Notes
650
gellae du genre Spurnella Cienk (=Heterochromonas Pascher =Monas 0. F. Muller), chrysomonadine leucoplastidiee. Protistologica 13: 2 19231.
PARKE,M.,I.MANTON,ANDB.
J. CLARKE. 1955,1956.
Studies on marine flagellates 2. Three new species
of Chrysochromulina.
3. Three further species of
Chrysochromulina. J. Mar. Biol. Ass. U.K. 34: 579609; 35: 387-414.
PIENAAR, R. N. 1980. Chrysophytes, p. 213-242. In
E. R. Cox [ed.], Phytoflagellates.
Elsevier-North
Holland.
RICKETTS, T. R. 1965. Chlorophyll
c in some members of the Chrysophyceae. Phytochemistry 4: 725730.
SCAGEL,
R. F., AND J. R. STEIN.
1961. Marine nannoplankton from a British Columbia fjord. Can.
J. Bot. 39: 1205-1213.
SHERR, E. B., AND B. F. SHERR. 1983. Double-staining
epifluorescence technique to assess frequency of
dividing cells and bacterivory in natural popula-
Limnol. Oceanogr.. 31(3), 1986, 650-653
0 1986, by the American Society of Limnology
and Oceanography,
tions of heterotrophic
microprotozoa.
Appl. Environ. Microbial. 46: 1388-l 393.
SIEBURTH, J. McN., AND P. G. DAVIS. 1982. The role
of heterotrophic nanoplankton in the grazing and
nurturing of planktonic bacteria in the Sargasso
and Caribbean
Seas. Ann. Inst. Oceanogr.
58(suppl.): 285-296.
WATERBURY, J. B., S. W. WATSON, R. R. GUILLARD,
AND L. E. BRAND. 1979. Widespread occurrence
of a unicellular, marine, planktonic cyanobacterium. Nature 277: 293-294.
WAWRIK, F. 1979. Eisschlu& und Iesbruchvegetationen in den Teichen des nijredlichen Waldviertels
1977/1978. Arch. Protistenk. 122: 247-266.
WRIGHT,
R. T., AND B. COFFIN. 1984. Measuring
microzooplankton
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Submitted: 2 July 1985
Accepted: 31 January 1986
Inc.
Long range vertical migration of Vdvox in tropical Lake
Cahora Bassa (Mozambique)
Abstract- Volvox sp. performed diel vertical
migrations in Lake Cahora Bassa, the amplitude
of which greatly exceeded those reported for other
species of freshwater algae. Migration velocities
even exceeded the maxima attained by marine
dinoflagellates. The daytime depth distribution
is attributed to the light regime and the nighttime
depth distribution to phosphorus uptake in deeper water layers.
The diel vertical migration of motile phytoplankton does not span the amplitudes
characteristic of zooplankton.
The maximum depth ranges reported for freshwater
phytoplankton
species are 8- 10 m for Peridinium cinctum in Lake Kinneret (Berman
and Rodhe 197 l), 5-7.5 m for Cryptomonas
ovata, Gymnodinium uberrimum, and MalZomonassp. in Finstertaler See (Tilzer 1973),
and 5 m for Ceratium hirundinella in EsthWaite Water (Talling 197 1; Frempong 1984)
and Peridinium penardii in Lake Beryessa
(Sibley et al. 1974). Migrational amplitudes
of marine dinoflagellates reach lo-20 m
(Eppley et al. 1968; Blasco 1978).
Three types of migration patterns have
been reported. Flagellates can be concentrated in the upper water by day and in deeper strata at night (e.g. P. cinctum in Lake
Kinneret, P. penardii in Lake Beryessa).
Flagellates can be concentrated in the upper
water during the day and disperse during
the night (Gymnodinium lacustre in Finstertaler See, Rhodomonas spp. in Lake
Constance: Sommer 1982). A slight descent
during the period of maximum irradiance
may be superimposed on both patterns. A
reverse migration
pattern (concentration
near the bottom during daytime, dispersal
during night) was reported only for the high
mountain Finstertaler See (G. uberrimum,
C. ovata, Mallomonas sp.: Tilzer 1973). The
migrational
behavior of a species may
change during the year (e.g. C. hirundinella
in Esthwaite Water: Frempong 1984).
Lake Cahora Bassa is a large (270 km
long, 32 km max width, 130 m max depth),
manmade reservoir on the Zambezi River.
It stratifies from September to April. As in
most southern African reservoirs, its light
regime is controlled predominantly
by high
concentrations of suspended clay. The an-
Notes
I51
25 Feb
1015
4 Fcb
7Jan
1600
651
2200
137
1630
2030
1600
239
194.5
59
2030
Otll
60
73
Fig. 1. Numbers at bottom-areal
population density in lo3 colonies m-2. Column diagrams-depth
distribution in % of total population. Stippled region-interquartile
zone. Solid lines-vertical
displacement of
transparency in m.
median depth; numbers give migration velocities in m h- I. Broken lines-Secchi-disk
nual maximum of phytoplankton
biomass
(up to 10 g fresh wt m-2) occurs during
stratification, when water transparency is at
its maximum due to the seasonal minimum
of clay concentrations (Gliwicz in press).
The vertical migration of Volvox in Lake
Cahora Bassa was studied on four occasions
l-2
1600
IO15
from January to March 1983. Duplicate
samples were taken at 5-m intervals with a
5-liter Friedinger bottle and sieved through
a 50-pm net to concentrate large plankton.
Volvox colonies had a diameter of 80-l 3 5
pm; daughter colonies grew to > 50 pm before being released from the mother colo-
Mar
OLOO
il5
0030
SRP pg.1-'
500
1000
8
_I
AI
I
d
4..
