Brooding in Epiactis
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Epiactis prolifera is common on the rocky open coast of central
California, attached to rocks, eelgrass and algae (Hand 1955). The
young are brooded externally. The large eggs do not pass through
a planula stage in development. They are extruded from the mouth
of the parent and attach to the ectoderm of the parental column,
where they mature directly into tiny anemones.
Tle
The most thorough and inclusive study of the life history and
reproduotive biology of this specie is that of Dunn (1972, 1975).
The present investigation centers on aspects of reproduction and
brooding not fully covered by Dunn, particularly the process of
spawning and egg attachment, and the possible selective advantages
of brooding to the young in terms of better protection,, more secure
attachment, and nutritional benefits which they may receive from
their mothers.
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Brooding in Epiactis
All Epiactis used were collected from Pt. Pinos at the south-
ern tip of Montery Bay, and Stillwater Cove, Carmel, California,
within an intertidal range of 12 to -2 feet. Animals were maintained
at the Hopkins Marine Station of Stanford University in aquaria,
fingerbowls or plastic tubs supplied with constantly running sea
water at 12-130 C.
SPAWNING
During the morning of May 21, three Epiactis out of four which
were brooding young in a fingerbowl, were observed spawning. Two
of these were in an unusual, contorted shape. Only one wedge of
the oral disc and body wall comprising about one-fifth of the dia¬
meter of the animal was contracted, creating a valley extending in
towards the pharynx and down one side. The body wall below the
limbus (as described by Dunn 1972) i.e. the upper pedal disc, was
extremely puffed, exaggerating the indentation of the brood groove.
One adult appeared more active and this animal, basal diameter j5mm.
limbus diameter iimm, from Pt. Pinos, was observed intently for 1i
hours.
Brooding in Epiactis
pag
A string of pinkish orange eggs about 400,, in diameter extended
from the slightly everted lips of the pharynx, down the valley of
the contracted body wall. The contraction, under prolonged obser-
vation, passed in a very slow clockwise wave around the circumference
of the adult, taking about an hour to complete a full revolution.
The body wall, at each successive point on the circumference of the
disc, contracted and bent inward forming a valley to receive the
eggs.
Tentacles preceeding the contraction wave retracted and lay
flush against the oral disc so that they were almost completely co-
vered by the infolding upper margin of the column.
The eggs were bound by a mucus string which held them in a
linear series rather than in a bundle. The lower portion of the
egg chain, although obscured by tentacles and re-expanded body wall,
was evidently attached to the column in the limbus region. In the
process of re-expanding after the contraction had passed, the body
wall drew this adherent chain of eggs from the pharynx, which prob-
ably assisted egg ejection by ciliary currents. As the wave of
contraction subsided, the unfolding tentacles and puffed lower body
wall provided protection for the freshly spawned eggs which lay
attached to the body wall in a belt encircling the limbus region.
This behavior continued for an hour and during that time about
sixty eggs were spawned. This corresponds to Dunn's (1972) obser-
vations of fifty eggs spawned in the same amount of time.
Young previously attached to the column wall were observed swal-
lowing eggs which came within reach of their oral discs. Dunn (1972
found freshly spawned ova in the throats of sectioned, sterile
juveniles. After an indeterminant amount of time, the ingested egg
Brooding in Epiactis
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become a mass of material within the young, rather than retaining
their spherical form, indicating that the offspring are probably
digesting the yolk. Juveniles as small as 0.7mm were found stuffed
with pinkish-orange egg matter.
The third animal spawning in the same fingerbowl simply extruded
its eggs, with only slight bulging of the pharyngeal lips, onto its
oral disc where they remained for over an hour until they were taken
for microscopic examination. The animal remained fully expanded,
did not form a valley and attached none of the eggs spawned.
Dunn (1972) also observed epidemic spawning in the field and
in the lab on at least four occasions. She describes a constricting
of the throat and lips which extruded the eggs onto the oral disc,
from where they "... eventually drifted over the edge of the disc...
Spawning behavior is ap
and some of them adhered to the column,
parently variable.
