FURTHER OBSERVATIONS ON THE DIURNAL MIGRATION OF COPEPODS IN THE GULF OF MAINE

¹ From the Woods Hole Oceanographic Institution and the Laboratory of General Physiology, Harvard University

1. Observations were made on the diurnal migration of copepods in relation to submarine irradiation and other external factors at a 54-hour and a 24-hour station in the Gulf of Maine using the same methods as previously. The zoöplankton consisted almost entirely of Calanus finmarchicus with a small number of Metridia lucens. The length of the copepods varied much less than was the case previously.

2. The variation with depth of the light intensity, the temperature, chemical constituents, and the phytoplankton was observed. During the first station the temperature was found to fluctuate widely.

3. At the station in the deep part of the Gulf all groups of Calanus and Metridia migrated to a depth of 120 meters or more during the daytime and moved upwards to levels of from 6 meters to 42 meters at night. At the station on Georges Bank Calanus was confined to the surface strata, undergoing only a very limited migration, but Metridia carried out an extensive migration.

4. The migration of the copepods was found to be more closely correlated with the changes in the submarine irradiation than with changes in the hydrographic conditions or in the phytoplankton. However, great variability in the behavior was observed. This appears to be due to differences in the physiological condition of the animals and represents the indirect action of the environment.

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