Abstract:
Endogenous rhythm study on deep sea organisms has been very limited in the
past. In this light, he suggestion by Riise of a circadian or circatidal rhythm in the soft
coral Anthomastus ritterii becomes extremely interesting. The purpose of this study
was to verify this hypothesis as well as to entrain the creatures to a controlled thythmic
stimuli. The data collected does not verify that hypothesis, but interestingly enough,
does point to an endogenous rhythm. The colonies appear to be quite periodic, but
follow a highly individual cycle, with period times ranging from 16.8 hours to 38.8
hours. The cycle seems to be unperturbed by controlled environmental cues such as
light, feeding, and mechanical distrubance. Study of a juvenile with a radically shorter
period of 7.7 hours suggests important changes in development with respect to this
periodicity.
Introduction:
Research pertaining to the soft deep-sea coral Anthomastus ritterii (Alcyonacea:
Alcyonidae), which inhabits the rock face and sediment cover of the Monterey Canvon.
has been slight, despite its discovery nearly 90 years ago. [Abbott, 19871. This
octocoral lives as a colony with two distinct polyp forms: large feeding polyps called
autozooids and small bump-like polyps known as siphonizooids, which serve to
circulate water through the colony. The gastrovascular cavities of the polyps extend
through a common lobe called the capitulum. [Nutting, 1913), allowing for a common
nutrient pool. The portion of the autozooids which emerge from the capitulum are
collectively known as the anthocodia. [Hyman, 1940).
In response to the lack of study on this coral, Riise undertook a basic
behavioural analysis on A. ritterii. Suggested in the course of his study was a possible
circadian or circatidal rhythm associated with anthocodia and capitulum contraction,
fairly routine behaviour exhibited by the coral. [Riise, 1990). Though similar rhythms
have been found in other marine species-sea pens (Mori, 1961), anemone [Buisson,
1988), various bivalve species, and numerous higher organisms including shoreline
crabs-no such rhythm has been upturned in a non-littoral species. This makes Riise's
suggestion tremendously fascinating; indeed, the habitat of A. ritterii would not seem to
hold the possibility, nor the need, of an endogenous rhythm. Because the colonies
reside in a benthic habitat, with a depth range of 210m to 1236m in Monterey Canyon,
many would not be affected be diel light or temperature changes to any appreciable
degree, nor would they be affected by wave exposure, which are predominant
environmental time cues for circadian and circatidal rhythms respectively. Even more
startling is the fact that neighbouring colonies are often seen out of phase with each
other, some with retracted anthocodia while others have extended anthocodia.
The force driving my research was to verify, in part, Riise's hypothesis of a
circadian or circatidal rhythm, and also to attempt to alter the periods of the colonies
Page 2.
using controlled environmental stimuli. My research supports only part of Riise's
supposition: individual colonies of A. ritterii have a very precise endogenous rhythm
of anthocodia contraction/expansion, but the free-running rhythm, the cycle displayed
in the absence of environmental time cues, is highly variable between individuals and
does not necessarily approach a diel or tidal periodicity. My attempts to alter the
periodicity of the colonies were not successful, leaving the endogenous rhythm even
more intriguing.
Materials and Methods:
The set of experiments discussed below were undertaken with a set of ten
separate colonies obtained using the Monterey Bay Aquarium Research Institute
(MBARI) remotely operated vehicle (ROV). Samples were obtained from depths
between 670m-700m, at a site near Soquel Canyon (37°12N, 122°03W). The
colonies were then placed in a large tank with continuously flowing seawater chilled to
5°C. Observations were recorded using time-lapse video recording. The series of
experiments are detailed below:
Continuous bright light recording.
Alternating bright light/dark periods (LD 12:12)
The colonies were left in bright light and dark for alternating periods of 12
hours each. Light period observations were done using time-lapse video
recording; dark period data were recorded by direct observation at 2 hour
intervals using red light.
Feeding study
The colonies were fed three to four drops of homogenized krill approximately
every 25 hours.
Mechanical stimulation
Using forceps, the colonies were triggered into retracting their anthocodia. This
stimulation was done every 24 hours.
• Young colony study-continuous bright light
This study employed a colony which had settled approximately three months
prior, and had three autozooids.
Page 4.
Results:
The results for the constant light recording are detailed in Table 1. Notable is
the wide range of periods, from 16.8 hours to 38.8 hours, as well as the precision of
the rhythm, with variation in individual colonies of only. 45 hours to 1.46 hours.
