Vertical Migration of Daphnia dubia and Hours of Sunshine in Previous Diel PhotoperiodAuthor(s): Charles B. Reif and Donald W. TappaSource: Transactions of the American Microscopical Society, Vol. 87, No. 3 (Jul., 1968), pp.350-353Published by: Wiley on behalf of American Microscopical SocietyStable URL: http://www.jstor.org/stable/3224820 .

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VERTICAL MIGRATION OF DAPHNIA DUBIA AND HOURS OF SUNSHINE IN PREVIOUS DIEL PHOTOPERIOD

CHARLES B. REIF and DONALD W. TAPPA Wilkes College, Wilkes-Barre, Pennsylvania

ABSTRACT: Collections of Daphnia dubia were made with pump and net through a fixed intake at 3 m depth, each night between 2100 and 2400 hr, in Harveys Lake, Pennsylvania, from 27 June through 7 August 1966. No correlation existed between upward movements of daphnids and moonlight, but a significant correlation was noted between the number of daphnids caught at 3 m from 2100 to 2400 hr and the number of hours of unclouded sunshine during the previous diel photoperiod; the more hours of sunshine the smaller the number of daphnids taken.

Observation of the vertical migration of Daphnia pulex in Harveys Lake near Wilkes-Barre, Pennsylvania, was begun in 1950. Generally, at that time, the population of this species made marked vertical migrations, such that most of the population moved above the thermocline during the night but went well below the thermocline during the period of daylight. This vigorous migration of D. pulex in the early fifties was decidedly greater than the migrations of the population of D. dubia during 1965 and 1966, D. dubia being the species which replaced D. pulex in Harveys Lake, as reported by Reif & Tappa (1966).

MATERIALS AND METHODS

During the summer of 1965, sampling was accomplished every night from 15 June through 15 August with pump, hose, and nets. Our boat was on station, over 50 ft of water, from 2000 until 0100 hr each night. One set of samples (composed of 20-liter samples from each of 1, 3, 5, 7, 9, 11, and 13 m depth) was taken each hour by passing the water through a no. 20 nylon net (a different net for each depth) and into a measuring tub. Each plankton sample was removed from the net and put into a half-pint mason jar with 3% formalin and a crystal of malachite green dye which stained the daphnids and made them more apparent for counting. The following morning each collection was placed on lined filter paper, and the daphnids were counted under 30 x binocular stereomicroscopes.

Early in June 1966 a fixed intake was placed in 6 m of water, 40 m from shore, in such a way that the opening of the intake was 3 m below the surface of Harveys Lake. The intake was connected with a pump located in a boathouse. Taking samples in this manner obviated variables encountered in sampling from a boat, as in 1965. The depth of 3 m for the opening of the intake was selected because the data for 1965 indicated generally a greater concentration of daphnids near that depth between the hours of 2100 and 2400.

Sampling through the fixed intake was begun on 27 June and continued through 7 August 1966. One 20-liter sample, requiring about 4 min to pump, was taken every 15 min from 2100-2400 hr by passing the desired volume of water through the net and counting the number of daphnids thus taken the next morning, in the same fashion as described previously. The counts are given in columns C and D of Table II.

Each night at approximately 2200 hr the light intensity was measured at each meter from surface to bottom with a bathyphotometer of the kind developed by Clarke & Wertheim (1956). Usually light intensity was related to the phase of the moon, the position of the moon, and cloud cover.

Another light factor was introduced, namely the number of hours of sunlight for each day of the sampling period, the information having been taken by the

TRANS. AMER. MICROSC. SOC. 87(3): 350-353. 1968.

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REIF & TAPPA-VERTICAL MIGRATION OF DAPHNIA DUBIA 351

TABLE I Numbers of Daphnia dubia taken at various depths (in meters), at 1-hr intervals from

2100-0200 hr 15-16 June 1965 from Harveys Lake

Depths 2100 2200 2300 2400 0100 0200

2 419 686 6,81 318 381 273 4 314 519 413 12 206 331 6 597 578 601 465 172 337 8 368 262 230 781 329 421

10 347 263 365 260 285 397 12 73 142 137 343 228 152 14 158 44 354 201 202 292 16 27 21 110 237 360 421

Totals 2,303 2,515 2,891 2,617 2,163 2,624

Avoca (Pennsylvania) Weather Station which is 12 miles from the point of sampling in Harveys Lake.

