This work presents a discrete time model for the dynamics of a size-classified benthic population with planktonic larvae. Recruitment, decoupled from local reproduction by larval dispersal, is represented in the model as an external subsidy to the local population. Analysis of the model reveals the importance of recruitment and growth plasticity in determining the stability of an equilibrium which always exists. Growth plasticity promotes stability, while recruitment plays the opposite role. The stability results provide a scale to which observed levels of recruitment, mortality, and growth can be compared, in terms of their effects on population dynamics.