About once or twice a month I see a question
posted on one of the reef bulletin boards asking about adding a Linckia sea star to
someone’s reef tank. It may be a red, blue or purple Linckia, but the
questions are usually pretty similar otherwise. How do I care for this animal? What is the
best way to acclimate them? And, are there any differences among the different color
variations of these sea stars? This month, I’ll try to answer these questions, and
provide some information about how best to select, introduce, and maintain one of these
beautiful sea stars in the reef aquarium.
A picture of a blue linkia in the aiuthor’s reef tank. Photo: Rob Toonen
The most commonly imported "Linkia" sea star in
the pet trade is Linckia laevigata, but despite its beauty and the frequency with
which these animals are imported, there is very little known about the natural history of
this animal. In fact, it turns out that we are not even very good at telling the different
species of Linckia apart, because L. laevigata (the blue Linckia) and
L. multifora (the red Linckia) turn out to apparently be the same species!
Using molecular genetic techniques, Williams (2000) showed that L. columbiae and L.
bouvieri were good species, but L. guildingi consists of two different
"cryptic" species (non-interbreeding species that look so similar that they can
not always be told apart by eye). Although the two species currently known under the name L.
guildingi look the same to our eye, the genetic evidence shows that they have not been
able to interbreed for about 1 million years! Unlike the cryptic differences in L.
guildingi, the obvious differences we can see between L. laevigata and L.
multifora are apparently insufficient to warrant them being classified as different
species according to Williams (2000). Despite the differences between these two
morphologically distinct groups of sea stars (individuals can be reliably distinguished by
their color and color pattern, number of madreporites and ratio of arm length to breadth),
researchers found no evidence that these sea stars were genetically isolated from one
another in the same way as the two groups currently known as L. guildingi are .
In terms of the different color morphs, most people
generally want to know if they all behave the same, or whether different colors of sea
stars have different behaviors in the aquarium. The simple answer to that question is
maybe. The problem is that there is quite a bit of natural variation in color among L.
laevigata collected from different areas, and there are some regions where L.
laevigata are almost always brilliant blue, while in other areas the stars may be
predominantly pale, brownish, or even orange in color. Given that the taxonomy of the
group is a little fuzzy still, and we’re not even really sure of the species, the
importance of differences between the color morphs are somewhat hard to pin down, exactly.
What is known about Linckia is that the animals gets their color from a blue
pigment called linckiacyanin and some accessory yellow carotenoids that give the star its
rich blue color . Depending on the exact ratio and combination of pigments in the star,
the colors of the starfish can range from blue, to brown or orange, but it is not clear
whether there are any behavioral or ecological differences among sea stars that have these
different colors. Although certain color variations are more common in some areas than
others, researchers do not know whether these color differences result from some
ecological or genetic differences among the sea stars.
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The "purple
linkia" is a different story, however. There are some purplish morphs of L.
guildingi in both the Caribbean and Indo-Pacific, but they are not commonly the ones
offered for sale in pet shops (in fact, I have yet to see a purple one of these stars in a
pet shop). Instead, the purple star offered for sale under the name "purple
linkia" is most likely to be Tamaria stria. As with the case of the true Linckia
stars, however, little is known about the biology of these stars. The only reference I
know of that gives a firm answer as to their feeding biology is the Baensch Marine Atlas ,
which claims that the star feeds by "grazing Aufwuchs from hard
substrates" - the basic translation being essentially unknown scum-eater. That’s
still not the most specific of descriptions about the diet of these animals, though. There
have been a number of reports on various bulletin boards about these stars turning out to
be predatory in some reef tanks, but in this case the difficulty is knowing whether or not
the animal has been correctly identified at any step in the chain of supply.
As I mentioned above, there are several species of Linckia,
and not all of them are blue, red or purple, and some of the stars commonly sold in pet
shops under the name of Linckia may very well belong to other genera. I have no
doubt as to the authenticity of these reports - i.e., that some people have been sold a
sea star that was labeled "purple linckia" and have subsequently had problems
with that animal in their tanks. However, that does not mean that the "purple
linckia" in their tank is the same species as the one in yours or mine. The variation
reported in the behavior of these stars may represent a case of individual variation, or
it could indicate that there is a lot of misidentification going on.
Linckia multiflora, the Maldives. Photo: Alf
Nilsen.
