In Part IV of this podcast, I described how sea ice forms and traps marine algae that can grow in the ice before it’s released back into the ocean when the ice melts. This process drives marine productivity in Antarctica starting with krill, a small crustacean that is a keystone species there. In this episode, the life cycle of krill is described and why it is so important in the marine food web. The rich diversity of benthic invertebrates also is presented and the current threat to this community by the invasion of king crabs from South America. A unique group of ice fish also is described and how these species evolved in isolation in Antarctica in waters at less than 5 degrees C.  These fish can withstand freezing temperatures and some absorb oxygen from the water directly through their skin.