Activity Patterns of Cyanoplax
LYMAN
ABSTRACT
The chiton Cyanoplax hartwegii (Carpenter, 1855), found inter-
tidally on Mussel Point, Pacific Grove, California under the brown
alga Pelvetia fastigiata (J. G. Agardh) DeToni, was found to be more
active at night and negatively phototactic in the lab. Protection
afforded by the Pelvetia habitat could explain the considerable day-
time activity that does occur. The tidal cycle affected the animals'
activity, greatest activity occurring at dry and awash periods.
Lesser activity during the high tides may be due to the strength of
the surge or to the difficulty in feeding on Felvetia during these
times. Although strict homing was not exhibited by the C. hartwegii,
certain "campsites on the substratum were occupied successively by
different individuals. This behavior may have survival significance,
as these campsites may be consistently well-protected spots.
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Activity Patterns of Cyanoplax
page 2
INTRODUCTION
The chiton Cyanoplax hartwegii (Carpenter, 1855) has
been studied taxonomically (e.g., Tryon and Pilsbry, 1992:
Berry, 1922), and Ricketts and Calvin (1952) note that the
chiton is found under clumps of Pelvetia during the day and
prefers relatively quiet waters. There appears to be little
known about the animal beyond this. To gather more information
on its biology I observed the daily and nightly activities
of a population of C. hartwegii on Mussell Point in Pacific
Grove, California, during the spring of 1974. My findings
on when and where the animals move, their homing behavior
and phototactic behavior are herein reported along with a
discussion on possible selective advantages of this behavior.
HABITAT OF CYANOPLAX
The Mussel Point Cyanoplax hartwegii were commonly found
under the brown alga Pelvetia fastigiata (J. G. Agardh) DeToni
in areas of moderate or weak surf action. The animals were
generally on bare granite or on the encrusting red algae
Hildenbrandia occidentalis Setchell, Petrocelis franciscana
Setchell and Gardner, or crustose corallines. Numerous
tufts of the red algae Gigartina papillata (C. A. Agardh)
J. G. Agardh, Endocladia muricata (Postels and Ruprecht)
J. G. Agardh and some Corallina officinalis Linnaeus were found
in these areas. Such mobile fauna as the snail Tegula
funebralis (Adams, 1854), the limpets Acmaea pelta Eschscholtz,
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Activity Patterns of Cyanoplax
page 3
1833, A. digitalis Eschscholtz, 1833, A. limatula Carpenter, 1864,
and A. scabra (Gould, 1846), the crab Pachygrapsus crassipes
Randall, 1839, the hermit crabs, Pagurus spp. and a variety
of gammarid amphipods were frequently found in all my study
areas. Of the sessile animals present, the anemone
Anthopleura elegantissima (Brandt, 1835), the small barnacle
Chthamalus sp. and the annelid worm Phragmatopoma californica
(Fewkes, 1889) were the most common.
ACTIVITY PATTERNS
To mark individual chitons whose movements were to be
followed, small numbered labels of waterproof paper were
attached to the shell plates utilizing a reportedly non-toxic,
quick-drying contact glue ("ZIP-GRIP" 10; Devcon Corporation,
Danvers, Mass.). To monitor the positions of the chitons,
I used a 50 cm x 50 cm grid marked off in 10 cm intervals
which was aligned to marked reference points on the transect
during times of data collection.
To investigate the chitons' diurnal activity patterns,
I labelled in situ thirteen Cyanoplax hartwegii from Mussel
Point found living within an area approximately 3 mxIm
between the +2.5 and +4.0 foot tidal levels. Starting
approximately 6 hours after the labelling, the animals were
observed at one hour intervals begiining at 1800 on May 13th
and ending at 2000 on May 15th, and their positions were
recorded for each observation. Night-time observations were
Lyman Activity Patterns of Cyanoplax
page 4
using a dim red flashlight. A second set of hourly observations
was made on the same population from 2000 on May 19th to 0800
on May 22nd, a time when the tidal cycle was six to seven
hours out of phase with the previous cycle. The number of
animals located each hour varied from ten to all thirteen.
