Zooplankton community structure in response to turbulent flow over a sill in Nootka Sound

Senior thesis written for Oceanography 445

[author abstract] Zooplankton behaviors have been well studied, and their movement in the water column can be activated by a number of reasons. They may migrate or maintain position in preferred light levels, avoid predation or relocate in search of food sources. In this study, I focused specifically on Euphausia pacificas’ response to small-scale turbulent flow over a sill in Muchalat inlet of Vancouver Island, Canada. ...The study consisted of continuous transects over the same location to compare responses to different tidal currents. As expected, the zooplankton aggregations were forced against the sill on the upstream side. Movement of these aggregations tracked the targets moving below their preferred depth or above. I suggest that their movements are a response to turbulence caused by tidal flow against the sill. My results show that euphausiids must actively swim downward to avoid being pulled over the sill by currents.

University of Washington School of Oceanography