PLANKTON OF 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 lor 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 

 Bav 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 

 medusas 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 , Rathkea blumenbachii, Tiaropsis dia- 

 demata, Obelia, and Staurophora were all abundant, and .ZEquorea 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 



» 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 Hceck, 1909. 



» 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. 



