SECTION 1.— GENERAL SURVEY OF THE ANIMAL PLANKTON 



(ZOOPLANKTON) 



Few living zoologists have been as fortunately placed as were we on setting 

 sail on the Grampus from Gloucester on our first ocean ographic cruise in the Gulf of 

 Maine on July 9, 1912, for a veritable mare incognitum lay before us, so far as its 

 floating life was concerned, though the bottom fauna can be described as compara- 

 tively well known. Not but what an extensive list of pelagic crustaceans, ccelenter- 

 ates, and other planktonic animals had been recorded thence, but everything was 

 yet to be learned as to what groups or species would prove predominant in the 

 pelagic fauna; their relative importance in the natural economy of the Gulf; their 

 geographic and bathymetric variations; their seasonal successions, migrations, and 

 annual fluctuations; their temperature affinities, whether arctic, boreal, or tropic; 

 and whether they were oceanic or creatures of the coastal zone. We even had no 

 idea (incredible though it may seem at this place and day) what we should prob- 

 ably catch when we first lowered our tow nets into deeper strata of Massachusetts 

 Bay, for, so far as we could learn, tows had never previously been tried more than 

 a few fathoms below its surface. Nor did we at first realize, when the catch was 

 examined in our floating laboratory, that the little reddish copepods (Calanus) 

 darting to and fro in the glass dish, with a few large Sagittae (S. elegans) and young 

 euphausiids among them, would prove the backbone of the local planktonic fauna. 

 Such, however, has proved to be the case; for station after station, cruise after 

 cruise, year after year, have yielded cumulative evidence that (taken by and large) 

 the calanoid copepods are its predominant members at all seasons, except where 

 deposed from the leading role by the local or temporary swarming of some other 

 and usually larger animal. Our first summer's cruise was enough to show that 

 Calanus finmarchicus (large among copepods but small if judged by more familiar 

 standards) is the most important member of the plankton of the Gulf of Maine, if 

 bulk and numbers both be taken into account, and that it plays much the same 

 role there that it does in North European waters (Bigelow, 1914, p. 99). 



Calanus, as "red feed" or "cayenne," is well known to the local fishermen, 

 who are quite aware of its importance as food for fishes. 4 Side by side with Calanus 

 we have everywhere found its relative, Pseudocalanus elongatus (p. 275) ; but even 

 where the latter outnumbers the former, as sometimes happens, it adds but little to 

 the bulk of the catch, so tiny is it. We have so constantly found the copepod 

 Metridia lucens (p. 253), the chsetognath, or "glassworm," Sagitta elegans (p. 308), 

 the amphipod genus Euthemisto (p. 156), the euphausiid genera Thysanoessa (several 

 species, p. 133) and Meganyctiphanes (p. 147), the pteropod Limacina retroversa 

 (p. 116), the ctenophore Pleurobrachia pileus (p. 365), and (in deep water) the larger 

 copepod Euchseta (p. 230), associated with Calanus, that all these together may be 

 spoken of as the " Calanus community" (figs. 10 and 11), a community that domi- 

 nates the animal plankton from the Grand Banks on the north to Cape Cod (in 

 winter even to Chesapeake Bay) on the south, and from the coast line, on the one 

 hand, out to the continental slope, on the other. 



' See page 188 for a further account of this copepod. 

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