Antarctic silverfish: life strategies of a key species in the highAntarctic ecosystem

Introduction 242 Biology of the Antarctic silverfish 243 Pleuragramma and the neutrally buoyant clade of nototheniids 243 The evolution of the neutrally buoyant clade and the Antarctic silverfish 243 Paedomorphy and the pelagic lifestyle of the Antarctic silverfish 244 Body morphology 244 Depth and geographic distribution 244 Early life history 245 Reproduction 246 Age, growth and mortality 247 Feeding 249 Mechanisms of buoyancy 252 The Antarctic silverfish is relatively inactive for a pelagic species 253 Freezing resistance in adults and larvae 255 Sensory systems: eye and retina 256 Sensory systems: mechanosensory lateral line 256 Abstract Among the endemic notothenioid fish of Antarctica, the Antarctic silverfish (Pleuragramma antarcticum) is the only species in which all developmental stages live throughout the water column. It is widely distributed in the shelf waters around the continent, inhabiting both open waters and areas of pack ice at depths from 0 to 900 m. In successfully occupying this habitat, it evolved a suite of specific biological, ecological and physiological adaptations to the environmental conditions in the cold and highly seasonal Antarctic waters. Specialization for the pelagic environment evolved over millions of years enabled life under unusual environmental constraints and colonization of the pelagic realm of the Antarctic continental shelf. A sudden change of environmental conditions driven by the current rapid climate change could negatively affect this weak equilibrium, with a catastrophic cascade effecting higher trophic levels. Indeed, as both adults and early life stages of the Antarctic silverfish appear to be strongly dependent on sea-ice, this species would be especially sensitive to climatic or oceanic changes that reduce the extent of sea-ice cover or the timing of formation of coastal polynyas.