I just got an orange and a red branch warty gorgonian (I think that
they are from the Caribbean) for my tank. I have them in areas that get[s] low light and
medium-strong current. It took them a few days to acclimate, but now their polyps appear
to be fully open. As far as I can tell, the gorgonians seem to be doing fine in my tank so
far. My question is besides DT's Live Phytoplankton, can I also feed them any small meaty
foods like Prime Reef or should I get some sort of invert food or something else? If so,
how many times a week? Anything else that I should know about them? Thanks! Mike"
Mike,
Just to bring everyone to same starting point, let me
start off by explaining exactly what a gorgonian is. Gorgonians are in the Class Anthozoa
and together with the sea pens, the ‘true’ soft corals, and the stoloniferans
(like the pipe-organ coral, Tubipora) form the subclass Octocorallia. The other
subclass of anthozoans is the Hexacorallia, which includes all the stony corals, the
anemones, the zoanthids and the corallimorphs (commonly called mushroom polyps). Although
greatly oversimplified, the octocorals usually have feeding tentacles in multiples of
eight, while the hexacorals usually have multiples of six feeding tentacles per polyp.
There are a lot of other differences, of course, and Eric Borneman (2001) has a nice
description of the classifications of cnidarians in his book Aquarium Corals, if
you’re looking for a more detailed and accurate explanation than I have given here.
The Order Gorgonacea includes the sea fans, sea whips, sea rods, black corals, and other
gorgonians that have a firm interior axial skeleton (the hard rod inside the animal
that keeps it upright). This axial skeleton is usually composed of a tough proteinaceous
compound called gorgonin (although some may be calcareous), and the colony forms a
thin, rough layer of living tissue (usually loaded with spicules) that grows over that
axial skeleton.
I’m glad to hear that your animals seem to be
settling into your tank, but in truth, it is pretty hard to say for sure whether or not a
gorgonian is doing well in an aquarium over the short term. Although a complete failure to
extend the feeding polyps is likely to be a sign that the animal is not doing well, the
converse is not necessarily true. Simply extending the feeding polyps is not an obvious
sign either way; gorgonians can continue to expand and look ‘normal’ while
slowly starving for months before showing obvious signs of decline. The only really clear
indication that your animal is thriving in the aquarium is that it shows significant new
growth through time.
Although gorgonians are
amazingly resilient, and many of them can make a complete recovery from losing even a
considerable amount of tissue (in fact, the animals are often propagated by simply cutting
off a healthy branch), it is still generally a good idea to avoid purchasing an animal
with exposed skeleton. If there are extensive portions of the skeleton showing, you know
that the live tissue has died and rotted (or been cut or rubbed) away from that area.
Unless you really know what you’re doing, the problem with selecting a gorgonian that
shows exposed skeleton is that: 1) you know that something has caused some of the colony
to die recently, but you don’t know whether that was mistreatment during collecting
or a systemic problem, such as a disease; and 2) the exposed skeleton provides substrate
upon which algae can grow, and that makes it more difficult for you to establish the
animal in your aquarium. If the animal looks to be in great health otherwise, and you are
determined to buy an animal with exposed skeleton, it is a good idea to simply cut off the
dead portions of the colony before securing it in your tank.
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I’ll assume that you
are correct that your gorgonian has come from the Caribbean, and will guess that the
colorful warty sea rod you describe is most likely Diodogorgia nodulifera (there
are plenty of suitable coral identification books out there, such as the Aquarium
Corals book I mentioned above). These lovely gorgonians are very common throughout the
Caribbean, and are both hardy and adaptable to a wide variety of habitats in deeper
waters. In nature, they are found almost exclusively in deeper waters. They usually appear
at about 40 or 50 feet and are common to depths as great as about 600 ft. They are often
found in shaded areas, such as under ledge overhangs on walls and in caves, on shallower
patch reefs. At greater depths, they are much less restricted, and are found out in the
open on deep reefs, as well as growing from hard substrates on both sandy and rocky bottom
areas.
Because these animals lack symbiotic algae
from which to gain any nutrition, there is no specific lighting requirement for these
animals. I think that your choice of a lower light area is a good one; however, I have
seen them kept in tanks with both intense and subdued lighting, but if their natural
distribution is any indication, they should probably be kept out of strong lighting. If
nothing else, these gorgonians make a beautiful addition to a shaded area which would be
suboptimal for most corals, and shading also reduces the risk of algal growth on the
gorgonian. In my experience, people generally have more success with D. nodulifera which
are kept in shaded regions of the aquarium.