The results of the two watches are shown in Figures 1
and 2. These indicate that the animals moved much more at
night than in the day, a pattern observed in other species
of polyplacophorans (Heath, 1899; Glynn, 1970; Smith, 1974).
There is also an indication that the animals moved more
when they were dry (completely exposed to air) or awash
(covered less than half the time by lapping waves) than
when they were submerged (covered more than half the time).
Assignments of the categories "awash", "submerged" and "dry'
were subjective and conditions could vary at one particular
tidal height, depending upon the surge. The relation of
activity to tidal height and conditions of exposure to sea
and air is illustrated in Figure 4. In Figure 3, the data
is organized to show the relationship of activity to conditions
of tidal exposure and the light cycle.
During the day, fewer animals moved when submerged than
when dry (Mann-Whitney U-Test; P(.001) or awash (P(.01).
and a slightly larger number moved when dry than when awash
(.I( PV.2). For the average distance moved, there is a
similar relationship: lesser movement while submerged than
awash (.05(P(.1) or dry (P(.05) and slightly greater
movement when dry than when awash (.2 (P (.4). A night.
Lyähn
Activity Patterns of Cyanoplax
page 5
activity patterns were similar-i.e., the animals moved more y
when awash (P £.002) or dry (P (.002) than when submerged.
Their activity was approximately equal during both their dry
and awash paeriods. Contrasting diurnal with nocturnal
patterns, more animals were moving nightly while submerged
(.05(P (.1), awash (P(.001), and dry (P£.001) than during
the day. They also moved greater distances at night while
awash (.02( P (.04) and dry (P(.002) than during the day.
There was very little difference between day and night
movement when they were submerged (P(.1).
PHOTOTACTIC BEHAVIOR
Negative phototaxis has been observed in some chiton
species (Crozier, 1920; Heath, 1899; Westersund, 1974) and is
possibly related to their nocturnal behavior; consequently
I tested Cyanoplax hartwegii for a light response. Sixteen
animals, laboratory and dark adapted for 12 days, were placed
in the middle of a shallow tray, with eight facing toward a
light source and eight away. The light source was a 500-watt
incandescent bulb placed about six inches above one end of
the tray and about 11 inches away from the chitons. After
the chitons had settled (usually two to three minutes), the
light was turend on for twenty minutes. I ran four trials
with the same sixteen chitons, rinsing and turning the tray
180° and allowing the animals to dark adapt for 30 minutes
between trials. The first three trials were run with the
animals on a thin film of seawater. Hoping to diminish
any response to heat from the bulb, I ran the fourth test
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Activity Patterns of Cyanoplax
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with the animals totally submerged infresh seawater. The
results were similar for all the tests: out of 64 choice
situations, 52 responses were away from the light, two were
toward the light, and ten showed no response.
HOMING BEHAVIOR
My activity studies showed that the chitons' overall
activity is greater during periods when they are not submerged.
In those studies, some animals returned to their starting
points after periods of movement while others did not.
To examine further the incidence of homing behavior,
marked 84 chitons with numbered labels and recorded their
positions once daily during low tide for 14 days, starting
April 27th, 1974. Homing was considered to exist when
animals were repeatedly found in a precise location or home¬
site. Only ten of these animals displayed homing over the
entire period, while another 22 homed for periods varying
from three to thirteen days. I displaced the eleven most
consistent homers not more than 10 cm from their respective
homes. Only two returned home within 24 hours; three weeks
later, only one was found in its original home.
I returned on June Ist to the same area at low tide
and attempted to locate the 84 marked chitons. One-third
(28) were found, of which 17, though for the most part not
in their original homesites, were still in their original
areas (either under the same Pelvetia clump or not more than
20 cm from it). Of the remaining eleven animals, nine had
moved to different Pelvetia clumps ranging from 30 to 104 cm
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Activity Patterns of Cyanoplax
page 7
away. Only two left the Pelvetia community altogether and
both were found on exposed granite among clusters of Anthopleura
elegantissima. One had traveled 65 cm., and the other had
gone an impressive 186 cm., made notable by the fact that.
in order to reach this new area, the animal either had to
cross a stretch of sand, or follow a rather lengthy, circuitous
route over a rock bridge.
