Seagrass corridors and tidal state modify how fish use habitats on intertidal coral reef flats

Identifying pathways that animals use to move among ecosystems has become a focus for improving conservation planning. The function of habitat corridors in facilitating animal movement among terrestrial ecosystems is well established. By contrast, the role of habitat corridors for the movement of marine animals is poorly understood. We used underwater video cameras to evaluate the effects of seagrass corridors and water depth on fish abundance, and the arrival of prey and predatory species on intertidal coral reef flats in eastern Australia. Cameras were placed in intertidal seagrass and unvegetated habitats during incoming tides and recorded fish that moved across these habitats. We found some evidence that fish were more abundant over intertidal seagrass, particularly garfish Hyporhamphus regularis ardelio, striped barracuda Sphyraena obtusata and striped grunter Pelates sexlineatus, but most species did not appear to use the intertidal seagrass as a corridor. Prey fish were generally more abundant at shallower water depths, whereas predators were more common in deeper water, but many species were present over intertidal flats throughout the incoming tide. Our findings show that the movement of fishes across intertidal flats is dynamic, and depends on the species of interest, the composition of intertidal seascapes and tidal condition. Understanding how biotic and abiotic factors interact to influence fish movement and shape patterns in habitat use is a critical challenge for conservation planning in shallow coral reef seascapes.