Hydrography and distribution of chaetognaths over the 



continental shelf olV North Carolina |()3 



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Fig. 11. Temperature-salinity diagrams, upper for Caryn Cruise 64, May and June 1953; lower for 

 Atlantis Cruise 196, January 1954. The stippled line in the diagrams is the left side of an envelope 

 describing the T-S characteristics of the Florida Current, Parr's (1937) stations in the Straits of 



Florida. 



Sagitta helenae was found all over the continental shelf south of Cape Hatteras but it disappeared 

 at the stations beyond the edge (Fig. 12). The greatest concentrations were found in the middle of 

 the shelf where as many as 94 specimens per ten cubic metres were collected. This species is able to 

 tolerate a rather wide range of salinity, varying from approximately 32 to 36^o,. Although present 

 in the edge of the Florida Current at times, it was never found far inside the current proper, and it 

 does not appear from these data that it is a true inhabitant of such water. 



This species has been closely associated with continental shelf water from the Gulf of Mexico 

 (Ritter-Zahony, 1910; Pierce, 1951, 1953) to Cape Hatteras. Apparently it disappears jusi north 

 of the cape where the colder, less saline water is encountered over the shelf. Only a few specimens 

 were taken near the edge of the shelf above Hatteras in the spring and winter cruises. Bigelow and 

 Sears (1939) do not record this species in their plankton studies from Chesapeake Bay to Cape Cod. 

 Because of its close relation to continental shelf waters from North Carolina southward, this species 

 appears to be of special interest in its relation to the hydrography of this area. 1 he movement of 

 Virginian Coastal water around Hatteras in January displaced this species from the inshore stations 

 jn Raleigh Bay where it usually occurs (Fig. 12). 