The above results clearly show that individual chitons
may reside at, or consistently return to, a homesite for a
period of at least two weeks, and they indicate that homing
is a rather transient phenomenon. However, the results
of the activity studis show that at low tide, when observations
for homing were made, more of the chitons are moving and, therefore,
they are less likely to be in their homesites. Thus, the chitons
may be more consistent in their homing behavior than my studies
suggest.
DISCUSSION
In populations of Cyanoplax hartwegii living under
Pelvetia, movement was mainly nocturnal. Some animals were
active during the day, which behavior may in part be related
to the fact that the Pelvetia affords some protection from
heat, desiccation, and predation. The chitons moved more
during periods when they were dry or awash than while submerged.
This is not the case for the chiton Mopalia muscosa (Gould, 1846)
page 8
Lyman Activity Patterns of Cyanoplax
whose activity is far greater when submerged (Smith, 1974).
Possible advantages of this behavior to Cyanoplax are discussed
below.
Many Cyanoplax hartwegii are located on smooth rock, and
they cling less firmly and are thus more readily dislodged
from the rock substratum than Mopalia muscosa or Nuttallina
californica (Reeve, 1847), which are found in the same area.
It is possible that the strength of the surge is strong
enough to detach moving Cyanoplax, but not ones which are
inactive on the rock.
Another possible advantage of decreased activity during
submerged periods is suggested by Connor (1974) and concerns
the animal's diet. Cyanoplax hartwegii were frequently
observed feeding on Pelvetia and this alga makes up the
great bulk of their gut contents (Robb, 1974). While the
Cyanoplax are submerged, the Pelvetia clumps, attached by one
relatively small holdfast to the rock, are afloat and
considerably agitated by the surge. This would make feeding
on the thallus difficult. This is not the case when the chitons
are merely awash or dry, and it is during these periods, in
the day or night when Pelvetia lies prostrate on the rocks,
that I have observed the animals feeding onbranches of the
alga.
Although I did not find consistent homing behavior in
Cyanoplax hartwegii, they did appear to prefer certain areas
on the substrate to others. These "campsites" were frequently
occupied by a chiton during the animal's less active periods.
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Activity Patterns of Cyanoplax
page 9
Sometimes the same chiton would home to one location consistently
for days, but eventually it would leave and another Cyanoplax
would take its place. There were over a dozen such locations
on the transect used for the two lengthy watches and I could
see this phenomenon occurring in other transects where I
had marked C. hartwegii. The high frequency of habitation of
these particular sites versus other possible sites suggests
strongly that these sites are "recognizable" by the
animals, possibly by recognition of chemical cues. Thorne
(1967) suggests that such an accumulation of chemicals on the
substratum at the homesite is the cue for homing in the chiton
Acanthozostera gemmata (Blainville). Most of the sites
appeared to offer the Cyanoplax some protection, being
located in a crevice, depression, tidepool, or among
Phragmatopoma or Anthopleura elegantissima. It seems
likely, whatever the mechanism involved, that this behavior
has some survival value for the animal, such as consistent
protection from desiccation.
SUMMARY
1. The chiton Cyanoplax hartwegii found on Mussel Point in
Pacific Grove, California under the brown alga Pelvetia
fastigiata, is more active at night and is negatively phototactic
in the lab. Progection afforded by the Pelvetia habitat might
explain the considerable daytime activity that does occur.
2. The tidal cycle affects the animals' activity, greatest
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Activity Patterns of Cyanoplax
page 10
activity occurring at dry and awash periods. Lesser activity
during the high tides may be due to the strength of the
surge or to the difficulty in feeding on Pelvetia during these
times.
3. Although strict homing is not eghibited by C. hartwegii.
certain "campsiteg" on the substratum are occupied successively
by different individuals. This behavior may have survival
value as these sites may be consistently well-protected spots.
ACKNOWLEDGMENTS
I am grateful to the faculty and staff of Hopkins Marine
Station and my Biology 175H classmates for being an integral
part of an unforgettable learning experience. Particular
thanks go to the Drs. Isabella A. and Donald P. Abbott for
their enthusiasm, sincerity, and hospitality. Even more
particular thanks are given to Dr. Robin Burnett, whose
patience, willing help, copious advice and equally abundant
criticism have been greatly appreciated. Also, I thank Dr.
