In this article I’m going to discuss a few commonly available species that are difficult, if not impossible, to maintain in captivity.
People often complain about the cost of the reef aquarium hobby, well one way you can save a little money is by only buying species that are within the capabilities of you and your reef system, avoiding those that are more difficult to maintain and, to be blunt about it, destined to die prematurely in captivity. Some more advanced reefkeepers may quibble with my views and there is always that exception to the rule, the aquarist who has managed to keep some impossible to maintain species for many years. That does not negate the fact that the vast majority of these species will die in the hands of less experienced reefkeepers.
Why Don’t These Species Thrive in the Aquarium?
In nearly every case, the problem is one of nutrition. The majority of the species listed below are heterotrophic, that is organisms that, unlike photosynthetic (or zooxanthellate) corals cannot manufacture their own food. This can be further broken down into the amount of food required by a particular organisms or whether there is a specialised feeding requirement.
It may be possible to maintain some heterotrophic species long-term if they are fed large quantities of planktonic food, phytoplankton and or zooplankton, but this has the downside of producing a polluted environment requiring an onerous amount of tank maintenance.
This mitigates against keeping these organisms with nutrient sensitive corals species.
Specialised Feeding Requirements.
This includes many factors: particle size, diets restricted to a single food source often a specific algae, sponge, or other invertebrate such as a coral species.
Specialised System Required.
In particular, this applies to jelly species; with one exception, all jelly species need to be kept suspended in the water column. This requires the use of a specially designed system known as a Kreisel, which imparts a circular flow to the system, keeping the jellies in suspension.
Short Life Span.
Many of the animals discussed in this article have a short life span, depending on species this can be as short as a few months up to a year, possibly two, as a maximum. Although some aquarists may accept keeping an animal with a short life span, the major problem here is that is almost impossible to tell how old these organisms are; you may find you’ve been fortunate enough to have purchased a juvenile but you’re just as likely to have bought a specimen on the verge of senescence.
Commonly Available Species to Avoid.
Porifera – Sponges
The majority of the decorative sponges do poorly in captivity, they are heterotrophic animals i.e. organisms that, unlike photosynthetic (or zooxanthellate corals) cannot manufacture their own food. The exceptions to this tend to be the autotrophic sponges coloured green, through blue, to purple, that contain symbiotic blue-green algae which can utilise light, contributing towards the sponge’s nutritional requirements much as in zooxanthellate corals.
Heterotrophic sponges however are filter feeders and are reliant on a combination of dissolved organics, bacteria, and phytoplankton. For their aquarium maintenance, I would suggest feeding with a quality live phytoplankton such as DT’s.
Many sponges produce toxins as a form of defence, hence limiting the number of animals that predate on them. Dead sponges can release these toxins to the detriment of soft corals. On the whole it’s difficult to say which sponges are heterotrophic, which are autotrophic, which are toxic, etc as, with the exception of a handful of distinctive species, these are difficult animals to ID with any certainty. This also makes it difficult to make recommendations on placement, although many sponges will benefit from lower levels of light, there are also those which can be found in shallow water even though they have no photosynthesising symbiont.
A further factor in lack of success with sponges may be that of Silicate limitation owing to the widespread use of RO water in reef aquaria.
Stylaster and Distichopora species. Common Name: Lace Corals
These hydrozoan corals don’t have as powerful a sting as their close relations, the Fire Corals, what they do have though is vivid colouration making them attractive to aquarists. Unfortunately, these azooxanthellate corals are very difficult to maintain owing to their dietary requirements of plankton and possibly nutrients absorbed directly from the water. The colours, blues, violet, pink, through to red are derived from foods rich in the caratanoid, astaxanthin, so perhaps CyclopEeze FreezerBar may be a useful addition to their diet. They are also adapted to strong current, which may also be a factor in their poor survival in the aquarium.
Cassiopaea species. Common Name: Upside-down Jellies. Aurelia species. Common Name: Moon Jellies.
Whereas Upside-down jellies can be accommodated in a conventional aquarium if attention is paid to their requirements, all other species of jelly need to be kept suspended in the water column.
Jellies have a complicated life cycle and none but the most advanced aquarists or public aquariums will have much success in raising these animals. Life span is dependent upon species and environment, can be from months up to a year in the wild. Note: Aurelia species are cold water, not tropical.
Cavernularia species. Common name: Sea Pens
In addition to being a heterotroph requiring targeted feeding of planktonic food, sea pens need a very deep substrate. These unusual and interesting soft corals dig their peduncle or “foot’ into the substrate as an anchor, this can be more than half the body length of the animal, depending on species, and considering that some species can grow to a height of 40 cms or more, we can be looking at a considerable depth of substrate, deeper than some aquaria.
Nephtheidae and Nidaliidae
Stereonephthya, Scleronephthya, Dendronephthya, Siphonogorgia species. Common name: Carnation Corals
Heterotrophic. These gorgeous, brightly coloured corals are difficult to accurately identify to genus, let alone species level. All require large amounts of food if they are to be kept alive for any length of time but all are destined to waste away over time
Sometime over the last couple of years a long-time US aquarium writer, I can’t remember whom, made an observation to the affect, “Back in the eighties, when corals led short lives in the aquarium, we used to feel that we’d done well when a specimen of Goniopora lasted as long as twelve months. Today we can keep most corals indefinitely, yet Goniopora still rarely survive for more than a year!”
