ATOLL RESEARCH BULLETIN No. 151
BACTERIAL COUNTS IN SURFACE OPEN WATERS OF ENIWETOK ATOLL, MARSHALL ISLANDS
by Louis H. DiSalvo
Issued
byTHE SMITHSONIAN INSTITUTION
Washington, D. C., U. S. A.
BACTERIAL COUNTS IN SURFACE OPEN WATERS OF ENIWETOK ATOLL, MARSHALL ISLANDS
by Louis H. DiSalvo'
INTRODUCTION AND METHODS
During my investigations of c o r a l reef microbiology at Eniwetok Atoll, Marshall Islands in 1968, l a r g e numbers of bacteria were found inhabiting c o r a l reef internal sediments (lo7-lo8 colonies/g; DiSalvo, 1969). With the high level of metazoan activity on r e e f s i t was expected that sediment processing and disturbance might cause the r e l e a s e of bacteria, contributing to the organic particulate enrichment of lagoon w a t e r s (Marshall, 1965; Johannes, 1967). T o my knowledge, no bacteriological data were available which compared oceanic counts to lagoonal counts n e a r a n atoll, and therefore the following m e a s u r e m e n t s were made both in r e f e r e n c e to the work a t hand and a s a general contribution to atoll ecology.
Open w a t e r sampling f o r aerobic h e t e r o t r o p h i c bacteria was c a r r i e d out on s i x bi-weekly d a t e s in June and July 1968. A total of 24 s a m p l e s of s u r f a c e seawater w e r e obtained a t oceanic and lagoonal stations. In addition, a total of 14 s a m p l e s were obtained downstream f r o m the Japtan r e e f a t the s u r f a c e and a t 2 m e t e r s depth. Sample locations a r e shown in Figure 1. Surface (top 5 cm) water s a m p l e s w e r e obtained in s t e r i l e 200 m l prescription bottles f r o m a boat. Skin diving was employed to obtain the 2 m samples. Samples w e r e kept on i c e f o r r e t u r n to the laboratory, and plated f o r b a c t e r i a l counts within five hours of collec- tion. The plating medium was ZoBell 2216e (Oppenheimer and ZoBell, 1952) solidified with 1.5% (w/v) a g a r . Duplicate pour p l a t e s w e r e made using 0.1 m l r a w Seawater inocula and 10 m l medium which had been cooled to 40-45OC. P l a t e s w e r e incubated a t ambient tempera- t u r e (30°C) f o r 48 h o u r s and then counted f o r total colonies.
RESULTS AND DISCUSSION
Bacterial counts f o r numbered sam.3les located by Figure 1 a r e listed in Table 1. T h e s e counts a r e within o r d e r of magnitude limits established by other investigators using s i m i l a r methods on w a t e r s n e a r non-atoll r e e f s (Table 3). Table 2 l i s t s counts for two depths immedi- ately behind the Japtan Reef. Summarized r e s u l t s in Table 3 suggest there was no significant difference between oceanic and back-reef counts.
Conclusions f r o m these data a r e tentative and preliminary. Comparisons with plate counts of other w o r k e r s in Table 3 have been made f o r convenience, although they may be invalidated by slight differences in methodology and materials. The limitations of the plate count technique in obtaining "true counts" a r e well known (ZoBell, 1946; J o n e s and Jannasch, 1959) and p r e s e n t r e s u l t s can only be considered a s a m e a s u r e of relative microbial activity. The counts a r e
' p r e s e n t a d d r e s s : Naval Biomi?dical Laboratory, NavalSupply Center, Oakland, Calif. 94625.
(Manuscript r e c e i v e d J u l y 1970--Eds.)
within higher r a n g e s expected f o r c l e a r tropical pelagic waters, and it may t h e r e f o r e be hypo- thesized that the w a t e r s surrounding the atoll a r e enriched in some way, perhaps by local up- welling o r organic enrichment f r o m the reefs.
The s m a l l numbers of sample platings preclude rigorous statistical interpretations of the data. M o r e seriously, I w a s unable to s a m p l e t h e s a m a water m a s s flowing f r o m ocean to lagoon o v e r the Japtan Reef f o r the before-after measuremsnts. Both t h e s e f a c t o r s were the r e s u l t of logistical problems, helping to explain why t h e r e a r e essentially no microbiological data available f o r atoll waters. Since i t h a s previously been suggested that the Japtan Reef was i n a steady s t a t e with r e g a r d to the i m p o r t and export of m a t t e r and energy (Odum and Odum, 19651, i t i s not unreasonable to deduce f r o m :he available data that this reef is i n equilibrium with r e g a r d t o input and output of heterotrophic bacteria.
Future studies should attem2t to confirm p r e s e n t r e s u l t s under various seasonal and tidal r e g i m e s , and extend the m-.asuremsnts to representative depths within and outside the atoll.
