FISHERY BULLETIN: VOL. 81, NO. 4 



GULF OF MAINE 



/ 



FIGURE 1.— The four geographic areas of the northwest Atlantic 

 sampled for zooplankton during MARMAP operations from 1977 to 

 1981, with MARMAP station locations indicated by dots. 



water strained are used to represent standing stocks 

 of zooplankton. The seasonal patterns of zoo- 

 plankton biomass observed each year and compared 

 with the 5-yr means in each of the subareas, were 

 coherent (Fig. 2a). The term coherent is used here to 

 describe the recurring seasonal patterns of zoo- 

 plankton biomass in which annual deviations from 

 the 5-yr mean are insignificant at the 0.05 level 

 (Table 1). On Georges Bank, the annual peak in spring 

 (May) is followed by a sharp decline from late spring 



(June) through summer (August), and less pre- 

 cipitous decline from late summer through autumn to 

 an annual low in winter. In the Gulf of Maine seasonal 

 changes are not as pronounced as on Georges Bank, 

 with the annual low in winter. The greatest change in 

 biomass begins in April and reaches its annual high in 

 May. From July until November, the standing stock 

 does not undergo marked change, but declines 

 gradually from November to a winter low in Feb- 

 ruary. In Southern New England, zooplankton 

 biomass is bimodal: an initial pulse occurs in May 

 followed by a low in July, and a second peak occurs in 

 August, followed by a decline in autumn and winter. 

 In the Mid- Atlantic Bight biomass increases from an 

 annual low in winter to an annual high in autumn. 



Table 1. — Summary of probability statistics for the two- tailed 

 Fisher-sign test for year-to-year coherence in the zooplankton 

 volumes, dominance, and three dominant species — Calanus fin- 

 marchicus, Pseudocalanus minutus, andCentropages typicus. Annual 

 departures from the MARMAP 5-yr mean annual cycle were tested 

 for each subarea The ranges of the probability of the Fisher- sign 

 statistic are tabulated. Of the 100 tests (5 yrX 4 areas X 5 variables) 

 only four reject the null hypothesis at 0.05 significance. H : annual 

 cycle = 5-yr mean cycle; * = significant difference in the year 

 indicated in parentheses. 



Subarea 



Coherence in Dominance 



The Fager and McGowan (1963) index was used to 

 identify the dominant zooplankters in each subarea 

 by season. Of the 394 taxa in the samples, 50 were 

 dominant in at least one location in one or more 

 seasons. Summary statistics for all taxa, including 

 rank, abundance, dominance, median abundance, 

 and Delta-mean abundance (Pennington 1983), are 

 available from the authors. Twelve taxa, all 

 copepods, comprised 857c of the dominance — 

 Calanus finmarchicus, Pseudocalanus sp., Cen- 

 tropages typicus, Metridia lucens, Temora longicornis, 

 Centropages hamatus, Acartia clausi, Acartia tonsa, 

 Acartia spp. {A. clausi-A. longiremis), Oithona spp., 

 Calanus spp., and Paracalanus parvus. Among these 

 12 taxa, Calanus finmarchicus, Pseudocalanus 

 minutus, and Centropages typicus accounted for 75% 

 of the total dominance. 



856 



