Meeting Abstract
Sunlight in the ocean exponentially decreases with depth, creating a structured and directional optical environment in the midwater habitat. Because of decreasing light availability, it is thought that the distance over which visual interactions among marine animals can occur decreases with depth. This is thought to have major ecological and evolutionary effects; for example, the lower metabolisms of deep-sea cephalopods have been explained by relaxed visual predation with depth. However, species inhabiting the dim twilight zone are also thought to increase relative eye size with depth to cope with low light levels; we previously demonstrated this in cephalopods by comparing measured eye size and body size from species in the Smithsonian collection to species depth distributions and light habitats. Here, we use these data to model maximum theoretical visual ranges for ecologically relevant visual targets such as non-bioluminescent patterning, silhouettes against background light, and bioluminescent patterning. We use a new computational model of contrast attenuation and sighting distances in low-light environments to determine best-case sighting distances for visual targets given eye size, water clarity, downwelling light level, and target size. We discuss how cephalopod eye size affects the potential for resolution with depth, maximum distances over which vision can be used for various tasks, and ultimately the distances over which visual interactions among animals can occur in the deep sea.