During the summer of 1966, several checks were made to assure that a diel vertical movement was characteristic of D. dubia. To this end the pump attached to the fixed intake was run continuously from 0130 until 0455 and again from 1330 until 1650. Several nets were used, and the water was allowed to pass through a net for 5 min. At the end of each 5-min period a fresh net was placed in position until 42 samples were taken for each run. The pump was checked for efficiency at times which did not interfere with the nightly collecting periods but were sufficiently close to reveal the difference between populations present at the intake during the night and those present during the day. The data for 16 July are typical of those gathered-from 0130 to 0455 the average number of daphnids taken during a 5-min period was 313. The average number for the 5-min periods between 1330 and 1650 was only 1.33.

RESULTS A typical night pattern of the movement of individuals of D. dubia during

the months of June, July, and August 1965 in Harveys Lake is shown in Table I. It is clear that the upward movement placed the greatest numbers of daphnids in the epilimnion (thermocline between 6 and 8 m) at 2100 to 2300 hr. Sub- sequent samples showed a downward drift beginning at midnight. Several sets of collections taken through 24 hr reveal that many individuals of D. dubia remained in the epilimnion during hours of daylight, and many remained in the hypolimnion during hours of darkness. The movements of D. dubia were by no means as clear-cut as those of D. pulex. The similarity in totals for the number of individuals in the sampled columns of water for each hour indicates that the migration was chiefly vertical with only a negligible horizontal shift.

The data of 1966 are summarized in Table II. In column A are the dates on which the collections and other observations were made. In column B are the values of light intensity at 3 m in Harveys Lake at 2200 hr for each of the nights on which collections were made, all in foot-candles with a value of n times ten to the minus fourth power. In columns C and D are the figures representing the numbers of daphnids collected. The populations in column C are those for the middle hour (samples taken at 2200, 2215, 2230, and 2245 hr) of the popula- tions shown for 3 hr in column D. In column E are the values for hours of sunlight for each daylight period previous to the collections indicated. In column F are values assigned to the phase of the moon: a value of zero repre- sents new moon and a value of 15 represents full moon.

From Table II various sets of linear coefficients of correlation were deter- mined as follows:

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352 TRANS. AMER. MICROSC. SOC., VOL. 87, NO. 3, JULY 1968

TABLE II Data from Harveys Lake for summer of 1966

B C D E F A Light* Daphnids Daphnids Hours of Value for

Date at 3 m 2200-2245 2100-2345 sunlight moon's phase

27 June 28 29 30

1 July 2 3 6 7 8 9

10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31

1 Aug. 2 3 4 5 6 7

1.2 1.4 8.0

10.0 9.0 7.0 7.0 1.4 6.0 7.2 5.9 3.0 4.2 2.9 7.5 0.05 2.3 2.4 2.2 2.4 1.4 2.1 3.0 0.7 1.5 0.8 0.2

13.0 0.1 0.05 9.0 9.0 7.4 1.3 1.4 6.1 1.9 5.8 5.7 2.9

55 20 21

112 23

166 133 223 150 181 133 28

183 21 97

472 1,081

180 136 168 46

1,039 10 27 38

277 21 22

113 572

2,043 283

65 21

1,442 19 60

104 101 50'9

165 43

280 186 85

302 388 877 867

2,298 443 168

1,213 182 303

2,385 2,821 1,359

505 274 158

3,573 53

190 271 655

50 101 262 958

4,767 845 184 134

4,024 67

344 303 977

1,078

9.3 5.3

10.7 14.2 15.1 15.1 13.5 7.8

11.3 13.4 14.8 10.2 11.0 13.3 13.4

5.6 13.0 14.9 14.0 14.5

1.1 12.3 12.9 13.4 10.7 13.2 11.9 8.2 6.4 1.2

10.3 5.7

14.4 13.0 0.8

12.8 12.0 12.1 12.1 11.9

10 11 12 13 14 15 14 11 10

91 8 7 6 5 4 3 2 1 0 1 1 2 3 5 6 7 8 9

10 11 12 13 14 13 12 11 10 9! 8 7

* Foot-candles = n X 10-4.

daphnids caught, 2200-2245, vs. light intensity, p is -0.022, daphnids caught, 2100-2345, vs. light intensity, p is -0.035, daphnids caught, 2200-2245, vs. phase of moon, p is -0.006, daphnids caught, 2100-2345, vs. phase of moon, p is -0.102, daphnids caught, 2200-2245, vs. preceding hours of daylight, p is -0.266, daphnids caught, 2100-2345, vs. preceding hours of daylight, p is -0.225.

