SHORT COMMUNICATION Vertical distribution of virus-like particles (VLP) and viruses infecting Micromonas pusilla during late summer in the south- eastern Skagerrak, North Atlantic

Vertical profiles were made at one offshore station and one coastal station, on 4-5 September 1996, in the south-eastern Skagerrak. The surface water of the two stations differed significantly with respect to both temperature and salinity, as the outer station (A) was situated in high-saline water originating from the North Sea, while the low-saline surface water at the inner station (B) was influ- enced by the Baltic current. Virus-like particle (VLP) abundance was 5 x 109-25 x 10' H in the 0-50 m water column. Maximal VLP values were found in the surface water, although a lower number was detected in the low-saline surface water (0 m depth) at station B. Viruses infective to Micromonas pusilla were estimated to -0.01% of the VLP number. The ambient concentrations of dissolved inorganic nutrients were typical for a stratified summer situation, i.e. generally low in the surface waters, although a raised ammonium concentration was associated with the sharp halocline at 5 m depth at station B, and all nutrient levels were increasing below 30 m depth.