The profiles were different because beaches have distinct width. The erosive ones are narrower. The length was determined originated in dune crist top towards the upper zone beach, so according to the erosion condition the dune systems are less or ore different in length.
I have data (presence absence from 0.5 to 0.5 m) from plant species occurrences from 30 sites (10 beaches with 3 replications for each one; 6 beaches not in erosive process; 4 in erosive process) in coastal dunes vegetation. At each site I have made data collection along one transect (so all the 30 transects have different lengths and sometimes very different (namely between beaches), the smaller with 8 m and the bigger with 130 m). I have calculated different ecological indices which gave me naturally 30 different values for each site. Now, I grouped the 10 beaches in two groups (2 different environmental conditions: erosive beaches (12) and not erosive beaches (18)). May I compare the two groups with all the data (with all the complete transects) or I have to previously to cut to a common length to all the 30 transects in order to compare the data between erosive beaches and the other group of beaches?