No it isn't a mystery at all. Read up a little on invasive marine species and how they travel in the ballast tanks of ships.
All of the things in the pictures are small swimmers. Now think about the ships that do cold water research near the North Pole. Anyone want to bet they have ballast tanks.
Next think about what happens when it gets warm at the North Pole. That's right, it gets cold at the South Pole. Where do you think those ships go?
Invasive Marine Species
This map shows the range of ther Blue whale and you can see that he can be found everywhere.