The importance of larval supply to the community ecology of rocky shores is described in Chapter III. Production of larvae depends on the size of the reproducing population, the rate at which offspring are produced, and the length of the reproductive season. Rate of reproduction may depend on food supply, in turn influenced by water movement, light availability, temperature and competition. Recruitment in species with widely-dispersed larval stages may be more sensitive to variation in those environmental factors affecting conditions for successful development and transport to appropriate habitats. Survival of larvae will be affected by water temperature and food supply. The inshore transport of larvae can depend on water movement which, in turn, is influenced by wind direction.

Community structure and dynamics are strongly influenced by larval supply. Much of the natural variation around the mean abundance in stable communities might be due to variations in larval supply. However, more unstable systems can easily be pushed in a particular direction by a series of chance events. For example, in a Fucus-barnacle mosaic, a low recruitment of limpets or a high recruitment of barnacles might lead to reduced limpet grazing and, therefore, more Fucus escapes resulting in a Fucus-dominated community. Variable recruitment can generate instability. If a dominant competitor has a low recruitment, an inferior competitor might be able to invade the community, exploiting new space that becomes available.

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