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There's a Fungiid Among Us!! by Eric Borneman Aquarium.Net August 1997

An article by Eric Borneman on funggid corals for the reef aquarium, Aquarium Net has numerous articles written by the leading authors for the advanced aquarist

There's a Fungiid Among Us!!

by Eric Borneman

Fungia , the mushroom coral

family: Fungiidae genus: fungia species: fungites, danai, horrida, repanda, concinna, scutaria, echinata and perhaps 60 others!! common names: disk, mushroom, plate, fungus, chinaman hat

reef friendliness: 7 (1-10)

fungia are the primary member of the corals belonging to the family Fungiidae. This group also encompasses the familiar tongue corals ( Herpolitha ), slipper corals ( Polyphyllia ), long tentacled plate coral ( Helio fungia ) and others from the genera, Cyclolites, Diaseris, Sandalolitha, Halomitra, Lithophyllon and others.

The most obvious characteristic of the group is that they are solitary corals. Indeed, they are among the largest solitary corals in the world, often found with diameters exceeding a foot across. fungia are uniquely designed, forming slightly dome-shaped saucers that may naturally have "dented" or folded edges. Some may be slightly elongated, and all are generally convex on top and somewhat concave on the bottom. Most are found living on soft or rubble-covered bottoms in fairly shallow water. Colored in virtually every bright hue of the rainbow, fungia have polyps that normally remain retracted during the day in nature, emerging to feed at night. The polyps extend randomly from between very prominent and obvious septa that radiate outward from the center. The polyps are usually so retracted during the day that the coral may appear to be a dead skeleton on the bottom. However, fungia is often dramatically swollen with both polyps and coenosarc extended day and night in the aquarium. The speciation of fungia depends on careful consideration of the many blade like septo-costae and other skeletal features. Thus, the exact species identification by the untrained hobbyist (or those without a key to the species) is extremely difficult in most cases. Interestingly, the septa are all on the top surface of the coral, while the costae are on the bottom.

Among the many unique attributes of the fungiids, including fungia , is their remarkable ability for limited movement. Through asymmetrical inflation or deflation of their tissues in a type of peristalsis, fungia can move across the substrate. This is apparent in a maximal movement of up to 30 cm per day!! As such, it may not be surprising to find a fungia on the completely opposite side of the aquarium after waking up in the morning!

Their movement is usually phototaxic, meaning they move towards a light. This seems to be an adaptive behavior since they are photosynthetic and require light. Strong wave action, the burrowing of animals and fish, storm surges, and tides have a tendency to easily disturb these free living corals, and such actions can distribute them to areas of less than adequate sunlight. Therfore, such phototaxis is required to allow them access to the photysnthetic energy of the sun. Their remarkable capacity for movement does not end with simple horizontal strolls across the bottom; fungia can climb a slope of up to 30 degrees from horizontal! The disk corals would have to be quite adaptive to survive in such a cautiously precarious environment, and it is obvious they are well suited to the challenge. Not only are they frequently tossed around the bottom, but they often land upside down in the process....and they even have the amazing ability to right themselves using the same method of tissue inflation/deflation that they use for "walking."

Another characteristic coat of fungia that is quite phenomenal is their mucus coat. It is quite heavy, and allows them to easily and quickly reject sediments deposited on their top surface. This same "feature" allows them to be able to completely unbury themselves, if necessary. But, the adaptive qualities of their mucus coat does not stop with simple sedimentary duties! Not by any means! It contains a large amount of nematocysts which the coral uses not only in defense, but to aid in effective food capture of plankton and particulate matter that does not already become ensnared in the mucus as it drifts by. So powerful is the mucus and "sting" of fungia , that it is possibly the most "dangerous" coral in the ocean. Fungia causes damage to almost 100% of other corals it comes in contact with, yet is almost totally unaffected by the stings of other corals. The only corals it does not seem to affect at all are other fungiids. I have even watched the necrosis and consumption of a sweeper tentacle from a nearby Euphyllia fimbriata (hammer coral) that had attached to the surface of a fungia in my own aquarium. I feel certain that the Euphyllia was as shocked as I was! It is not known whether it is the particular composition of the nematocysts which cause the damage, the fact that the mucus sticks and remains on the "enemy" coral allowing a prolonged discharge of nematocysts, if the mucus causes local suffocation of the affected coral tissue, or a combination of all the factors. Whatever the reason, it is apparent that careful placement of fungia is mandatory in the aquarium especially in consideration of its ability to move up, down, and across without difficulty.

