The distribution of siphonophores in a transect across the North Atlantic Ocean at 32°N

A study has been made of the distribution of siphonophores in a series of twelve oblique (0–1000 m) hauls made in a transect across the North Atlantic at 32°N, from 16°W to 60°W. A total of 66 species was identified, of which twelve were physonect siphonophores and the remainder calycophorans. In order to assess the changes in the population of the nineteen most abundant species, the species correlation coefficient matrix was calculated and six factors were extracted and rotated to simple structure. The first two factors indicated a clear east-west trend in the distributional pattern for thirteen of these siphonophore species. The coefficient of proportional similarity between stations was also calculated using the data for all of the species present.From this it was possible to divide the stations into two clear zones, namely the first three and the last eight, while the fourth station was intermediate. A comparison of these results with the TSD data for these stations showed that the fourth station was in the transitional zone between the eastern North Atlantic water and that characteristic of the Sargasso Sea, and that these two major water masses were distinguishable at all the depths where siphonophores would be expected to be found. It is concluded that there was some interrelationship between the physical features of the separate water masses and the composition of the siphonophore populations found in each. The problems involved in deciding on a sampling programme for such a study as this are also discussed.