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STONY CORALS FROM THE FAMILY FUNGIIDAE A.J. Nilsen October 1997 Aquarium.Net

Alf Nilsen writes on fungiids corals, Aquarium Net has numerous articles written by the leading authors for the advanced aquarist

STONY CORALS FROM THE FAMILY FUNGIIDAE - DANA, 1846

By Alf Jacob Nilsen Reprintedwith permission from DasAquarium

The marine aquarium hobby has at last reached a level where the aquarists can observe animal behaviour and study biological events that hardly can be examined in detail anywhere else other than in the aquarium. Today many of the private reef tanks can show far better results with respect to the growth of corals than the majority of public marine aquariums, which are still run by heavy biological filters and have an extensive growth of algae. In this article we shall concentrate on the Scleractinian family Fungiidae (“Piltzkoralle”), which has proven to very durable, and which has shown us some very interesting examples of unisexual breeding through the development of a structure called “acanthocauli” - which we shall return to.

Coral Organization

There are two basic type of stony corals; those who live as colonies and those who lives as individual polyps, called solitary corals. In the family Fungiidae we do find both kinds, but some species are rather difficult to place in either of the two groups.

There are discussions among scientists of how to define the term “solitary”. As a general rule, corals with one mouth only are called solitary while those with many mouths are called colonial. The majority of fungiids are solitary corals. Most species in the largest genus Fungia , have one mouth only, but the species Fungia simplex always has several mouths. The closely related species Fungia echinata does, however, only have one single mouth. Abnormal developments can also result in the development of an unusual number of mouths. It is accepted that the solitary corals are the oldest evolutionary form and that colonial forms have evolved from the solitary form. The Fungiidae does also contain one hermatypic genus - Fungiacyathus . Altogether this family contains a number of highly interesting species some of which are very durable in the reef aquarium. But again.....the term “solitary” is very diffuse.

Systematic

I know that most aquarists take little notice of what name a coral has. To most of us it does not matter weather a coral is Fungia danai or Fungia fungites . Personally I have always enjoyed to classify the animals that I keep in my aquarium. To be aware of the morphological characters that split one coral from the other always reminds me of the most important continuous process taking place - the evolution of life. In the Fungiidae some genus and even species can very easily be recognized. The genera Herpolitha and Polyphyllia and the two species in Fungia - F. echinata and F. simplex , all have the same elongated shape. They are therefore easily distinguished from the members of the family with the common round shape. The very often imported Heliofungia actiniformis (often wrongly talked about as “a Fungia”) cannot be misclassified because of it extremely long tentacles. The individuals of this species do, however, have several colors - everything from green via brown to purple - and color is not an character for classification in any coral family. To make a certain classification one have to look at the calcerous skeleton. In Fungiidae it consists of elongated septa running from the center of the polyp/colony towards the edge. On the upper side of the colony the structure have septal teeth and on the lower side coastal spines. It is the shape of these structures we must examine to make a certain classification. I highly recommend Veron, (1986) for this purpose.

THE AUSTRALIAN AND INDO-PACIFIC SPECIES OF THE FAMILY FUNGIIDAE

Genus Cycloseris

C.cyclolites, C.costulata, C. sommervillei, C. erosa, C. patelliformis, C. vaughani, C. marginata

Genus Diaseris

D. distorta, D. fragilis

Genus Heliofungia

H. actiniformis

Genus Fungia

F.fungites, F.danai, F. corona, F. scruposa, F. horrida, F. valida, F. klunzingeri, F. repanda, F. concinna, F. scabra, F. grannulosa, F. scutaria, F. paumotensis, F. moluccensis, F. echinata, F. simplex.

Genus Herpolitha

H. limax, H. weberi.

Genus Polyphyllia

P. talpina

Genus Halomitra

H. pileus

Genus Sandalolitha

S. robusta

Genus Lithophyllon

L. edwardsi

Genus Podabacia

P. crustacea

Genus Zoopilus

Z. echinatus

(Based on Veron, 1986).