PROTECTION
Open Epiactis extend some tentacles laterally, parallel to the
disc; others extend diagonally upward away from the base, but many
tentacles also curve down toward the base, creating a curtain sur-
rounding the brooded young. Adults maintained this 'umbrella" under
gentle proding, but contracted if repeatedly poked with needles or
disturbed by hermit crabs (Pagurus) placed in the same bowl. Appro-
ximately 75% of the time adults re-expanded within 5 to 10 seconds
after contraction. Larger attached offspring, greater than 2.5 mm
in basal diameter, were usually exposed when the parent contracted:
however the smaller young were often entirely enveloped in the folds
Brooding in Epiactis
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of the limbus, which is consistent with Dunn's observations (1972).
This was not always the case although, as many adults maintain a
smooth limbus rather than forming the conspicuous indentation in
the limbus region termed a " brood groove" by Dunn (1972). The
"brood pits" referred to by Ricketts and Calvin (1968), were not
found by Dunn (1975). However, in some brooding adults from Pacific
Grove, portions of the body wall overlying the edge of the foot were
expanded, leaving pockets or deppressions in the region of the limbus
where young are attached. Adults appeared to be able to control the
degree of indentation by contracting, and by varying the puffines
the pedal disc.
Dunn (1972) found that ".... adult Epiactis retract their ten
tacles when touched by an Aeolidia, but then partly expand again so
that any young being brooded are exposed." She noted that several
young were detached from the limbus in one encounter with this nudi-
branch. But protection of the young by a screen of parental tentacles,
need not be 100% effective to confer advantage. Dunn (1972) sug
gests that the size of the adult relative to the young affords pro-
tection. An Aeolidia may be sated after consuming a portion of the
adult basal disc, and leave most of the offspring unharmed.
ATTACHMENT
From the standpoint of attachment, brooding of the young could
be advantageous in two ways. First, space for attachment to the
substratum is a limited resource in the intertidal and shallow subtidal
zones on rocky shores. External brooding of young on the parent
body wall at least assures an area for attachment of offspring
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Brooding in Epiactis
Second, brooding could involve a strong attachment bond between
parent and offspring during a period when the young are too small
to attach themselves to other substrata. Numerous mucoprotein gland
cells and large nematocysts noted by Dunn (1972) in the limbus re-
gion of the parent body wall suggest the latter possibility. Although
artificially detached young as small as 0.9 mm in basal diameter
attach quite easily to glass plates and rocks in aquaria, Dunn (1972
never observed solitary individuals in the field less than 4 mm in
basal diameter.
To investigate attachment ability vs. size, 25 Epiactis rang
ing from 1.5-18.0 mm in basal diameter were tested individually in
a glass drum 5" in diameter , 6" in length, and 70% filled with
1300 seawater. An animal was placed in the drum and the apparatus
was rotated about its longitudinal axis at the rate of 1 revolution
per 80 seconds for 2 minutes, stopped for 1 minute, and revolved
again for 2 minutes. The animal was considered attached when it
began to rotate with the drum. Only 2 animals out of 25 tested (8%)
were unable to attach for at least 5 seconds. There was no relation-
ship between size and time required to attach. A second criteron,
maintaining adhesion for one complete revolution through the air-
water interface, was used to assess the strength of attachment.
The percentage capable of maintaining attachment for one revolution
increases with each size class. See table below.
no. attached
SIZE CLASS mm
no. tested
1.5-2.4 mm
30%
2.5-8.5 mm
506
9.0-18.0 mm
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Brooding in Epiactis
During the experiment, many animals were observed to have at-
tached initially by the side of the column and/or by the tentacles,
rather than by the pedal disc. Dunn (1972) found no nematocysts
nor mucoprotein gland cells in the column of even a "relatively
large juvenile " (3-4mm); yet these were conspicuous in adults.
They may represent mechanisms by which a larger animal initially
attaches to the substrate,as well as means by which parents securely
attach brooding young.
FEEDING
The intriguing possibility that brooding may provide nutri-
tional benefits for the young through transfer of food from parent
to offspring has not been thoroughly investigated. Three possible
mechanisms were proposed and studied; 1.. transport of particles
to the young by ciliary currents on the parental tentacles and co-
lumn; 2. movement of particles from the parental coelenteron to the
young through the pores in the tips of parental tentacles drooped
over the young; and 3. transfer of soluble materials through the
parental body wall into the attached pedal discs of the offspring.
