Abstract. - Eighteen species of 

 chaetognaths were identified from 

 shelf waters in the Middle Atlantic 

 Bight. Species composition in the 

 water column and the hyponeuston 

 was nearly identical, but the percent 

 frequencies of the more common 

 cold-temperate species were general- 

 ly lower in surface collections. Mean 

 surface salinity, weighted for abun- 

 dance of individual chaetognath spe- 

 cies in the hyponeuston collections, 

 varied from 32.6 and 32.8 "/« for 

 the coastal- and estuarine-inhabiting 

 Sagitta tenuis and Parasagitta ele- 

 gans, to 34.8 and 34.9 for the offshore 

 Pterosagitta draco and Krohnitta 

 pacifica. Weighted mean tempera- 

 tures ranged from below 14°C for 

 Mesosagitta minima, P. elegans, and 

 Serratosagitta tasmanica to over 

 24 °C forK pacifica. Overall associa- 

 tion among Middle Atlantic Bight 

 chaetognaths, measured for the 15 

 most frequent species in 716 collec- 

 tions by variance ratio, was signifi- 

 cantly positive. Association between 

 pairs of species was therefore also 

 largely positive, with the important 

 exception of Parasagitta elegans. 

 This species, with a unique regional 

 niche in low salinities and tempera- 

 tures, was negatively associated 

 (p<0.01) with five warm-water spe- 

 cies (Krohnitta pacifica, Ferosagitta 

 hispida, Sagitta tenuis, Sagitta hele- 

 nae, and Flaccisagitta enflata). Most 

 species reached maximum abundance 

 at the surface near midnight. Excep- 

 tions included Sagitta helenae, with 

 daylight maxima, and Krohnitta pa- 

 cifica, Ferosagitta hispida and Ser- 

 ratosagitta serratodentata, showing 

 crepuscular increases in abundance. 



Chaetognatha from the 

 Central and Southern Middle 

 Atlantic Bight: Species Composition, 

 Temperature -Salinity Relationships, 

 and Interspecific Associations* 



George C. Grant 



Virginia Institute of Marine Science and School of Marine Science 

 The College of William and Mary, Gloucester Point, Virginia 23062 



Recognition of several chaetognath 

 species along the northeastern coast 

 of the United States is quite recent. 

 Until 1960, only eight species had 

 been identified from shelf waters off 

 the Middle Atlantic states, i.e., the 

 Middle Atlantic Bight from Cape Cod 

 to Cape Hatteras; these were in- 

 cluded in Bigelow and Sears (1939): 

 Eukrohnia hamata, Parasagitta ele- 

 gans, Flaccisagitta enflata, Serrato- 

 sagitta serratodentata (including the 

 then undescribed Serratosagitta tas- 

 manica), Flaccisagitta hexaptera, 

 Pseudosagitta maxima, Krohnitta 

 subtilis, and Pterosagitta draco**. 

 Deevey (I960), in a study of the Dela- 

 ware Bay region, added Ferosagitta 

 hispida, Sagitta helenae, and Meso- 

 sagitta minima to the list of recog- 

 nized species. Since her material had 

 been collected three decades earlier 

 (1929-31), it appears that pre-1960 

 studies had simply failed to distin- 

 guish between grossly similar spe- 

 cies. Sagitta tenuis, Sagitta bipunc- 

 tata, and Krohnitta pacifica were 

 added by Grant (1963a, b) to the list 

 of shelf species, and Grant (1967) 



Manuscript accepted 12 October 1990. 

 Fishery Bulletin, U.S. 89:33-40 (1991). 



'Contribution No. 1624 from the Virginia 

 Institute of Marine Science and School of 

 Marine Science, The College of William and 

 Mary. 

 * * Taxonomy in this paper generally follows 

 the revisions of Tokioka (1965) and Kassat- 

 kina (1971), but removes Pseudosagitta lyra 

 and P. maxima, from the genus Flacci- 

 sagitta in agreement with species groupings 

 of Alvarino (1963). 



later confirmed that the endemic 

 shelf population of "S. serratoden- 

 tata'' in this region was actually S. 

 tasmanica. Grice and Hart (1962) 

 found other species in slope waters 

 southeast of Long Island, New York, 

 including Pseudosagitta lyra, Meso- 

 sagitta decipiens, and Solidosagitta 

 planctonis. Thus, at the close of the 

 1960s, some 15 species were known 

 from the shelf and the presence of 

 others in surface slope waters sug- 

 gested their likely occurrence over 

 the shelf as well. 



This study of Middle Atlantic Bight 

 chaetognaths is based on an intensive 

 series of collections from the central 

 and southern bight. Presented here 

 are the species composition in hypo- 

 neuston and subsurface collections, 

 temperature-salinity-plankton (T-S-P) 

 diagrams for the more common surface 

 species, measurements of interspe- 

 cific associations among chaetognaths, 

 and a summary of diel abundance in 

 the hyponeuston. 



Methods and materials 



Chaetognath collections 



A transect of six stations (Cl-Jl, Fig. 

 1) off southern New Jersey was sam- 

 pled quarterly for two years, October 

 1975- August 1977. Two more north- 

 erly stations (A2, B5) and a southern 

 transect of four stations (L1-L6) were 

 added in the second survey year 



33 



