Gagbrn
Abstract
Caprella californica, C. brevirostris, and C. penantis
may occur together on the hydroid Aglaophenia struthionides.
Caprella incisa may occur on the bryozoan Tricellaria
occidentalis growing in close proximity. Cleaning and feeding
behavior of these caprellid species were compared under
conditions simulating natural water flow. All species were
seen to engage in filter feeding and some in scraping and
macrophagous feeding. Quantitative comparison of the main
components of feeding behavior in the three species on
Aglaophenia shows little obvious evidence of resource
partitioning, and the role of motility and positioning are con-
sidered.
Grogborn
Introduction
Mayer (1882) and subsequent workers have noted that the
vast majority of caprellids are found on living substrates.
Numerous species occur on hydroids, and a variety of rela¬
tionships between the caprellid and its hydroid host have
been reported. Lockington (1875), Mayer (1882), and Mackay
(1945) stated that caprellids eat or parasitize hydroids.
Green (1963) concluded that hydroids were utilized solely
as a substratum, while McDougal (1943), reported that the
major food source of caprellids were sessile protozoans
and diatoms growing on the hydroids. Food acquisition by
filter feeding was noted by Saunders (1965), Patton (1968).
and Keith (1969). Keith concluded that caprellids were
opportunists, utilizing the most readily available organic
material as food. This appears to consist mainly of floating
organic detritus in their natural habitat. Caine (1974)
examined the possible relationship between food sources and
appendage structure in various sympatric caprellid species,
In a subsequent paper (Caine,1977), he reported that most
co-occuring, filter-feeding caprellids don't utilize the
same size of particle at the same height above the substratum.
At Mussel Point, Pacific Grove, California, 3 species
of Caprella (C. penantis, C. brevirostris, C. californica)
occuring on the hydroid Aglaophenia struthionides (Murray)
and one species (C. incisa) associated with the bryozoan
Tricellaria occidentalis (Trask) were examined. Since four
species of caprellids have been found in the same small
area, three of these in the same microhabitat,it seems
likely that resource partitioning of some type occurs,
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particularly with respect to food. This possibility
was investigated in the present study.
Materials and Methods
Four species of Caprella were collected from intertidal
waters surrounding the northeast shore of Mussel Point,
California. C. californica, C. penantis, C. brevirostris,
and C. incisa were collected by gathering colonies of
Aglaophenia struthionides and nearby substrates. Prionitis
was the substrate for A. struthionides in all cases and
Tricellaria occidentalis was found growing at the base of
A. struthionides in approximately one fifth of the collections.
Specimens were gathered within one hour of low tide and
transferred to the lab in jars filled with sea water. Only
specimens submerged at low tide were collected. Upon return
to the lab, caprellids and their substrates were placed in
bowls filled with seawater and most of the Prionitis (hydroid
substrate) was removed. Fresh seawater at a temperature of
10-15 degrees C was allowed to flow into the bowls. The
T. occidentalis was identified by C. Baxter of Hopkins Marine
Station.
Feeding behaviors were observed for each species with
the aid of an event recorder coupled to a strip chart recorder,
permitting the recording of 8 different categories of stereo-
typed behaviors. A chamber for the observation of caprellids
on Aglaophenia consisted of a 15 cm length of glass tubing
2.2 cm in inside diameter, fitted at both ends with single
hole rubber stoppers and provided with a constant supply of
fresh seawater flowing at the rate of 132 ml per minute. Linear
flow past caprellids was approximately i cm per second. This
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system was designed to simulate in some degree the effects
of local turbulance and water flow in the natural habitat.
Substrates with resident caprellids were pinned to the inlet
rubber stopper. Feeding behaviors were observed with a stereo-
microscope. Two ten minute feeding observations were made of
the same individual caprellid on the same Aglaophenia plume
at twelve hour intervals. After two 10 minute observations
were completed, milk was injected to study turbulance and
particle settling in the region occupied by the caprellid.
Caprellids were seen to move in response to contact with the
milk. No further behavioral observations were made until all
visible traces of milk in the tube had disappeared. All in-
dividuals were examined 12 hours after the last experiment in
which they were used, and results are presented only for animals
still alive at that time.
Distribution information was obtained in the lab within
2 hours of collecting A. struthionides in the field. Hydroid
colonies were collected submerged in separate glass jars,
and placed in glass bowls filled with seawater. With a bowl
under the dissecting scope, the number of adult and juvenile
caprellids on the proximal and distal half of each frond were
recorded under minimal illumination. Species identification
of juveniles was not feasible. After caprellid size, species,
and distribution was recorded, the frond under consideration was
removed from the colony with forceps and measured. Once removed,
fronds and accompanying caprellids were not returned to the bowl.
Line drawings of feeding appendages of the four caprellid
