MEPS 329:225-238 (2007)  -  doi:10.3354/meps329225

ABSTRACT: Habitat structural complexity is often considered beneficial for prey species because it reduces the foraging efficiency of predators. However, for site-attached, territorial prey, such as many damselfishes, structural complexity at specific scales may be detrimental. Since the location of territorial prey could be highly predictable to predators, the ability of such prey to detect approaching predators may be limited by high-relief structural complexity. The bicolor damselfish Stegastes partitus is abundant and randomly dispersed on coral heads in fore reef habitats in the Florida Keys but is less abundant on back reef habitats, where it aggregates in open patches within fields of gorgonian soft corals. We hypothesized that the complex gorgonian habitat limits the visual field for S. partitus, increasing the uncertainty about predation risk, and is therefore a low quality habitat. We found that males occupy territories with visual fields larger than the fields around randomly selected points. Experimentally reducing the visual field around males decreased both their courting rates and the distance they ventured away from the nest. Males in the back reef spent more time away from their nests—potentially taking greater risks—towards the peak of the spawning cycle than males in the fore reef, which may be related to their lower reproductive success on the back reef. Experiments exposing male S. partitus to a fish predator suggest that a limited visual field (an uncertain situation) presents a more risky situation than a clearly visible but ‘contained’ predator. Our results demonstrate that a limited visual field around territorial, site-attached prey fish alters their behavior such that mating and feeding may be compromised. Fish abundance was negatively correlated with soft coral density but not with the number of potential territories or surface rugosity, suggesting that the visual seascape may be important for the fish distribution patterns. We suggest that habitat complexity at the appropriate scale mediates the distribution and possibly also the abundance of territorial prey fishes through the effects of the size of the visual field on fish behavior.

KEY WORDS: Seascape · Habitat complexity · Animal distribution · Visual field · Behavior · Fish