BIGELOW: COAST WATER EXPLORATION OF 1913. 265 



uniformity from season to season. Below say sixty fathoms the 

 extreme range of temperature over the entire Gulf, throughout the 

 year is probably not over 10° (38°-48°) ; at 100 fathoms the extreme 

 range is about 8° (38°^6°) . And the deep parts of the western half 

 of the Gulf are still more uniform ; the extreme temperature variation 

 at all depths below sixty fathoms, being not more than 4° in the basins 

 and troughs next the western shore. Salinity, too, is surprisingly uni- 

 form in the deeper parts of the Gulf. In short, the fauna which 

 occupies these depths enjoys an environment whose physical factors 

 are practically unchanging from year's end to year's end. 



But quite the opposite is true of the surface layers of the Gulf, 

 where there are violent seasonal fluctuations of both temperature 

 and salinity. Along the western shore, and in Massachusetts Bay, 

 the surface temperature rises from about 36° in winter to 63° or 64° in 

 summer, i. e., a range of almost 30°. And though the annual range is 

 smaller along the eastern side, it is still considerable. The salinity, too, 

 oscillates betAveen wide limits, and the changes are very sudden in 

 spring. For example, north of Cape Ann, the range is from about 

 32.8%o in February to about 29%o early in May. 



In addition to these regular seasonal changes, the Gulf is subject to 

 sporadic invasions, on the one hand by water from the Gulf Stream, 

 with its characteristic fauna, on the other by St. Lawrence water. 

 But these are not extensive enough to cause much change in the Gulf 

 as an environment, though they do alter the fades of the plankton 

 by the addition of either southern, or northern organisms, as the case 

 may be. 



South and west of Cape Cod there are no parts of the continental 

 shelf where the water is as uniform, from season to season, as it is in 

 the deeps of the Gulf of Maine. On the contrary, the entire water 

 mass over the shelf is subject to violent fluctuations, both seasonal 

 and sporadic. These are most violent, of course, near the surface and 

 next the coast. For example, the surface temperature off New York 

 ranges from about 38° to over 70° during the year; the salinity from 

 about 31%o to possibly 34%o. And even as deep as sixty fathoms the 

 temperature may rise from below 45° to nearly 60° in a month (p. 349), 

 the salinity from 33.5%o to 35.1%o in the same short period. And 

 this general statement is true all along the coast, at least as far as 

 Chesapeake Bay. Thus any bottom animal may be subjected to 

 great and sudden changes. x\t the edge of the shelf, where the water 

 is deeper (75-125 fathoms), conditions are more uniform. And this 

 is a particularly interesting zone zoologically, as Verrill (1880, 1884a) 