The alternating periods of bright light and dark (LD 12:12), the periodic feeding
study, and the mechanical stimulation did not succeed in altering the periodicity of the
Anthomastus colonies. The colonies maintained roughly the same periods as in the
constant bright light, and hence, this data has not been repeated.
The data for the juvenile has been included in Table 1 to facilitate comparison.
Notable is its much shorter periodicity of 7.7 hours, as well as the precise time-
measuring, varying only .52 hours.
Discussion:
Continuous bright light recording
The continuous bright light recording in the controlled environment of the
chilled seawater tank provides data on the free-running period of the colonies, the
endogenous cycle which occurs when environmental time cues (Zeitgebers) are
removed. This data shows a strong endogenous cycle of behaviour, but does not
support à free-running circadian behaviour. The periods ranging from 17-39 hours,
though, can incorporate Riise’s observation of a 27 hour period.
Additionally, as is suggested in Table 1, the periodicity should be judged on the
basis of anthocodia retraction, or secondarily, capitulum contraction. The duration of
time between anthocodia retraction and capitulum contraction is virtually constant in an
individual, and the period judged by anthocodia retraction is very rhythmic. However,
the periods judged by anthocodia extension are only vaguely periodic, agreeing well
with the observation that the anthocodia retraction is coordinated and simultaneous,
while anthocodia extension is more individual lacking evidence of central control. The
durations of expanded and closed postures seem to be substantially more variable than
the periodicity judged by the anthocodia retraction, but do corroborate Riise's finding
of a 60:40 time ratio between expanded and closed postures.
Bright light treatment, while providing free-running oscillation data, has the
disadvantage of adding photic stress as well as thermal stress to the colonies. In other
creatures, continuous bright light has been show to lengthen periodic behaviour cycles,
(Parker, 1974), and a similar alteration may be occuring here.
Alternating light/dark periods (LD 12:12)
Page 6.
The conditions of this experiment were designed to duplicate light conditions
for the shallower members of A. ritterii, as well as a shallow-water relative, A.
grandflorus, which inhabits depths of 20m-200m off the South African coast [Nutting,
1908]. A. grandflorus could use light change as a Zeitgeber to perform a circadian
rhythm, and were this true, A. ritterii could show a similar behaviour despite its lack of
exposure to light change. The data for this experiment, though, does not support any
change in periodicity for A. ritterii.
Feeding study
These organisms, from Riise's assessment, are filter feeders, ingesting small
planktonic species. Because of the well-documented circatidal planktonic migration
rhythm, and additionally because feeding can form a common Zeitgeber, observations
were recorded under a periodic feeding schedule. Once again, because of the depth of
habitat, A. ritterii are not exposed to the planktonic migration to any significant degree.
This data, as with the LD 12:12 cycle, showed no change in the periodicity for A.
ritterii.
• Juvenile study
This study showed the same behaviour as seen in the adults under constant
bright light, but with a markedly shorter period than that found in any of the adults.
Page 7.
The picture which this series of experiments presents is extremely difficult to
decipher: a benthic species which within individual colonies maintains a carefully
controlled endogenous cycle of behaviour, but which does not coordinate its activities
neither with environmental cues nor the activity cycle of its neighbors.
The deep-sea aspect of A. ritterii's behaviour is intriguing alone. Little has been
discovered concerning an endogenous rhythm in a creature inhabiting the region below
the intertidal zone. Without light exposure or radical temperature change, one would
hardly expect evidence of a rhythmic behaviour. Notable however, is Willows'
suggestion of circatidal behaviour in the nudibranch Tritonia diamedia, which inhabits
the same depths as A. ritterii. This activity rhythm involves orientation with the Earth's
magnetic pole according to the phase of the tidal cycle. T. diamedia has been implicated
as a possible predator of A. ritterii, which could suggest that the rhythm of one evolved
in response to the other. For the nudibranch, the circatidal rhythm could prepare it for
the increased availability of food, while for the coral, an endogenous rhythm could helr
avoid anticipated predation.
The lack of response to controlled environmental stimuli is also troubling.
While we could postulate reasons for a biological clock which quickly reacted to light
or feeding cycles, reasons come to mind much more slowly in the unresponsive case of
A. ritterii. Light and feeding are generally the two most powerful Zeitgebers, which
seem to have little effect in altering the periods of the coral, certainly failing in