species encountered were made with the aid of a camera lucida
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and a compound microscope.
Results
Distribution
Distribution of adult and juvenile caprellids on
Aglaophenia half fronds is presented in figure i. More
juveniles than adults were present on Aglaophenia fronds of
all size classes. Species of juveniles was not determined.
The distinction between adults and juveniles was based on
size and to some extent, color. Transparent individuals
smaller than 2.2 mm were classified as juveniles. Transparent
individuals larger than 2.2 mm and caprellids with coloration
in regions other than the gut (generally larger than 2.0 mm)
were considered as adults. Distribution of adult species is
summarized in table 1.
Only one species (C. penantis) is common on A. struthionides,
It therefore seems likely that most juveniles are C. penantis.
Other species occur only sporadically, and their main dis-
tribution may be elsewhere. The skewed distribution of species
suggests that resource partitioning may not be important in
this microhabitat.
Feeding Behavior
Five types of feeding mechanisms have been described in
adult caprellids, including browsing, filter feeding, predation,
scavenging, and scraping (Caine, 1977). In the present study,
predation and scavenging were not observed. The lack of
predation may be due to rem val of prey items by filter
feeders present in the laboratory seawater pipes. The current
maintained in the observation chamber may have washed away
organisms which weren't actively clinging to the substrate,
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thus offering a possible reason why scavenging wasn't noted.
Of the remaining three types of feeding, filter-feeding was
frequently seen; no distinction was made between browsing and
scraping, and these are considered together.
Caprellids were observed to situate and orient themselves
such that they were out of the main current and exposed to
flow rates generally less than 1 cm per second. The adults
of all 4 species investigated often stood virtually motionless,
taking advantage of eddy currents created by the substrates.
Positioning was such that particulate matter present in the
water column drifted past or fell slowly on the caprellid.
Browsing and scraping seem to be related to the side of
the frond where a caprellid is found. Observation of both
sides of Aglaophenia fronds showed a much greater frequency of
encrusting organisms on the abaxial side. In the flow tube,
C. californica was found on the abaxial side of the Aglaophenia
frond 78% of the times observed, while C. penantis and
C. brevirostris were found in this orientation 70% and 65%
of the time respectively.
Filter-feeding and related behaviors, as well as scraping,
were subdivided into eight classes of stereotyped behavior,
defined below. A summary of feeding behaviors of four species of
caprellids is presented in figure 2.
Behavior 1 represents the bending of the first antenna
over the cephalon. Gnathopod 1 on the same side of the body
is then closed around the base of Al, which is drawn through
Gi, presumably removing trapped particles (figs. 3 & 4).
Behavior 2 is similar to behavior 1, except that antenna
2 is being cleaned instead of antenna 1 (figs. 3 & 4).
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Behavior 3 represents simultaneous bending of antennae
1 and 2 over the cephalon. Gnathopod 1 on the same side of
the body is then closed around the bases of Al and A2, which
are drawn through Gl, removing trapped particles (figs. 3 & 4).
Behavior 4 signifies bodily cleaning from the gills to
the distal pereopod. Gnathopod 1 picks and/or scrapes
material from the body (figs. 3 & 4).
Behavior 5 represents the removal of material from G2
by Gl (figs. 3 & 4).
Behavior 6. This involves pulling or scraping material
from the substrate by Gl (figs 3 & 4).
Behavior 7 represents active gathering of food. It
includes removal of detritus directly from the water column
with both first gnathopods, where it is then held in place.
Larger detritus may be similarly captured by all four gnath¬
opods and held in place (figs. 3 & 4). In C. incisa, waving
of both first gnathopods through the water, presumably
filtering food from the water, has been observed. This feeding
mechanism is also included in tabulated results.
Behavior 8 considers movement of Gl to the caprellid's
mouth, where the maxillipeds contact it (figs. 3 & 4).
Statistical analysis using the Student-Newman-Keuls
test indicated significant differences (p=0.05) between
C. incisa and C. californica in frequency of behaviors 4
(cleaning of body with Gl from gills to distal pereopod)
and 7 (active gathering of food, including catching of large
detritus with Gl and G2, and combing of water with G1);
between C. incisa and C. brevirostris in behaviors 4 and 5
(cleaning of G2 with G1), and in behavior 5 for C. incisa
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and C. penantis.
Some of the behaviors found in all four species occured
in typical coordinated sequences. Cleaning of antennae, G2,
and the body with Gl, and scraping were often followed by clean¬
ing of Gl with the maxillipeds. Walking was carried out in
the inchworm fashion typical of the caprellid. Variance for
data related to walking was high, so this information is
presented in two ways. First, data were pooled and the average
number of walks per individual per 10 minute trial was determined
for each of the four species examined (table 2). Next, the
number of 10 minute trials in which walking occured and the
number of trials in which it was absent are compared for
