35

Materials for the Study of Reef-building Corals (3)

from Science of the South Sea (Kagaku Nanyo) Volume 5, Number 1, pp. 95-106 (September, 1942)

Cover page of the original issue (in Japanese)

37

19. Extended and contracted polyps in the praetorta, as reported previously. daytime There are three types of polyp shape in fungiid As described in Report no. 1 in this issue, in some corals. Fungia actiniformis, which has very dense reef-building coral species, there is a tendency for zooxanthellae in the tentacles, fully extends its body zooxanthellae to assemble within the tentacles of in the daytime (Fig. 5; Discriptions in Fig. 5 indi­ polyps that extend in the daytime. I assumed that cates Pocillopora damicornis instead of Fungia ac­ coral polyps harboring dense zooxanthellae assem­ tiniformis). Fungia repunda does not have many blages would exhibit positive phototaxis like many zooxanthellae in its tentacles, and it extends­ its other zooxanthellate animals. In fact, many coral tentacles moderately in the daytime (Fig. 6). Fungia species having dense zooxanthellae within their echinata has very few zooxanthellae in its tentacles. tentacles extend their polyps in the daytime. How­ This species has dense zooxanthellae in the oral disk, ever, there are some exceptions. Galaxea (Report no. and it completely contracts its tentacles in the 16) and Acropora have few zooxanthellae in their daytime (Figs. 7, 8). polyp bodies or tentacles, but they extend their Lobophyllia usually contracts its tentacles in the polyps in the daytime. Lobophyllia does not need to daytime. Assemblages of zooxanthellae exist in the extend polyps in the daytime, because dense zoo­ tentacle tips, which are always facing outward even xanthellae assemblages are located in the tentacle if polyps are contracted. As shown in Fig. 9, zoo­ tips that always face the outside of the colony. xanthellae assemblages are also located on the tips Similarly, coral species that have thin coenosarcs or of projected tissues of the coenosarc and oral disks epithelia often contract their polyps in the daytime, with red and green colors. These assemblages can be as sufficient sunlight may penetrate through them to observed by the naked eye as small dots. Zooxan­ reach the zooxanthellae. Therefore, I hypothesized thellae are believed to align so as to utilize light in that the shape of coral polyps is determined by the the most effective way. When a polyp receives light need to maximize light reception by zooxanthellae. while extending its tentacles, other parts of the polyp Corals containing dense zooxanthellae in either retract to uncover the coenosarc and oral disk. I their polyps or tentacles extend their polyps in the observed a colony of Lobophyllia that fully extended daytime. The specific characteristics of these coral its tentacles in the daytime. This colony had dense species are either a large coenosarc compared with zooxanthellae in its tentacles. the size of the polyps or very large polyps with wide Acropora and Galaxea have tentacles or polyps oral disks. These corals are Acropora, Montipora, containing few zooxanthellae extending dur­ing day­ Goniopora, Porites, Pavona decussata, Fungia ac­ time. The phototaxic reaction caused by zooxanthellae tiniformis, Hydnophora, Euphyllia, Plerogyra, may not fully transmitted between the coenosarc and Physogyra, Acrhelia, Pocillopora, Seriatopora, and polyps, because polyps of these species are relatively Stylophora. distant from each other. Al­ternatively, their trans­ Porites are often observed to contract their polyps parent tentacles and polyps may function as a light in the daytime, though the polyps have dense zoo­ diffuser. For example, Galaxea has dark-colored xanthellae. The contraction may be due to some type zoo­xanthellae, which are similar to those of other of extrinsic physical stimuli or negative phototaxis­ coral species occurring in deep or shaded habitats. from strong sunlight. Strong sunlight is also a cause As described above, the difference between ex­ of the decrease in the density of zooxanthellae in the tended and contracted polyps can be explained by cases of Pocillopora (Report no. 10) and Pavona positive phototaxis derived from symbiotic zooxanth­ 38

