Some Observations on the Lagoon Plankton of Eniwetok Atoll 1 
Malvern Gilmartin 2 
During the course of a translagoon eco- 
logical study conducted in the northern 
Marshall Islands during 1955, a series of 
plankton hauls were taken. Subsequent analy- 
sis revealed several interesting aspects of 
lagoon plankton, in addition to recording the 
forms present. 
Eniwetok Atoll lies at about 11° 30' N. 
latitude and 162° 15' W. longitude. The atoll 
is composed of 38 islets on a reef surrounding 
an oval lagoon approximately 30 kilometers 
wide and 40 kilometers long. The lagoon is 
essentially a self-contained body of water with 
a maximum depth of 65 meters. There are 3 
major passes between the lagoon and the open 
ocean; southeast pass, 550 meters wide with 
an average depth of 31 meters, south pass, 
9.5 kilometers wide with an average depth of 
18 meters, and southwest pass, 4.3 kilometers 
wide with an average depth of 7 meters. 
From 4 April 1955 to 29 December 1955, 
21 plankton hauls were made along a transect 
extending from between Giriinien and Rigili 
islets to Aniyaanii Islet (Fig. 1). Each indi- 
vidual series contained a haul made just in- 
side the reef on the east end of the transect, 
from 1 to 3 hauls equidistantly placed along 
the transect, and a haul taken just inside the 
reef on the west end of the transect. All series 
were completed during periods within 2Vi 
hours of local apparent noon. Individual 
series were taken at speeds from 1 to 2 Vi knots 
at depths ranging from 1 to 3 meters. The 
plankton collected were stored in 10 per cent 
sea water-formalin for subsequent treatment. 
All hauls were taken using a one-half meter 
1 This study was financially supported under U. S. 
Atomic Energy Commission research contract AT- 
(04-3)-15. Manuscript received February 1, 1957. 
2 Institute of Oceanography, University of British 
Columbia, Vancouver 8, B. C, Canada. 
plankton net constructed for quantitative 
work (Tester, 1955) with an internally mount- 
ed Atlas-style flow meter. 
During this period, standard oceanographic 
observations were made. The mean value, 
range, and standard deviation of certain phys- 
ical and chemical characteristics of the transect 
surface water is indicated below. 
Tempera- Salinity Oxygen 
ture °C. %o % sat. 
mean 28.61 34.37 90.0 
range 28.31-29T3 34.05-34.67 59-9-104.7 
<x .023 .046 7.9 
No apparent correlation was noted between 
these factors and the intralagoon plankton 
distribution. 
The results of the plankton hauls, as indi- 
cated for occurrence in Table 1, for dominance 
in Figure 2, and for volume in Figure 3, sug- 
gest a surprisingly "endemic” (as opposed to 
313 
