Phytoplankton odor modifies the response of Euphausia superba to flow

Antarctic krill, Euphausia superba, are critical components of the Antarctic food web as well as important targets for conservation and management. Krill behavior has important effects on demographic properties and aggregation characteristics, but remains incompletely known. Krill clearly respond to different environmental stimuli such as light, flow and chemicals, but few studies have quantified these behaviors. We examined the behavior of krill in well-quantified current speeds in a laboratory flume and examined interactions of phytoplankton odor and flow. Krill are sensitive to flow speeds as low as 1 mm s−1, and flow polarizes krill swimming and orientation in the up-current direction. Phytoplankton odor increases the sensitivity of krill to flow, and induces area-restricted search behaviors that presumably allow krill to exploit food patches efficiently. The ability to quantify krill behavior could have important consequences for understanding demographic processes and the properties of krill aggregations.