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ADDITIONAL INFORMATION, IF ANY, CONCERNING AUTHORS, ADDRESS, TITLE, OR CITATION DATA
PLEASE TYPE ABSTRACT DOUBLE SPACED BELOW
JOHNSON, SAMUEL E. (Hopkins Marine Station,
Pacific Grove, Calif., USA.) Occurence and Behavior of
Hyale grandicornis, a gammarid amphipod commensal in
the genus Acmaea. The Veliger
Immature individuals of the amphipod Hyale grandicornis
were found under the limpets Acmaea scabra, A. scutum,
A. digitalis, A. limatula, and A. pelta on intertidal rocks
1 - 6 feet above mean lower low water along the California
coast. H. grandocornis was not found in other situations
in the adjacent habitat. During the day the amphipods lie
deep in the mantle groove or nuchal cavity; at night they
move to the rim or upper surface of the shell and apparently
feed on algae growing on the shell. The percentage of
Acmaea hosting immature H. grandicornis increases with
decreasing height in the intertidal region. Hyale exhibits
no definite preference for particular species of Acmaea.--Author
PLEASE DO NOT TYPE BELOW THIS LINE
213
Occurrence and Behavior of Hyale grandicornis,
A Gammarid Amphipod Commensal in the Genus Acmaea
(Mollusca : Gastropoda : Prosobranchia)
by
Samuel E. Johnson II
Hopkins Marine Station of Stanford University
Pacific Grove, California*
(7 Text figures)
In the course of preliminary studies of the genus
Acmaea at Hopkins Marine Station, Pacific Grove, California,
mottled grey-green amphipods were frequently encountered
under the shells of Acmaea digitalis Eschscholtz, 1833,
Acmaea limatula Carpenter, 1864, Acmaea pelta Eschscholtz,
1833, Acmaea scabra (Gould, 1846), Acmaea scutum
Eschscholtz, 1833, and Lottia gigantea Sowerby, 1843. Dr.
J. Laurens Barnard of the Smithsonian Institution has
identified the amphipods as immature specimens of Hyale
grandicornis (Kryer, 1845) (Figure 1). No mature amphipods
have been found in association with any of the above lim¬
pets. Dr. Barnard (personal communication) states that
he found mature specimens on cobbles and with Ulva in
Carmel Bay, California. An examination
* Footnote 1
2/
muel
the algae Endocladia, Sigartina, Ulva, and irid
growing in areas adjacent to the Agmasa populations
vielded no amphipods resembling those found with Acmaes
although an unidentified species of Hyale, mentioned
lynn (1965), does occur here and has been found in t
present study. This species differs from immature
grandicornis in the pattern of its dorsal markin
and in having brown rather than black, silver-spotted
The Ha grandicornis found under Acmaea spp.
oyes.
averaging 2-3 mm in length (the range is 1-6 mm
much emaller than this unidentified Hvale, which has ar
e length of 6 m.
ver
grandicornis occurs under individuals of Aemaea epp
nmany different localities along the coast of the
Monterey Pennsula.. Population studies on this amphipod
carried out at Pescadero Foint, on the open coast
ust north of the northern edge of Carmel Bay, California
m 25 April to 30 May 1966. The intense wave action ir
hie area, the presence of vertical granite surfaces
canging to 30 feet above the level of mean lower low water
and the varying conditions of exposure and protection
afforded by large boulders and sheltered pools provide a
variety of different habitats. The sites selected for
(Figures 3-5) vere not exposed to direct wave action
study
ituated either oblique to the line of waves or
Samuel E. Johnson
the shore side of large boulders. The sites chosen
were divided up into zones (Figures 3-5) based on both
plant and animal indices, and following natural grouping
forganisms on the rocks. Correlation of these zones
with those of Ricketts and Calvin (1939) and Doty (1946)
is shown in Figure 2. Intertidal elevations were
determined by measurement from a United States Geological
Survey bench mark on Pescadero Point and wore checked
against the theoretical tidal heighte as determined from
the United States Coast and Geodetic Survey Tide Tables
the Pacific Coast, using the time and height corrections
for Nonterey.
The population of the five species of Acmaea studied
determined by dividing the surface of the campling
sites into quadrats of 400 cm2, and recording numbers
of each Acmaen species present. The total area of each
zone studied in the sampling sites ranged from 2,5 to
3 m2. After determining the distribution and numbers of
Acmaed spp., the distribution and frequency of occurence
of H. grandicornis was determined by sampling of Acmaea
species in the individual zones. Attempts were made to
sollect representative numbers of the five species
studied from each zone but certain species in some areas
were extremely scarce or non-existänt. Extreme care was
Samuel E. Johnson
needed in collecting, for the amphipods often jump
away when the limpet is lifted from the substrate.
