PLANKTON OP THE GULF OF MAINE 
43 
of the gulf, especially its southwestern part including the Massachusetts Bay region, as 
the chief source of the copepod plankton of its center. It is probable, also, that 
Georges Bank is an important nursery for copepods, since nauplii occurred in some 
numbers among the adult calanoids off its northern slope on March 11, 1920 
(station 20064). 
The vernal increase in the numbers of copepods present in the Massachusetts 
Ba}^ region, and wherever else reproduction takes place actively, is many times greater 
than the bulks of the catches might suggest, the production of young coupled with 
the dying off of the parent stock giving the copepod plankton of the coastal waters a 
juvenile character in spring with relatively few large adults. Thus, there were only 
about 8,000 adult Calanus per square meter among some 500,000 copepods, mostly 
young Calanus, off Gloucester on May 4, 1915 (station 20066)— that is, a little less 
than 2 per cent. After the peak of production is past, however, and with the growth 
of its product toward maturity, the percentage of large Calanus and adults of other 
species once more increases, until they form about one-third of the copepod popula- 
tion at the mouth of Massachusetts Bay by the end of June or first week in July 
(Bigelow, 1922, p. 136). During the late summer, when the stock of copepods of all 
species and ages dwindles, adults may locally amount to as much as one-half or two- 
thirds of the total (fig. 30). 
Coincident with the vernal propagation of copepods various young medusae 
commence their period of pelagic existence, as, for example, Staurophora, which ap- 
pears in swarms in Massachusetts Bay in May. Although we have never found young 
medusae more than a minor factor in the zooplankton of the gulf outside the outer 
headlands in spring, they often dominate inclosed waters for a brief period in May. 
This, for instance, was the case in Gloucester outer harbor on May 3, 1913, when 
Sarsia tubulosa, Bougainvillea superciliaris, Ratkkea blumenbachii, Tiaropsis dia- 
demata, Obelia, and Staurophora were all abundant, and iEquorea and Cyanea 
tolerably common — all of them, no doubt, liberated close at hand, and certainly very 
recently, for none was found there a month earlier. We also found young hydro- 
medusae swarming in the harbor of Yarmouth, Nova Scotia, in May, 1915, and this 
probably applies to similar situations all along the complex coast line of the gulf from 
Cape Cod to Cape Sable; also to the shallow waters of Georges Bank, where young 
Hybocodon and Staurophora are sometimes sufficiently plentiful to "color” the tow 
in April (Bigelow, 1914a, p. 414). 
The larvae of echinoderms, worms, and mollusks of many kinds likewise 
appear in the plankton along shore in spring. Most of these, in fact most of the 
pelagic animals of coastwise origin, are confined to estuarine situations in the Gulf 
of Maine, to sounds and bays among the islands, or to a coastal belt only a few 
miles wide at most, as noted above (p. 32), and hence may be passed over without 
further comment here. The early stages of the common rock barnacle (genus 
Balanus), however, are so abundant and so conspicuous that they deserve a word of 
mention. In 1913, as I have elsewhere described (Bigelow, 1914a), barnacle 
nauplii 20 were taken in large numbers in the Isles of Shoals-Boon Island region 31 
20 Here let me correct an error in an earlier paper, namely, that “ barnacle ” eggs were taken in the tow in March and April of 
1913 (Bigelow, 1914a, p. 108). Barnacle eggs are not set free to float, but are nursed by the mother until the nauplii hatch out. 
For accounts and figures of the early stages of Balanus see Hoeek, 1909. 
21 No doubt young barnacles are as common in Massachusetts Bay as in any part of the gulf, though somehow we have chanced 
to miss their season there. 
