Oct 96 Aquarium.Net Millepora
The Fire Corals
By Eric Borneman
(Stinging Coral, False Coral, Karang Gatal, Itching Coral)
Class: Hydrozoa Order: Milleporina Family: Milleporidae Genus: Millepora species: (Caribbean) alcicornis, complanata, squarrosa; (Pacific) dichotoma, tenella, platyphyllia, others
Why would anyone deliberately keep Fire coral in their tank? For that matter, is it even a coral? Before delving into the intricacies of these misunderstood and diverse corals, I would like take the time, in my first column for this thoroughly unique magazine, to thank everyone who has allowed me to participate in the company of so many great hobbyists, scientists, researchers, and experts in the field; all of whom have come together to offer particularly brilliant insights into the keeping of aquariums. It is indeed an honor to be among such company, and I hope that everyone can gain as much from my passion for corals, as they do from the subjects of the other great people who are writing here.
As the understanding of reef environments and the proficiency of designed systems has allowed so many people to successfully keep corals, there are many who are becoming acutely aware of the abundance of coral species in nature. Yet, there has been a limited variety of genera available to the public at a majority of retail outlets. While some may see this as ecologically beneficial, I feel that some of the greatest understandings of species care needs, behavior, and reproduction abilities have come from successful caretaking of captive corals. Therefore, it is not surprising that many are looking for new challenges to their reef keeping skills, or for new additions to further diversify a thriving reef community. Fire corals are excellent choices that meet these criteria quite well.
All Fire corals belong to the genus, Millepora , which is comprised of calcareous hydrozoans. These are not true stony corals, although their abundance does allow them to be a major contributor to reef structure and sediments. Odd as it may seem, the fact that they are hydrozoans makes all species of Fire coral more closely related to jellyfish than true corals. Fire corals are found worldwide, predominantly on reef crests and in shallow waters subject to high water movement. For an unknown reason, they are conspicuously absent from the reefs of Hawaii. Exposure to constant surge allows for rapid proliferation, growth and encrustation of Millepora on the windward reef crests, provided wave action is not too severe.
Unfortunately, the taxonomy of the Fire corals is limited. There are over 48 reported species of Millepora throughout the world. However, because of inter-specific variations of form and color due to different lighting intensities, water movement, and other environmental factors, it is not known how many species are actually distinct. In the Caribbean, three types of Fire corals predominate: a branching or crenelated form ( M. alcicornis ), a plate-like or flat-topped form ( M. complanata ), and an encrusting or box-like form ( M. squarrosa ). Similar morphological types are found in the Indo-Pacific regions, although the regional differences are more varied, and more species (both classified and unclassified) are reported from these oceans. Commonly seen Fire corals from these regions include encrusting, clavate, blade-like, upright, and branching calcareous growth patterns. A behavior common to encrusting Millepora species worldwide is a tendency to completely encrust living sessile organisms, particularly gorgonians. The result is a shape that is often taken to be representative of the Millepora species, when in fact it is representative of the shape of the encrusted object. Given the varied forms of this hydrozoan, it may be surprising to learn that the living animals are so similar.
Anatomy and Behavior
Although they are more closely related to jellyfish, the Fire corals certainly resemble stony corals. They are calcareous, although their skeleton evolved to almost completely enclose the living polyps. Despite the often textured pattern of the skeleton, the surface is quite smooth. Upon close examination, tiny pinholes, or pores, can be seen scattered across the surface , or coenosteum. Understandably, Millepora means many pores. There are two types of pores that dot the coenosteum: gastropores and dactylopores.
The gastropores contain the gastrozoids, or feeding polyps. These polyps are short and plump, containing from four to six tentacles that are reduced to nematocyst knobs ( Hyman, 1940 ). The gastrozoids are completely retracted into the skeleton, and rarely emerge. If seen at all, they tend to form a white fuzzy film over the coral surface. The gastrozoids are connected beneath the skeleton in a network or canal system (secreta) connected by plates, called coenosarcs . This canal system serves to allow nutrient movement within the colony that is provided predominantly from the capture of small planktonic animals. The coenosarcs and coenosteum are areas of Fire coral heavily laden with zooxanthellae. While these symbiotic algae may be found elsewhere on the coral surface and within the living polyps, the concentration around these areas greatly enhances the ability of the polyps to meet their energy requirements in a most efficient manner.
The most often visible structures of Fire corals are the short, thin, hollow, stinging tentacles of the mouthless dactylozoids. These potent stinging tentacles, that look like fine transparent hairs, are very important functional elements. The nematocyst laden tentacles provide for both the corals defense and their primary method of food capture. They are also a primary means of aggressive takeover of territory occupied by other species, along with the overshadowing and crowding out of nearby competitors through rapid growth.. Although sometimes randomly scattered across the surface, there is often a pattern of five to nine dactylopores that surround each gastropore. The dactylozoids within are equipped with three types of nematocysts: stenoles, isorhizas and macrobasic mastigophores. The latter type is unique to Millepora species, and is the definitive reason for their taxonomic classification.
