Download Predation in Sea Urchins

PREDATION
IN SEA URCHINS1
BARRY G. QUINN2
Instilllte of Marine Science, University of Miami
ABSTRACT
Two individuals of the long-spined West Indian sea urchin, Diadema
an tillarum , attacked other sea urchins after food deprivation. Spines,
pedicellariae, and tests were devoured. Only certain species of sea urchins
were attacked. Whether "taste preference" was involved here or whether
Diadema physically could not or preferred not to devour other species of
urchins is not known. It is believed that Diadema does not prey on other
urchins under natural conditions unless food is scarce. A case in which
a Pacific diadematid, Astropyga pulvinata, fed on another urchin is also
cited.
INTRODUCTION
Mention in the literature of sea urchins preying on other species of sea
urchins seems to be non-existent so far as the author can determine. Hyman (1955), in her volume on the echinoderms, notes that Echinus escuLentus feeds on tube worms, crustaceans, hydroids, and echinoderms, but
no mention is made as to what kinds of echinoderms are attacked. So far
as can be determined, Mortensen (1928-1951), in his tremendous monograph on the Echinoidea, makes no mention of sea urchins preying on
other species of sea urchins. He mentions that the food of the diadematids,
to which the predatory sea urchins described in this paper belong, consists
mainly of various encrusting organisms which grow on coral reefs or on
hard bottoms.
Two cases of predation by Diadema an til/arum on other sea urchins are
described. One case of predation by a Pacific species of the family Diadematidae, Astropyga puLvinata, is cited.
ACKNOWLEDGMENTS
Grateful acknowledgment is given to Dr. Hilary Moore, Mr. Sheldon
Dobkin, and Mr. Ben McPherson, of the Institute of Marine Science, for
their aid.
DISCUSSION
Two cases of predation by the long-spined black sea urchin of the West
Indies, Diadema antillarum Philippi, on certain other species of sea urchins
were observed in equaria at the Institute of Marine Science of the University of Miami during the summer of 1963. In one aquarium were a slateIContribution
No. 592 from the Institute of Marine Science, University of Miami. This work
was supported by a National Institutes of Health post-doctoral fellowship under the
direction of Dr. Charles E. Lane, Institute of Marine Science, University of Miami.
2Permanent address: Department of Biology, Westminster College, Salt Lake City, Utah
84105.
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Bulletin at Marine Science
[15(1)
pencil urchin, Eucidaris tribulaides (Lamarck),
a cake urchin, Clypeaster
rosaceus (Linnaeus), several sea stars, and a single specimen of Diadema
antillurum. One afternoon, after the animals had been unintentionally starv~
ed for a week, it was noticed that the short spines on the cake urchin either
had been removed by one of the other urchins or had dropped off due to
an ailment. A few days later, a specimen of the urchin Tripneustes esculen~
tus (Leske) was added to the collection. The next day several square
centimeters of spines were found removed from Tripneustes, but the urchin
was otherwise intact. The following day, approximately ten days after food
deprivation began, Diadema was found on top of Tripneustes and had
chewed away all of the spines, pedicellariae, and podia of the upper surface. It also had bored through the test, making an irregular, elongated
hole eight to nine square centimeters in area (Fig. 1). The test of Tripneustes showed the imprint of the five teeth of Diadema in another area
where it had begun gnawing but had changed positions. Both urchins were
removed from the aquarium and photographed,
after which Diadema was
/'
FIGURE
1. Most of the spines have been browsed off and an irregular hole has
been made in the test of Tripneustes (right) by Diadema (left).
1965]
Quinn: Predation in Sea Urchins
261
returned. The remaining spines on Tripneustes were still moving at the
time of removal from the aquarium. Two hours after Tripneustes was removed, Diadema ejected a stream of fecal pellets. Upon examination, the
fecal pellets were found to consist mainly of fragments of spines, from 1-4
mm in length, and of the same color and thickness as the spines of Tripneustes. In life, this particular Tripneustes had spines 8-9 mm in length,
and a test about equal to Diadema in size. Lasker & Giese (1954), working on Strongylocentrotus purpuratus, reported that starved urchins continue to pass fecal pellets for about two weeks. However, the author is
reasonably certain that the fecal pellets ejected by Diadema were formed
from the spines and test of Tripneustes and not from other material ingested previously. This would mean that the fecal pellets were formed no
longer than 48 hours before they were ejected. Diadema was later seen to
make some exploratory nips on the arm of a sea star, Linckia sp., but soon
moved on. The following day, Diadema made a more determined effort on
an unidentified species of spiny sea star and was actively biting off spines
when separated.
