We British call them “Starfish”, but surely the translated popular name from most other European nations makes more sense. They call them “Sea Stars”. We all know very well they are not fish, and this part of their identifying name is confusing. Whatever you care to name them, these mostly five-armed sea creatures are well known to us all, probably starting with illustrations in books for even the youngest children. A starfish pictured on a sandy beach is almost as obligatory as a sand castle to set the seaside scene. Starfish come in a wide range of shapes, sizes and colours. Being generally unappreciated as being the particular feeders they are, starfish may often prove difficult or even troublesome for aquarium culture, and their requirements should be studied carefully before making a purchase. Whether they are difficult to feed or potentially destructive, either way they will not be welcomed into the established reef aquarium.
One popular species is the Blue Starfish (Linkia laevigata) which seems to do nicely on a diet of just organic detritus and algae. In the tropical Indo-Pacific areas where it is found this species frequently hosts two free-loading passengers which cling to its underside. One is a tiny commensal shrimp (Periclimenes soror) which simply enjoys the shelter of the slowly moving host starfish and the continuous availability of food particles which are presented in the course of its travels. The other passenger, however, is a parasitic mollusc (Thyca crystallina) which can fatally damage the vulnerable skin of the starfish as it feeds from its body tissue. While it is highly unlikely you will find a shrimp still living on an imported starfish, the mollusc may well arrive still firmly attached to the underside of an arm or two. If found it should be removed and disposed of. Imported specimens are usually sub-adult and it should be realised that the Blue Starfish is capable of growing to a large size – as much as 8 inches (20 cms) or more from tip to tip across its widest parts. I have come across Super-large specimens in the sea off the island of Komodo, where the water temperature is significantly lower than adjacent areas, and where the noticeably smaller Blue Starfish are found.
Knobbed Starfish (Protoreaster lincki) is another highly decorative species which is frequently available to the hobbyist. Its bold shape, large size, and bright colours can be compulsive to the reef aquarium keeper looking for something striking and mobile to enhance the aquarium. But they are voracious scavengers, capable of consuming a range of marine creatures and growths. Their potential for wreaking havoc in the reef aquarium is for real! They are more suited to a marine aquarium without other invertebrate life, where they may be purposely fed with pieces of fish, shrimp, or other titbits when there is insufficent left-overs from feeding the fish population. (But, of course, there should never be any uneaten food left to go to waste!).
Feather Stars, or Crinoids, are very beautiful animals, but feeding them adequately in the aquarium is very difficult to achieve without fouling the system. In nature these many-armed (they often carry up to about 130 arms!) creatures choose to anchor their wiry feet onto rocky prominences where the strong currents sweep planktonic material through the numerous cilli projecting from the spindly central “spine” of the arms. Such conditions would be difficult if not impossible to emulate in aquarium culture. Without those racy currents bearing copious food particles the Feather Starfish stand the slimmest of chances to adapt to aquarium life, and usually suffer an early demise. There are a number of fish and invertebrates which are quite commonly associated with Crinoids, all of which find shelter by practising very convincing mimicry to blend with the ornate host. Cling fish are often found firmly within the protection of the dense concentration of the arms where they join the main body of the crinoid. Crinoid Shrimps (Periclimenes amboinensis) are other frequently found commensal animals, and can be any of a whole range of matching colours, depending on that of their chosen host. One of the most fascinating associated fishes are the Ghost Pipefish (Solenostomus paradoxus) whose whispy cilli-covered and elongated bodies enable them to blend amazingly well with the feather starfish. Yet displaced by a sudden current, or the crinoid protectively closing down its arms to an unwelcoming ball-shape, the exposed pipefish becomes quite obvious and vulnerable. A species tank with crinoids and these associated animals would make a fascinating exhibit, but the problems of creating a suitable, workable environment, within the confines of an aquarium would challenge even the most inventive of aquarium keepers.
Another fairly frequently imported starfish is Fromia elegans. The beautifully designed markings and pleasing colouration of this species makes it instantly attractive to any prospective buyer. In nature I have seen specimens of this common starfish apparently feeding on sponges, but in aquarium life individuals will often adapt quite well to taking other more conveniently available foods. Another Fromia which appears from time to time also has an intricate design of markings and beautiful colours. This is Fromia nodosa. For both species it seems that some experimentation is necessary to establish what a particular individual appears to be ready to accept as its staple diet in captivity. But be prepared to find that some individuals might not adapt at all, and eventually “fade away” and die. Occasionally four-armed specimens are found, yet show no readily discernable sign of damage where a fifth arm has been lost. It is not clear if this is a defect from birth, or the result of some past accident or aggression by a would-be predator.
One of the most spectacular starfish on the tropical coral reef is the Crown of Thorns Starfish (Acanthaster planci). This large predator preys on stony (scleractinean) corals, enveloping large sections and secreting a substance which enables the extended stomach to absorb the “processed” polyps, leaving behind a white skeleton as it progresses onwards from one coral head to another. The upper dorsal surfaces of its many arms are covered with fearsome, sturdy, venom-loaded spines which can inflict a seriously painful wound to the unwary. Generally the colour of the Crown of Thorns Starfish is a pale, nondescript buff, but the strain which is found commonly in the Andaman Sea has a beautiful black and rich purple colouring. However, this impressive animal is unwanted wherever it appears, and certainly does not endear itself to the aquarium keeper. Huge numbers are frequently collected to be destroyed by people engaged in the dive industry in an attempt to control the extreme damage caused by their coral feeding habit. Healthy corals make the reefs the top attraction they are to the diving and snorkelling fraternity, and those which have been killed by this starfish become stark skeletons ready to be colonised by ugly algae infestations, rapidly transforming a formerly beautiful coral head into a sad monument to the fragility of the reef. The need for live coral polyps as its staple diet renders the Crown of Thorns to be a completely unsuitable species for aquarium culture, although it is sometimes seen in aquarium exhibits within easy reach of its known habitats. These usually badly-run exhibitions either choose to be satisfied to keep the animal until it starves to death, or even collect live corals for it to feed on. Neither approach is to be commended!