I am not sure exactly what "medium-strong
current" means in terms of a flow rate, but I am glad to see that you are thinking
about the flow conditions. Flow is critical to the survival of most gorgonians, because
their feeding ability is more-or-less directly related to the current flow in which they
are kept. Unfortunately, recommended flow rates are also where my ability to give you a
specific recommendation for your gorgonian becomes much more complicated, because to the
best of my knowledge, there are no specific studies of feeding or current requirements for
D. nodulifera. The conditions under which an animal will thrive varies with each
species of gorgonian, and no single set of conditions or current velocities are best for
all species. That makes it pretty hard to offer generalities about how best to keep a
species, such as D. nodulifera, for which there has been no specific research.
A photosynthetic seafan from the
carribean - these are much easier to maintain in a home aquarium.
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One clue that we can use
to guess the appropriate flow conditions for a gorgonian is the size of the polyps.
Research by Dai and Lin (1993) found that each of the three species of Taiwanese
gorgonians they studied occurred in specific habitats, apparently as a result of their
ability to feed effectively. The larger the polyps, the greater they were deformed by high
current speeds, and the less effectively the animals were able to feed in extreme currents
(e.g., Sponaugle 1991, Sponaugle and LaBarbara 1991, Dai and Lin 1993). As a result,
gorgonians with the largest polyps had the narrowest range of currents in which they were
able to feed, and the smaller the polyps, the more capable the animals were of feeding in
a wide range of current speeds. For example, Dai and Lin (1993) found that the gorgonian
with the largest polyps in their study (Subergorgia suberosa) was restricted to
lower reef slopes or sheltered outcroppings where currents averaged less than 10 cm/s. In
contrast, the species of gorgonian with the smallest polyps in their study (Melithaea
ochracea) was able to feed at the highest flow rates (as great as 40 cm/s in this
study).
It is interesting to note that
regardless of the polyp size, or the range of current speeds at which the animals were
capable of feeding at all, all three species tested by Dai and Lin (1993) fed best at
about 8 cm/s. In a similar study with two Jamaican gorgonians, Sponaugle and LaBarbara
(1991) found that both species fed best at current velocities between 10 - 15 cm/s. D.
nodulifera has pretty large polyps for a gorgonian, and in my experience, D.
nodulifera is found primarily in the same approximate current regimen as S.
suberosa, so in the absence of any specific data on the feeding behaviors and flow
preferences of D. nodulifera, we’ll just have to assume that intermediate
flows are also going to be the best bet for successfully feeding your gorgonian. If
we’re willing to accept that assumption, I would guess that variable current speeds
on the order of about 6-10 cm/s would likely be the best bet for the successful feeding of
D. nodulifera.
OK, great, but what exactly does 10 cm/s mean
when it comes to flow in your tank? Well, although it sounds silly, the best way to
determine current speed in your tank is to simply measure it. Locate a bubble, a baby
brine shrimp or some other tiny marker you can easily follow, and place one finger on the
aquarium where that marker is first seen (this should ideally be upstream of where you
want to locate your gorgonian). Watch that marker for 2 seconds and place another finger
on the tank where ever the item you were following has ended up. Simply divide that
distance by 2 and you have a very rough estimate of the current speed in your aquarium. Do
this a few times to get an idea of the average flow velocity in that spot, and that will
help you to decide whether there is sufficient flow in the area in which you hope to keep
the gorgonian.
Before I go any further, I have to say that
in general, asymbiotic (lacking symbiotic zooxanthellae, and therefore
non-photosynthetic) gorgonians do not have a good record of survival in reef aquaria to
date. You have taken the first step and are asking about the feeding requirements of your
animal, so you are obviously prepared to start feeding it regularly. Of course, I would
prefer that you had asked these questions before you purchased the animal rather
than afterwards, but that’s another issue. Feeding is essential for any asymbiotic
gorgonian, because in even the best stocked tanks, it is unlikely to get enough food
without some effort to directly feed it. Again, there is no specific studies of the
feeding requirements of D. nodulifera, so we’re left with looking at the
feeding requirements and prey preferences of other gorgonians, and hoping that your
gorgonian is fairly similar.
Sadly, there are not many studies on the
natural diet or feeding behaviors of gorgonians on coral reefs at all. The studies that
have been done suggest that most gorgonians likely feed on a variety of small plankton,
detritus, marine snow, phytoplankton and even bacteria (e.g., Coma et al. 1994, Ribes et
al. 1998, 1999). Although these studies suggest that gorgonians will take a variety of
prey items, all prey items consumed by gorgonians in the wild are very small, and
gorgonians eat a lot of them. In fact, based on the studies cited in this article, I would
go so far as to say any gorgonians kept in aquaria require some food, regardless of
whether they contain symbiotic zooxanthellae or not.