Interested in whether Diadema would attack other urchins, th~ author
introduced three individuals of Lytechinus variegatus Clark into the aquarium a few days after Diadema had demonstrated its feeding behavior
toward its fellow aquarium inhabitants. These urchins all had tests as large
as Diadema. Their spines ranged in length from 6-7 mm on the aboral surface to ] 0-12 mm near the ambit. After four days, none of the Lytechinus
appeared harmed. A single specimen of Tripneustes was now added and
the aquarium was kept under periodic observation. At first, Diadema
seemed to take no notice of Tripneustes, but a day and a half later it was
found to have browsed off all but the oral spines of Tripneustes. When
observed, Diadema was holding Tripneustes against the wall of the aquarium and free of the bottom. The victim had been rotated so that its oral
spines were adjacent to the mouth of Diadema. At this time, a yellow substance was seen issuing from the genital pores of Tripneustes. Upon microscopic examination, the substance proved to be sperm. The two urchins
were separated and placed at opposite ends of the aquarium. Four and a
half hours later, Diadema was seen moving down the side of the aquarium.
Reaching the bottom, it moved toward Tripneustes, coverinq, the 45centimeter distance in two minutes. This is fairly rapid motion for a sea
urchin. Diadema is capable of motion more rapid than this, especially
when prodded. As Diadema moved, its podia picked up spines that had
been broken off from Tripneustes earlier and passed them to the mouth.
As the spines of Diadema encountered Tripneustes, the latter twice moved
jerkily away on its few remaining spines. Its podia did not seem to be
functioning. Diadema affixed its podia to Tripneustes and climbed on top.
Tripneustes did not appear to release any more sperm during this period
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Bulletin of Marine Science
[15 (l)
of observation. Diadema moved over the surface of Tripneustes and, then,
with its podia and spines touching the bottom of the aquarium, moved
Tripneustes around, as if seeking an area of uneaten spines. By the next
morning, Diadema had gnawed a roughly circular hole, 6 square em. in
area, in the test of Tripneustes.
To see whether or not this was an isolated case, another aquarium was
set up, containing a single Diadema, several individuals of Lytechinus, and
a new urchin, Echinometra lucunter (Linnaeus). None of the animals in
this aquarium was fed during the period of observation. Diadema I, the
original Diadema, and the other urchins in the first aquarium were kept
well fed on red algae, which they readily ate. Four days later, a small
Tripneustes (diameter of test 5 em, length of spines 5-7 mm) was introduced into each aquarium. DiademalI seemed to take no interest in Tripneustes during the first seven days, although the two encountered each
other occasionally. On the 11th day of food deprivation, Diadema II
cornered Tripneustes and proceeded to browse on the latter's spines.
Twenty-four hours later, Tripneustes had been consumed completely, including the test as well as the spines. None of the other urchins in the
aquarium was ever found feeding on Tripneustes. Since many echinoids
tend to be scavengers,. there is a possibility that urchins other than Diadema fed on Tripneustes. However, in the time interval involved, their
effect would have been small, as will be pointed out later. The bottoms of
the aquaria were kept clean in order to observe when fecal pellets were
ejected. Diadem a II ejected fecal pellets within the 24-hour period. During
the entire period of these later observations, the well-fed Diadema I did
not attack the Tripneustes in its aquarium.
Thus, these observations show that Diadema, if starved, will attack and
devour Tripneustes. Diadema I also attacked the cake urchin, Clypeaster
rosaceus, but other species were apparently not bothered. Whether "taste
preference" was involved here or whether Diadema physically could not
devour the other species of urchins is not known. It may have been able to
feed on all of the species of urchins, but chose the one with the shortest or
weakest spines. However, few echinoderms should present difficulties'Pto a
persistent Diadema with its strong teeth and powerful jaw apparatus. It
should be noted that diadematids normally browse mainly on corals and
their encrusting organisms.
In nature, Diadema and Tripneustes often occur together, sometimes
within a few centimeters of each other on the same rock or within the
same rock hollow. It is doubtful whether Diadema would prey on Tripneustes or any other urchin under natural conditions unless it found food
scarce.