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My reason for taking
reports of voracious predation by Tamaria stria with a grain of salt is that
I’ve had one for years without any sign of trouble in my own reef tank. As I just
mentioned, there is always the possibility that individual differences may be important
when different animals behave differently in different tanks; even though they belong to
the same species, it is possible that some stars may be docile and harmless, while others
turn out the stuff of horror movies. Another common pattern is when an animal that appears
harmless in some tanks turns out to be a real trouble-maker if moved to another. These
differences among individuals and different tanks are one reason to always err towards
caution if you have any concern. Widespread misidentification of the stars being sold as
"linkia" in the pet shops is another reason that I speculate that reports of
predation by T. stria may be somewhat overblown. Various Fromia species as
well as Leiaster, Ophidiaster, Echinaster and Nardoa species
are occasionally offered for sale as Linckia in petshops, and I have even seen
"knobby linkia" (really the predatory star, Gomophia egyptiaca) offered
for sale in a prominent San Francisco fish store. Many of these misidentified
"linkia" stars are predatory on colonial tunicates, sponges, or other
permanently attached marine invertebrates. Given that so many stars are occasionally sold
under the common name "linkia" there is little doubt in my mind that the
misidentifications are not perfectly consistent, and there may be multiple species of
these unknown sea stars being sold in the trade.
I should also emphasize that I do not think that the
majority of dealers are making a deliberate attempt to mislead you when this sort of
misidentification happens, but I would argue that very few retailers know the biology of
these animals well enough to identify them or predict the potential risks of introducing
them into a reef tank. If a dealer gets in a new critter that they know nothing about,
they are left with either not calling it anything more specific than "starfish"
(which generally doesn’t sell well, because people want to know what it is) or
labeling it with their best guess at identification. By default, popular and well-known
common names (such as "linkia") have a way of being applied pretty broadly
sometimes. Thus, as a consumer, you have to make some effort to educate yourself to make
sure that you are really buying the animal that you expect, or you’re likely to end
up with a surprise sometimes.
OK, so even now that
we’re all aware that there is an important distinction between the true Linckia
and other look-alike sea stars, we’re still only slightly further ahead in terms of
understanding exactly what they need in an aquarium. Even if we limit the discussion here
to only the true Linckia stars, the problem is that there is just not a lot of good
information on their biology. Despite the beauty and obvious widespread interest in these
stars, surprisingly little is really known about the exact feeding behaviors or
preferences of these animals in the wild, and only anecdotal accounts are available for
their needs in the aquarium. That is kind of surprising, given that Linckia is one
of the most common and obvious sea stars on many Indo-pacific reefs.
Linckia multiflora regenerating , the
Maldives. Photo: Alf Nilsen.
Linkia
laevigata from the Solomons. This one was in deeper water and was brown. Photo: Julian
Sprung.
Based on the anecdotal evidence from aquaria, however, L.
laevigata is generally thought to be primarily an opportunistic scavenger, perhaps
being even saprophytic (preferring to consume dead items as they begin to decay), but as
also been observed to apparently feed on algae and microbial films as a non-selective
surface grazer. I say ‘apparently feed’ because to the best of my knowledge
there has never been a single scientific study on the natural diet or nutritional
requirements of these stars, and controlled feeding experiments are rarely done on animals
in reef tanks at home. Therefore, all we really have are observations of what the animals
seem to be sitting on and look like they might be eating - anecdotal reports of the diet
and feeding preferences, but no real evidence that the animals really ingest and gain
nutritional benefits from the stuff we think that they are eating in the aquarium. Having
said that, however, this is the only information that we have currently on what these
animals eat, so that’s what we must go with. Most sea stars feed by everting their
stomachs (they extend the outer section of the stomach to surround the food), secreting
digestive enzymes onto the food item to break it down, and then pulling the stomach
together with the digested food back into the body (see Shimek 1997, 1998 for further
detail on this process). Although this process is much more obvious and easy to observe in
a variety of other sea stars commonly sold in the hobby (such as the popular chocolate
chip starfish, Protoreaster nodosus), it is likely to occur in the same way, albeit
far less obviously, during feeding by Linckia laevigata as well. Based on their
behavior in the aquarium, these sea stars appear to feed by grazing surface films off live
rock or similar substrate. In his book Invertebrates: A Quick Reference Guide,
Julian Sprung (2001) reports that the aquarium diet of L. laevigata and L.
multifora typically include bacterial films, small encrusting sponges, and dead
mollusks.