Direct capture of small organisms from the water by the young was
also investigated.
Ciliary Feeding in Adults and the Possibility of External Transport
of Food
Observations were made on over 50 adult animals feeding on a
variety of substances ; mussel, limpet, squid, bouillon, gelatin,
and Artemia nauplii. Pieces of material 1-3 mm in diameter were
Brooding in Epiactis
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force fed using a Pasteur pipette, or were placed on portions of
the oral disc and tentacles. Lenhoff (1965) notes that objects must
contact tentacles in order to mechanically stimulate the feeding
response, but gelatin on the oral disc alone often initiated feed-
ing and tentacles subsequently became involved.
Ciliary currents were never evident on the oral disc, tentacles,
or body wall. Rather the adult contracted the radial muscles in
the portion of its oral disc closest to the food, drawing only that
section of the body toward the everted pharynx. Here vigorous
ciliary action on the expanded lips drew particles into the body:
reversed ciliary action in the pharynx also regurgitated rejected
food. Only if relatively large amounts of desirable food covered
an animal, did it completely contract.
Brooding young often captured particles tumbling from parental
grasp. Dunn (1972) also observed young ingesting bits of food
".. hanging down over the oral disc." This appears to me to be
scavenging behavior on the part of the offspring, not "deliberate"
feeding of young by adults.
The Possibility of Food Transfer Through Tentacles.
Hand (1955) noted that in Epiactis, each tentacle tip was
perforated by a small pore, controlled by a sphincter. A touch
on the tentacle tip caused the pore to close and when an animal was
stimulated to contract, a stream of water was ejected from the hole.
My own observations indicate that in body contractions, most excess
water was forced out through the pharynx, and only if that passage
was blocked, was fluid ejected through the tentacles. But the
Brooding in Epiactis
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capability of Epiactis to pass material through the tentacle tips,
combined with the posture of animals previously noted, (see Protection)
suggested to Dr. D.P. Abbott( pers. comm.) the possibility that
adults may be ejecting particles on, or "nursing", their young.
In an effort to determine if food particles were transfered by this
mechanism, dyed gelatin and other food material coated with graphite,
methylene blue or carmine red particles, was force fed to adults
with a Pasteur pipette. Some adults were also permitted to feed
themselves once food was placed on the oral disc.
Particles Were often seen circulating within the coelenteron
inside the tentacles, but no actual elimination of particles or food
transfer to the young was observed. If adults were eliminating
particles from the tentacle tips, these were too small to be visible
under the dissecting microscope.
The Possibility of Translocation of Food Through the Body Wall
Dunn (1972) investigated the possibility suggested by Verrill
(1869) that attached offspring receive dissolved material trans-
located through the parental tissue. Her studies, using brooding
adults fed on radioactively labelled rat liver, gave inconclusive
results.
A modified version of Dunn's experiment was conducted. Five
brooding adults, each carrying several young, were placed in sepa-
rate dishes. To each dish were added several offspring carefully
removed from other adults. These young were induced to settle in
near proximity to the brooding adult. The adults were then fed
particles of hard boiled egg yolk suspended in seawater and combined
Brooding in Epiactis
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with a radioactive algal mix of C14 amino acids. (U.L. mixture
New England Nuclear Corp.) At intervals of 6, 12, 24, and 48 hours,
experimental (attached) and peripheral (control) babies were removed
to assay their radioactivity. Each sample was dehydrated under a
hood, weighted and minced. One ml of NOS (Amersham/Searle)
was added and the vial shaken for at least 12 hours to solubilize
the tissue. 10 ml of Aquasol was then added and after a period of
24 hours, the samples were counted in a Nuclear Chicago Unilux II
Liquid Scintillation unit. Efficiency ranged between 64-72%.
The adults regurgitated some of the material fed to them, re-
sulting in contamination of the surrounding water. Both control
and experimental young became radioactively labelled. A paired
Student t test showed no significant differences in radioactivity
between brooded and non-brooded young in each bowl.
If direct translocation of food occurred, it either represented
an increment too slight to be detectable against backround conta-
mination, or it occurred too slowly to be significant within the
48 hour time frame of this experiment.
