Thanks @Abhijit Mitra for sharing this article about CVI.
I didn't find any information about Conservation value index (CVI) used for plankton analysis in this document. If you know that concern, could you please inform here...?
Conservation value index can be calculated by taking the log transformed value of abundance of the species recorded during the survey in considered habitat strip and conservation status of the species. Article by Terraube et al., 2016 attached below might help you Man Kumar Dhamala sir in this regard.