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

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Abstract
Observations were made in relation to submarine irradiation and other external factors at a 54-hr. and a 24-hr. station. The zooplankton consisted almost entirely of Calanus finmarchicus with a small number of Metridia lucens. The length of the copepods varied much less than in earlier studies. The variation with depth of the light intensity, temp., chemical constituents and phyto-plankton was observed. During the 1st station the temp. fluctuated widely. At the station in the deep part of the Gulf all groups of Calanus and Metridia migrated to a depth of 120 m. or more during the daytime and moved upwards to levels of 6-42 m. 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. The migration was 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, apparently due to differences in the physiological condition of the animals and representing the indirect action of the environment.