As if these attributes are not sufficiently unique, fungia also has a special mode of reproduction. While normal sexual reproduction occurs with a release of gametes into the surrounding water, fungia reproduce asexually through the formation of anthocauli. These genetically identical daughter colonies are formed from bit of skeleton and tissue of the parent colony. Often, if there is an injury or if the parent is partially buried in substrate, the coral begins an active decalcification process whereby the injured area of skeleton dissolves and separates through the formation of certain biochemical controls and enzymes. These cellular processes seem to initiate a calcium gradient where the intracellular calcium concentration is actively pumped out, allowing a net efflux of calcium from the skeleton. The actions of the normally present burrowing algae, Cliona sp., is then able to initiate further decalcification. Following the process, the result of which is akin to the coral "cutting off its own arm, the remaining fragments of skeleton with attached tissue separate from the parent colony and move outward to begin their own solitary life. These specialized anthocauli daughter colonies can also form from planulae under non-traumatic conditions. There is yet another method of reproduction in fungia that is also asexual. The fungiids are all highly regenerative, and provided that at least 1/6th of the skeleton is intact if broken, a new coral can regenerate wholly from the part. Thus, fungia is obviously well adapted to survival and the continuance of its progeny.

In the aquarium, fungia is both fragile and hardy. They are very resistant to the common diseases that affect many corals, possibly due to their heavy mucus coat and unique physical construct. Yet, there seem to be some notable precautions that are mandatory in handling the corals in captivity. Provided these few conditions are met, fungia seems to have a high likelihood of survival and reproduction in the aquarium. First, the corals should always be placed on a soft bottom where they can receive full light and a moderate wafting current that delivers them adequate dissolved and particulate food sources. It is not only important to place them so they cannot come in contact with nearby corals, but also to avoid placing them on the rockwork where their propensity for movement inadvertently causes them to fall and become damaged. Second, fungia should not be removed from the water while fully expanded since the weight of the water filled tissue can tear and cause the demise of the polyp. Because it is a solitary coral, they cannot afford the loss of several polyps as can most scleractinia. Third, it is important to prevent the accumulation of pockets of air from the concave underside of the coral when placing them into the water. The air pockets seem to act as an irritant, and these may create stress with possibly the ultimate demise of the coral. Finally, most species (except F. scutaria ) do not tolerate cooler or fluctuating water temperatures. As such, they are found in the greatest abundance in the warm stable central Indo-Pacific regions. Provided that these conditions are met, fungia proves to be a hardy and beautiful addition to reef aquariums. They accept feedings readily, and can ingest surprisingly large amounts and sizes of fresh shrimp and other acceptable food sources.

There are many species of fungia commonly available in the aquarium trade. They are, by nature, easy to collect and quite prevalent. In areas of the forereef where they are commonly found, the number of fungiids present can literally cover the entire bottom. Still, there may be some confusion regarding the proper identification of these solitary disks. The evolutionary predecessor of fungia is Cycloseris. This coral is very similar in shape and form to fungia , but is a normally smaller coral. Nonetheless, small specimens of fungia may be so similar to Cycloseris as to appear superficially identical. A specimen of the less common Cycloseris will soon be evident; most do not grow larger than approximately 3 inches across, while most fungia do not grow to be less than 3 inches across. Diaseris is also similar to fungia except that its skeleton is neatly delineated into pie shaped wedges. These are clearly visible by the indentations on the bottom of the coral. Other similar genera, including Sandalolitha and Halomitra are much heavier and more rounded. Herpolitha is distinct with its always extended anemone-like tentacles.

In summary, fungia are unique and beautiful corals that have a good record of survival in captivity. They can be placed together without fear of injury to each other, and are fairly tolerant of moderate light levels. Their behavior and characteristics are exceptionally interesting, and their abundance and ease of reproduction (both sexually and asexually) makes them comparatively "reef friendly." This newly coined phrase implies that their harvest from natural reefs is relatively non-invasive and poses less of a strain on wild populations. It also indicates a relative abundance of specimens. Furthermore, "reef friendly" corals can be asexually bred in captivity with a high degree of success and are well suited to captivity in terms of their longevity and resistance to disease and other problems. I will be using the term in future articles in hopes of generating a degree of awareness and respect for the delicate and threatened coral reef ecosystems in this International Year of the Coral Reef.

Eric Borneman

(Eric Hugo@aol.com)

References:

Chadwick, Nanette. 1988. Competition and locomotion in a free-living fungiid coral. J. Exp. Mar. Biol. Ecol 123: 189-200.

Ikeda, Y., T. Maruyama, and S. Miyachi. 1992. Decalcification by a solitary coral, fungia sp. in the medium with calcium ion concentration lower than aragonite saturation. Proc. Seventh Int'l Coral Reef Symp. 2: 1157-60.

Veron, J.E.N. 1986. Corals of Australia and the Indo-Pacific. University of Hawaii Press, Honolulu: 317-61.

Wells, John W. 1966. Evolutionary development in the scleractinian family Fungiidae. The Cnidaria and Their Evolution. Symposia of the Zoologic Society of London 16: 223-46.

Yamashiro, Hideyuki. 1992. Skeletal dissolution by scleractinian corals. Proc. Seventh Int'l Coral Reef Symp. 2: 1142-5.

Yamashiro, Hideyuki, and Moritaka Nishihira. 1995. Phototaxis in Fungiidae corals (Scleractinia). Marine Biology 124: 461-5.

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Last modified 2006-11-19 01:25
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