four caprellid species (table 3). The four species of caprellids
taken as a group were found to differ significantly (p=0.05)
in regard to the number of trials in which walking was or
was not present.
Miscellaneous natural history
Caprellids can be kept alive for periods of 2 weeks
and perhaps indefinitely at room temperature in glass bowls
using 1 mm mesh nylon screen as the sole substrate. If held
down with glass rods, caprellids could easily walk on it, or
cling to one location. Nauplius larvae from the goose barnacle
Pollicipes polymerus were used as a food source and provided
every 3-4 days. Larvae were stained with toluidine blue and
the guts of caprellids began to assume this color soon after
larvae were introduced. A stirring bar with a plastic blade
at the tip, suspended from a motor above the bowl, was used
to prevent the nauplii from sinking to the bottom where they
were unavailable to the caprellids. In cases where hydroids,
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algae, or bryozoans were left in the bowl,the water was fouled
within a few days.
Cryptic coloration was obvious in various species of
caprellids. All juveniles observed were transparent, making
them difficult to see. On adults of C. incisa found on
T. occidentalis, short bars of deep red against a light
background made this species inconspicuous on its substrate,
This caprellid was not found further than 1.5 cm from T.
occidentalis. C. penantis adults had a mottled orange brown col-
oration matching well the background presented by Aglaophenia
C. californica adults possessed red bars running across their
bodies and gnathopods. Adults of C. brevirostris were
transparent except for their eyes, as well as their guts, which
tended to assume the color of food material within.
Discussion
The need for resource partitioning among co-occuring
species of caprellids was addressed by Caine (1977). He
found that co-occuring, filter-feeding caprellids tend to
utilize particles of different sizes, collected at different
heights above the substratum. He noted that niche diversity
in caprellids may involve morphological, behavioral, or
physiological features of the species. Few differences in
feeding behavior and morphology of feeding appendages were
found between the species present on A. struthionides.
Due to the great abundance of C. penantis relative to other
species, resource partitioning may not occur. Competition may
well be limited and other species (such as C. incisa) may
have other preferred substrates. In addition, it may be that
experimental designcombined with the opportunistic nature of
10
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feeding has obscured certain secondary feeding behaviors.
The caprellids investigated differ in the amount of
walking done, and in the positions and locations they assumed
(tables 2 & 3 ). Characteristically in Aglaophenia a group
of fronds radiate from a compact holdfast at the base, such
that different fronds receive different amounts of exposure,
some being shielded by surrounding fronds. Shielding may
influence the location a caprellid uses for feeding. This
is evidenced by caprellid positioning in slow currents to
take advantage of particle settling. Positioning on the
axial or abaxial side of a frond seems to be related to the
availability of encrusting organisms which can be utilized
as food, since caprellids have been observed more frequently
on the abaxial side. Caprellids found on Aglaophenia were
sometimes observed to scrape a certain region and then move.
Walking may be a response to depleted local supplies of
encrusting organisms available as food. In addition, a wa king
caprellid may be "seeking" a site suitable for filter-feeding
in terms of currents and food.
Acknowledgements
I would like to thank Dr. D. P. Abbott, whose comments
and criticisms aided and added to this paper, and without
whose help this paper would not have been possible.
Gragburn
Literature cited
Caine,E.A., 1974. Comparative functional morphology of
feeding in three species of caprellids (Crustacea:
Amphipoda) from the northwestern Florida Gulf Coast,
J. exp. mar. Biol. Ecol. 15, 81-96.
Caine,E.A., 1977. Feeding mechanisms and possible resource
partitioning of the Caprellidae (Crustacea: Amphipoda)
from Puget Sound, USA. Mar. Biol. 42, 331-336.
Costa,S., 1960. Note preliminaire sur l'ethologie alimentaire
de deux Caprellides de la rade de Villefranche-sur-Mer.
Trav. Sta. zool. Villefranche, 19 (20): 103-105.
Green, J., 1963. A biology of Crustacea. H.F. & G. Withersby,
Ltd., London, 180 pp.
Keith, D. E. 1969. Aspects of feeding in Caprella californica
Stimpson and Caprella equilibra Say (Amphipoda).
Crustaceana, vol. 16, no. 2, pp. 119-124.
Lockington, W.N. 1875. Observations on the genus Caprella,
and description of a new species. Proc. Calif. Acad. Sci.,
vol. 5, pp. 405-406.
Mackay, D.C.G., 1945. Notes on the aggregating marine
invertebrates of Hawaii. Ecology, vol. 26, pp. 205-207.
Gragbot
Mayer, P. 1882. Die Caprelliden des Golfes von Neapel.
Fauna and Flora des Golfes von Neapel, vol. 6, pp. 1-201.
MoDougal,K.D., 1943. Sessile marine invertebrates of Beaufort,
North Carolina. Ecol. Monogr. vol. 13, pp. 321-374.
Patton, W.K., 1968. Feeding habits, behavior and host
specificity of Caprella grahami, an amphipod commensal
with the starfish Asterias forbesi. Biol. Bull. mar.
biol. Lab, Woods Hole, 134 (1), 148-153.
Saunders, C.G., 1965. Dietary analysis of caprellids (Amphipoda).
Crustaceana, Vol. 10, pp. 314-316.
2
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Species
C. californica
C. penantis.

