108 Dean F. Bumpus and E. Lowe Pierce 



records do not show that S. helenae, S. hispida and S. tenuis are found over the con- 

 tinental shelf much farther north than Cape Hatteras. 5'. minima was found in 

 the slope water over Block Canyon off Long Island in October 1952.* S. serratodentata 

 in addition to being found in Florida Current, Carolinian and Virginian Coastal 

 water, is found in Virginian and Boreal Slope waters (Bigelow and Sears, 1939; 

 Clarke, Pierce and Bumpus, 1943; Redfield and Beale, 1940; Huntsman, 1919). 



Table III 

 Distribution of chaetognaths with respect to water types* 



Florida Current Carolinian Virginian 



S. bipunctata 



S. enflata S. enflata 



S. helenae 



S. hispida 

 S. minima S. minima S. minima 



S. serratodentata S. serratodentata S. serratodentata 



S. tenuis S. tenuis 



K. pacifica 

 K. subtilis 

 P. draco 

 S. hexaptera 

 S. lyra 



* No inference is made that these chaetognaths are indicators of the above 

 water types, see text. 



The Virginian Coastal water in the area just north of Cape Hatteras had relatively 

 few chaetognaths present and none which could be selected as indicators of that 

 water type. S. elegans, which occurs in abundance farther north in coastal water was 

 observed by Bigelow and Sears (1939) to diminish in numbers in the offing of Chesa- 

 peake Bay. None were found in either of the Wimble Shoal sections in the present 

 study. The higher temperature found in the southern portion of its range may be a 

 limiting factor. Cowles (1930) reports it in Chesapeake Bay in salinities as low as 



137oo. 



The presence of a barrier to the southward movement of plankton in the Hatteras 

 area is not as clearly demonstrated by the chaetognath distribution as one would 

 expect in comparison with the hydrographic evidence. This is due to the lack of 

 Virginian indicator species. f Evidence of the breaching of the barrier as far as Raleigh 

 Bay in January 1954 is provided by the absence of the truly Carolinian species of 

 chaetognaths, Sagitta enflata and S. helenae, at the inshore stations. Their distribution 

 is compatible with the hydrographic evidence. 



The occurrence and distribution of chaetognaths described in this study is in 

 substantial agreement with the earlier investigation (Pierce, 1953). Pierce's Zones 

 I and II have been labelled Carolinian Coastal water. The difference between Zones I 

 and II is a matter of dilution with river effluent. Zone III remains as unmodified 

 Florida Current water. As was found to be the case in the earlier collections, the 

 largest number of species was taken near the outer part of the continental shelf. 



* Personal communication from Dr. Richard Backus. 



t The distribution of other elements of the plankton communities sampled in these collections is 

 being examined by Philip St. John, a student at Harvard College. 