Fig. 2. Evening descent and morning ascent of Volvox on l-2 March. Symbols as in Fig. 1, but additional
broken line-euphotic
depth (1% light penetration depth, measured directly). Concentration of soluble reactive
phosphorus-P,
water temperature-T.
652
Notes
the vertical displacement of the median of
depth distribution. They ranged from 1.8 to
3.6 m h-l, higher than the maximum velocities of l-2 m h-l of marine dinoflagellates (Hasle 19 50; Eppley et al. 1968; Blasco
1978). The migrational amplitudes of about
18 m on 7 January and l-2 March are close
to the maximum amplitudes of marine phytoplankton and exceed any value for freshwater algae so far reported. The smaller am2boo
2ioo
1600
OLOO obooplitudes on 4 and 25 February are possibly
time
due to the fact that at 2030 hours downward
vertical migration was not yet complete, as
Fig. 3. Proportion of Volvox population within the
indicated by the flat shape of the distribueuphotic water layer (0) and within SRP-containing
tion diagrams.
water layer (0) on l-2 March.
The migration pattern of Volvox conforms to the first type mentioned above,
nies. The entire samples were counted, which
concentration in deep layers during the night.
meant 2 1-126 colonies at peak depths.
Diurnal depth distribution seems to be conTriplicate vertical net tows from 50 m to trolled by the need of light for photosynthe surface were made to obtain an indithesis; on 27 February maximum photocation of horizontal heterogeneity in the synthesis occurred at 2.5 m and significant
Volvox concentration per unit surface area. photosynthesis was found down to 8.5 m
Minimum-to-maximum
ranges were 1.6 5- (Gliwicz 1984). The nocturnal depth distribution could be an adaptation to a lack of
2.45 x lo5 colonies on 7 January, 0.9-1.45
available phosphorus in the upper water
on 4 February, 0.55-1.1 on 25 February,
layers (Salonen et al. 1984). The Volvox
and 0.4-0.75 on 1 March.
species studied so far belong to the algae
The study period fell in a phase of steadily
with the highest phosphorus requirements
declining phytoplankton
biomass (Gliwicz
constants of P-limited
19 84) also reflected by an increase in Secchi (half-saturation
growth, 19-59 pugP liter- l: Senft et al. 198 1).
disk transparency from 1.7 m on 7 January
The importance of the temporal partitionto 3.2 m on 1 March. Throughout the period
ing between diurnal photosynthesis
and
Volvox was an important-in
mid-February
nocturnal phosphorus uptake (Salonen et al.
even dominant-component
of the phyto1984) is strongly suggested by the migration
plankton. The mixing depth was 2.5-5 m.
From the surface down to 10 m soluble re- of the Volvox population in Lake Cahora
active phosphorus was undetectable (detec- Bassa between the euphotic stratum and the
tion limit 2 pg P liter-‘). On 7 January and stratum with detectable amounts of SRP
4 and 25 February only the evening descent (Fig. 3).
of Volvox was followed (Fig. 1); on l-2
UZrich Sommer
March the complete diel pattern of migration was studied (Fig. 2). The shifts in verMax Planck Institute of Limnology
tical distribution were clear enough to preBox 165
clude any misinterpretation
of data because
D-2320 Pliin, FRG
of patchy distribution.
Diel minimum-tomaximum ratios on l-2 March were 1 : 12
Z. Maciej Gliwicz
in the 5-m sample (daytime maximum) and
University of Warsaw
1 : 23 in the 25-m sample (nighttime maxDepartment of Hydrobiology
imum), as opposed to a minimum-to-maximum ratio of only 1 : 2 in areal concentraInstitute of Zoology
Nowy Swiat 67
tion.
00-046 Warsaw, Poland
Descent velocities were calculated from
Notes
References
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M. M. 1973. Diurnal periodicity in the phytoplankton assemblage of a high mountain lake.
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Submitted: I5 May I985
Accepted: 20 November 1985
Inc.
Organic carbon in the Caura River, Venezuela’
Abstract-Samples
were taken weekly over a
2-year period near the mouth of the Caura River,
which drains a large watershed on Precambrian
shield covered with tropical moist forest. The
concentrations of dissolved organic carbon were
essentially static despite a 1O-fold seasonal change
in discharge. Particulate carbon showed an unexpected but relatively weak inverse relationship
to discharge. Yield of total organic carbon (12.3
g C m-2 yr- I) was higher than would have been
expected from the literature. Yield can be predicted accurately from discharge because of the
strong homeostasis in concentration of dissolved
organic carbon.
Information on concentrations of organic
carbon in rivers throughout the world has
become considerably richer over the last 10
years (Degens et al. 1984). Even so, detailed
1 This work was supported by National
Science
Foundation grant BSR 83- 154 10 and by the Venezuelan Ministerio de1 Ambiente y Recursos Naturales Renovables. J. Meyer and an anonymous reviewer commented on the manuscript.
information on organic carbon in large rivers
draining tropical moist forest is still very
scarce (Schlesinger and Melack 198 1). Our
2-year study of the Caura River, a tributary
of the Orinoco, provides concurrent measurements of particulate organic carbon,
dissolved organic carbon, and discharge for
a large river draining undisturbed tropical
moist forest.
The Caura River watershed (47,500 km2)
is located between 4” and 8”N lat within
Venezuela. The watershed, which is virtually uninhabited, occupies a portion of the
Guayana shield, a highly weathered Precambrian formation. The vegetation of the
watershed is a mixture of premontane rainforest (29%) with precipitation
of about
6,000 mm yr-l, very humid tropical and
premontane forest (42%; 3,000 mm yr-l),
and humid tropical forest (29%; 2,200 mm
yr- ‘) (Ewe1 et al. 1976). Average runoff is
close to 2,400 mm yr-l.
We sampled the mouth of the Caura at