PLANKTON OF THE GULF OF MAINE 33 



The most conspicuous planktonic inhabitants of the gulf, of neritic nature, are 

 the two large scyphomedusan genera Aurelia (p. 362) and Cyanea (p. 357). Their 

 value as indices of coast water has long been appreciated in north European seas, 

 and they are both so large that they are usually visible as they float on or near the 

 surface, if present in any numbers; consequently, notes on their local presence or 

 absence, as seen from the vessel, afford a closer record of their distribution than do 

 the actual captures of specimens at the tow-net stations. Both of these medusae 

 are abundant along the shores of the gulf in summer, but Aurelia is so closely con- 

 fined to the immediate vicinity of the land that we have seldom seen it more than 

 a mile or two outside the 100-meter contour (or more than 15 miles from land), 

 while the zone within which it occurs regularly, if not abundantly, extends hardly 

 10 miles seaward beyond the outer headlands and islands (p. 363) ; nor have we found 

 it on Georges Bank, though the shallowness of the water there suggests this as a 

 possible breeding ground for it. Cyanea, the common "red jellyfish," which often 

 grows to a breadth of 3 feet across the disk and sometimes to a tremendous size 

 (A. Agassiz, 1865), is not so closely confined to the immediate vicinity of the land as 

 is Aurelia, for it occurs regularly in the coastal zone, on Nantucket Shoals, and on 

 Georges Bank, which must be important centers of production for it, judging from 

 the abundance of the young medusae there in spring and summer (p. 359) . However, 

 it is a rare occurrence to find a Cyanea outside the 100-meter contour in the Gulf of 

 Maine (on July 15, 1912, we captured a very large Cyanea in a haul from 120-0 

 meters in the western basin). The hydromedusa Melicertum campanula, 10 so abun- 

 dant all along the coasts of the Gulf of Maine (p. 341), is an even more precise neritic 

 indicator than Aurelia, for it is still more closely confined to the coastal zone, not 

 because the waters of the open sea are fatal to it (its abundance in Massachusetts 

 Bay proves the contrary), but because it passes through its fixed stage only in 

 sheltered localities, estuaries, etc., and because its free-floating (medusa) stage is of 

 shorter duration. Although Melicertum often swarms in localities as open to the 

 ocean as Massachusetts Bay and the outer parts of Penobscot Bay, as well as in 

 more inclosed waters, a single example from the western basin (August, 1913, station 

 10088) is our only record of it more than 15 miles from land. 



The medusae of the genus Sarsia, which are plentiful in season (p. 43) in bays 

 and estuarine situations all along the shallow coastal zone of the gulf, where they are 

 detached from their hydroids in great numbers in spring, are similarly restricted 

 to the coast line, for we have never taken them in the offshore parts of the gulf and 

 rarely more than 4 or 5 miles from land. This is equally true of many other small 

 hydroid medusae, most of which appear in the gulf for a brief period only, and then 

 far more numerously close to shore than outside the outer islands. 



As I have pointed out elsewhere (Bigelow, 1917, p. 252), an interesting example 

 of neritic occurrence among Coelenterates is afforded by the hydroid colonies we have 

 found floating in considerable numbers over Nantucket Shoals and Georges Bank 

 in July of 1913, 1914, and 1916, and in February, 1920, as well (p. 379). These are 

 so closely confined to the immediate vicinity of the localities where they are torn 

 from the bottom that we have never found them or their free medusae (which some- 

 times swarm on the banks) anywhere in the deeps of the gulf to the north. 



>• Large catches of Melicertum 38 miles off Cape Co I and near Browns Bank on August 12 and 19, 19211, prove that it drift 

 farther offshore. 



