Seeing in the deep
The deep sea is the largest habitat on earth. Its three great faunal environments – the twilight mesopelagic zone, the dark bathypelagic zone and the vast flat expanses of the benthic habitat – are home to a rich fauna of vertebrates and invertebrates. These animals experience a visual scene that changes drastically with depth – from extended scenes illuminated by the down-welling daylight in the upper layers of the ocean to scenes dominated by point source bioluminescence in the deep. This has had a profound effect on the designs of deep-sea eyes, both optically and neurally, and this has led to the evolution of a great diversity of visual adaptations in deep-sea animals. By using portable electrophysiological and optical methods at sea, we have previously shed light on how well deep-sea fishes and cephalopods (squids and octopuses) are able to see. By theoretically modelling the eyes and visual environments of deep-sea animals it has also been possible to predict what these animals are able to see and why certain visual adaptations – such as gigantic eyes – have evolved. Some of the questions we are currently pursuing include:
1. How much information can deep-sea eyes provide their owners, and how is this related to lifestyle and habitat depth?