysophytes, was computed using the log of the ratio of the number of species that increase to the number that decrease in relative abundance in the treatment relative to the control. The index indicates that dinoflagellates are the most sensitive group to oil and oil-dispersant treatments while the Chrysophytes benefit under oil exposure compared to the other groups examined. The phytoplankton group sensitivity index can be generally applied to quantify and rank the relative sensitivity of diverse microbial groups to environmental conditions and pollutants.