ART. 15 COPEPOD CRUSTACEANS OF CHESAPEAKE BAY WILSON 19 



Suborder CALANOIDA 



ACARTIA CLAUSII Giesbrecht 



Acartia clausii Giesbeecht, J"'auna und Flora des Golfes von Neapel, vol. 19, 



Pelagische Copepoden, p. 507, pis. 30, 42, and 43, 1892. 

 Acartia clausi G. O. Sabs, Crustacea of Norway, vol. 4, p. 150, pi. 101, 1903. 



OccuiTence. — Taken at every station in the bay, in the surface, the 

 bottom, and the vertical nets. Most abundant in March after the 

 winter breeding season. 



Remarks. — This species is undoubtedly the chief component of the 

 copepod famia of the bay. Repeated hauls by every kind of net 

 used during the survey yielded no other Acartias except these. The 

 proportion of the two Acartia species, however, usually averaged 

 about 3 specimens of clausii to 2 of longireniis, A. claitsii, therefore, 

 occupies in Chesapeake Bay a position corresponding to that of 

 Calanus finmaj'chicus in the Gulf of Maine and elsewhere along the 

 northern Atlantic coast. The total numbers of specimens captured 

 furnish a good idea of the absolute abundance of these two Acartia 

 species in the bay. The great majority of these totals run into the 

 thousands, 20 of them are 10,000 or more, and 2 of them were esti- 

 mated at 100,000 each. And yet practically none of the nets was 

 towed longer than 10 minutes. 



In view of such large numbers, these two species very likely form 

 the bulk of the plankton food supply in the bay. This fact neces- 

 sarily gives them great economic value, and they should no longer 

 be regarded as merely two species of minute crustaceans possessed of 

 moderate scientific interest. They may well assume a place of vastly 

 higher importance in the life of the bay and take their stand beside 

 the shad and the oysters, and the crabs and the terrapin, as one of the 

 valuable resources of the bay. 



In a paper by Prof. Arthur Willey, of McGill University, on the 

 distribution of free-living Copepoda in Canadian waters ^ it was 

 said that the stomach contents of shad, caught at Scotsman Bay, 

 Nova Scotia, was a copious chyme made up almost wholly of Acartia 

 claitsii. The presence of the shad in such abundance in the bay, 

 therefore, may be directly the result of the abundance of food await- 

 ing them there. 



Sars said of this species that it seemed to be a more southern 

 form than longiremis, and this assumption is fully borne out by a 

 comparison of the relative abundance of the two species in the Gulf 

 of Maine and in Chesapeake Bay. In the former locality longire^nis 

 is much more abundant than clausii, but in the bay the proportion 

 is reversed. Farran reported the present species as taken all through 



■Cont. to Biol., vol. 1 (new ser.), no. 16, pp. 305-334, 1923. 



