PLANKTON OF THE GULF OF MAINE 
25 
forms and the smallest Crustacea and phytoplankton. In fact, Had we relied on 
surface hauls by daylight alone, we would hardly have suspected the existence of 
the abundant and varied planktonic fauna which peoples its deeper water layers. 
True, we have occasionally made rich catches of Calanus, with its companion 
animals, right on the surface in the middle of the day, as, for example, near Gloucester 
on July 22, 1912 (station 10012), near Lurcher Shoal on August 12, and off Penobscot 
Bay and Cape Elizabeth on August 14, 1914 (stations 10245, 10250, and 10251), and 
near Seguin Island on August 4, 1915 (station 10303) 13 ; while the extraordinary 
abundance of Calanus that characterized the40-100 meter stratum in the western side 
of the gulf during late July, 1916 (p. 18), was reflected in the presence of consid- 
erable numbers of these little crustaceans on the surface at the time, by day as well 
as by night. However, such occurrences have been exceptional. Huntsman, 
similarly, has characterized “ the presence of Calanus en masse at the surface between 
3 and 4 p. m., under a bright sun,” in the Bay of Fundy in September as an unusual 
event (Willey, 1919, p. 181). On the other hand, surface tows made in the gulf 
during the hours of darkness, especially if near midnight, have usually yielded an 
abundance of the calanoid copepods (even including the deep-water genus Euchseta). 
And the geographic locations of the stations where we have made rich surface catches 
by night point to a general diurnal migration of the Calanus community — upward 
after dark, downward about daylight — in the inner parts of the Gulf of Maine in 
summer, such as Esterly (1911 and 1912) and Michael (1911) describe for the San 
Diego region, 14 and with all the major planktonic groups sharing in it more or less, 
though perhaps none so regularly as the copepods. The data bearing on this point 
are not extensive, no particular attention having been paid to it in arranging the 
stations. We have occasionally found the surface practically barren some hours 
after sunset and before the first sign of sunrise, even at localities where the deeper 
waters supported a rich and varied plankton, as was the case in the western basin 
on August 9, 1913 (station 10088), and again on the 22d of that month a year later 
(station 10254). 
Of course, there is nothing novel in a vertical migration of this kind, similar 
phenomena having long been known and widely heralded in other seas; nor is it 
necessary to seek far afield to find a parallel in New England waters, for Peck (1896) 
long ago described the copepods as deserting the surface of Buzzards Bay almost 
completely during the daytime, to reappear there after dusk. 
It is unfortunate that our hauls have not been arranged to show at what precise 
time after sunset the copepods rise to the surface in largest number or how soon 
after midnight they sink again, a question of great interest from the physiological 
standpoint (p. 204). Few data have been gathered as to the actual vertical range 
through which this migration takes place in the Gulf of Maine; that is, how far up and 
down any individual animal may swim, or how universally or regularly the members 
of any group of animals indulge in it. It must be very widespread occasionally, at 
least among the copepods, for at times we have towed them in great numbers right 
13 In an earlier report (Bigelow, 1914a) it was stated by error that a largo haul of Calanus was obtained on the surface by day 
at station 10027; actually this station was occupied at about midnight. 
14 Data on the euphausiids, amphipods, pteropods, etc., will be found summarized in the accounts of these several groups. 
