The position maintenance behaviour of Neomysis integer (Peracarida: Mysidacea) in response to current velocity, substratum and salinity

The mysid Neomysis integer (Leach) is a common member of the hyperbenthos of the upper reaches of European estuaries. How this species maintains its position against the conflicting influence of tides and river flow forms the underlying question addressed in this study. The swimming behaviour of N. integer was examined in the laboratory by means of a novel annular flume with variable water current velocity. A range of experimental conditions was examined, including water current velocity, substratum type and salinity. Variations in behaviour (e.g. positioning in the water column, swimming speed and orientation to the flow) were recorded with video equipment. Current velocities, salinity and distribution of N. integer over a range of tides (including seasonal variations as well as spring and neap tides) were measured at the collection site at the East Looe River Estuary (Cornwall, England). Neomysis integer was found to sustain a swimming speed of 6 cm s(-1) in the laboratory and showed better position maintenance with a mud rather than sand substratum. This agrees with field observations at the East Looe River Estuary, where N. integer was found at the periphery of the water channel where flow velocity was ca. 8 cm s(-1). No clear behavioural trends were observed in relation to variations in salinity. In the field, N. integer occurred in salinities of 1-34 parts per thousand. (C) 1998 Elsevier Science B.V.