C. brevirostris
C. incisa
—
Average no. walks/
10 min. trial
0.92
0.12
1.52
0.06
No. trials
12
21
17
Jable 2
0
Species
C. californica
C. penantis
C. incisa
C. brevirostris
Jahle 3
+ trials walking
observed

—
f trials walking
absent
16
16
11
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Gragborn
17
f
o
93
KEY
Juveniles
Adults
114
48
34
97
32
55
.



.

.
.
.
1-5 6-10 11-20 21-30 31-40 41-50 51-80
Length of A. struthionides frond, mm
Gragborn
15
15

8
Caprella penantis
-

16)

C. californica
Ss

E
(12)
C. incisa
E



(18)
C. brevirostris
H
e
(21)
L
2 6 5 4 3
1
Behavior Type
2
Graborn
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A2

4

A

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a
61 im
F2
A2
D
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G2
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7


G2
O.1 mm
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G1.
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G1
Graybirn
Table captions
Table 1. Summary of the distribution of adult caprellids
on Aglaophenia struthionides.
Table 2. Average number of times spent walking per ten
minute trial at constant flow rate.
Table 3. Comparison of number of 10 minute trials in
which walking was seen and in which it was absent.
.
Gragborn
Figure captions
Figure 1. Average number of caprellids per A. struthionides
half frond versus length of A. struthionides frond. Total
number of caprellids are indicated above each bar.
Figure 2. Frequency versus feeding behavior type for
caprellids associated with the A. struthionides community.
Number of 10 minute observations is indicated to the right
of each graph. 1: cleaning of Al with G1;2: cleaning of A2
with Gi ;3: cleaning of Al & A2 simultaneously wiyh Gl;
4: cleaning of body with Gl from gills to distal pereopod;
5: cleaning of G2 with G1;6: scraping of substrate with Gl
or contact of maxillipeds with substrate; 7: active gathering
of food, including catching of large detritus with Gl & G2,
and combing of water with G1;8: cleaning of Gl with maxillipeds,
Figure 3. A. Caprella californica: female ; antenna 1,
antenna 2; B.C. penantis: male ; antenna 1, antenna 2;
C. C. brevirostris: female ; antenna 1, antenna 2; D.
C. incisa: female; antenna 1, antenna 2.
Figure 4. A. Caprella californica: female ; gnathopod 1,
gnathopod 2; B. C. penantis: male; gnathopod 1, gnathopod 2;
C. C. brevirostris: female; gnathopod 1, gnathopod 2;
D. C. incisa: female; gnathopod 1, gnathopod 2.
22