We analyze an age-structured population model of marine invertebrates with life stages composed of sessile adults and pelagic larvae contained in a local habitat. In the model, space is the principal limiting resource. The long time simulation of this kind of coupled systems is difficult. Here, we propose a numerical method in order to investigate the asymptotic behavior of the solutions. Our numerical analysis provides an original knowledge about the mechanisms that govern the stability of the system as, for example, the different performance depending on the vital functions. (C) 2013 Elsevier B. V. All rights reserved.