Although it has also been reported to feed on surface
films like it’s blue cousin, the red Linckia (still widely referred to as L.
multifora), on the other hand, is thought to derive much of its nutrition from
suspension feeding on organic detritus and particulates. Depending on the source, the
primary feeding method of the red linckia may be either: 1) sitting with their arms raised
into the water column and using secreted mucus strands to capture floating particles which
they then collect and eat, or 2) everting their stomachs onto algae and microbial films in
much the same manner as described for L. laevigata above. Given the recent evidence
that both these groups of stars are actually the same species, I would lean towards the
red and blue morphs feeding in largely the same manner. However, I would also emphasize to
readers that until some scientific studies of the feeding preferences and behavior of
these stars become available, any report of the feeding methods and requirements for Linckia
remains essentially a matter of at best well-informed opinion.
Linckia guildingi, the Maldives. Photo: Alf
Nilsen.
Linckia guildingi, Puerto Rico. Photo: Alf
Nilsen.
In any case, assuming that we are right to at least some
extent in our estimations of what these sea stars are feeding upon, much of the nutrition
for these species probably comes from diatoms, bacteria and other filming organisms found
on live rock. It is widely known that these stars often reject any attempts at artificial
feeding in the aquarium, and will typically crawl off pieces of fish, shrimp, squid or
prepared food that other stars (such as the popular chocolate chip starfish, Protoreaster
nodosus or its more attractive cousin, the bahama or general star, Protoreaster
lincki) will readily consume (e.g., see Shimek 1998). Because Linckia stars
appear to derive the vast majority of their nutrition from surface films, and are known
for actively rejecting attempts to feed them, they are unlikely to do well in a tank that
is recently, (within 6 months) set up, or one in which there is not enough live rock for
them to continually find new surface films from which to graze. Therefore, they are not
really recommended for reef tanks smaller than about 50 gallons or so for the long-term.
Although small stars may do well in smaller tanks for some time, they will eventually
require more space. The problem is that in such small tanks, even if the star is
successfully acclimated (I’ll come back to this important detail in a moment), a
reasonably-sized sea star (say about the size of your hand) will not have enough well-aged
rock surface to continue to find food for extended periods of time. Another important
consideration for tanks smaller than about 50 gallons is that Linckia laevigata can
get quite large (30 cm or more across) and the amount of food they require will increase
with their size -- obviously, the amount of established live rock in your tank will have
to be quite large to support a grazing star which is about a foot in diameter!!
In general, there is no need to worry about a species of Linckia
being compatible with other reef tank inhabitants, because these animals are not
aggressive (eating slime off your live rock does not threaten many animals in a reef
tank), and the stars themselves are chemically defended from many fish predators (they
possess chemical defense compounds called saponins). These saponins turn out to be a
highly effective way of discouraging potential predators. In fact, Linckia has a
complex assortment of these defensive chemicals, some of which it shares with the highly
distasteful Crown of Thorns starfish (Acanthaster planci), the famous sea star that
eats reef corals . Unlike the chemical defenses of sea apples (Pseudocolchirus spp.)
and some sponges and tunicates, however, these chemical defenses do not pose a risk to
tank-mates because they are not released from the skin even under duress (see Toonen 1998
for more detail on chemical defenses), and should not be a concern to anything other than
predators which try to nip at the star. Despite these defenses, however, they are not safe
with all fish that are commonly maintained in aquaria. For example, the dog-faced puffer (Arothron
nigropunctatus) is a common predator of sea stars in captivity, and even if well-fed,
these fish may make a snack out of any starfish added to their tank.
This calico-colored sea star is very large (more than
12 inches tip to tip), and is distinct from L. multiflora (note tapered tips).
I’m not sure what genus it belongs to. Photo: Julian Sprung.
So, after reading all that, you decide
that you can provide for the requirements of the star, and want to get one, there are a
few considerations before buying one. First, make sure that the star is active, firm to
the touch and without any discolored patches across the body. There is considerable color
variation in L. laevigata, making it is sometimes hard to recognize discolored
patches from mottled colors on some animals (Bob Fenner has some pictures of sea star
discoloration in his article linked from the references below). I would say that unless
you are familiar with the natural color patterns of the species, it is best to err on the
side of caution and avoid buying a really mottled Linckia. Also, as I mentioned
above, you’ll want to make sure that you’re actually getting Linckia
rather than some other sea star for your reef tank. If you are reasonably confident about
the identity of the star, check to see if the animal is at least partially hidden from
intense illumination and actively crawls about (although they are often not really active
during the day, it should at least move every night). These animals are largely nocturnal,
and should be actively searching for food when the lights are dimmed or off on the
aquarium. If the star is lying inactive under intense lighting, I would wait until you see
one that is behaving in a more natural way before buying it.
