The distribution of planktonic dinoflagellates and their cysts in the eastern and northeastern Atlantic Ocean



Data are presented on the distribution of both planktonic dinoflagellates and their cysts from 20° N to 70° N and from the western coasts of Europe and Africa to 25° W in the eastern and northeastern Atlantic Ocean. Although most of the thecate dinoflagellates are widely distributed, sometimes with a discontinuous pattern, the cysts are generally more restricted. There is an increase in the ratio of cyst types to thecate plankton and in cyst diversity from ocean to inshore and from low to high latitudes; in both cases paralleling an increase in diversity of the plankton. Cyst distributions may also be discontinuous, occurring around the British Isles and also in the upwelling area off N.W. Africa. Particular species show similar distribution patterns for cyst and thecae e.g. Polykrikos schwarzii; distribution patterns where the cyst is less widely distributed than the thecae e.g. Spiniferites bentori/Gonyaulax digitalis; and where the cysts are more widespread than the thecae as in the problematical Gonyaulax spinifera‘complex’. Difficulties identified in comparing data sets include the lack of detailed knowledge of dinoflagellate life cycles, the need to know more about environmental parameters affecting encystment, and knowledge of cyst transportation and preservation in sediments. Overall cyst distribution patterns may be compared to the broad coccolithophorid zones recognised in the Atlantic Ocean.