JUDKINS ET AL : ZOOPLANKTON IN THE NEW YORK BIGHT 



warmwater oceanic distributions (Pierce 1953; 

 Grice and Hart 1962; Jefferies 1967; Pennell 

 1976; Fleminger and Hulsemann 1977). 



Mean Abundance, Frequency, 

 Average Rank, and Dominance 



We calculated mean abundances for various 

 taxa and found that copepods, on the average, 

 composed 62% of the zooplankton in our samples 

 (Table 2). Pteropods and gastropod veligers to- 

 gether contributed 15% to the total, and cladoce- 

 rans (Penilia avirostris plus Evadne spp.) and 

 urochordates (doliolids and appendicularians) 

 yielded another 10 and &fc, respectively. No other 

 group (e.g., echinoderm plutei, medusae, 

 polychaete larvae, chaetognaths), on the average, 

 composed more than about \% of the zooplankton. 

 At the species level, Pseudocalanus sp. and Cen- 

 tropages typicus were codominant in 1974-75, 

 their annual mean abundances (number/square 

 meter) each equaling approximatesly 13% of the 

 annual mean for total zooplankton. Pteropods 

 composed another 13% of the zooplankton, and 

 these consisted almost exclusively of one species, 

 Limacina retroversa (Wormuth'*). Paracalanus 

 parvus, Penilia avirostris, Calanus finmarchicus, 

 and Temora longicornis each composed between 5 

 and 10% of total zooplankton over the period, and 

 severalother taxa had values exceeding 1% (Table 

 2). 



In addition to mean standing stocks and con- 

 centrations, we calculated frequency of occurrence, 

 average rank (rank of most abundant taxon in a 

 sample = 1), and an index of dominance (Pager 

 and McGowan 1963) for the 20 taxa having the 

 highest mean abundance in our samples (Table 2). 

 These measures showed similar trends, and, in 

 general, frequency of occurrence and dominance 

 tended to decline and average rank to increase as 

 mean abundance decreased. There were, however, 

 a number of exceptions to this pattern. For in- 

 stance, the highly seasonal species P. avirostris 

 and T. longicornis had high mean abundances but 

 disproportionately low frequency and dominance 

 values and high average ranks. Conversely, other 

 taxa, which were seldom abundant, nevertheless 

 occurred frequently (e.g., S. elegans, O. atlantica, 

 polychaete larvae, medusae). 



'J. H. Wormuth, Department of Oceanography. Texas A&M 

 University. College Station, pers. commun. August 1978. 



Seasonality in Abundance 



Total zooplankton in the New York Bight de- 

 clined nearly fourfold in mean abundance between 

 late summer (September) and autumn (October- 

 November) 1974 (Table 3), primarily because of a 

 drastic decline in the abundance of P. avirostris 

 after September. In 1975, numbers of total zoo- 

 plankton did not vary as greatly between seasons, 

 and the highest mean value (April-May) differed 

 from the lowest (August-September) by less than a 

 factor of two. Copepods were least numerous in 

 winter (February-March), but increased through 

 spring (April-May) to an early summer (June- 

 July) peak before declining in late summer 

 (August-September). Other zooplankton com- 

 bined exceeded copepods in mean abundance only 

 during winter, and this primarily was due to the 

 large standing stocks of the pteropodL. retroversa 

 present in the Bight during that period. 



We calculated mean abundances by season for 

 the 20 taxa having the highest overall mean val- 

 ues in our samples (Table 2) and found thatmost of 

 these taxa underwent marked and often statisti- 

 cally significant (P<0.05) seasonal fluctuations in 

 standing stock (Table 3). Penilia avirostris, 

 doliolids, echinoderm plutei, and Acartia tonsa 

 reached maximum or near maximum levels of 

 abundance in late summer 1974 and again in late 

 summer 1975. With the exception of echinoderm 

 plutei, these taxa were virtually absent from our 

 samples during the intervening winter and 

 spring. The relatively low numbers of small 

 copepods in 1974 may have been due to escape- 

 ment through the coarse mesh (333 /xm) nets used 

 then. We found that Paracalanus parvus, 

 Pseudocalanus sp., O. similis, and Clausocalanus 

 pergens were significantly less abundant (paired 

 sample /-test, P<0.05) in collections from 60 cm 

 diameter 333 /u.m mesh nets than in simultaneous 

 samples from 20 cm diameter 253 and 223 nm 

 mesh nets. 



Only 1 taxa (L. retroversa) peaked in winter 

 1975, but 10 taxa [Pseudocalanus sp., Calanus 

 finmarchicus, O. similis. Metridia lucens. 

 Clausocalanus pergens, Evadne spp., appen- 

 dicularians, gastropod veligers, medusae, and 

 polychaete larvae) reached their highest levels of 

 abundance during spring 1975. Centropages 

 typicus, T. longicornis, and S. elegans attained 

 maximum levels of abundance in early summer, 

 and Paracalanus parvus peaked in late summer 

 1975. Among the 20 taxa listed in Table 3, O. at- 



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