These animals are notoriously delicate shippers, and more
often than not a beautiful blue star starts to show white discoloration and begins to
literally disintegrate a week or two after shipping. There are many ideas about why this
happens (including osmotic or pH shock, bacterial and fungal infections, etc.), but
unfortunately no one really knows what the ultimate cause of this problem is. The fact
that we don’t know exactly what causes this problem does not make it any less serious
- it still appears to be the most common pattern of mortality in these sea stars in
captivity, so take it seriously. Because we do not know the exact cause, there is also no
known cure, so this is a case where a little preventative care is likely to really pay
off. The best advice I can offer you is to be patient - it often takes a while to find a Linckia
in really good shape at the local pet shop, but a little patience in that search will be
repaid if the animal survives and thrives in your tank. There is nothing quite as
disheartening as getting an exciting new animal, only to watch as it slowly disintegrates
into goo because the animal was not healthy from the beginning.
Another consideration is that these stars are particularly
prone to parasitic infections of the small snails (Thyca crystallina), and in some
regions as many as 1/4 of the Linckia are infected with these pests . You should
check for these snails clinging to or boring into the underside of the arms before you pay
for the star. Females of these parasitic snails have a proboscis (elongated mouth) that
penetrates the skin of the sea star and sucks the hemolymph (the echinoderm equivalent of
blood) almost like a small, shelled mosquito. Unlike a mosquito, however, the adult snail
actually burrows into and becomes permanently fused to the sea star, and should never be
picked off! Because it is physically attached to the sea star, removing the snail will
almost certainly result in more damage than leaving the snail attached. Besides, these
parasitic snails turn out to be a relatively minor problem. Other than a slight alteration
in some of the skeletal elements around the proboscis, the main effect of these snails on
the star appears to be the loss of tube feet under the snail’s shell (which probably
has no effect on the health of a star in the aquarium over the long-term).
Although research suggests that these parasitic snails
cause little ultimate harm to their hosts , their presence is an additional stress that
the stars can do without when being moved to an aquarium, and their presence provides a
potential vector for infection. So, if you have your choice of several healthy stars, take
one without any parasitic snails first; if you don’t have a choice, it probably
won’t matter to the star in the long-run.
Again, just in case you didn’t take me seriously the
first time, the single biggest problem with Linckia sea stars, even more so than
other echinoderms, is that they require proper acclimation and tend to ship poorly. Their
delicate nature makes it all the more important to start with a healthy specimen if you
decide to introduce one of these animals to your reef tank. Therefore, it is exceptionally
important to acclimate this animal carefully (of course, all animals should be acclimated
carefully, but it seems to be just that much more important to the survival of these
stars). If you can find a healthy star, you should make every effort to bring it home
quickly (long periods of time in a bag seem particularly hard for them to handle as well),
and then acclimate it to your tank water slowly to minimize the stress on the animal as it
is transplanted into your aquarium. This is also a case where it turns out to be important
to check the water conditions of the supplier from which you are getting the animal. If
your local shop maintains a salinity that is much lower than your own tank (natural
seawater is ~ 35 ppt, or roughly 1.025 SG at 80ºF), then acclimation will be more
difficult and survival of the star becomes more of a gamble. If your aquarium is more than
a couple of parts per thousand (ppt) different from that of your supplier, then you are
more likely to have problems introducing one of these stars to your tank. In this case,
you need to try some more extreme measures to introduce the star to your aquarium. There
are a number of suggestions in an article archived in the reefs.org library (Various
Authors 2000), but one of the options if you have a quarantine tank (and you should), is
to set it up with the conditions of the water in the pet shop and slowly acclimate the
star to the conditions at which you maintain your reef tank before transferring it.
If the salinity of the water at your supplier is
relatively close to your tanks, then it’s in the best interest of the star to be
brought home quickly and acclimated to the aquarium. Personally, I usually use a drip
system to acclimate the animals, but this is a hassle, and most people find the cup method
to be much easier and equally as effective. This is simpler because it doesn’t take
anything more sophisticated than a small cup to accomplish. After the sealed bag has been
floated for about 10 - 15 minutes to equalize the water temperature, you start to add
about ½ cup (~125 ml) of water every five minutes until you’ve filled the bag. Once
the bag is full, dump half of that water down the drain (not into your tank) and repeat
this until the bag is full again. Fill the bag at least twice, perhaps even three times
just to be sure that the animal has sufficient time to acclimate to your water conditions.
