ISSN 1063-0740, Russian Journal of Marine Biology, 2006, Vol. 32, No. 1, pp. 12–19. © Pleiades Publishing, Inc., 2006.
Original Russian Text © E.A. Titlyanov, T.V. Titlyanova, I.M. Yakovleva, T.L. Kalita, 2006, published in Biologiya Morya.
The symbiotic intracellular zooxanthellae
(dinoﬂagellates) of some marine invertebrates, includ-
ing reef corals, have well expressed daily variations of
cell division [4, 15, 20]. Hoegh-Guldberg and Smith [6,
8] determined that the peak of cell division of zooxan-
thella in the coral
falls in the
period from 12 a.m. to 6 a.m., in the coral
—from 4 a.m. to 6 a.m. Patton and Burris 
detected the daily division rhythm of symbionts in
and ascertained the peak of this pro-
cess to be at night. However, Wilkerson et al. [30, 31]
did not ﬁnd a daily cyclicity of zooxanthella division in
nor in nine species of reef-building corals in
Jamaica. Periodicity of zooxanthella division was not
detected in the coral
collected at depths of
20–40 m in Eilat Bay .
Intracellular digestion or degradation of zooxanthel-
lae by the cells of the corals
also have daily cyclicity peaking in
the second half of the night . The maximal number
of zooxanthellae at the stage of degradation and of
those already dead is found within the tissues of the
at midnight [4, 5].
Reimer and Hoegh-Guldberg et al. [7, 16] detected
the daily ejection rhythmicity of healthy zooxanthella
and those that appeared healthy from the coral tissues.
However, Titlyanov et al. [20, 22, 24] did not observe
the daily ejection periodicity of healthy zooxanthellae
from scleractinian corals in the time of both starvation
and additional feeding by zooplankton.
The daily periodicity of division and digestion of
zooxanthellae in different body parts of the scleractin-
has been stud-
ied by us [20, 29]. These two processes are shown to
peak in the second half of the night (from 3 till 5 a.m.).
Under normal physiological conditions, the share of
newly produced zooxanthellae during the day is
counted to be 2–4% of the total within the coral tissues.
It almost coincides with the number of zooxanthellae
digested per diem.
Zooxanthellae of the scleractinian coral
from Eilat Bay were noticed by us for the ﬁrst time to
have more than a daily proliferation periodicity of
zooxanthellae . Symbiotic algae of the same coral
species from the reefs of Sesoko Island show two types
of long-term rhythmical changes in the proliferation
speed with periods of three and six days .
The reasons for disturbances in the proliferation
rhythmicity in zooxanthellae of symbiotic cnidarians
are poorly known. The daily proliferation rhythms both
in the host cells and in symbionts are mainly connected
with the natural light (sun) rhythm . At the same
time, the period and the proliferation intensity of sym-
bionts are inﬂuenced by periodic supply of zooxanthel-
lae and mineral food (inorganic nitrogen) [3, 4].
Rhythmical Changes in the Division and Degradation
of Symbiotic Algae in Hermatypic Corals
E. A. Titlyanov
, T. V. Titlyanova
, I. M. Yakovleva
, and T. L. Kalita
Institute of Marine Biology, Far East Division, Russian Academy of Sciences, Vladivostok, 690041 Russia
Sesoko Station of Tropical Biosphere Research Center, Okinawa, 905-0227 Japan
Received March 18, 2005
—Three types of rhythmical changes in division and degradation (digestion) have been found and
described in the symbiotic zooxanthellae of the scleractinian coral
and in the colonial
collected at the reef of Sesoko Island (Okinawa, Japan). The ﬁrst type of changes
is daily variation of the intensity of these two processes peaking at night. The second
type of rhythm changes described in
is opposing variations of cell division and
degradation levels with a period of three days. The rhythm is disturbed by sudden weather changes or by vari-
ations in light. Rhythmical alterations of zooxanthella proliferation and degradation of the third type found in
have a period of 5–6 days and are connected with oppositely directed changes as well as with
alterations of the second type. The rhythm of such alterations is not disturbed by abrupt weather changes. All
three types of rhythmical changes in zooxanthellae division and digestion observed in hermatypic coral are sup-
posed to be directed to the regulation of the population density of zooxanthellae in organism tissues.
corals, zooxanthellae, rhythm, zooxanthella division, zooxanthella degradation.