How do fragmented seascapes influence fish movement behaviour? Insights from an individual-based model (IBM) using potential fields

Analysing movement is essential for understanding population dynamics and spatial distributions and has strong implications for the design of natural reserves. In coral reef systems movement patterns of fishes are particularly important as they are an essential part of the ecosystem and many fish species undertake diel migrations using different habitats. However, guidance mechanisms of these movements are not yet well understood. In this study we thus aim to elucidate potential causal mechanisms and spatiotemporal patterns of reef fish movements. To this end, we simulate the movement decision-making of the parrotfish Chlorurus sordidus by linking it with two main functional landscape features (food availability and predation risk) in a novel approach combining individual-based modelling (IBM) with potential field methods. Model results indicate that populations are more irregularly distributed among coral reef patches the more the coral reef habitat becomes fragmented and reduced. The spatial configuration of the seascape thus influences spatial exploitation of microhabitats, which may have far-reaching consequences on the ecosystem. By shaping individual space use patterns, the physical features of the environment may also impact encounter rates between individuals and thus the overall social structure of a population. Based on our findings we believe our model can provide valuable insights into the spatio-temporal variability of local herbivore fish populations. Moreover, the integration of potential field methods into IBMs seems a promising strategy to represent the complexity of dynamic decision-making of animals in applied models.