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Figure 1: Top-down picture of my hitchhiking
nudibranch; its length is approximately 1.5" (38
mm).
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As virtually every
live rock owner can attest, aquarists receive a mixture of
desirable, undesirable and ugly hitchhikers. With my first
shipment of live rock for my new tank, I received some rather
ugly and undesirable hitchhikers: Cirolanid
isopods. I later received a shipment of live rock from
Tampa
Bay Saltwater on July 24th,
2005.
On August 2nd, 2005 I was
doing my nightly tank observation and discovered a "worm"
crawling on my aquarium's glass. I retrieved it and moved
it to my quarantine tank so I could attempt identification
at a later date. Two days later I discovered another "worm"
about half the size of the first. Fearing an outbreak of another
undesireable hitchhiker, I intensified my search for an identification
of this unknown animal, and soon discovered that I had a nudibranch
of the sub-order Aeolidacea, animals more commonly referred
to as aeolids.
Nudibranchs are marine snails that are often called "sea
slugs." For more background information on nudibranchs
I suggest reading Ron Shimek's articles Naked...Gills
on Snails and Beautiful,
But Unwelcome; Aeolid Nudibranchs in the Reef Aquarium,
or visiting what I consider a great online resource: http://www.seaslugforum.net/.
These resources were very helpful in my nudibranch research.
Additional information and pictures of nudibranchs commonly
seen in the hobby can be found in Marine Invertebrates
(Shimek, 2004), Coral Reef Animals of the Indo-Pacific
(Gosliner et al., 1996), 1001 Nudibranchs - Catalogue
of Indo-Pacific Sea Slugs (Coleman, 2001), Invertebrates
- A Quick Reference Guide (Sprung, 2001) and Nudibranchs
and Sea Snails Indo Pacific Field Guide (Debelius, 1996).
Keep in mind that many of these guides (with the exception
of Dr. Gosliner's book, who is a nudibranch taxonomist) most
likely contain identification errors.
Virtually all nudibranchs have specialized mouth parts and
digestive tracts. This means that they consume only one or
a few very closely-related foods, typically sponges or other
sessile invertebrates that cannot be supplied adequately in
aquariums. For this reason, then, most nudibranchs are doomed
to slow starvation in our care.
Problematic Identification
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Figure 2: A close-up of the head area showing
the lack of zooxanthellae "veins."
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The aeolids in my tank, however, were
soon discovered to eat anemones. Arguably the most recognized
aeolids in the aquarium hobby are Berghia verrucicornis
(Costa, A., 1864) and Aeolidiella stephanieae (Valdes,
2005), famous for their ability to eat Aiptasia anemones
and for not being fatally toxic to most tank inhabitants when
expiring in captivity en masse. After consulting additional
resources (Garcia-Gomez and Cervera, 1985; Gosliner, 1979;
Marcus and Marcus, 1977), it appears that my nudibranchs could
be Spurilla neapolitana. It should be noted that this
is a tentative identification based on pictures, diet and
egg mass similarities (see here
for Spurilla neapolitana egg mass photos), and is in
no way a definitive identification. Like most aquarists, I
like knowing the scientific name of the creatures in my care.
Nudibranch identification to species, however, is nearly impossible
without dissection. This nudibranch, therefore, could easily
be any of a number of closely related aeolids. Well-fed Spurilla
neapolitana are often cited as having distinct "veins"
of ingested zooxanthellae near their head (see here
for pictures). As can be seen in Figure 2 below, my nudibranchs
lacked these "veins," which further complicated
identification attempts.
Diet, Care and Handling
What was more important to me than
its scientific name was determining my nudibranchs' diet.
I did not want to introduce them back into my tank to feast
on my easily identified Acropora yongei, Acropora
nobilis or Acropora aculeus (a little identification
humor). I immediately put out a call to my fellow MARSH (Marine
Aquarium and Reef Society of Houston, TX) club members for
pest anemones as it appeared the nudibranchs were nearly starved
(see Figure 3).
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Figure 3: My nearly starved nudibranchs with
a distinctive lack of color beginning their first meal
of a "tulip" anemone.
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I quickly received some "tulip" anemones that look
remarkably similar to Majano anemones. This was an
acceptable first food as both specimens began to feed immediately
(see Figure 3). I later acquired two different morphs of Aiptasia
spp. anemones that were also readily consumed (see Figures
4 and 5). It is interesting to note that I had several rock
anemones from my first live rock shipment that appeared to
be healthy and growing before I added my second shipment of
live rock. They all disappeared within a number of days of
each other after the second shipment of live rock was added.
While it is only speculation, it is possible that the nudibranchs
consumed these as well before I removed them from the tank.
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Figure 4: Aiptasia morph #1 being ingested.
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Figure 5: Aiptasia morph #2 with first
egg mass above it.