Biology

Almost any coral reef contains Fungiids. The family is distributed from the west coast of Central America through the whole Indo-Pacific to the Red Sea and as far south as South Africa. The highest number of species is found in the Central Indo-Pacific. The family lacks in the Caribbean. Fungiids can most often be seen in the lagoon or on the reef flat, often in high numbers. As older individuals are free living and not attached to the substrate, (as youngsters from the genus Fungia are), they are strongly affected by the waves and tends to gather between boulders and rubbles. This often courses them to lay up side down. Some, but far from all, are able to turn themselves towards the light again. For this reason it is not uncommon to find polyps where only remains of the tissue are still alive. Their tentacles are in nature only fully extended during the night. In the reef aquarium, however, they tend to lay with exposed tentacles the whole day long. The light intensity, being lower in the aquarium than on the extremely light-exposed reef flat, might be one reason for this. The lack of predators and/or sufficient plankton might be another. We have observed expanded Fungiids in the Maldives in full sunlight when the water was rich in plankton.

The polyps of Fungiidae are among the very largest of all coral polyps, and the very often imported species Heliofungia actiniformis can reach a diameter of over 50 cm. It also has very long tentacles usually with green and brown colors, but occasionally colored beautifully purple. There is little known about the feeding habits of Fungiids, but it is for certain that these corals, like another hermatypic corals, are utilizing the energy produced by the symbiotic algae. Most likely the majority of the species catch and utilize plankton as well. Like most corals Fungiids do have parasites. The bivalve Fungicava eilatensis lives inside the mouth of the corals and is found nowhere else. I have, however, not heard of any aquarists that have detected it in an aquarium yet.

Fungiids in the aquarium

I have kept these corals ever since I started with marine aquarium in the late seventies. The great majority of Fungids imported to Norway are belonging to the species Heliofungia actiniformis . This species, which is the only one in the genus, is easily recognized by its very long tentacles and its single, large mouth. It is the largest known solitary coral. The color is, as mentioned earlier, very beautiful varying from brown and green to purple. In nature this species is restricted to the very central Indo-Pacific. It is found as far north as Ryukyu Island and as far south as New Caledonia while Singapore is as far west as this species lives. Even in “the old fashioned” aquarium with thread algae and biological filters this species proved to be very hardy. In the modern reef tanks, with efficient skimming, metal halide lamps and calcareous water, this stony coral is expanding, growing and will live for years. They are, like in nature, extended during the day. When the light decreases and the blue evening-light turns on, they retract totally. I prefer to keep Heliofungia actiniformis , like the rest of the family, on the sandy bottom on my tank. They do, however, need a lot of space as they can easily reach a diameter of 30 cm or more when fully expanded. An aquarium with a rather large area filled with coral sand as a home for different Fungiids, is something special indeed. Besides Heliofungia I now keep four other species. Fungia fungites was bought out of a shipment from Hawaii, and of six individuals, five have so far survived excellent in three different aquariums. The tentacles are very short and the polyps have a large, central mouth making it a typical solitary coral. The color is dark brown. This species, like the latter, seems to depend on the zooxanthellae. It must be characterized as a “hardy” species. As my tank are decorated with living stones only, it possesses a lot of crabs and other highly predatory animals. It is therefore not unusual that from time to time, a coral are attached and eaten on food during the night. This happened with Fungia fungites as well, and I have a strong suspicion that it was the beautiful shrimp Saron inermis that was hungry. They have been picking on corals before, but who can remove such beauties from a reef tank ? However, the wound, which measured 5 x 5 cm, was healed during three days, and since then no further attacks has happened. For years I have kept the rough and elongated Herpolitha sp. , which most likely is H. limax , but which is hard to distinguish from the closely related H.weberi . This species does not seem to like very strong light from my two metal halide lamps, but to prefer semi-shadow in the entrance to a small cave. Here it developed nice brown tentacles from a green fluorescent coenenchyme, but it took months until it adapted to the aquarium condition. Now the colony is nearly three years and has definitely grown. This coral illustrate the problematic term “solitary” versus “colonial”. If one look closely one can see numerous mouths, not only along the centerline of the animal, but also along the lateral lines of the colony. It is, however, a clearly free living colony which might reach a size more than one meter in nature. Recently a colony from the genus Polyphyllia showed up in a shop in Oslo, it was of course purchased and put into my aquarium. And what a sight ! The colony was bright green and densely covered with brown to gray tentacles which are expanded the whole day long. Like with Herpolitha numerous mouths can be seen.

All my Fungiids are placed closely together and they do not seem to have any negative influence to each other. Their stinging cells seem to be harmless, and other nearby animals like a Galaxea sp . and some Actinodiscus sp. do not react negative at all. They are all living like a happy family. Even the anenomfish Premnas biaculeatus have joined them.