I say this because even gorgonians with
photosynthetic symbionts (such as the commonly imported Plexaura, or Eunicea
species) are capable of capturing and ingesting a considerable number of small to
medium-sized zooplankton (in the approximate range of 5 - 700 micrometers). In addition to
the nutrients provided to the gorgonian by symbiotic zooxanthellae, prey capture may be an
important source of food energy for all gorgonians studied to date. One recent study
(Ribes, et al. 1998) on feeding in Plexaura found that this ‘photosynthetic
gorgonian’ eats roughly 7.2 ± 1.9 prey items per polyp per day (primarily ciliates,
dinoflagellates, and diatoms in this study). That is a lot of food for an animal that
isn’t supposed to require any feeding! Although these prey contributed a negligible
proportion of the annual carbon budget (~ 0.4%), feeding was necessary for the animal to
meet it’s energy requirements for growth and reproduction; almost 20% of the annual
nitrogen requirement for growth and reproduction in Plexaura flexuosa came from
zooplankton and microbial prey items (Ribes et al. 1998).
Among those gorgonians lacking symbiotic
zooxanthellae, much of the diet appears to derive from a range of tiny prey including
invertebrate eggs and larvae, ciliates, copepods and other microzooplankton, particulate
organic detritus, diatoms, dinoflagellates and other phytoplankton. For example, in the
small-polyped gorgonian Paramuricea clavata, Coma et al. (1994) found that copepod
eggs, copepod nauplii, other invertebrate eggs and larvae, and other small zooplankton
(primarily 100-200 micrometer size range) prey items accounted for > 75% of the diet.
Adult calanoid copepods (roughly the size of a newly hatched brine shrimp) were also
captured from time-to-time. Although the copepods were not captured as often as the food
items listed above, they are so large and nutritious relative to the other plankton prey
that they are likely an important component of the natural diet. There is no mention of
phytoplankton capture by P. clavata by Coma et al. (1994), but another study found
that this species also feeds extensively on diatoms, phytoplankton, ciliates and detrital
particulates (Ribes et al. 1999). Neither of these studies found any evidence for
significant uptake of dissolved organic compounds, bacteria or other nanoplankton less
than about 3 micrometers in diameter by this small-polyped gorgonian.
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Given the results from
studies such as these on gorgonian feeding, I suspect that the large-polyped D.
nodulifera you plan to keep would probably prey primarily on planktonic prey such as
diatoms, ciliates, rotifers, invertebrate eggs and larvae, the occasional copepod (if they
are lucky enough to catch some), and the like. It is hard to say for sure what is the
smallest prey item that an animal can consume, but studies on a variety of gorgonians
suggest that nanoplankton less than about 3 - 5 micrometers in diameter are a minor
component of the natural diet (e.g., Coma et al. 1994, Ribes et al. 1998, 1999). As such,
although DT’s Live Phytoplankton is a great product, it is probably not the best
choice for a primary food item for D. nodulifera. DT’s is a live culture of
one of the smaller phytoplankton species (Nannochloropsis), and the phytoplankton
cells contained in this product are probably a little small (< 3 micrometers, on
average) to simulate the natural diet of any of the gorgonian species studied to date.
That is not to say that the animals cannot or will not eat DT’s (they may very well
eat it quite happily), just that based on the gorgonians studied to date, the vast
majority of the natural diet of these animals is composed of larger particles.
So, what should you be
feeding, then? Well, if you happen to have a tank with a well-established live sand bed or
refugium of some sort, live foods (such as ciliates, copepods, invertebrate larvae and
eggs) are likely being released on a regular basis and providing your tank with some
plankton from time-to-time. Especially if you’re feeding DT’s regularly to your
tank already, then the reproductive rate of some of these tiny invertebrates can be quite
high, and may provide a considerable number of invertebrate larvae to the planktonic food
chain in your aquarium (Shimek 1997). Furthermore, food supplied by the occasional algae
scraping from the aquarium walls (usually consisting primarily of diatoms) and
resuspension of particulate organic detritus from the aquarium substrate and live rock
structure is also a bonus treat for these animals.
However, while such foods may be sufficient
for a gorgonian with photosynthetic symbionts, they should not be solely relied upon to
feed a gorgonian that lacks zooxanthellae. Personally, I consider any food captured in
this way a treat for a non-photosynthetic gorgonian, and an effort to feed them directly
seems important to the long-term survival of the animal. Most gorgonians will gladly
capture rotifers, and if you happen to culture (e.g., see Moe 1997, or Wilkerson 2001) or
buy live rotifers to feed your tank already, that will certainly help with keeping your
gorgonian well-fed. Gorgonians with polyps as large as those of D. nodulifera are
also likely to consume newly-hatched brine shrimp nauplii. It is important to keep in
mind, however, that capture rates for relatively strong-swimming plankton (such as baby
brine shrimp) are often much lower than for more easily captured prey (such as
invertebrate eggs and larvae), and even a large-polyped gorgonian like D. nodulifera
may have trouble capturing many baby brine shrimp unless you feed a lot of them. If you
don’t have access to these foods, there are a variety of artificial plankton foods,
frozen and preserved Daphnia, frozen copepods, commercial invertebrate foods, and
even finely ground fish foods that will probably help to keep the animal alive (see Toonen
et al. 2002 for a comparison of the relative performance of some common phytoplankton
products).
