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Experimental Evidence for Aggregation of Salmon Louse Copepodids (Lepeophtheirus Salmonis) in Step Salinity Gradients

Published online by Cambridge University Press:  11 May 2009

Peter Andreas Heuch
Peter Andreas Heuch
Affiliation:
Department of Biology, Section of Marine Zoology and Marine Chemistry, University of Oslo, PO Box 1064 Blindern, N-0316 Oslo, Norway
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Extract

The copepod Lepeophtheirus salmonis Krayer (Copepoda: Caligida), the salmon louse, is a parasite of salmonids. The vertical distribution of the infective stage, the copepodid, was studied in salinity gradients with one step increase of 15‰ (154%e> on top of 304‰), 5‰ (25–4‰ on top of 30–4‰) and 2%> (28–4‰ on top of 304‰) in 1-m perspex columns. Copepodid distribution in a linear gradient, where the salinity increased from 154‰ at 0 cm depth to 304‰ at 87–5 cm, was also recorded. Homogeneous 304‰ salinity columns served as the control. In these, the animals gathered in the top section of the water column in response to 1 h of light from above, and spread downwards in response to 4 h of darkness. In columns with a 15‰ step increase in salinity with depth, copepodids aggregated just underneath the discontinuity irrespective of light conditions. In step salinity gradients of 5‰ and 2‰ S, under both light regimes, animals were significantly more numerous in the step sections compared with the control. In the linear gradient, significant numbers of copepodids accumulated at approximately 20‰ salinity when subjected to 1 h of light. In the dark, there were no significant aggregations. Copepodids were found in 15–17–2‰ salinity in all linear gradient experiments.

Type
Research Article
Information
Journal of the Marine Biological Association of the United Kingdom , Volume 75 , Issue 4 , November 1995 , pp. 927 - 939
Copyright
Copyright © Marine Biological Association of the United Kingdom 1995

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