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Care of these nudibranchs was relatively easy. My specimens
tolerated a specific gravity ranging from 1.023 - 1.030 and
temperatures of 74-82°F (23-28°C), but I usually kept
their containers at 79°F (26°C) and 1.026 SG. The
holding containers were bare buckets and cups that were un-aerated
and contained no filtration; one 19-watt 6500K power compact
bulb provided illumination. Regular 30-90% water changes were
performed using filtered and aged tank water every two to
five days. The water changes were important as the nudibranchs
frequently sloughed off waste when eating or moving (see Figure
6). I first mistook this for an egg mass, but as you will
see later, the eggs look very different from their waste.
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Figure 6: Nudibranch waste/mucous accumulation.
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Handling and transfer of nudibranchs is best performed by
blowing water with a turkey baster gently near their foot
until they release their hold on the substrate. They can then
be scooped up using a small bowl to transfer them without
breaking their fragile cerata
that are easily snagged on nets or intentionally released
by the animal when threatened.
Feeding Behavior
Most nudibranchs
lack eyes and I did not detect any on my specimens. They hunt
their prey by using a combination of their rhinophores
and oral
tentacles (see Figure 7). In my situation I noticed some
interesting behavior. I typically kept my specimens in a container
without anemones to keep the water quality more stable. If
they were well-fed, the nudibranchs would typically move only
at night. After the addition of an anemone, however, they
would go into hunting mode within 10-60 seconds.
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Figure 7: Rhinophores, oral tentacles and ceras
of a nudibranch, seen here in hunting mode.
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Hunting begins by moving the rhinophores into various positions.
It is speculated this is done to smell the anemone and determine
its general direction (see here).
The nudibranch then begins to move forward with some side-to-side
sweeps in an ever-widening cone shape. During this entire
time its rhinophores are in constant motion, and its oral
tentacles are held in front and slightly to the sides of its
head (see Figure 7).
Once the oral tentacles make contact with
the anemone, they determine the prey's orientation, as this
nudibranch always ate beginning with the anemone's foot and
consuming its tentacles last. The anemones would sting the
nudibranchs, but they would only briefly recoil and then resume
their feeding (see Figures 8 & 9 for feeding pictures).
The nudibranchs would consume even a very large anemone in
one feeding, with their mouth constantly attached to the food.
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Figure 8: Beginning to feed, the nudibranch would
slowly detach the anemone's foot from the substrate.
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Figure 9: Here the anemone is roughly 50% consumed;
smaller anemones such as this one were often overturned
during feeding.
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Feeding would typically take over two
hours to consume a large tulip anemone and around 45-60 minutes
for a similarly-sized Aiptasia. After feeding, the
nudibranchs would rest and excrete waste. They have substantial
appetites, however, and when supplied with a constant food
source they ate 30 anemones in 10 days.
Reproductive Observations
Nudibranchs are
sexually hermaphroditic. This means that one individual contains
both male and female sexual organs. They are rarely self-fertilizing,
though, and usually require two specimens to reproduce. I
observed a mating "dance" that was essentially identical
to the one described for Berghia by Anthony Calfo (2004).
When provided with enough food an adult laid an egg mass in
my system on average every one to three days. As shown in
Figure 10, egg masses are typically laid in a loose spiral,
but not always.
It is interesting to note that when I first started feeding
the nudibranchs on August 2nd,
2005, one specimen was 1.5" (38mm) in length while the
other was barely 0.5" (13mm). While the larger specimen
began laying eggs on August 5th,
the smaller one did not begin to lay eggs until August 27th
when it was 1" (25mm) long. Its first egg masses were
very small and contained only a few hundred eggs.
Once both adults were full-sized and laying
eggs, each mass contained thousands or even tens of thousands
of eggs. Each individual egg was well under 1mm in diameter,
but I did not have a way to measure anything
smaller than 1mm. It would take between five to eight days
for an egg mass to hatch. Several images of egg masses in
the process of hatching are seen below (Figures 11-14).
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Figure 11: This egg mass is just beginning to
hatch (4x magnification).
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Figure 12: The egg mass is seen here disintegrating
during hatch with larvae clearly visible in the lower
center (4x magnification).
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Figure 13: Each loop in an egg mass contains
hundreds or thousands of eggs (60x magnification).
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Figure 14: The larvae are seen here one hour
after hatching (200x magnification).
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Raising Efforts
Good documentation is available (Calfo,
2004; Borneman, 1998; Carroll & Kempf, 1990) on raising
Berghia nudibranchs, but I could not find any information
on raising Spurilla neapolitana. I set up a system
similar to that described by Calfo (2004) and Carroll &
Kempf (1990). However, after 45 days of attempts, I was unable
to raise the babies successfully. Raising aeolids is a time
intensive task, and I simply did not have enough time. If
hobbyists acquire a breeding pair of these aeolids and want
to attempt raising their young, they should be prepared to
spend 7-20 hours per week to adequately care for the adults,
eggs and babies, and to culture their anemone food supply.
