A Survey of the Standing Crop of Plankton of the Florida Current.

VI. A Study of the Distribution of the Pteropods of the Florida Current

Of the local pteropod population, 29 species were identified, 21 of Euthecosomata, the rest Peracle, Cymbulia, Corolla, Desmopterus and Thliptodon. The abundance and distribution of this population showed the following variations in relation to the water masses. Comparing the population in Bermuda with the 10-mile station and the 40-mile station the ratio of the mean catch per mile was 1 : 6.5 : 16.7 for the upper 300 meters though the volume of the total plankton population in Bermuda was greater than in the Florida Current. For the deeper Tongue of the Ocean the mean catch per mile for the same zone was much greater than at the 40-mile station. The percentage of Limacina at the same three stations, same order, was 82 per cent, 50 per cent, 35 per cent. Of the two series at the 10-mile station a positive correlation of the mean day level and the depth of the 15°C isotherm was found for seven species common to both series. The second series in warmer water showed a level 96 meters lower. A similar situation with seven soecies common to the second series and the 40-mile station showed the same relation, the latter being 51 meters deeper. At each of the three series of the Florida Current positive correlation was shown of the mean day level with both the degree of vertical diffuseness and the degree of diurnal migration. For both the SL 10-mile station and the SL 40-mile station the juvenile Cavolinidae give evidence of a double diurnal migration. Three tables and 39 graphs are included.