vertical migrations of daphnia and copepods under the ice

Vertical Migrations of Daphnia and Copepods Under the IceAuthor(s): Linda CunninghamSource: Limnology and Oceanography, Vol. 17, No. 2 (Mar., 1972), pp. 301-303Published by: American Society of Limnology and OceanographyStable URL: http://www.jstor.org/stable/2834449 .

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N-OTES 301

upward migration at noon the following day in the absence of any drop in light intensity. In view of the small number of specimens involved, however, this last con- clusion must be viewed as highly specula- tory.

THOMAS BRIGHT

FRANK FERRARI

DOUGLAS MARTIN

Department of Oceanography, Texas A&M University, College Station 77843.

GuY A. FRANCESCHINI

Department of Meteorology, Texas A&M University, College Station 77843.

REFERENCES

BACKUS, R. H., R. C. CLARK, AND A. S. WING. 1965. Behavior of certain organisms during the solar eclipse of July 20, 1963. Nature 205: 989-991.

BRINTON, E. 1962. The distribution of Pacific

euphausiids. Bull. Scripps Inst. Oceanogr. 8: 51-270.

FRANCESCHINI, G. A., T. J. BRIGHT, J. W. CARUTHERS, S. Z. EL-SAYED, AND A. C. VASTANO. 1970. Solar eclipse of March 7, 1970: effects on migration of marine organisms in the Gulf of Mexico. Nature 226: 1155-1156.

LEWIS, J. B. 1954. The occurrence and vertical distribution of the Euphausiacea of the Flor- ida Current. Bull. Mar. Sci. Gulf Carribean 4: 265-301.

MOORE, H. B., AND D. L. O'BERRY. 1957. Plank- ton of the Florida Current. 4. Bull. Mar. Sci. Gulf Carribean 7: 297-315.

PETIPA, T. S. 1955. Observations on the be- haviour of zooplankton during a solar eclipse [in Russian]. Dokl. Akad. Nauk SSSR 104: 323-325.

ROEHR, M. G., AND H. B. MOORE. 1965. The vertical distribution of some common copepods in the Strait of Florida. Bull. Mar. Sci. Gulf Caribbean 15: 565-570.

SHERMAN, K., AND K. A. HONEY. 1970. Vertical movement of zooplankton during a solar eclipse. Nature 277: 1156-1158.

SKUD, B. E. 1967. Responses of marine organisms during the solar eclipse of July 1963. U.S. Fish Wildl. Serv. Fish. Bull. 66, p. 259- 271.

VERTICAL MIGRATIONS OF DAPHNIA AND COPEPODS UNDER THE ICE

ABSTRACT

Quantitative sampling through the ice of the copepods Diaptomus minutus and Cy- clops scutifer showed a pronounced reverse nocturnal migration for these species. Daph- nia galeata mendotae, sampled at the same time, showed little vertical migration.

An experiment was designed to determine the behavior of zooplankton under the ice of Fuller Pond, a 17.8-ha mesotrophic kettle lake in northwestern Connecticut. A list of the species known to be present in the lake in summer and some information on the vertical distribution of Daphnia galeata mendotae in the lake in summer was available (Burns, unpublished).

Three types of vertical migration have been described by Hutchinson (1967). The first of these involves a rise at night from deeper to more superficial layers of the

water with a single maximum at the surface sometime between sunset and sunrise and is known as nocturnal migration. The second case is twilight migration, where there are two maxima corresponding to dawn and dusk. Finally, a reverse migration may occur, in which there is a single maximum at the surface during the day. Various ex- planations for these patterns have been pro- posed, ranging from temperature or light gradients (Hutchinson 1967) to predator avoidance (S. Suffern, personal communica- tion) and pH (Bayly 1963).

MATERIALS AND METHODS

Sampling was done on 20 and 21 Feb- ruary 1971. A hole about 0.71 m in diam- eter was cut through the ice near the middle of the lake where the depth is greatest. The hole was completed as the sun was setting so that it was not exposed to direct sun-



302 NOTES

100.0

Light Intensity

- Temperature I0

0

E |I

- 1.0_" 4.0

2 / ! ~ 3.0

< /IT *C

0.1 _ 2.0

1.0

S 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Depth (meters)

FIG. 1. Light intensity and temperature plotted against depth.

light while it was being dug. The ice was about 0.6 m thick, largely blue ice with about 11 cm of white granular ice on top. There was no snow cover. To avoid creat- ing a bright spot where the ice had been removed, I used a box (0.76 m/side) with a hinged top to shield the hole from direct sunlight. As can be seen from the light curve (Fig. 1), this tended to cast a shadow over the surface of the water just below the ice but had little effect below the first meter. The day was overcast, so total light intensity was low.