Also from Table II, multiple correlation was determined for the number of daphnids caught versus the light intensities and the phase of moon as -0.015. Using the same two factors but holding light intensity constant, the partial correlation value is +0.0138. Again, using the same two factors but holding moon phase constant, the partial correlation value is +0.0161. The multiple coefficient value for the number of daphnids caught between 2200 and 2245 vs. preceding hours of sunlight and the light intensities is -0.206. The multiple

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REIF & TAPPA-VERTICAL MIGRATION OF DAPHNIA DUBIA 353

coefficient of correlation value for number of daphnids caught between 2100 and 2345 vs. preceding hours of sunlight and light intensities is 0.224.

DISCUSSION

No correlation existed between the phase of the moon and the vertical migra- tions of D. dubia in Harveys Lake during the summer of 1966.

A noticeable negative correlation existed between the number of hours of sunlight preceding the night in which the daphnids were collected and the number of daphnids taken at the 3-m level. The more the hours of sunlight during the preceding day, the smaller the number of daphnids reaching the 3-m level during the sampling periods. Apparently the daphnids moved down- ward into Harveys Lake to greater depths on brighter days and thus did not reach the 3-m level in as great numbers during the sampling periods.

Several authors have established that populations of cladocerans tend to seek optimum isophots within a lake and thus move in response to changes in light intensity throughout a diel period. Siebeck (1960) has suggested that dark- conditioned animals are more sensitive and so avoid light more actively in the morning than they do increasing light intensities during the day; thus the daphnids he observed were at higher isophots in the afternoon than they were in the morning. That the daphnids move according to the positions of the isophots and that daphnids have several kinds of photoreceptors which apparently operate on different frequencies has been reported by McNaught (1966) and McNaught & Hasler (1966). Our observations in Harveys Lake support the idea that, at least for D. dubia, the longer the isophots are in deeper water, such as on a clear day, the deeper the daphnids apparently move during the period of daylight, and thus the fewer that reach the upper levels during the first half of the period of darkness.

LITERATURE CITED

CLARKE, G. L. & WERTHEIM, G. K. 1956. Measurements of illumination at great depths and at night in the Atlantic Ocean by means of a new bathyphotometer. Deep-Sea Res., 3: 189-205.

ELSTER, H. J. 1954. Uber die Populations dynamik von Eudiaptomus gracilis Sars und

Heterocope borealis Fischer in Bodensee-Obersee. Arch. Hydrobiol., Suppl., 20: 546- 614.

LOZERON, H. 1902. Sur la repartition verticale du plankton dans le lac de Zurich, de decem- bre 1900 a decembre 1901. Vjschr. naturf. Ges. Ziirich, 47: 115-198.

MCNAUGHT, D. C. 1966. Depth control by planktonic cladocerans in Lake Michigan. Publ. no. 15, Great Lakes Res. Div., Univ. of Mich.

MCNAUGHT, D. C. & HASLER, A. D. 1966. Photoenvironments of planktonic Crustacea in Lake Michigan. Verh. Int. Verein. Limnol., 16: 194-203.

REIF, C. B. & TAPPA, D. W. 1966. Selective predation: Smelt and Cladocerans in Harveys Lake. Limnol. Oceanog., 11: 437-438.

SIEBECK, 0. 1960. Untersuchungen iiber die Vertikalwanderung planktischer Crustaceen unter besonderer Beriicksichtigung der Strahlungsverhaltnisse. Int. Revue ges. Hydro- biol. Hydrogr., 45: 381-454.

WALDFOGEL, T. 1900. Der Liitzelsee und das Lautikerreid, ein Beitrag zur Landeskunde. Vjschr. naturf. Ges. Zurich, 45: 277-350.

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