Other Methods of Feeding of Young
It appears unlikely that there is any substantial feeding of
attached young by brooding adults via the three mechanisms proposed
above. Dunn (1972) points out that the developing embryo has been
supplied with a large amount of yolk which is still evident in the
endodermalccells of post embryonic juveniles. Present observations,
consistent with those of Dunn, show that offspring 0.6 mm in basal
diameter already bear 6 tentacles containing nematocysts which
fire when the animal is place under a coverslip in a solution of
Brooding in Epiactis
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methylene blue and tap water.
Artemia nauplii were fed to brooded offspring in an attempt
to determine the smallest size at which young are capable of captur-
ing and eating small living prey. Young only 1.0 mmin basal dia-
meter and bearing 12 tentacles, immobilized and ingested the nauplii
within minutes. Thus it may be unnecessary for the adults to
provide a supplemental food supply to the developing young once the
yolk reserve has been exhausted.
One further source of nourishment should be noted. Dunn (1972)
suggests that spawning occurs during most of the year. It is not
known how often an individual spawns, but the egg ingestion by
attached young, noted earlier, may represent an infrequent but
substantial feeding by the adult to the young. In this way a large
brood, precluding attachment of additional eggs in the limbus
region, may utilize reproductive products which would otherwise be
wasted.
SUFMARY
1. Studies were conducted at Hopkins Marine Station in Pacific
Grove, California to determine what benefits the externally
brooded young may derive from their parents.
2. In spawning behavior, the body column contracts one one side
to form a valley, extending between pharynx and limbus, which chan-
nels the spawned egg chain to the attachment site. The contraction
passes slowly, in a wave around the circumference of the adult,
depositing a belt of spawned eggs encircling the limbus region.
3. Strength of attachment appears to increase with body size.
Brooding in Epiactis
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Ability to attach effectively, may be a factor determining the
size at which Epiactis can survive independently of the parent.
5. Three possible mechanisms of food transfer between parent and
young were investigated: a. adult ciliary action transports food
to young; b. adults "nurse" young by passing particles from the
coelenteron through the holes in the tips of the tentacles; c. adults
translocate food to the offspring through the parental body wall.
Results indicate that probably none of these representsaaniimportant
food source for the young.
6. My observations and those of Dunn (1972) suggest that the young
capable of feeding themselves on smalllactive food by the time the
yolk supply is exhausted.
7. Some eggs spawned by brooding adults were consumed by attached
young.
ACKNOWTLEDGENENTS
Sincerest thanks are due D.P. Abbott for his infectious
energy and patience, and Chuck Baxter for his thoughtful suggestions.
I am also grateful to Robin Burnett for his encouragement and
his roses.
Brooding in Epiactis
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Captions for figures.
a. Posture of animal forms a curtain of tentacles surrounding young.
b. Top view of contracted body wall in spawning, creating a valley
extending from pharynx to limbus.
c. Side view of 12 o clock section through b. showing the valley.
Contraction has passed clockwise around the body.
d.
e. Side view of animal after the wave of contraction has subsided.
Note the puffed portion of the pedal disc, below the limbus.
Brooding in Epiactis
BIBLIOCRAPE
Dunn, D.F. 1972. Natural history of the sea anemone Epiactis prolifera
Verrill, 1869, with special reference to its reproductive biology.
Ph.D. thesis, University of California, Berkeley, 187 pages.
Dunn, D.F. 1975. Reproduction of the externally brooding sea anemone
Epiactis prolifera Verrill, 1869. Biol. Bull. 148:199-218.
Hand, C. 1955. The sea anemones of central California. Part II. The
endomyarian and mesomyarian anemones. Wasmann J. Biol. 13:37-99.
Lenhoff, H.M. 1965. Mechanical stimulation of feeding in Epiactis
prolifera. Nature 207: 1003,
Ricketts, E.F. and Calvin, J. 1968. Between pacific tides, (4th edition,
revised by J.W. Hedgpeth). Stanford University Press, Stanford,
California. 614 pages.
Verrill, A.E. 1869. Notes on Radiata in the museum of Yale College,
with descriptions of the new genera and species, V. Trans. Conn.
Acad. 1:247-596.
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