The abundance index measures the quantity of submersed species using presence or absence and the plant density rating. It is calculated using the following formula:

Where V i is the presence or absence (1,0) and R i is the plant density ranking (0,1,2,3,4,5) data for the i th subsampling areas at the site ( i =1,2,3,4,5,6). Data are treated before computation so that V i =1 if R i >=1 and, vice versa, R i >=1 if V i =1.