transport of marine plankton through the panama canal

Transport of Marine Plankton Through the Panama CanalAuthor(s): Richard H. ChesherSource: Limnology and Oceanography, Vol. 13, No. 2 (Apr., 1968), pp. 387-388Published by: American Society of Limnology and OceanographyStable URL: http://www.jstor.org/stable/2833961 .

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NOTES AND COMMENT 387

will additionally be heated by terrestrial heat flow giving rise to convection currents. Mixing will occur in the dividing region where temperatures are lowest and ex- tremely fine temperature gradients exist, so that this region will occupy a considerable interval of depth. The temperatures main- tained there and deeper will be influenced by the amount of water upwelling season- ally. The extent to which cool water sink- ing at the lake margins is mixed into the upper system of circulation will depend largely upon bottom slope at the lake sides. Where the slope is precipitous, most of the descending flow may enter the lower system. Main features of this hypothetical regime are illustrated in Fig. 1.

The circulatory systems are made possible by the relatively large density differences which characterize small temperature differences at these high temperatures, and the permanence of the systems and of stratification will be dependent upon annual fluctuations in the budget of total heat loss and gain in the main strata being small.

G. W. COULTER

Ministry of Lands and Natural Resources, Department of Game and Fisheries, P. 0. Box 1, Chilanga, Zambia.

REFERENCES CAPART, A. 1952. Le milieu geographique et

geophysique. Results Sci. Exploration Hydro- biol. Lac Tanganika, (1946-47). Inst. Roy. Sci. Nat. Belg., 1: 3-27.

COULTER, G. W. 1963. Hydrological changes in relation to biological production in southern Lake Tanganyika. Limnol. Oceanog., 8: 463- 477. - . 1966. Hydrological processes and the deep-water fish community in Lake Tangan- yika. Ph.D. thesis, The Queen's University, Belfast, North Ireland. 204 p.

ECCLES, D. H. 1965. Hydrology notes, p. 19- 24. Ann. Rept. Malawi Dept. Agr. Fisheries 1963-64, Govt. Printer, Zomba, Malawi.

HUTCHINSON, G. E. 1957. A treatise on rim- nology, v. 1. Wiley, New York. 1015 p.

KUFFERATH, J. 1952. Le milieu biochimique. Results Sci. Exploration Hydrobiol. Lac Tan- ganika, (1946-47). Inst. Roy. Sci. Nat. Belg., 1: 31-47.

LIVINGSTONE, D. A. 1965. Sedimentation and the history of water level change in Lake Tan- ganyika. Limnol. Oceanog., 10: 607-610.

SVERDRUP, H. U., M. W. JOHNSON, AND R. H. FLEMING. 1942. The oceans. Prentice Hall, Englewood Cliffs, N.J. 1060 p.

TALLING, J. F. 1963. Origin of stratification in an African Rift lake. Limnol. Oceanog., 8: 68-78.

VON HERZEN, R. P., AND V. VACQUIER. 1967. Terrestrial heat flow in Lake Malawi, Africa. J. Geophys. Res., 72: 4221-4226.

ZoBELL, C. E. 1959. Thermal changes accom- panying the compression of aqueous solutions to deep-sea conditions. Limnol. Oceanog., 4: 463-471.

TRANSPORT OF MARINE PLANKTON THROUGH THE PANAMA CANAL

The proposed construction of a sea-level canal in Panama has stimulated biological interest in the Panamic marine fauna and flora. Several investigations are being planned for a comprehensive study of the before and after effects of such a canal. A possibility exists, however, that marine plants and animals have been traversing the present canal since its opening.

In 1956, the Panama Canal Company enacted a required draft regulation for tankers and freighters (Rodimon 1956). Due to their large "sail area," improperly ballasted ships may become unmanageable on windy days in narrow parts of the canal or in the locks. Large ships are therefore

required to maintain a minimum draft (Dertien 1966) while passing through the canal. Company representatives board ships waiting to pass through the canal, and if the ships do not have the required minimum draft, their officers are instructed to increase the salt-water ballast.

To avoid delay, ships using the canal frequently attain the correct draft before reaching the canal harbor. When the draft requirements were put into use 12 years ago, nearly every empty ship was required to take on water. Today, Mr. J. Jones, Ad- measurer of the Panama Canal Company, estimates that about two ships a month are asked to take on additional ballast.



388 NOTES AND COMMENT

Oil tankers pump salt water into special bilge tanks, used exclusively for the pur- pose. The opening to the intake pipe is located from 1 to 3 m below the surface of the water, and substantial amounts of water are taken aboard. About 18 metric tons of salt water are required to lower a tanker 131 m long 1 cm. A tanker 202 m long requires 46 metric tons to lower it 1 cm. Thus, a conservative estimate of the amount of water transported from ocean to ocean can be derived. Assuming two small ships ballast down a total of 2 m, 3,600 metric tons of water would be carried through the canal each month. Over a one- year period, 43,200 metric tons of salt water would be carried through the canal not in- cluding any water transported by ships that had ballasted down before reaching the canal.

The water is pumped through large im- peller pumps. This is, of course, fatal to large organisms but planktonic larvae and other microscopic organisms almost surely survive. A variety of invertebrates are known to pass through the pumps of salt- water aquarium systems as larvae to settle in the holding tanks and aquaria.

The greatest traffic in empty ships is from the Pacific to the Atlantic Ocean. Water is taken into the ballast tanks in the Bay of Panama and dumped in Cristobal Harbor where many ships refuel. It requires about 6 hr to pass through the canal. Water is also carried from the Atlantic to the Pacific Ocean but, as the ships do not commonly refuel in Balboa, the bilges are either pumped at sea or in the next port.

It is evident, therefore, that large quan- tities of salt water frequently pass through the present Panama Canal. Although the transport is greater today than ever before, there is some possibility that it has gone on since the canal opened in 1914. Marine organisms of microscopic size may have been transported from ocean to ocean many times over the past 54 years. It is not prac- tical to assume that populations of marine organisms on different sides of the isthmus are ipso facto genetically separated. Recent finds of geminate species should be re- examined and efforts made to augment comparative systematic and ecological surveys of the Panamic area. It may be that such surveys are 50 years too late to de- scribe the uncontaminated condition.

I am grateful to Mr. and Mrs. L. T. Williams of the Panama Canal Company for their assistance in gathering information relevant to this study. These observations were made during a brief visit to the Panama Canal Zone that was supported by a National Science Foundation postdoctoral fellowship and by the Smithsonian Institu- tion.

RICHARD H. CHESHER

Museum of Comparative Zoology, Harvard University, Cambridge, Massachusetts 02138.

REFERENCES

DELRTIEN, D. A. 1966. Marine Director's Memo- randum 6-66-shipping. Panama Canal Co., Balboa Heights, C.Z.

RODINION, W. S. 1956. Marine Director's Memo- randum No. 8-55, revised. Panama Canal Co., Balboa HIeights, C.Z.

A COMPARISON OF PROFILES OF NUTRIENT AND CHLOROPHYLL CONCEN-

TRATIONS TAKEN FROM DISCRETE DEPTHS AND BY CONTINUOUS RECORDING

With the development of the Auto- analyzer for the determination of nutrients and of the in vivo fluorescence method for chlorophyll (Lorenzen 1966), it becomes possible to make continuous measurements on station of phytoplankton crop (via plant

pigment) and the concentration of nutrients available to this crop. The methods used have already been mentioned (Armstrong, Stearns, and Strickland 1967) and full de- tails will be found in the text by Strickland and Parsons (1968).



transport of marine plankton through the panama canal

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