Nudibranch larvae hatch in a wide variety of forms, but there
are two extremes. On one end of the scale the nudibranchs
hatch as miniature sea slugs and begin seeking a food source
immediately. On the other end are eggs that hatch as free-swimming
larvae that feed for a long time in their planktonic stage.
Larvae that need to feed while in their planktonic stage make
aquarium rearing very difficult. For a longer discussion of
larval size, see "When
Nudibranchs hatch, are they just smaller versions?"
by Bill Rudman.
Berghia verrucicornis have been reported to be lecithotrophic,
which means free-swimming at first, but they do not need to
feed in the planktonic stage and quickly transform into small
sea slugs and begin feeding. While my nudibranchs did hatch
out as free-swimming larvae (see Figures 11
& 12 and these videos: video
1, video
2, video
3), they appear to be non-feeding and around 90% of them
settle in eight hours if the appropriate Majano anemones
are present (Rozsenich, pers. comm.).
Because I did not have enough time to dedicate to their raising,
I arranged to have a dedicated Berghia breeder, Yvonne
Rozsenich, take over the breeding efforts. While Yvonne has
raised the larvae only to 30 days on her best attempt, it
appears likely that she will succeed. I have combined my observations
with hers to find several factors that could help others attempt
to raise them, and these are detailed in the list below. It
appears that the babies prefer to settle near Majano
anemones, as settling near Aiptasia spp. has not yet
been observed (Rozsenich, pers. comm.).
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Tips to help increase success
in raising the larvae:
1. The large number of eggs in each egg mass
means that the hatched larvae will cause a lot
of damage and kill large anemones before they
can be consumed. This causes rapid fouling of
the water and larval deaths. It is suggested that
immediately after the egg mass is laid, a small
portion of the egg mass should be severed and
used to raise a smaller number of larvae.1
2. As with Berghia, very small anemones,
or diced anemone flesh, should be present when
the egg mass hatches in order to induce larval
settlement.1
3. Egg masses should not be exposed to air as
they were not observed to hatch after prolonged
exposure to air. Instead, either the adults should
be moved after laying an egg mass or the egg masses
should be scraped from the surface using a credit
card or razor blade and transferred using a cup
or bowl.2
4. The egg masses are extremely sticky and nearly
impossible to remove from live rock or other uneven
surfaces. The egg laying adults should be kept
in bare containers with flat surfaces.2
5. All of the animals' life stages should be kept
in aged and filtered water (a coffee filter minimally,
a 0.45 µm filter would be the preferred
option) and with no live rock, as it is a potential
source of predators for all stages.2
6. 6. Feeding each adult one medium-sized (15-25mm
diameter, measured tentacle tip to tentacle tip)
anemone every two to three days was enough to
maintain egg mass production at one mass every
two to three days. At this rate of feeding, egg
masses hatched after five to eight days, and the
larvae moved vigorously. However, it is unknown
whether feeding the adults additional food would
have led to better survival rates for the larvae.2
7. Heavily feeding the adults reduced the frequency
of egg mass production to every three to five
days and increased the difficulty in maintaining
water quality.2
1Tip
provided by Yvonne Rozsenich (pers. comm.).
2Tip
provided by Brian Plankis.
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Conclusion
With their documented consumption
of Aiptasia spp., tulip and Majano anemones,
this is potentially a valuable aeolid species for the aquarium
industry for pest anemone control. My tank contained several
species of Zoanthus spp., mushroom polyps and soft
corals that did not appear to suffer during the period when
my nudibranchs were wandering undiscovered, nearly starved,
in my tank. This species, however, appears to be a generalist
feeder on cnidarians and more research will need to be completed
to determine if it consumes other, more desirable, anemones
or closely-related cnidarians in a reef aquarium.
This testing should be fairly easy to conduct once the juveniles
are raised to sexual maturity, which should result in a corresponding
increase in broodstock. I wish Yvonne the best of luck in
successfully completing this task. In the meantime, aquarists
receiving livestock from Florida or the Caribbean should keep
their eyes out for this species in their shipments.
If you have the time and skill to dedicate, it is an interesting
and beautiful species (although my wife would disagree on
the last point) to attempt to care for and breed. If you do
not have the time or desire to raise them, however, feel free
to contact me or a local Berghia breeder to increase
the knowledge base and broodstock on this poorly studied (in
aquaria) species. Join me in my author forum
if you have any questions or comments on this article.
Acknowledgements
I would like to thank my wife, Christine, for her patience
during the time intensive care of these animals, and Dr. John
Ramsey for lending me the microscope that allowed me to capture
the magnified images and video included in this article. I
would also like to thank several members of Reef Central and
MARSH for their help in narrowing down the identification
of these specimens and for supplying me with a steady supply
of pest anemones. Finally, Yvonne Rozsenich and Bryan Green
should be commended for their efforts to help me find a new
home for these specimens and for their continuing efforts
to study them.
All photographs are copyrighted
by Brian Plankis and should not be used without his written
permission.
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