Another spectacular species of starfish has a legless form. The Pincusion Starfish (Culcita novaeguineae) is very variable in colour, and has numerous tiny spots covering its large body, often with some grouping of these spots forming random patches of colour. Some specimens have a very colourful underside, and are commonly known as “Pentagon Stars” when located by divers who upturn them to discover their beautiful hidden secret. This big starfish is another favourite host for the starfish shrimp (Periclimenes soror), and they are often seen in small groups on the underside of the Pincusion starfish. If dislodged and comes to rest upside down the Pincusion Starfish can partially inflate its body so that it can right itself. I have never seen this big animal imported into the UK hobby market, and to date I have yet to discover for sure what they appear to favour as their food source. They are said to be coral feeders, but I have not seen evidence of this.
Perhaps the Brittle Starfish are the most suitable species for aquarium culture. Their comparatively compact central body, or disk, supports very long and articulate arms. They can move remarkably fast, and have the ability to disappear into any hole or crevice with amazing speed and agility. Some species filter feed at night on the reef, and may be found with one arm firmly hidden away within its sheltering burrow, while the other four arms are sinuously waving above the substrate, gathering tiny food particles from the passing current. Most seem to be willing to scavenge on a whole variety of organic detritus. It is this scavenging activity coupled with their ability to squeeze into impossibly cramped spaces that makes them a desirable aquarium species. The range of colours and forms, which are such notable features of the “Brittle Stars”, afford some interesting options for the aquarium keeper looking for an industrious scavenger to work in the reef tank.
There is, indeed, a vast range of Starfish to consider as potential aquarium species, but there are not that many which have so far been offered on a regular basis for the average home reef aquarium set-up. Those which do adapt and flourish bring another delightful dimension to the aquarium invertebrate population, as well as often bringing the added benefit of doing a useful job.
The Blue Starfish (Linkia laevigata) is found in a range of blue colouring, from a pale sky-blue through a range of other shades to something as rich as the speciemen pictured here. It is probably the most freely available starfish to come to the aquarium hobby market.
This parasitic mollusc (Thyca crystallina) is a potential danger to the unwitting host animal, and should be carefully removed if found on newly imported starfish. The specimen pictured here is greatly enlarged. It is actually minute in size, and would sit comfortably within the circumference of a pencil, for example.
The Knobbed Starfish (Protoreaster lincki) is an eye-catching species, variable in colour and body texture. But there are serious drawbacks to keeping it in a mixed “Reef” style aquarium..
Feather Stars, or Crinoids, appear in a dazzling range of colours. The specimens pictured are clinging to a massive boulder-sized Porites coral head, where they may enjoy the essential nutrients sweeping by in the current patterns. The numerous arms have fine cili which collect the food particles and pass them along down to the oral disk of the comparatively small body.
The Crinoid shrimps (Periclimenes amboinensis) are able to adapt to the colouring of their host Feather Star with remarkable accuracy, making them very difficult to detect, and when the Crinoid is disturbed the arms fold down into a globular form, giving the shrimp even more effective protection from any imminent danger.
The black etched design set on a warm-red body of Fromia elegans has an intricacy which only close examination reveals. The black tips to the arms should be a deep sooty colour as an indication of a healthy animal. Any specimens with signs of tissue damage or lacking the dense black tips to the arms will almost certainly die and should not be purchased.
The beautiful Fromia nodosa also carries a very intricate design, which is emphasised by the various colours. The overall colouring is very variable between individuals, but the basic patterning of the body is more or less consistent. This species comes to the market only infrequently and is less hardy than F. elegans
The rogue of the reef, the Crown-of-Thorns Starfish (Acanthaster planci), is shown here at its dastardly work. The bleached white Acropora coral trails behind the starfish as it moves on to attack the healthy area still sporting its living polyps, but about to become food.
The Pincusion Starfish (Culcita novaeguineae) is a favourite host animal for the tiny commensal shrimp, Periclimenes soror. This mini shrimp can match its body colour to the host starfish. It is often found on the Blue Starfish, for instance, when it will have assumed blue colouring exactly matching the host. The shrimp is shown here on the underside of the starfish, greatly magnified and adjacent to a row of feet which eases the cumbersome Pincusion starfish around the obstacles of the reef topography.
Brittle starfish are remarkably agile creatures, able to squeeze into the most unlikely cracks and crevices. They are mostly hidden in the daytime, but are active scavengers at night, searching out any morsals of food from even quite inaccessible places with the fine tips of their elongated arms. This Green Brittle Starfish (Ophiarachna incrassata) is often available to the aquarium hobby, and is pleasingly ornamental – something which is not true of all Brittle Stars!