Allyn G. Smith of the California Academy of Sciences for
confirming several identifications of chitons.
LYMAN—PAGE 10 1
Activity Patterns of Cyanoplax
LITERATURE CITED
Berry, Samuel Stillman
1922. Fossil chitons of western North America. Proc. Calif.
Acad. Sci., 4th Ser., 11 (18): 399-526; 11 figs.; 16 plts.
(16 May 1922)
Connor, Michael Stewart
1974. Niche apportionment among the chitons Cyanoplax hartwegii
and Mopalia muscosa, and the limpets Acmaea limatula and Acmaea
pelta under the brown alga Pelvetia fastigiata. The Veliger
Crozier, W.J.
1920. Note on the photic sensitivity of the chitons. Amer. Natur.
(August 1920)
54: 376-380.
Glynn, Peter W.
1970. On the ecology of the Caribbean chitons Acanthopleura
granulata Gmelin and Chiton tuberculatus Linne: density, mortality,
feeding, reproduction, and growth. Smithson. Contrib. Zool. 66:
1-21; 10 figs.
Heath, Harold
1899. The development of Ishnochiton. Zool. Jahrb. Abt. Anat.
12: 1-90; 5 figs.; 5 plts.
Ricketts, Edward F. and Jack Calvin
1952. Between Pacific tides. 3rd ed. Revised by Joel W. Hedgpeth.
xiii + 502 pp.; 134 text figs.; 46 plts. Stanford, Calif. (Stanford
Univ. Press)
Activity Patterns of Cyanoplax
LYMAN—PAGE 12
Robb, Mark Francis
Cyanoplax hartwegii
1974. The diet of the chiton
in various intertidal habitats with remarks on
taxonomy. The Veliger
Smith, Suanne Yvonne
1974. Temporal and spatial activity patterns for the intertidal
chiton Mopalia muscosa. The Veliger
Thorne, M.J.
1967. Homing in the chiton Acanthozostera gemmata (Blainville).
Proc. R. Soc. Queensl. 79 (9): 99-108; 1 fig.
Tryon, George W., Jr. and Henry Augustus Pilsbry
1892. Manual of Conchology. Vol. 14. xxxiv + 350 pp.; 68 plts.
Philadelphia, Penna. (Acad. natur. Sci. Philad.)
Westersund, Kristen R.
1974. Phototaxis and a tidal rhythm in the chiton Mopalia
muscosa (Mollusca: Polyplacophora). The Veliger
page 13
Lyman
Activity Patterns of Cyanoplax
FIGURE CAPTIONS
Figure 1. Activity patterns of 13 Cyanoplax hartwegii
observed hourly from May 13th to May 15th, 1974.
A. Conditions of tide and light. The horizontal bars
indicate tidal exposure of Cyanoplax: S - submerged,
D = dry, and blacked out areas - awash. Light
cycle is indicated on each graph.
B. Total number of animals that moved each hour.
C. Average distance moved by the animals each hour.
Figure 2. Activity patterns of 13 Cyanoplax hartwegii observed
hourly from May 19th to May 22nd, 1974. Key and explanations
are the same as in Figure 1.
Figure 3. Activity shown in relation to conditions of tidal
exposure and the light cycle. The bottom of the vertical
bars indicate the minimum levels of activity recorded
for a given condition. The top indicates the maximum
and the line within the bar indicates the mean of recorded
values. Clear bars represent data from May 13th to May
15th; stippled bars represent data from May 19th to May 22nd.
A. Total number of animals that moved.
B. Average distance moved by the animals.
Figure 4. Activity versus the tidal height. Approximate
conditions of tidal exposure are indicated on horizontal
bar. Dotted line represents activity from May 13th to
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Activity Patterns of Cyanoplax
page 14
May 15th; solid line represents activity from May 19th
to May 22nd.
A. The sum of the total number of animals that moved
during a particular tidal height for the entire
watch divided by the number of times that tidal
height occurred during the watch.
B. The sum of the average distances moved by the
animals during a particular tidal height for the
entire watch divided by the number of times that
tidal height occurred during the watch.
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