The Fucales Index: A new tool for monitoring subtidal rocky habitats, and its application to an Atlantic bay subjected to nuclear power plant's effluents

Highlights: • Proposal of an index based on the abundance of Fucales • Tool for monitoring rocky shore communities by scientists, managers and regulatory agencies • Index easy to apply, calculate and interpret • Validation of the index in an area under the impact of an effluent plume Ecological indices are useful tools for environmental managers to monitor and detect changes caused by natural or anthropogenic disturbances. Despite the fact that descriptors of Fucales species are often included in indices for evaluating changes in coastal marine habitats, there is no index based solely on Fucales abundance. This study proposes the Fucales Index (FI), based on four classes of abundance of a selected Fucales species. The ability of FI to detect changes in the abundance of Sargassum sp. was tested in a Brazilian bay that is subjected to the effluent plume from a nuclear power plant. FI was significantly different when comparing areas inside and outside of the plume area, and it increased with increasing distance from the source of the disturbance. These findings suggest that FI is a suitable tool for assessing the effect of an effluent plume and potentially of other disturbances on rocky shores hosting Fucales.