Plankton distributions in relation to physical oceanographic features on the southern Malin Shelf, August 1996

The distribution of plankton in relation to physical oceanographic features on the southern Malin Shelf and in the North Channel of the Irish Sea was investigated during August 1996. The near surface 13.5 degrees C isotherm a nd 35.20 isohaline marked the location of the Islay and Irish coastal front s, respectively. An additional salinity front was observed to the south-eas t of Islay. A mergence of the Irish coastal front and the salinity componen t of the Islay front suggested that, at certain times, a frontal boundary s eparating coastal and oceanic water may extend from south-west Ireland nort h along the western Scottish Shelf. The presence of highly saline (>35.35) water on the outer shelf indicated the intrusion of Atlantic water. The frontal boundaries influenced the distribution of plankton on the south ern Malin Shelf and in the North Channel. The outer shelf region was charac terized by the presence of Chaetoceros atlanticus, Gonyaulax polygramma, Ox ytoxum scolopax, Doliolum gegenbauri, Sagitta tasmanica, and S. maxima. Hal osphaera minor and Limacina retroversa were distributed between the shelf e dge and the Irish coastal and Islay fronts. Gyrodinium aureolum dominated t he phytoplankton of the Islay front but in contrast, Ceratium longipes was restricted to the east of the Islay Front. The distinct spatial separation of species suggested that there was no exchange of southern Malin Shelf and North Channel water at the time of the study.