Once you have completed the acclimation, remove the star from the bag (discarding the
water left behind), and place the animal onto an open rock area in your tank. The star
should promptly (within minutes) adhere to the rock, and then move off in search of a
partially shaded area to begin feeding. Once these stars are successfully introduced to an
aquarium, they seem to be quite hardy and few people report problems with a
well-established animal. It appears to be largely a problem of shipping and acclimation
that gives these animals their delicate reputation, so take your time and give your animal
a fighting chance at surviving the move to your tank.
Like the majority of other sea stars, the sexes appear to
be separate in Linckia, and the animals spawn gametes freely into the water column.
Most often, they will hold onto the substrate with the tips of their arms, arch the body
high into the water and spray either sperm or eggs into the water above them. If a male
and female happen to spawn in close proximity to one another, the fertilized eggs develop
into feeding larvae within a couple of days. These larvae spend about 28-30 days in the
water column before settling onto a hard surface on the reef and metamorphosing into a
tiny version of the adult star . Spawning of these stars in home aquaria is rare, and
although larval culture techniques for echinoderms are well-established (see Toonen 1996
for details), the long planktonic lifespan of the larvae of Linckia makes raising
them at home a difficult prospect.
Although these stars require extra care in the initial
selection, once a blue Linckia is successfully introduced into a large, well
established aquarium with plenty of live rock to explore, they are usually quite hardy and
are certainly a beautiful addition to a reef aquarium. In closing, I just want to thank
everyone at the Omaha Marine Society for some great discussions about sea stars that have
helped with this article.
Literature Cited:
Baensch Marine Atlas, H. Erhardt & H.
Moosleitner. 1998. Volume 3: Invertebrates, with the collaboration of R.A. Patzner,
translated and revised by G.W. Fischer & S.E. Borrer. Microcosm, Shelburne, Vermont,
pp. 737 - 1326.
Bouillon, J., and M. Jangoux. 1984. "Note on the
relationship between the parasitic mollusk Thyca crystallina (Gastropoda,
Prosobranchia) and the starfish Linckia laevigata (Echinodermata) on Laing Island
reef (Papua New Guinea)." Annales de la Societe Royale Zoologique de Belgique
114:249-256.
Egloff, D. A., D. T. Smouse, Jr., and J. E. Pembroke.
1988. "Penetration of the radial hemal and perihemal systems of Linckia laevigata (Asteroidea)
by the proboscis of Thyca crystallina, an ectoparasitic gastropod." Veliger
30:342-346.
Fenner, R. "Sea Stars, Class Asteroidea." WetWeb
Media (http://www.wetwebmedia.com/seastars.htm)
Minale, L., C. Pizza, R. Riccio, F. Zollo, J. Pusset, and
P. Laboute. 1984. "Starfish Saponins 13. Occurrence of Nodososide in the Starfish Acanthaster
planci and Linckia laevigata." Journal of Natural Products 47:558.
Riccio, R., O. S. Greco, L. Minale, J. Pusset, and J. L.
Menou. 1985. "Starfish saponins: 18. Steroidal glycoside sulfates from the starfish Linckia
laevigata." Journal of Natural Products 48:97-101.
Various authors. 2000. "Starfish
Acclimatization." Reefs.org online library article
(http://www.reefs.org/library/article/starfish_acclimatisation.html)
Williams, S. T. 2000. "Species boundaries in the
starfish genus Linckia." Marine Biology. 136:137-148.
Williams, S. T., and J. A. H. Benzie. 1993. "Genetic
consequences of long larval life in the starfish Linckia laevigata (Echinodermata:
Asteroidea) on the Great Barrier Reef." Marine Biology 117:71-77.
Zagalsky, P. F., F. Haxo, S. Hertzberg, and S.
Liaaen-Jensen. 1989. "Studies on a blue carotenoprotein, linckiacyanin, isolated from
the starfish Linckia laevigata (Echinodermata: Asteroidea)." Comparative
Biochemistry and Physiology B Comparative Biochemistry and Molecular Biology
93:339-354.
Sprung, J. 2001. Invertebrates: A Quick Reference Guide
Ricordea Publishing, Miami, Florida
