Assessing the impact of biodiversity changes on reef fisheries using an individual based model

June 28 to July 02, 2004, Okinawa, Japan Higher biodiversity is usually loosely associated with good quality systems relative to human use. But does biodiversity really have an effect on the quality of ecosystem services, such as coral reef fisheries yield? To address this question, we built an individual-based model of a hypothetical coral reef ecosystem wherein fish and invertebrate diversity is interpreted as individual variability among a set of static traits. The model is composed of 2 interacting layers: a cellular-automata reef bottom and an individual-based simulation of fishes, invertebrates and fishers, which interact with each other. It incorporates foraging, predation, and competition among fish agents; movement, growth, reproduction, and mutation for each fish agent; and fishing for fisher agents. The model was first run through an evolutionary phase wherein initial parameter values were fed into the model and then run for 52,000 time steps to generate a system of diverse fish and invertebrate agents. In the ecological phase, mutation was turned off and fisher agents were introduced to selectively fish high biomass cells until the system was depleted. Several simulations for the ecological phase were run at different initial levels of diversity and fishing pressure. Results showed that the effect of diversity on cumulative total fish catch was most evident in the runs wherein the starting diversity was only 1% of the original number of unique agents generated through the evolutionary phase. Above this, individual genotypic variability had no significant effect on total fish catch.