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Response of Euphausia pacifica to small-scale shear in turbulent flow over a sill in a fjord.
MedLine Citation:
PMID:  21954320     Owner:  NLM     Status:  Publisher    
Abstract/OtherAbstract:
Zooplankton in the ocean respond to visual and hydro-mechanical cues such as small-scale shear in turbulent flow. In addition, they form strong aggregations where currents intersect sloping bottoms. Strong and predictable tidal currents over a sill in Knight Inlet, Canada, make it an ideal location to investigate biological behaviour in turbulent cross-isobath flow. We examine acoustic data (38, 120 and 200 kHz) collected there during the daylight hours, when the dominant zooplankters, Euphausia pacifica have descended into low light levels at ∼90 m. As expected, these data reveal strong aggregations at the sill. However, they occur consistently 10-20 m below the preferred light depth of the animals. We have constructed a simple model of the flow to investigate this phenomenon. Tracks of individual animals are traced in the flow and a variety of zooplankton behaviours tested. Our results indicate that the euphausiids must actively swim downward when they encounter the bottom boundary layer (bbl) to reproduce the observed downward shift in aggregation patterns. We suggest that this behaviour is cued by the small-scale shear in the bbl. Furthermore, this behaviour is likely to enhance aggregations found in strong flows at sills and on continental shelves.
Authors:
Debby Ianson; Susan E Allen; David L Mackas; Mark V Trevorrow; Mark C Benfield
Publication Detail:
Type:  JOURNAL ARTICLE     Date:  2011-9-4
Journal Detail:
Title:  Journal of plankton research     Volume:  33     ISSN:  1464-3774     ISO Abbreviation:  -     Publication Date:  2011 Nov 
Date Detail:
Created Date:  2011-9-28     Completed Date:  -     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  9882936     Medline TA:  J Plankton Res     Country:  -    
Other Details:
Languages:  ENG     Pagination:  1679-1695     Citation Subset:  -    
Affiliation:
Fisheries and Oceans Canada , Institute of Ocean Sciences , Po Box 6000, Sidney, BC , Canada V8L 4B2.
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