The role of cephalopods in the world’s oceans: general conclusions and the future

Abstract

In this volume we have considered the problems of investigation special to cephalopods. Almost all our knowledge of their general biology is restricted to the shelf-living, muscular, negatively buoyant (the Loliginidae and Octopodidae) or gas-supported species (the Sepiidae and Nautilidae) and members of the Ommastrephidae which move on to the continental shelves at certain seasons. These species of the continental shelves comprise only about 15% of all cephalopod genera and live in water of less than 300 m depth, which covers only 6% of the Earth’s surface. They do not represent the majority of cephalopod species or much of their total biomass; 85 % of genera are spread in the upper 2000 m and across the bottom of the deep oceans, which occupy 66 % of the Earth’s surface. Over 40% of these genera are neutrally buoyant by oil or chemical means and may have very different lifestyles from the forms we know from shallow water. Improvement of our knowledge of the ecology of deep water forms is hindered by our poor direct sampling methods and rests largely upon sampling from stomachs or regurgitations of the predators that eat cephalopods.