DIURNAL MIGRATION OF PLANKTON IN THE GULF OF MAINE AND ITS CORRELATION WITH CHANGES IN SUBMARINE IRRADIATION

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Abstract
Observations on the vertical distribution of copepods were made during 12-, 24-, and 48-hr. periods using 5 closing nets towed simultaneously at different depths. The penetration of daylight into the sea was measured at the same time (previously reported) . The vertical distribution of the 3 spp. studied was: Centropages typicus inhabited the stratum above the thermocline (10-20 m.), Calanus finmarchicus was irregularly distributed, and Metridia lucens occurred below the thermocline. Length measurements in each group showed that the longer individuals tend to be found at the greater depths. The adult [female][female] of Metridia exhibited the most marked diurnal migration, the level of maximum abundance rising in the afternoon and during the night and falling in the morning. These movements coincided to a considerable extent with changes in submarine irradiation. The changes in the cases of the other groups of copepods were slight or quite irregular. Light appears to be the most important factor controlling diurnal migration, and information is obtained on various of the theories regarding the manner in which light exerts its effect.

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