Reproduction

The sexes in Fungiidae can be both separate and hermaphrodite depending in the species. Heliofungia actiniformis is for instance recognized to be a hermaphrodite. Like in all coral families the sexual reproduction takes place when egg- and sperm cells melt to form a zygote which develop into a free swimming planula larvae, which in turn settles and grows from a primary polyp to an new coral colony. The primary polyp is in the genus Fungia called “Acanthocauli”. The acanyhocauli can also be formed through asexual reproduction, for instance on the coral surface after damaging. When swimming over a shallow lagoon it is easy to count hundreds of sessile acanthocauli, both sexually and asexually formed. An attached, fast-growing young polyp ensures the coral to reach a certain size before being washed away by storms and huge waves. In turn the great potential for asexual formation of genetic similar acanthocauli secures the production of sexual formed acanthocauli and carries the genes to the next generation - all together an adaptation to a life in turbulent water. In early 1985 I bought a large giant calm, Tridacna squamosa and placed it in my aquarium. The animal was very big and its mantel extended so far outside the shells that it created shadow on the shells sides. Here several organisms lived and made the shell decorative and colorful. Among the organisms were two acanthocaulis. I did, at the moment take little notice of them, but remarked that they easily recovered after various mechanical damages. I did also notice that the grew, and when they were photographed in Autumn 1987, they measured 15mm I diameter when fully expanded. Then in late 1988 the clam has grown more than 10 cm and reached a size of 45 cm, which was simply too big for the front of my tank - much better in the back between large boulders of living stones and soft corals. I moved the animal and got a nice, free space in front fit for coral sand and Fungiids. But then in January 1989 I suddenly discovered a free living Fungia sp . on the sandy bottom of my aquarium ! The acanthocauli had loosened ! Two weeks later the other did the same, both now measuring 25mm in diameter fully expanded. They were able to move by their tissue from a rather dark place to the light beams from the metal halide lamps. What an astonishing event !

I have tried to classify the species and most likely it is F. danai . but I am far from sure. I placed both polyps in good light and on sandy bottom. They are doing excellent, are expanded the whole day long and have during 1989 shown the following growth:

January -89: diameter app. 25mm

February -89: “ “ 30mm

May -89: “ “ 40mm

August -89: “ “ 50mm

October -89: “ “ 60mm This gives an average growth of 3,5mm diameter pr. month. If the average thickness of the skeleton is estimated roughly to 2.0 mm and the specific weight of app. 1,5 g/ccm, these two colonies alone have fixed app. 17 gr. calcium carbonate, all very roughly estimated of course. As we clearly see that stony corals, serpulide worms, vermetide snails, different crustaceans, molluscs, the calcareous red- , green- and brown algae and many other calcium fixers are growing heavily, how can anyone state that the adding of calcium and bicarbonate is not necessary !?

In August 1990 I once again measured the second generation acanthocauli on the shell-side of the giant calm. It had now grown to a diameter of 2 cm and as this was not enough, another three very small new acanthocauli-polyps are developing near by. Meanwhile the “older ones” have grown to a diameter of 8 cm.

When I examined the shells of the clam about two months after the event, I to my even bigger astonishment discovered that two new acanthocauli were growing from the same stalk ! In nature the stalk becomes weakened from calcareous destroying organisms like algae and sponges, and the polyp breaks off. Here the obvious reason for loosening was the decreasing in light intensity when the giant calm was moved backwards in my aquarium. When I visited Herr Dietrich Stüber, who is one of the world leading persons on hermatypic stony corals in captivity, in Berlin (BRD) in October 1989, In his excellent aquarium especially designed for the growth of Scleractinian corals, I was able to detect the asexual formation from several acanthocauli at an Fungia sp ., perhaps F. simplex . The pictures that follows this article clearly shows that we have now reached the technical point where natural conditions can be simulated and that natural events can be studied in detail. We can add something new to the knowledge of the reef corals. For all those especially interested in Scleractinian corals Veron, 1986 is a must and really an excellent work on the subject. The full reference is given below.

SUGGESTED READING:

VERON, J.E.N., 1986. Corals of Australia and The Indo-Pacific.

ANGUS & ROBERTSON PUBL., London, UK and North Ryde, Australia. 644 pp. Fully colored illustrated. ISBN 0 207 15116 4.

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