The identification of Fire corals by color is not always easy. They tend to look like dead corals, since there is no visible tissue, polyps, or mucus. Furthermore, there are no defined cups as found on the true stony corals ( Scleractinians ). However, all species have a characteristic white edge or tip that serves to warn the unwary that these corals are not to be touched. Blue coral ( Heliopora sp .), related hydrocorals such as Lace coral ( Stylaster sp . and Distichopora sp. ), and several other corals may have similar white edges, but the lack of polyps, muted colors, and white tips are the most evident characteristics to identify Fire corals. Some common colors seen in Fire corals are cream, brown, green, yellow, and purple, but mustard brown is by far the most common variation.
For the most part, reproduction of Fire corals takes place sexually. Small medusae with four or five nematocyst knobs are released by the colony. The medusae die within hours of free life, but only after sex cells are formed and released as free swimming planulae, which soon attach to a substrate to form new colonies. Fragmentation of the main colony is another possible method of reproduction, and most imported specimens arrive as pieces broken off a larger colony.
Fire corals have gained popularity in reef aquariums recently, especially along the West coast. This is understandable, since they can be quite tolerant of less than perfectÃ“water conditions. However, intense light and high current are necessary for maximum growth rate and survival. The hair-like tentacles will extend night and day to feed on plankton, but can be completely retracted into the skeleton if needed. In fact, waving an object over a colony will cause complete retraction of all stinging hairs, and will thus eliminate any potential for the dreaded burn of Fire coral. Given their capacity to sting, it may be surprising to observe how many fish and shrimp take refuge among the recesses and branches of Fire coral. The hawkfish, because of their skinless pectoral fins, are often found perched high atop Fire coral colonies with utter disregard for the potentially dangerous nematocysts. For humans, however, the sting can be quite painful to sensitive skin. Yet, touching these corals with the hand or fingers usually does not cause any burning sensation, since the nematocysts can not penetrate thicker skin.
Because there are no visible living polyps, it can be difficult to ascertain the happiness of a specimen in a tank. Other than through a visually maintained robust color without bleaching or algal overgrowth, little else may be apparent to ascertain the corals health. Color changes may be related to improper light intensity or rapid change in light or water conditions. Because they possess zooxanthellae, proper acclimation is as important with these hydrozoans as with any stony coral.
Well equipped to capture prey, these corals will probably not accept food. In this regard, they are not more or less difficult to care for than most Scleractinians. In terms of predators and disease, Fire corals are very resistant to attack and sickness. Fireworms have been known to graze on the skeleton of Millepora species, but these carnivorous polychaete worms are a far greater hazard to other corals, and should be removed long before deciding to dine on any Fire coral.
It Burns, It Burns!!!!
Although it can be quite painful, a sting from Fire Coral is rarely dangerous unless accompanied by allergic reaction. In fact, the most serious effects seen after extensive stings are possible nausea and vomiting for two to three hours afterwards. The sting caused by these animals is a result of the injection of a water-soluble, heat affected, proteinaceous toxin. The discharged nematocysts cause small welts on the skin with red lesions around the raised areas. Swelling, blisters, and pus filled encystations may occur soon after being stung. However, all symptoms generally disappear after 24 hours. If stung, treatment consists of a breakdown of the protein by soaking the affected area in hot water, swabbing the welts with vinegar, or applying a paste of meat tenderizer. After initial treatment, topical anesthetics may be applied to ease the burning sensation. It may also ease suffering to repeatedly issue forth numerous expletives in a loud voice.
Fire corals are a very natural addition to any reef tank, if given proper conditions for their success and growth. Because of their prolific nature and abundance in the wild, it seems almost inappropriate not to have a small colony as part of an indoor reef crest. All Millepora grow rapidly and are quite attractive, despite their lack of flowery polyps and bright colors.
Even if a careless brush with these corals can result in some unpleasantness, there is no real risk to any of the tank inhabitants. In fact, the shelter for many creatures afforded by the colonies provides them with a natural safe haven, and most likely results in lowered stress.
Rapid advances in the captive care of corals have caused many to seek to create realistic microcosms as close representations of natural ecosystems. For this reason, and as worldwide contributors to reef structure, Fire corals should fit in very well with such an endeavor. Unique and hardy, all members of Millepora make wonderful additions to any captive reef system.
If anyone has any questions about Millepora that have not been covered in this article, please feel free to drop me an email. I would be happy to answer any further inquiries.
More info on millepora
Questions or Comments? Eric Borneman
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Last modified 2006-11-20 03:05