Occurrence of Zooxanthellae in Anthopleura
elegantissima and A. xanthogrammica as a function of
light and depth in subtidal and intertidal zones.
Joan M. Glasser
Hopkins Marine Station
June 1975
(Glasser, page 2)
ABSTRACT
Using the amount of Chlorophyll A as an indicator of
numbers of zooxanthellse (Dinoflagellata) present per gram
tentacle of Anthopleura elegantissima and A. xanthogrammica,
it was found that the amount decreased with subtidal depth.
The scarcity of Anthopleura below 10 feet depth appears not
to be dependent on the availability of light, but on other
unknown factors.
(Glasser, page 3)
Introduction
Anthopleura elegantissima (Brandt 1835) and Anthopleura
xanthogrammica (Brandt 1835) are common sea anemones in the
intertidal and subtidal zones of the Monterey Peninsula.
Often these animals contain Dinoflagellates known as zooxan-
thellae living symbiotically in the gastrodermal tissue.
(Muscatine, 1961) These are unicellular brown or yellow-
brown algae and provide photosynthetic products to the host
anemone. (Muscatine and Hand, 1958)
I was interested in seeing whether the anemones Antho-
pleura xanthogrammica and A. elegantissima had differing
amounts of symbionts in the intertidal and subtidal zones.
I wanted to see whether there was a relationship between an
increase in depth subtidally to 30 to 710 feet and the
number of zooxanthellae in the anemones.
(Glasser, page 1)
Materials and Methods
To approach this problem some preliminary field obser-
vations were first made. After noticing that A. elegantissima
could be found as deep as -35 feet, anemones were sampled
at different depths in both the intertidal and subtidal zones.
Three A. elegantissima and three A. xanthogrammica were col-
lected at different depths. Each of these was tested re-
peatedly, serving as a control, in order to establish the
amount of variance in the pigment analysis procedure.
To get many different samples, three to five anemone
tentacles were snipped off with scissors underwater and placed
in a glass vial. Depth and unusual light conditions that
existed were recorded.
After collecting tentacle samples from depths of plus 3
to -37 feet, the amount of Chlorophyll A pergram of tentacle
(wet weight) was measured. The amount of Chlorophyll A was
assumed to be a function of the amount of zooxanthellae present.
Tentacle samples were blotted dry on a paper towel to
eliminate excess water, then weighed. Next water was added
to make a.5 ml equivalent of water and 4.5 mls of scetone
were added. This solution was homogenized and centrifuged
for 10 minutes. The optical density of the extract was
measured at three different wavelengths against an acetone
water blank in a Beckman Spectrophotometer Model 200. The
amount of ChlorophyllA present was determined by the equation
5( 15.6 (0D 665) - 2(0D 445) - 8(0D 630)) and was divided by
the weight of the sample to give mg of Chlorophyll A per
(Glasser, page
gram of tentacle.
The amount of light was measured using an underwater
Gold Crest photographic light meter. Light readings were
taken on four different dives at many different depths by
recording incident light. The light meter was calibrated
using a Photovolt Universal Photometer Model 200 to obtain
light values in foot candles.
Results
Data from experiments and field observations indicate
that the amount of Chlorophyll A present was a function of
light. This also correlated with depth since the light
intensity decreased as depth increased.
Figure 1 shows that as incident light available to the
anemone increases, the amount of Chlorophyll A per gram of
tentacle increases also. In very dark areas, almost no
zooxanthellae occurs in the tissue and in bright sunlight,
such as in the intertidal, the most numbers of zooxanthellae
are present.
Figure 2 shows a decrease in amount of Chlorophyll A
per gram tentacle as depth increases. The deepest anemones
sampled, usually A. elegantissima, have the least amount of
Chlorophyll A and also the least numbers of zooxanthellae.
Figure 3 shows a decrease in incident light as depth
increases. There can be also a lot of variability in light
c
(Glasser, page 6)
intensity due to the position of the kelp canopy.
In figure 4, a light reading was taken according to
the orientation of the anemone from which the tentacles were
taken. The low points between -30 and -40 feet were from
samples under the kelp bed. This graph shows how light and
the amount of Chlorophyll A paralleled each other as depths
went from -15 to -40 and back up to -15 feet.
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(Glasser, page 7)
Captions
Graph I: This graph shows the correlation between
light and Chlorophyll A. As light intensity increases,
the amount of Chlorophyll A increases.
Graph II: Each point represents a separate snemone sam-
ple of tentacles. As depth increases, the amount of Chloro-
phyll A decreases. This function is significant with a
99.9% probability.
Graph III: This shows the decrease in amount of light
as depth increases.
Graph IV: Here the amount of light was recorded where
each tentacle sample was taken. This shows the correlation
between Chlorophyll A and light intensity despite fluctations
with depth.
(Glasser, page 8
Discussion
The specific location of A. xanthogrammica and A. ele-
gantissima in the intertidal and subtidal zones influences
greatly the amount of zooxanthellse living in them (Muscatine,
1971). From the data, it appears that light determines the
amount of zooxanthellae and also decreases with depth. At
varying light conditions at a constant depth, the amount of
Chlorophyll A per gram of tentacle varies and if light is
constant and depth varies, the amount of Chlorophyll A is
constant also.
Some observations that support this are: 1) The deeper
anemones are found, the paler they are. Also, an anemone
slightly covered by an overhanging rock at -30 feet will be
much paler than an anemone covered by a similar overhanging
rock at-10 feet.
2) The anemones under the cannery are either white or
very pale with almost no zooxanthellae in them. (The cannery
blocks out most of the light.)
3) On the wharf pilings there is a gradation in amount
of pigment on individual pilings. The A. elegantissima and
A. xanthogrammica on the bright side of the pilings show
three times more zooxanthellae than those on the shady sides
of the pilings. These anemones can be of the same clone but
will vary greatly in the amount of pigment.
1) Under the kelp bed the anemones are paler than anem-
ones elsewhere. The kelp canopy cuts some light out which
(Glasser, page 9)
appears to affect the amount of zooxanthellae.
There is a considerable amount of variance in number of
zooxanthellae from anemone to anemone at a given depth due
to the changing light conditions subtidally (kelp cover and
orientation on or under rocks affect this greatly.)
Observations also show that light is not the factor lim-
iting the distribution of Anthopleura since without symbionts
they are found in dark areas such as under the cannery.
However, specific other factors controlling their occurrance
beyond 10 feet depth where they are scarce are not known.
In summary, the amount of Chlorophyll A decreases as
light decreases; this is apparent in the larger amount of
ChlorophyllA in the intertidal anemones. Light also decreases
as depth increases which tends to establish a vertical
gradient. Many factors influence the amount of light the
anemones receive such as their orientation, covering of over-
hanging rocks, their position on wharf pilings, the kelp
bed, and their depth. It would also be interesting to see
how the amount of photosynthetic products available to the
anemone changes as a function of light and depth and if a
change would affect the distribution of anemones.
(Glasser, page 10)
Literature Cited
Muscatine, L., 1961, Symbiosis in marine and fresh water
coelenterates. In: H. Lenhoff and W. F. Loomis, eds.,
The biology of hydra and of some other coelenterates,
pp. 255-268. Coral Gables, University of Miami Press,
Muscatine, L., 1971, Experiments on green algae coexistant
with zooxanthellae in sea anemones. Pac. Sci., 25,
pp. 13-21.
Muscatine, L. and C. H. Hand, 1958, Direct evidence for
transfer of materials from symbiotic algae to the tissues
of a coelenterate. Proc. Nat. Acad. Sci., 44, pp. 1259-1263.