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ACTIVITY
PATTERNS AND HOMING BEHAVIORS OF ACANTHOPLEURA
GEMMATA AND A.
TENUISPINOSA CHITONS
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Eiji
Yoshioka and Erika Fujitani |
Acanthopleura
gemmata
and A. tenuispinosa commonly inhabit the higher
intertidal zones of the Okinawa Islands. The activity patterns
and homing behaviors of these chitons were surveyed on the rocky
shores in the neighborhood of Sesoko Station,The Tropical
Biosphere Research Center (University of the Ryukyu’s),
Okinawa, Japan. This survey was carried out during the following
two periods: from July 17th to August 1st 2000 (16
days) and from September 21st until October 5th 2000 (15 days).
The objective chitons of this survey were 6 individuals of A.
gemmata and 6 individuals of the A. tenuispinosa in the
former days (7/16-8/1) and 8 individuals of A. gemmata
and 6 individuals of A. tenuispinosa in the latter days
(9/21-10/5). The objective chitons were marked with a small
piece of reflective adhesive tape for making the night search
easier; while the area surveyed was 1.2 m in length and 7.0 m in
width on an upright rocky shore of a sandy beach. While this
survey was conducted, the position and direction of the chitons
as well as the tidal and wave conditions were recorded every 30
minutes.
Motion in both A. gemmata and A. tenuispinosa were
observed during the daytime hours when they were washed by the
waves, and during the night they moved when exposed and when
washed by the water. Surface temperature of dried rock rose up
to 64.8 C (9/4-11:58). When submerged the two types of chitons
were found to suffer from various fish predators and other
carnivorous invertebrates. Therefore, the movement patterns can
be partly explained by the fact that they are avoiding both rock
surface high-temperatures and the avoidance of predators.
Almost
all chitons rest in fixed sites (‘home’) during the daytime
and when the rock was submerged. Homing behaviors of these
species were confirmed throughout the survey-as, at times, they
scrambled to the same site. When (and if) a chiton had its home
taken by an intruder, he quickly moved and got another
unoccupied ‘home’. Such behavior lends itself to the idea
that chitons recognize configurations of neighboring rock. |
