The maintenance of species diversity is influenced by processes originating both within and outside the ecological community of concern. Along the Norwegian Skagerrak coast, the number of fish species displays variability around a rather stable long-time average. Using a mechanistically based first-order autoregressive model with environmental forcing for the species number, we demonstrate for this system the presence of richness-dependent regulation of species diversity. We explicitly model the niche space as a carrying capacity of species diversity and the intrinsic community feedback as a richness-dependent regulation. Wind stress, temperature and the North Atlantic Oscillation (NAO) are used as environmental variables. This general and flexible model successfully captures the community dynamics of fish in the coastal areas of the Norwegian Skagerrak coast and thereby demonstrates the validity of developing general models of biodiversity patterns.