Floating offshore wind turbine (FOWT) plays a significant role in meeting emission targets over the next 20 years. The dynamic submarine electrical cable (DSEC) is a key component of FOWT. Its electric insulation system is intended to withstand a maximum conductor temperature of 90oC. However, biofouling growth, particularly mussel growth, can modify heat transfer around the cable and thus the maximum conductor temperature, as well as temperature fluctuation, affecting fatigue lifetime. In our work, we thermally character-ize mussels of various ages. The results revealed that the effective thermal conductivity of juvenile mussels is lower than that of mixed and only adult mussels. This variation in effective thermal conductivity with mussel’s age is related to the water porosity of the mussel’s layer. Using a numerical simulation, it founds that the thermal effect of the resulting global thermal resistance can lead the DSEC conductor wire to either overheat or cool down depending on the mussel’s age.