MORPHOLOGY AND DISTRIBUTION OF COSCINODISCUS SPECIES FROM THE OSLOFJORD, NORWAY, AND THE SKAGERRAK, NORTH ATLANTIC

Abstract

The morphological similarity of Coscinodiscus asteromphalus, C. centralis, and C. concinnus may cause identification problems, as stated in the first phytoplankton reports from the Oslofjord and the Skagerrak at the turn of the century. Light and electron microscope examinations of clonal cultures and field samples showed the distance of the single ring of labiate processes from the margin, the distance between the processes, the presence or absence of wide interstriae, and the structure of the valve centre to be distinctive features at the specific level. Observations made on plankton samples collected during the last 30 years have shown that C. radiatus, C. centralis, C. concinnus, C. granii and C. asteromphalus are regular members of the plankton flora of the Oslofjord and the Skagerrak, the two latter less common in number and occurrence than the others. Coscinodiscus wailesii was first observed in the area in the autumn of 1979, two years after its arrival in the English Channel. Our investigation includes examination of type material of C. wailesii.