The present dataset includes diverse information on individual traits and population parameters from a mussel population in a bathymetric gradient and with monthly frequency (from March 2019 to February 2020) from two rocky shores at Le Petit Minou, France (lon: -4.615860; lat: 48.339118). Each of the two shores was at the East and West side of the Le Petit Minou beach. Sampling was carried out on a triplicate quadrat from each rocky shore. The present dataset includes all the raw data from these quadrat samples as well as derived information.  “Length_data.csv” table includes: 36670 measures of shell length from all living individuals in each sample “Biometry_data.csv” includes the biometric measures from 10 individuals from each sample (n total = 720 individuals), including: total weight, flesh wet weight, dry flesh weight, shell wet weight, shell dry weight, shell length, and condition index (Flesh Dry Weight / Shell Length3) “Samples_summary.csv” includes: the geographic coordinates, bathymetric position, eastness and northness orientation of quadrats and the raw data including the number of counted individuals, number of recruits (shell length 1.07mm), observed covered area, proportion of covered area inside the quadrat, and crowding index (observed covered area/sum of individuals basal area) and the population parameters expressed per meter square of a fully covered area, including total density of individuals, density of non-recruits, density of recruits, median length of individuals, median length of non-recruits individuals, maximum length of individuals, total biomass.  All individual traits and population parameters are associated with their corresponding shore, date and replica, which is also represented by a Sample_ID, e.g., 2019.3ER1, where 2019 is the year, 3 is the month (March), E is the shore (East) and R1 is the replica number (1 out of 3).