entraining them to a 24 or 25 hour cycle. Generally, circadian or circatidal rhythms are
explained as adaptations which aid in anticipating environmental change. For example,
the anemone exhibits both circadian and circatidal rhythms in contraction, anticipating
the sharp change to a bright, hot, desiccating environment devoid of food. [Buisson,
1988]. The tidal rhythm of plankton migration, as well, is thought to have evolved as
predator avoidance, and seemingly exerts a rhythmic effect on creatures well up the
Page 8.
food chain from plankton. [Cloudsley-Thompson, 1961] Here though, the rhythm
does not approximate any known geophysical rhythm, and it is difficult to view this
rhythm as an adaptation for the benthic habitat of A. ritterii.
Most troubling of the details of the periodicity of A. ritterii is that colonies are
asynchronous in their contraction/expansion cycles. The variance in circadian or
circatidal rhythms for individual organisms has been reported at most, at four hours
from 24 or 25 hours under constant conditions. [Parker, 1974). Were the endogenous
rhythm of A. ritterii to be termed circadian, there would be an individual organismal
variance of at least 14 hours. The adaptive value of such an endogenous rhythm which
does not even roughly coincide with a neighbouring colony is at first highly
questionable. One possibility explaining this circumstance is the fact that variable
periods might avoid competition. Imagining two neighbouring colonies, one can
readily see the advantage of asynchrony in feeding times to avoid competition. One can
also posit that the clock of the Anthomastus, unlike higher organisms, has not evolved,
or perhaps does not need, a complex entailing an environmental time cue processor,
and works simply on the basis of a homeostat. This homeostatic control would explain
Riise's observation that the colonies spend 60% of their time open and 40% of their
time closed, as well as the individual variability in period length.
The juvenile study also poses some interesting questions. The excessively
short period of the juvenile with respect to the adults can be explained in three possible
ways. The first is that the juvenile has a period which is on the lower end of the
distribution of possible periods, which was simply not reflected in the period lengths of
the adult colonies. Another possibility is that the organisms have a size-related
mechanism of retraction. Were the mechanism of retraction more efficient in a smaller
organism, one might expect the juvenile to have such a period; this possibility, though,
is contradicted by the presence of smaller adults which have much longer periods, 36
and 38.8 hours. A final possibility is that there exists a correlation between maturity
Page 9.
and period length. As is seen in some intertidal organisms and many terrestrial
organisms, young organisms tend to short, fractured periods, while adults are capable
of more extended period lengths.
Literature Cited
Bayer, F. M. (1952). Descriptions and Redescriptions of the Hawaiian Octocorals
Collected by the U. S. Fish Commission Steamer "Albatross." Pacific Science. 6
(1): 126-128.
Buisson, B. (1988). Expansion/Contraction Rhythms in the Anemone. Bulletin de la
Société de Zoologistes Françaises. 113 (3): 279-284.
Cloudsley-Thompson, J. L. (1961). Adaptive Functions of Circadian Rhythms. Cold
Spring Harbor Symposium on Quantitative Biology. 25: 345-357.
Hyman, L. H. (1940). The Invertebrates: Protozoa through Ctenophora. McGraw-
Hill Book Company, Inc. New York. pp. 365-399, 538-551.
Mori, S. (1961). Analysis of Environmental and Physiological Factors on the Daily
Rhythmic Activity of a Sea-Pen. Cold Spring Harbor Symposium on Quantitative
Biology. 25 : 333-344.
Nutting, C. C. (1913). Descriptions of the Alcyonaria Collected by the U. S. Fisheries
Steamer "Albatross," Mainly in Japanese Waters, During 1906. Proceedings of the
United States National Museum. 43 : 22-25.
Palmer, J. D. (1974). Biological Clocks in Marine Organisms: The Control of
Physiological and Behavioural Tidal Rhythms. Wiley and Sons. New York. pp.
1-13.
Riise, S. (1990). Distribution, Feeding Behaviour, and Anthocodia Retraction of
Anthomastus ritterii Nutting, 1909, in Monterey Bay. (unpublished manuscript on
file at Hopkins Marine Station).
Page 11.
Table 1:
Mean period and deviation data for continuous bright light conditions.
Deviations are shaded; mean durations are clear.
Organism
Withdrawal
Extension
Transition
Perioc
13.40
8.80
0.22
22.20
.
.
.
......... 4.42
0
1.04
1.02
11.74
4.92
0.20
16.80
.
.
.
. .
0.84
02
0.0
19.60
3.75
23.4


.
.

0.0

3.60
0.00
22.40
18.60






.0

0.40
38.8
31.4

.
.
0.0
2


19.40
11.64
0.25
7.80
..........2.
...... .8
.......
1.0
26.64
5.50
0.00
32.10

.

4.0
1.90

20...
4.60
0.16
Young
3.10
7.68
...... 0.7........... .60
0.0
Colony
Page 12.
Uskrovledgenent
would like ko Hank Chick
Baxhar pa his genenons suppork
and conragionz exertemen.
May khe graen Ale Slow
neVarandengly,Chuck.





















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