Such m e a s u r e m e n t s might be useful i n studies of o u t e r slope upwelling and local enrichment due to the c o r a l reefs.
ACKNOWLEDGEMENT
The author wishes to thank the Eniwetok Marine Biological Laboratory and the University of Hawaii f o r support and facilities u s e d to accomplish this research.
LITERATURE CITED
DiSalvo, L.H. 1969. Regenerativefunctionsandmicrobialecologyofcoral r e e f s . Ph.D. Thesis.
Univ. of
N.
Carolina, Chapel Hill. 289 p.Gee, A.H. 1932. Lims? deposition and the bacteria. I. Estimate of b a c t e r i a l activity in the F l o r i d a Keys. Pap. Tortugas Lab., Carnegie Inst., Washington, D.C. 28: 67-82.
Gundersen, K.R. and D.B. Stroupe. 1967. Bacterial pollution of Kaneohe Bay, Oahu. Univ.
Hawaii Water Resources Res. Ctr., Tech. Rpt. 12. 24 p.
Johannes, R.E. 1967. Ecology of organic a g g r e g a t e s in the vicinity of a c o r a l reef. Limnol.
Oceanogr. 12: 89-195.
Jannasch, H. and G.E. Jones. 1959. Bacterial population inseawater a s determined by s e v e r a l methods of enumzration. Limnol. Oceanogr. 4: 128-139.
Marshall, N. 1965. Detritus o v e r the reef and i t s potential contribution to adjacent w a t e r s of Eniwetok Atoll. Ecology. 46: 343-344.
- - - - - - - -
1968. Observatious on organic aggregates in the vicinity of c o r a l reefs. Mar.Biol. 2: 50-53.
Odum: H.T. and E.P. Odum. 1955. Trophic s t r u c t u r e and productivity of a windward c o r a l reef community a t Eniwetok Atoll. Ecol. Monogr. 23: 291-320.
Oppenheimer, C.H. and C.E. ZoBell. 1952. The growth and viability of sixty-three s p e c i e s of m a r i n e bacteria a s influenced by hydrostatic p r e s s u r e . J. Mar. Res. 11: 10-18.
S i s l e r , F.D. 1962. Microbiology a n d biochemistry of sediments and overlying water, p. 64-69, in, P.E. Cloud, Jr., Environment of calcium carbonate deposition west of Andros I., Bahamas. Geol. Surv. Prof. Pap. 350. US. Govt. Printing Off., Washington, D.C. 138 p.
ZoBell, C.E. 1946. Marine microbiology. Chronica Botanica Pub., Waltham, Mass. 240 p.
Table 1. BACTERIAL COUNTS FOR ENIWETOX ATOLL OPEN WATERS
Date Sam.?le*
Colonies/ml**
19fiR :1
Date Sample
1968 it Colonies/ml
-
6/23 13 70
16 140
18 50
21 80
24 160
6/30 12 180
14 100
17 500
19 50
20 100
22 150
23 30
* F o r sample location, s e e Fig. 1.
**Colonies/ 0.1 m l plated x 10.
Table 2. BACTERIAL COLONY COUNTS FOR JAP'TAN I. BACK- R E E F WATERS*
-
Date Surface ~ ~ ~ ~ . . . s a m p l e s ~~ Samples ~ . . . ~ ~ ~ ~ ~ . . f r o m -~ .... 2m ~ depth**
1968 Sample ;I Colonies/ml Sample !i Colonies/ml
-
7/15 I d 250
2d 500
3d 350
7/17 3 4d 160
4 5d 150
5 550
7/19 6 6d 300
- - - -
-
Mean values 235
7d 330
8d 250
-
C3 = 285
-- I
* W a t e r depth approximately 4 m e t e r s .
**Obtained by diving.
Table 3. SUMMARY O F COLONY COUNTS FOR ENIWETOK ATOLL OPEN WATERS
Stations Number of samples Colonies/ml Ocean
(nos. 1-5, 7-11 10
Lagoon
(all Japtan*, nos.
20-24) 19
Previous data, near r e e f s
Gee (1932)' 3 100,150,700**
Sisler (1962)' nd < 10-lo3
Gundersen and Stroupe (a) 5 50,60,1360,12,42**
(196'7)~ (b) 3 13,2,5**
Sieburth ( ~ n p u b . ) ~ 4 215,235,250,700**
*See table 2.
**Individual results.
1
Open water near Florida reef t r a c t (Gulf Stream, BirdKey Harbor, Marquesas lagoon).
2
Water over Great Bahama Bank west of Andros I.
3
(a) immediately outside northern Kaneohe Bay, Hawaii.
(b) Kauai I., Hawaii, 1.5-2.5 mjles offshore.
4
