Mytilus galloprovincialis on concrete seawalls lives and becomes extinct within one generation. The population consisted of members of the same age found there is the first settlement cohort. The numbers of recruited cohorts settled onto the bed of such first settlement cohort are usually less one or two digits of the first settlement cohort. During the spat settlement period, the number of recruited cohorts is proportional to the population size or biomass of adult mussels. This is because recruited spat settle only on the byssus of adult mussels and never directly on concrete seawalls. The recruited cohort is thinned out quickly due to competition with adults and the predation intensity by crabs. Since this mussel does not sustain the next generations by recruitment, this species must continuously seek a new habitat every generation.