Two samples were taken at every meter from the surface to the bottom (14 m) with a 10-liter Juday trap every 6 hr from 1800 hours 20 February to 1800 hours 21 February.

Light and temperature readings were taken only for the noon sample because it was dark at the time of all other samplings. The light measurements were made with a Whitney underwater daylight meter. The irregularity in the light curve at 9 m was probably due to increased turbidity; the temperature curve (see Fig. 1) also showed a rise at 9 m. The increased turbidity and

Cyclops scuolder 2000 800 0 800 2000 2000 800 0 800 2000 2000 800 0 800 2000

6 _ 6 ~~~pm 12 pm 6am 6~~~~p

3200 1600 0 1600 3200 2000 800 0 800 2000

6 _ 12 noon s6p

Diaplomus rn/fu/us 200 100 0 100 200 200 100 0 100 200 200 100 0 100 200

46 6 pm 2 m 6c

300 200 100 0 100 200 300 300 200 100 0 100 200 300

6 - 12noon - 6pm

10

12

14

Daphn,a ga/eodo mendolce 500 200 0 200 500 500 200 0 200 500 500 200 0 200 500

14 6~~~P pmp 6IZ ii 12 _ tt6c

500 200 0 200 500 500 200 0 200 500

6 noon P

10 E 12lv

species, 0 -21 February 1971.



NOTES 303

temperature may both be due to the pres- ence of water which, on brighter days, was warmed by the sun near the shore and then circulated into the lake.

The samples were preserved in 10% Formalin before analysis in the laboratory.

RESULTS AND DISCUSSION

Three species were found in fairly large numbers in the samples-Daphnia galeata mendotae, Diaptomus minutus, and Cy- clops scutifer. Occasional specimens of Bosmina longirostris were also found.

Both copepods had striking reverse vertical migrations with a maximum surface abundance at 1200 hours, when the light intensity was maximal (Fig. 2). Also, the copepods concentrated, not exactly at the surface, where they would have been in the shadow of the box, but rather at 1 m, where the light intensity was greatest.

Although known to exhibit striking nocturnal vertical migration in Fuller Pond on bright summer days (Burns, unpublished), D. galeata showed only a slight tendency toward nocturnal migration under the ice. The fact that it did not exhibit strong vertical migration demonstrates that the migrations observed for the copepods are not artifacts of the sampling process.

The phenomenon of reverse migrations is relatively rare; known cases are described by Hutchinson (1967) and Pennak (1944). The occurrence of reverse migrations under the ice, where thernal gradients and light intensity are minimal, is of particular in- terest. The lake temperature varied with depth only between 3.5 and 4.0C; the temperature of 2C recorded at the surface was due to surface runoff. Although the copepods migrated through the temperature gradient, it was so slight a gradient that there is little possibility that it influenced the migrations; there was enough light for photosynthesis to occur, and important light and chemical gradients may have existed within the lake.

Predator avoidance could be a factor affecting vertical migrations, but it is un- likely that the copepod eye can form images clearly enough to see and avoid predatory fish (G. E. Hutchinson, personal communi- cation). Also, in many lakes in winter the fish are penned up in springfed pockets and are not moving in the upper waters. Finally, Bayly's (1963) pH hypothesis does not seem applicable as the pH of Fuller Pond was 6.5 on 10 December 1970- nowhere near the value of 8.2 believed by Bayly to cause reverse migrations.

It seems possible that, when the daily light cycle involves variation over quite low intensities, migratory behavior may be determined by positive phototaxis, at least in some species and under some conditions. George and Fernando (1970) found that rotifers in Sunfish Lake, Ontario, exhibited nocturnal migration during summer and reverse migration during winter. Some- thing of this nature may be happening with the copepods in Fuller Pond.

This project could not have been completed without the help of D. Cunningham, K. Porter, and S. Suffern. The cost of the box was defrayed by National Science Foundation Grant GB 12895.

LINDA CUNNINGHAM

Osborn Memorial Laboratories, Yale University, New Haven, Connecticut 06520.

REFERENCES

BAYLY, I. E. A. 1963. Reversed diurnal vertical migration of planktonic Crustacea in inland waters of low hydrogen ion concentration. Nature 200: 704-705.

GEORGE, M. F., AND C. H. FERNANDO. 1970. Diurnal migration in three species of rotifers in Sunfish Lake, Ontario. Limnol. Oceanogr. 12: 218-223.

HUTCHINSON, G. E. 1967. A treatise on limnology, v. 2. Wiley. 1115 p.

PENNAK, R. W. 1944. Diurnal movements of zooplankton organisms in some Colorado mountain lakes. Ecology 25: 387-403.



vertical migrations of daphnia and copepods under the ice

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