Each limpet collected was then identified, and its
shell length measured. The amphipods present with
each limpet were counted and sorted into three size
groups (0.5-2 mm, 2.-4 mm, and 4.-6 mm),
kinpertten.
Figure 6 shows the population density of each
species of Acmaea for each zone, and the percentage
of each Acmasa species which served as hosts to
H. grandicornis. In Zone A, no amphipode occur
even though suitable hosts are present. The Acma
species of Zone B, slightly lower in the intertidal
but overlapping Zone A, bear a small population of
amphipods. The large bouldere characterizing this
zone shade and protect it from deseidation, keeping
it moister than Zone A. From this point down to the
lowest populations of Acmaea examined, the population
of amphipods increases, with the exception of Zone D.
Zone Die characterized by the macroscopic algae
Endocladia, Sigartina, and Iridaea, while Zones C and
E are distinguished primarily by the encrusting algae
Hildenbrandis, Peyasonelia, Fetrocelis, and Ralfaia
Ulva was just beginning to grow in Zone E when field
studies were discontinued.
Samuel E. Johnson
The present studies do not indicate any clear preference
on the part of the amphipods for any particular species of
Acmaea. Moreover, for those limpets which did house amphipods,
there appears to be no clear correlation between the shell length
of the limpet and the number of amphipods present (Figure 7). Howe
ever, for limpets with a shell length of 8 mm or more there does
appear to be a slight positive correlation between shell length
and the percent of the population bearing amphipods (Figure 8).
Limpets less than 8 mm long did not accomodate amphipods.
Natural History
Field examinations carried out at Pescadero Point and at
Mussel Point during day and night and at high and low periods
indicate that the amphipods do not leave the limpet at any time,
unless the latter is removed from the substratum. These obser-
vations are supported by the absence of free-living immature
H. grandicornis in areas adjacent to the limpet populations.
The position of the amphipods under the shell was deter-
mined from laboratory observations using aquaria in which
field conditions were approximated. During the day the
amphipods are found behind the head in the nuchal
Samuel E. Johnse
cavity or deep in the groove between the mantle fold
and the foot. Sometimes an amphipod may be observed
at the edge of the mantle fold, but thie behavior i
rare in the daytime. In conditions of near darkness
and splash or submergence they are found lying on
their eides, in contact with the pallial tentaeles of
the limpet at the mantle margin. In this position the
amphipods groom themselves, and from it they also feed,
reaching around the edge of the shell or moving completel.
out onto its dorsal surface and seraping up the algae
growing there. Gut contente were unidentifiable, but
the material on the shell is composed of numerous
varities of diatoms and several types of blue-green
algae, primarily Enteromorpha. Occasionally small
growthe of Ulva are found on the shells. The amphipod
seem never to leave the limpet, but seek cover under
the sbell when disturbed. If an amphipod is trapped
outside and is unable to crawl under the host's shell
again, it either presses itself closely against the
edge of the shell and remains there, or moves away t
a nearby limpet. Other types of shelter, either in
field or laboratory, appear to be ignored. When
forced to awim, H. grandicornis moves very rapidly a
first, but quickly slows and appears to seek shelter.
If repeatedly disturbed, it soon ceases all movement.
Samuel E. Johnson
It is of particular interest that Dr. Barnard found
mature specimens of Hyale grandicornis in Ulva, and that
the present study has revealed only juvenile individuals
in the mantle groove and nuchal caviti of Acmaea. Ulva
occurs mainly in the warmer months in the region studied,
and at the end of the present study it was just beginning
to grow. Perhaps the immature forms of Hyale grandicornis
migrate to the Ulva as they attain sexual maturity and as
the alga appears each summer, and possibly the juvenile
amphipods survive during the winter and spring under Acmaea
shells.
The author plans to continue research on the problem.
Summary
1. Immature specimens of Hyale grandicornis (Krøyer, 1845)
are found in the nuchal cavity and pallial groove in five
species of Acmaea and in Lottia gigantea.
2. The percentage of limpets hosting immature H. grandicernis
increases with decreasing height in the intertidal region.
The amphipod shows no clear preference for particular lim-
pet host species.
4. No amphipods were found in any limpets less than 8 mm in
shell length. For limpets above this size there is a slight
positive correlation between shell length and the percent
of limpets bearing amphipods. However, for those limpets
which housed amphipods, there was no correlation between
280
4
Samuel
Johnson
Samuel E. Johnson
Acknowledem
shell length and number of amphipods borne by each limpet.
