Individual-based modeling of fish population dynamics of an artificial reef community: Effects of habitat quantity and degree of refuge provided

The objective of the model is to quantify the effects of artificial habitats on the dynamics and productivity of an associated three species community.  Hourly growth, reproduction, movement, and mortality are tracked.  We performed 50 year simulations with increasing numbers of artificial reefs uniformly placed on a grid, at three levels of fixed recruitment, and at two levels of refuge protection.  Model predictions of total abundances, weight-at-age, and spatial distributions compared favorably (qualitatively) with observed data.  Focal community biomass and abundance, and average individual growth are driven by density dependent competition for food resources.  Model simulations show depressed prey densities around the artificial reefs (feeding halos), and that total biomass of focal species was positively related to recruitment level and number of reefs on the grid.  The degree of refuge provided by the reefs highlights density dependent effects inherent in the model, showing that when refuges provide maximum protection biomass and abundance increases, but competition for resources intensifies and individual growth decreases.  There is a tradeoff between abundance/biomass of the population and growth.  The model is under development and field data targeted to estimate some key model inputs and corroborate model predictions are being collected in a parallel field study.