Buoyancy of post-fertilised Dissostichus mawsoni eggs and implications for early life history

Gametes from gravid Antarctic toothfish (Dissostichus mawsoni) were combined in vitro and buoyancy measurements were made on fertilised eggs during early development. Eggs were strongly positively buoyant, indicating that they would ascend quickly in the water column and reside near or in association with the underside of sea ice, which covers most of the spawning habitat during winter. An association with sea ice may provide: protection from the turbulence of ice-free surface waters, a mechanism that modifies the velocity of advection by surface currents, and a habitat with a concentrated planktonic food source during spring months. An association with sea ice would also create spatial differences in egg advection patterns for eggs produced spanning a large geographic area. The effects of climate change on sea ice formation and melting patterns, or fishery-induced changes in the spatial density of adults could then influence juvenile advection patterns and influence survival.