Immature H. grandicornis remain in contact with their lim-
pet hosts under all prevailing conditions of tide and
light. They appear to feed on algae growing on the surface
The author
tof limpet shells. 1212 grandicer
6. No mature H. grandicornis have been found in association
with any limpets. for pertinent literature
supplied
by Dr. Peter
Glynn of the Institute of Marine Biolo
University of Puerto Rico. Discussions with David A.
Egloff of Hopkins Marine Station proved helpful in
suggesting approaches to field and taxonomic problems.
Special thanks must go to Dr. Donald P. Abbott of
Hopkins Marine Station, Stanford University for his
time and effort spent in discussing the project with
the author, and particularly for his criticism and
editorial comments on this paper. The Monterey
Foundation authorized the use of Pescadero Point for field
studies.
2
Samuel E. Johnson
Acknowledgments
This work was made possible by grant GY806 from
the Undergraduate Research Participation Program of
the National Science Foundation. Dr. J. Laurens
Barnard of the Smithsonian Institution identified
the amphipods as Hyale grandicornis. The author is
very grateful for his help and suggestions. Appreciation
is also expressed for pertinent literature supplied
by Dr. Peter W. Glynn of the Institute of Marine Biology
University of Puerto Rico. Discussions with David A.
Egloff of Hopkins Marine Station proved helpful in
suggesting approaches to field and taxonomic problems.
Special thanks must go to Dr. Donald P. Abbott of
Hopkins Marine Station, Stanford University for his
time and effort spent in discussing the project with
the author, and particularly for his criticism and
editorial comments on this paper. The Monterey
Foundation authorized the use of Pescadero Point for field
studies.
228
Samuel E. Johnson
Literatu
Doty, Maxwell, S.
1946. Critical tide factors that are correlated
with the vertical distribution of marine algae
and other organisme along the Pacific coast. Ecol
27 1 315-28.
Glynn, Peter, W.
1965. Community composition, structure and inte
relaticnships in the marine intertidal Endocladi
muricata - Balanus glandula association in
Monterey Bay, California. Beeufortia, 12 : 1-198.
dicketts, E. F. & J. Calvin
1952. Between Facific tides (3rd. ed., rev., J.N.
Hedgpeth). Stanford University Press, Stanford, pp. 1-502.
(Page 1.) Permanent address:
Samuel E. Johnson
22
0
ure
nuelE.J
An immature Hyale
grandicorni
shoving dorsa.
and lateral markings.
The scale represents
mm.
Description and Vertical Position of zon
t Peccadero Foint, and Correlation sith
ones of Ricketts & Calvin (1939) and
5 April - 30 kay 1966.
Pescadero Point, Carme
Zones A, C, and D.
1966 at
California.
Taken on 23 May
Arrow points to marker representing
O A.M.
levation of 15.2
The scale represente
feet.
Zone B.
Pescadero Foint,
Carme
Bay, Californ
aken on 23 May 1966 at
100
Tho scale
epresents 2 feet
es
Point,
Zones A, D, and E.
Carm
California. Taken on
May
100 A.M. The scale represente
Distribution of Acmaen spp. and i
andieornis at Pescadero Point.
nia,
April - 30 May 1966. Figures i
or
ne right of the white square.
indicate
the
The
erage number of Acmaea per 400 om
ze of the square is proportional
to thie
Samuel E. Johnson

number. The black area within the squares is-
proportional to the percent of Acmaea hosting
amphipods; all % figures shown refer to the
percent of Acmaea bearing one or more amphipods.
The numbers below the boxes show the total
number of limpets of each species examined
from each zone.
Figure 7.
Dorrelation between limpet shell length and the
number of amphipods housed, for those limpets
which bore amphipods.
Figure 8. Correlation between limpet shell length and the
incidence of amphipods.
Figure 9. Amphipod orientation and feeding position in
Aomaea scabra. The scale represents 5 mm.
2
Samuel E. Johnson
Descriptions of Zones - To go on Figure 2,legt side)
Zone A.
Microscopic algae and diatoms in the
upper region, with the Balanua - Chthamalus
association near the lower margin.
Zone B.
Microscopic algae and diatome on the
undersides of large boulders, shaded and
protected from desigcation.
Zone C.
Leathery encrusting algae, primarily
Peyssonalia, Hildenbrandia, and Petrocelis.
Zone D.
Macroscopic algae, mainly Endocladia,
Gigartina, and Iridaea.
Zone E.
Encrusting algae, mainly Peyssonelia and
Ralfsia, associated with the barnacle
Tetraclita. Ulva appeared at the end of
the field study.
Below this zone the dominant plants on the rock face
are encrusting and branched coralline algae.
22
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