Seasonal Krill Aggregation

node · earth · High-latitude and eastern-boundary upwelling systems

The seasonal concentration of euphausiids into dense swarms where upwelling or ice-edge production makes enough phytoplankton to support them. It is the variable that decides the migration: blue whale feeding grounds are not where the water is nicest but where krill is dense enough for lunge feeding to pay. In the Southern Ocean the driver is the ice edge and the circumpolar production it supports; in the California Current it is wind-driven coastal upwelling, and the whales there preferentially target the larger, more lipid-rich Thysanoessa spinifera in shallow water over Euphausia pacifica offshore. The route follows the food, and the food follows the physics.