Arctic Zooplankton — Johnson 
313 
TABLE 1 
Water Temperature and Salinity in Coastal 
Lagoons Immediately South and North of 
Cape Thompson, Alaska, Aug* 1959 
(The lower sample was taken just above the bottom 
depth indicated) 
LAGOON 
TEMP. 
°c 
SALIN- 
ITY 
%o 
Lagoon no. 1 south, Aug. 12 
surface. 
11.0 
0,83 
bottom (1.5 m.). 
11.0 
0.83 
Lagoon no. 2 south/Aug. 12 
surface....... 
11.2 
14.31 
bottom (1.3 m.) 
11.1 
15.96 
Lagoon no. 3 south, Aug. 12 
surface. 
11.0 
0.16 
bottom (2.1 m.) 
10.4 
0.17 
Lagoon no. 4 south, Aug. 13 
surface........... 
12.3 
6.42 
bottom (1.3 m.)... 
12.1 
7.16 
Lagoon no. 5 south, Aug. 13 
surface..... 
13.6 
0.83 
bottom (1*3 m.) 
13.6 
0.83 
Lagoon no. 6 south, Aug. 13 
surface 
12.6 
0.73 
bottom (2.4 m.). 
12.4 
0.73 
Lagoon no. 7 south, Aug. 13 
surface 
12.6 
3.58 
bottom (2 m.) 
12.1 
3.58 
Lagoon no. 1 north, Aug. 14 
surface 
13*5 
0.18 
bottom (3m.) 
13.0 
0.18 
Lagoon no. 2 north, Aug. 1 5 
surface 
13.8 
0.46 
bottom (2.5 m.) 
13.0 
0.55 
and 4 south each have a narrow above-sea-level 
outlet that probably floods with sea water dur- 
ing high storms and undoubtedly accounts for 
the higher salinities observed there* 
Judged by the composition of the contained 
zooplankton, the lagoons are strikingly dissim- 
ilar ecologically. How persistent this dissimilar- 
ity is cannot be said from this preliminary sur- 
vey. Basically, the differences probably arise 
from the geographic position of each lagoon 
with respect to (1) extent of influx of fresh 
water in relation to the amount and frequency 
of that which spills over from the sea during 
high winds, (2) the height of the lagoon with 
respect to sea level, and (3) the effectiveness of 
the berm in serving as a barrier (reinforced by 
permafrost?) to water percolating out from the 
lagoon through the gravel* However, the envi- 
ronmental conditions characteristic of each la- 
goon have been sufficiently unique in the imme- 
diate past to permit selection and development 
of one or two species to a position of over- 
whelming dominance numerically, as shown by 
the analysis of the plankton fauna. 
Zooplankton 
The percentage composition of the fauna is 
shown in Table 2. Specific attention was given 
mainly to the calanoid copepods, because of the 
interest that some of the species hold as tran- 
sitory forms or as permanent residents in the 
overlapping environmental conditions between 
the sea and fresh water* In all cases the popula- 
tions were composed dominantly of fresh-water 
or brackish-water forms. But in lagoon no. 2 
south, there was a conspicuous element of 
marine plankton, which was probably only re- 
cently recruited from the sea (Table 2). Al- 
though Acartia bifilosa, a brackish-water species, 
was overwhelmingly dominant in this lagoon, 
several marine copepods were also present, but 
no larval stages of any species were found that 
might indicate local production. However, if 
only one generation is produced each year in 
the lagoon, as is common in some Arctic lakes, 
the season of nauplii-hatching was probably 
about past. Most of the marine species found 
are considered typical of strongly neritic waters, 
but Calanus finmarchicus , Pseudo calanus minu- 
tus, and Acartia longiremis do also occur well 
offshore and are very common in the Chukchi 
Sea, especially off the eastern coast and well 
north into the Arctic. 
Eurytemora pacifica is one of the more in- 
frequent neritic species encountered. Rather 
little is known regarding its preferred habitat. 
Hitherto, on the Alaskan coast it has been taken 
only at Grantley Harbor, and in the region of 
Point Hope, where it was reported by Willey 
(1920) as E. johanseni n. sp. Excepting lagoon 
no. 2 south, it was not found in any of the pres- 
ent lagoons, but it was common in a tow taken 
immediately offshore from lagoon no. 1 north. 
It is also common in Kivalina Lagoon, where it 
constituted 7 per cent of the calanoids in a sam- 
ple kindly provided by Mr. Robert W. Owen of 