Unfortunately, this species remains one of the corals imported in greatest quantities and one of the species least likely to last out a year.
Goniopora species contain zooxanthellae but even that is not enough for the coral to survive without wasting away. There is speculation that a large part of their food take up in the wild consists of a combination of phytoplankton and small particle zooplankton.
Nemenzophyllia turbida. Common name: Fox Coral.
Another zooxanthellate coral that does poorly in the reef aquarium. Again, it is possible that like Goniopora it has a particular feeding requirement that cannot be easily accommodated in the aquarium, in this case the animal may be reliant on absorbing nutrients from the water.
Additionally there is concern about the restricted distribution of this coral; hence, sustainability of collection is in question
Tubastrea species. Common name: Sun Corals.
This is a heterotrophic or azooxanthellate coral, and is completely dependent on receiving sufficient zooplankton to survive. I have mixed feelings about this coral as, although it is azooxanthellate, it is also the species I’d recommend to any one interested in trying to maintain heterotrophic corals. I would categorise it as being the easiest non-photosynthetic coral to keep alive long-term but to do this requires real dedication to its care. The finest example of an aquarium featuring this species belongs to Swiss aquarist, Daniela Stettler; her dedication is such that she feeds each individual polyp with artemia every evening.
Pseudoceros species. Common name, Flatworms
Phylidiidae species, Hexabranchus species, Chromodoridea species. Common Name: Nudibranchs, Sea Slugs.
Both Flatworms and Nudibranchs are often difficult to identify. They share the two main limitations of diet and longevity. They may have very specific diets relying on one single species of algae or animal and these foodstuffs may not be present in the aquarium. Although some of these animals may have vivid colouration making them attractive to aquarists, they appear to have short life spans so, even if you were fortunate enough to have the appropriate diet available, you may be dealing with a species that lives for six months or less. Some species may also be toxic with the potential to pollute the tank when they die.
Lima scabra. Common Name: Flame Scallops. Spondylus species. Common Name: Thorny Oysters.
Heterotrophic. Another couple of animals that require large amounts of food if they are to be kept alive for any significant length of time. Both species feed predominantly on phytoplankton although the addition of small particle size zooplankton such as rotifers may increase survival.
Flame scallops are short lived, maximum of three years, so given retailers preference for stocking bigger animals it may be that most of those in the trade are of an advanced age, explaining why they rarely survive for more than six months.
Order Octopoda – Octopuses, and Order Sepiida – Cuttlefish
These highly intelligent molluscs have specialised requirements for housing. Nearly every public aquarium, livestock supplier, and retailer that has kept octopuses will have tales to tell of these Houdini’s of the deep. These animals are master escapologists, capable of squeezing through the smallest gap and there are many stories of mysterious fish losses that have eventually been traced back to an octopus leaving it’s tank at night for a takeaway meal, then returning to it’s own aquarium afterwards.
Octopus and cuttlefish have short lives, living for one year, possibly two at the most. It can be distressing seeing these fantastic animals fade into senescence towards the end of their life and knowing that there is nothing you can do to help them.
Crinoidea Feather Stars and Ophiuroidea Basket Stars
These close relatives of the more familiar Sea Stars and Brittle Stars are filter feeders that rarely survive in captivity for any length of time. It is currently unknown whether this down to lack of food or selectivity of diet.
As they die there is a tendency for their arms to fragment, which can often be seen to continue moving after separation.
Pseudocolochirus species. Common name: Sea Apple
Heterotrophic. A brightly coloured member of the holothurids this animal is highly toxic. If not fed sufficient quantities of food it will waste away and die, this frequently results in the death of any fishes in the aquarium as the powerful toxin, holurathin, is released.
The Exception to the Rule.
There are a couple of possible explanations for those reports of aquarists having managed to keep seemingly impossible to maintain species long-term, which may hold out some hope of being able to maintain some of the animals in the future.
Given the difficulty in identifying many reef organisms accurately there is the possibility that these species may have been misidentified and that they have different requirements to the species in question. This includes the possibility that some look-alike species that do survive longer than usual in aquaria are undescribed species.
The animal in question may have been collected from a different part of the reef to where it would normally be found, and has adapted to conditions differing from its usual habitat making it more suited to life in the aquarium. For example, it has been reported that crinoids living in plankton poor environments may have arms that are longer and more highly branched than those inhabiting plankton rich environments.
These animals collected from abnormal habitats along with their adaptation to the environment, may mean that we are seeing organisms in the process of evolving into new species.
Although I have highlighted a number of factors that may improve the chances of keeping many of the animals discussed for longer periods, I do want to emphasise that the overwhelming majority of the animals listed will die in the marine aquarium within a few months of introduction.
Azooxanthellate coral – a coral that does not have symbiotic zooxanthellae in its tissues.
Heterotroph – an organism that cannot manufacture its own food, and therefore requires external sources of energy.
Hydrozoa – a class within the phylum Cnidaria, contains five orders that include colonial forms with massive aragonite skeletons, fire corals and Lace Corals.