During an observation made in July, 1964, the author saw a specimen
of Astropyga pulvinata (test diameter 5.5 em) in an aquarium feed on a
1965]
Quinn: Predation in Sea Urchins
263
specimen of Echinometra sp. (test diameter 3.5 cm). Astropyga pulvinata
(Lamarck) is a diadematid from the eastern Pacific. This individual was
collected by Mr. Richard Chesher off the coast of Panama. At the time
that the observations began, no food was observed in the aquarium, and it
is not known how long the various urchins in the aquarium had been without food. The Echinometra was resting on the bottom of the aquarium in
an inactive state and may have been dead, although a few spines wer~
moving. Astropyga had just commenced to feed on the aboral spines of
Echinometra. It grasped each spine at its tip and proceeded to chew toward
the base. Sections up to several millimeters long were broken off at each
bite. Each time a section was broken off, both animals jerked due to the
force of exertion. Often, the part of the test to which the spine was attached was eaten before Astropyga moved on to the next spine. Sometimes
a section of test several square millimeters in area was bitten off. Astropyga usually made a succession of bites 10 to 15 seconds apart, then explored for the next area to eat. It should be noted that both Diadema and
Astropyga have a very protrusible peristome and Aristotle's lantern, which
can be used to reach out for food materials. This would facilitate feeding
on spines. The buccal podia of Astropyga maintained contact with the
food, perhaps acting in a feeling capacity. The short secondary spines
around the peristome occasionally helped to guide a spine into the mouth
while brushing away the other spines of Echinometra. After six hours, the
entire top of Echinometra had been eaten, test as well as spines. Astropyga was now joined by another specimen of Echinometra, as well as by a
Eucidaris sp., both of which attached themselves to the victim. These two
individuals seemed to make little progress toward ingesting the test or
spines of the victim. Their rate of feeding may have been too slow to be
noticeable. Eucidaris was later found with a spine in its mouth, suggesting
that it could feed on spines. The next morning all of the victim had disappeared except the teeth and a few spines. At least half of it had been eaten
by Astropyga. It is not known how much of the remainder was eaten by
Astropyga and how much by other urchins in the aquarium, but most likely
Astropyga ate almost all of it.
Further information on the feeding behavior and behavior in general of
Astropyga and certain other urchins will be brought out in a paper by Mr.
Chesher.
SUMMARY
The literature states that sea urchins are mainly browsers on marine
plants and encrusting organisms, both plants and animals. A few are carnivorous, feeding on annelid worms, hydroids, and barnacles. Tn this study
it was found that the long-spined West Indian sea urchin, Diadema antillarum, when deprived of food, attacked other echinoderms, including sea
stars and other species of urchins. One species of urchin in particular,
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Bulletin of Marine Science
[15 (1)
Tripneustes esculentus, was preyed upon by Diadema. One entire specimen of Tripneustes was devoured in a little over 24 hours. One species of
cake urchin was attacked. Three other species of sea urchins were apparently unharmed. It is difficult to say why Diadema seemed to prefer
Tripneustes. Perhaps a "taste preference" was involved, or perhaps it was
physically impossible for Diadema to feed on some species of urchins.
There is the possibility that Diadema selected those urchins which had
weaker or softer spines.
To show that predation is not restricted to Diadema, a Pacific diadematid, Astropyga pulvinata, attacked and devoured all or most of a specimen of Echinometra while Astropyga was in an apparently starved condition.
Under natural conditions, Diadema and Astropyga might possibly attack
other urchins if food became scarce.
SUMARIO
CANIBALISMO
EN ERIZOS DE MAR
La literatura dice que los erizos de mar son principalmente
comedores
de plantas marinas y organismos incrustantes, tanto plantas como animales.
Unos pocos son carnivoros, alimentandose de gusanos anelidos, hidroides
y escaramujos. En este estudio se encontr6 que el erizo de espinas largas de
las AntiJIas, Diadema antillarum, cuando se Ie priva de ali mento, ataca
otros equinodermos, incluyendo estrellas de mar y otras especies de erizos.
Una especie de erizo, en particular, Tripneustes sculentus, fue presa de
Diadema. Un ejemplar completo de Tripneustes fue devorado en poco mas
de 24.horas. Una especie de erizo panque fue atacado. Otras tres especies
de erizos aparentemente
no sufrieron dano. Es dificil decir par que
Diadema parece preferir Tripneustes. Quizas sea cuesti6n de "sabor" 0
quizas fue flsicamente imposible para Diadema el alimentarse de otras
especies de erizos. Hay la posibilidad de que Diadema seleccionara aquellos
. erizos que tienen espinlls mas debiles 0 mas suaves.
.
REFERENCES
L. H.
1955. The Invertebrates: Echinodermata. McGraw-Hili, N~w York, vii +
763 pp.
LASKER, R. AND A. GIESE'
.
1954. Nutrition of the sea urchin, Strongylocentrotus' purpuratus. BioI.
Bull., 106 (3): 328-340.
HYMAN,
MORTENSEN, THEODOR
1928- Monograph
1951.
of the Echinoidea. C. A. Reitzel, Copenhagen,
15 vols.