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The problem with using
choices such as frozen plankton, commercial invertebrate foods, or pulverized fish foods
is that they don’t tend to stay in suspension very long, and it is easy to overfeed
your aquarium if you’re not careful. That usually means that hobbyists provide food
relatively infrequently, and very little at a time. By all reports from studies of feeding
in the wild, most gorgonians appear to be capturing numerous prey items per polyp per day,
and occasional sparse feedings may not be sufficient for keeping them healthy over the
long-term in captivity. Although live foods would certainly be the best bet, they are
generally more expensive and difficult to provide than an artificial alternative, and I
know that compromises are often made for cheaper and easier to use products. Perhaps the
easiest food to provide for these animals would be a dried plankton replacement such as
ESV’s Spray Dried Marine Phytoplankton or BSD’s Golden Pearls Clusters, both of
which appear to be a highly nutritious and eagerly accepted by my D. nodulifera.
Research into effective artificial feeds is ongoing, and there are new products such these
appearing on the market all the time. This is fortunate for us as hobbyists, because many
of them appear to provide a suitable alternative to the tiny zooplankton (on the order of
100 micrometers or less) that so many reef organisms prey upon. Hopefully, with a bit more
experience, hobbyists on the whole will be much more successful with keeping
non-photosynthetic animals than we have been in the past.
Even after giving you all this
information, you may still have difficulty caring for these animals. In fact, these
gorgonians are not recommended for beginners, and generally not recommended for even
advanced hobbyists who do not plan to feed them at least a couple of times a week (and
preferably every day). If you chose a healthy gorgonian, place it in a suitable
environment, and make sure that it gets enough food, there is a good chance that you will
be successful in keeping one of these beautiful animals. Of course, the same can be said
of almost any animal added to an aquarium, and knowing what constitutes a "suitable
environment" and "enough food" is one of the keys to success with any of
the animals we try to maintain in an aquarium. The bottom line is that success rates with
these animals among most reef enthusiasts remain pretty low. I hope that the information
that I’ve given you here will help you to provide your animals with a good home, and
prevent your gorgonian from the sad fate that so many of these nonphotosynthetic
cnidarians face in the aquarium.
Borneman, E. 2001. Aquarium Corals:
Selection, Husbandry, and Natural History. Microcosm, T.F.H. Professional Series,
Neptune City, NJ.
Coma, R., J.-M. Gili, M. Zabala, and T.
Riera. 1994. "Feeding and prey capture cycles in the aposymbiotic gorgonian Paramuricea
clavata." Marine Ecology Progress Series115:257-270.
Dai, C.-F., and M.-C. Lin. 1993. "The
effects of flow on feeding of three gorgonians from southern Taiwan." Journal of
Experimental Marine Biology and Ecology173:57-69.
Moe, M. 1997. Breeding the Orchid
Dottyback, Pseudochromis fridmani: An Aquarist's Journal. Green Turtle Publications,
Plantation, FL.
Ribes, M., R. Coma, and J.-M. Gili. 1998.
"Heterotrophic feeding by gorgonian corals with symbiotic zooxanthella." Limnology
and Oceanography43:1170-1179.
Ribes, M., R. Coma, and J.-M. Gili. 1999.
"Heterogeneous feeding in benthic suspension feeders: the natural diet and grazing
rate of the temperate gorgonian Paramuricea clavata (Cnidaria: Octocorallia) over a
year cycle." Marine Ecology Progress Series183:125-137.
Shimek, R. 1997. It’s (in) the water...
Aquarium.Net 09/97:1-8. http://www.aquarium.net/0997/0997_4.sht
Sponaugle, S. 1991. "Flow patterns and
velocities around a suspension-feeding gorgonian polyp: Evidence from physical
models." Journal of Experimental Marine Biology and Ecology148:135-145.
Sponaugle, S., and M. LaBarbara. 1991.
"Drag-induced deformation: A functional feeding strategy in two species of
gorgonians." Journal of Experimental Marine Biology and Ecology148:121-134.
Toonen, R., K. Batchelor, and T. Mai. 2002.
"Planktonic Foods for Reef Aquaria: If you feed the tank, are these foods for
you?" Marine Fish & Reef USA Annual 2002:18-31.
Wilkerson, J. D. 2001. Clownfishes: A
Guide to Their Captive Care, Breeding & Natural History. Microcosm, T.F.H.
Publications Professional Series, Neptune City, NJ.
