A model is proposed for studying the influence of the duration of a nonreproducing life stage on the dynamics of marine intertidal populations. Analysis of the model shows that this system, in which the time delay (the nonreproducing stage) is in a density independent term, has two solutions. When the nonzero solution exists it is a stable point. A randomly occurring environmental disturbance, to which only the nonreproducing stage is resistant, is superimposed on the basic deterministic equation. Average extinction time, estimated by simulation, appears as a a nonmonotonic function of the duration of disturbance. The graph of extinction time has multiple extrema with minima occuring where the ratio between the duration of the resistant stage and the duration of disturbance is an integer. This phenomenon is more sharply manifested when the intrinsic growth rate and frequency of disturbance are relatively large and when the variance in the duration of disturbance and the duration of the resistant stage is not too large. Increasing patchiness of the habitat has a minor effect on the pattern of dependence of the extinction time on the ratio between the juvenile and environmental periods. The suitability of the model for describing the marine intertidal system of the northern Red Sea is discussed, and it is suggested that the duration of the larval stage can determine adult population dynamics.