Ask the WWM Crew
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What do you think of when you hear of "dangers from the deep blue seas", giant squids, sharks, other divers? The actual cause of many, or most discomfort from dealing with marine life is from a group of stinging-celled organisms called hydrozoans; in particular the hydroids and fire-coral. The latter may serve another purpose other than stinging like begeesus when they come in contact with your skin; as aquarium specimens. "These stony-coral look-a-likes incorporate single celled algae to manufacture at-times massive colonies of reef-building limestone. They are relatively undemanding, fast-growing marine animals that require nominal "reef" set-up conditions of decent water quality and current.
The fire corals are members of the stinging-celled phylum, the Cnidaria (or Coelenterata); though they superficially look like "true corals" these tissue-grade animals are just as closely allied with jellyfishes and anemones. A quick review of the group: Taxonomists divide cnidarians into three Classes on the basis of predominant body-shape; sessile polyp-like and inverted medusa bell-like forms. Class Scyphozoa, the jellyfishes have a large medusa and small polyp life stages.
The Class Anthozoa are polyp stage only; these are the familiar anemones, soft and hard corals, sea fans, and more.
And the Class Hydrozoa, with small medusa stages and small-to-large polypoid stages. In turn hydrozoans are sub-divided into five Orders: including the hydroids and hydromedusae (e.g. Hydra);
the Order Siphonophora of planktonic, colonial animals, a bad example is the floating "Portuguese man-o-war", Physalia... and our Order du jour, the Hydrocorallina; colonial polypoid Hydrozoans that secrete massive calcium carbonate skeletons.
Suborder Stylasterina: /WA Corals: small branching, fan-like colonies • occur in sheltered high- current habitats • often bright colours • azooxanthellate • member of the Hydrozoa • common name lace corals
Suborder Milleporina, are the stinging or fire corals. Unlike the Stylasterines, their skeleton is only covered by a thin epidermal layer; and their defensive polyps arise from separate openings that encircle the gastrozooids (feeding polyps). Millepora is the single genus. As you study and observe corals and coral-like animals like the hydrozoans, you'll gain an appreciation for the term polymorphic or "many shapes"; describing the several physical forms a "species" can/does take dependent on nutrient and other growing conditions; sometimes heavily branched and delicate in appearance, other times more blade, fan-shaped and massive. The number of varieties of Millepora are in dispute. Veron states that there are at least 48 nominal species; an unknown number of true species. More to the point for our discussion is the question of "how to tell when you're looking at a fire coral?" period. There's always the touch test; ouch. Most of the time, the colonies are green or yellow-brown (due to endosymbiotic Zooxanthellae) fading to whitish at the tips, and "soft", "hairy" and rounded in appearance. On very close inspection, the arrangement of almost microscopic stinging and eating polyps can be seen (image above). /WA Corals: branching, columnar, submassive or encrusting tiny polyps visible as minute pores • zooxanthellate with stinging cells • member of the Hydrozoa
The genus is distributed throughout the worlds tropical reefs, and is very common in parts of the Indo-Pacific.
Selection: General to Specific
You might see fire coral offered for sale expressly, or very well get it as an "extra", or contaminant via a live-rock purchase. Don't be dissuaded by their human stinging habits (just be careful), Millepora can live in conditions that might otherwise be unbearable for "true" stony/Scleractinian corals. I've seen them do well in sediment and nutrient laden conditions, more turbulent than most stonies would tolerate. As with their close relatives, look for specimens that are unbroken/complete with no visible dead, whitish, (missing) material. Fire corals are collected with a substantial chunk of limestone "rock". The piece snapped-off should not have torn too much of the colony asunder.
Though marketed as "pieces" for the purpose supposedly of lowering cost per sale, I strongly prefer whole wild-collected colonies. Conversely don't be overly concerned with the initial size of specimens as the fire corals can grow quite quickly, an inch or more per month, covering substrates and other sessile animals.
Healthy individual's whose Zooxanthellae are in decline should be avoided. These necessary endo-symbionts are the majority of the color seen, so select for well-colored specimens.
Milleporans are found in areas of poorer water quality than many true corals; nevertheless good filtration and water flow are de rigueur.
Lighting is important. For folks with fluorescents only, place your fire coral near the surface. For metal halide, halogen users deeper placement (12 plus inches) is suggested.
The more current the better with these hydrozoans; power heads and/or other fluid moving pumps to keep the water in motion. Milleporans thrive in areas of brisk currents.
Place new specimens, sans shipping water a good three inches from other tank-mates and maintain an ongoing vigil such that they don't come near other living corals, anemones, or sea fans. Don't adjust the specimen's orientation if you can avoid same, as it has adjusted for flow and light conditions.
Due to their stinging propensity, fire corals are generally left alone by would-be nibblers; what does "get" them (other than outright hobbyist mistakes) is overgrowth by algae. This is generally "cured" by a careful consideration and elimination of causes: too little, or misplaced circulation, inadequate filtration.
On Getting Stung:
Prevention is, of course, preferable... on the reef, keep covered and don't touch ANYTHING. In aquariums, use a dedicated, full-length glove or two if/when you feel it's necessary to "take the plunge". Still zapped? Meat tenderizer, and/or very warm water quickly applied are my favorite treatments.
Feeding/Foods/Nutrition: Types, Frequency, Amount, Wastes
Fire corals are obligate symbionts with their Zooxanthellae. They utilize endo-symbiotic Dinoflagellates for food production and waste elimination. Additionally, Milleporans filter feed to some extent, utilizing their short furry tentacles stinging cells (nematocysts).
A mix of live brine or frozen/defrosted animal-based food may be offered by placement on the polyps or sprayed in their general direction. Leave the water pumps off for a while and guard against excess.
Minute free-swimming medusae are produced in sexual generations; asexual "breaking" and splitting also generate "new" individuals.
Fire corals may not be the most striking in terms of color or structure, but they are amongst the hardiest group of cnidarians and very coral-like, utilizing Zooxanthellae, and being true reef-builders. These false-corals can be easily maintained in "standard" or reef-type marine aquaria, with simple provision of adequate light and strong current; Very hardy, undemanding, good choices for intermediate to advanced marine hobbyists.
Allen, Gerald R. & Roger Steene, 1994. Indo-Pacific Coral Reef Field Guide. Tropical Reef Research, Singapore.
Barnes, Robert D. 1987. Invertebrate Zoology, 5th ed. Saunders College Publishing, FLA.
Colin, Patrick L. 1988. Marine invertebrates and plants of the living reef. T.F.H. Publ., Neptune City, NJ.
Fenner, Bob. 1992. Cnidaria: Stinging celled animals. FAMA 7/92.
Gosliner, Terrence M., David W. Behrens & Gary C. Williams, 1996. Coral Reef Animals of the Indo-Pacific. Sea Challengers, CA.
Gutierrez, Santiago. 1991. From a reef's point of view... Hydrozoa, Milleporina, Millepora. FAMA 2/93.
Haywood, Martyn. 1989. The Manual of Marine Invertebrates. Tetra Press, Morris Plains, NJ.
Straughan, Robert P.L. 1975. Keeping live corals and invertebrates. A.S. Barnes, S. Brunswick.
Veron, J.E.N., 1986. Corals of Australia and the Indo-Pacific. Angus & Robertson Publishers, Australia.