Fig. 5 An extended polyp of Pocillopora dami­ Fig. 6 A part of a tentacle of Fungia repunda, cornis in the daytime. (a) The tentacle tips are which extends its tentacles in the daytime. The dark­ened with dense zooxanthellae. (b) Assem­ density of zooxanthellae in the tentacles of this blages of zooxanthellae can be observed on the species is intermediate between those of other coenosarc as dark bands, which are equivalent in species that fully extend tentacles in the daytime number to the tentacles (×65) and those that fully contract their tentacles. The round black dots are zooxanthellae. The long dots are nematocysts (×65)

Fig. 7 Zooxanthellae are densely distributed on the oral disk of Fungia echinata, which does not extend its tentacles in the daytime. The black dots are zooxanthellae. A part of the oral disk is Fig. 8 Zooxanthellae are very scarce in the ten­ darkened with zooxanthellae assemblages (lower tacles of Fungia echinata. The density of zoo­xan­ right) (×65) thellae is much lower in tentacles than in the coenosarc (see Fig. 7) (×65)

ellae. There are a few similar examples in other zoo­ xanthellate coelenterates. It is considered that many physiological processes are involved in the photo­ taxic reactions of corals, although they are currently not well known. Based on his observations of Caulastraea furcata, AbeRef17 suggested that polyp extension at night is Fig. 9 A part of the oral disk of Lobophyllia caused by water absorption. He explained that the hemplichii, which does not extend its tentacles in osmotic pressure inside polyp tissues is decreased in the daytime. Zooxanthellae assemblages are lo­ cated on the tips of projected tissues of (a) the oral the dark due to the low pH of the coelomic fluid, disks and (b) the coenosarc which dis­solves unused carbon dioxide for assim­ 39 ilation by zooxanthellae. Yonge was also interested digestion. The flatworms exhibit strong positive in this explanation; however, I find it rather ques­ phototaxis. When individual flatworms were placed tionable. approximately 50 cm away from a 60 W incandescent lamp in a Petri dish, they soon moved toward the Ref17 Abe N (1939) On the expansion and contraction of the light. They turned back in the opposite direction, at a polyp of a reef-coral, Caulastraea furcuta Dana. rate of 3 cm in 5-10 seconds, as soon as the Petri Palao Trop Biol Stn Stud 4: 651-670 dish was turned around. Eye-dependent phototaxis has been well studied in many other flatworm 20. Phototaxis in zooxanthellate animals species, but I was unable to find either eyes or Most reef-building corals harbor zooxanthellae eyespots in live specimens. The flatworm is and form colonies that face their polyps toward the commonly found on the colonies of reef-building light. Coral larvae also have zooxanthellae and settle corals in the genera Montipora, Lobophyllia, Stylo­ onto appropriate substrates according to their posi­ phora, and Hydnophora. Based on my observations, tive phototaxic­ behavior (as I have reported pre­ the flatworm appears to inhabit coral colonies with viouslyRef18). During the course of my studies on large coenosarcs­ and oral disks when the corals are zooxanthellate animals, all animals exhibited posi­ in poor condition. A few other flatworm species are tive phototaxis. also found on coral colonies. These also have zooxanthellae and show weak positive phototaxis. i) Under laboratory conditions, reef-building corals iii) As previously reportedRef19, the upside-down jel­ expelled zooxanthellae as their condition deter­ lyfish Cassiopea harbors zooxanthellae and exhibits iorated. The expelled zooxanthellae initially settled positive phototaxis. Other zooxanthellate jellyfish evenly on the bottom surface of the container, but show similar phototactic behavior, as do soft corals after one or two days, they appeared to aggregate in and gorgonians harboring zooxanthellae species. spots. I found that the spots were individual slipper The positive phototactic behavior observed in Eu­ animalcules ingesting zooxanthellae. All of the dendrium and Pennaria by LoebRef20 may be as a paramecia with zooxanthellae in their guts displayed result of the existence of zooxanthellae. positive phototaxis. iv) YongeRef21 reported that giant clams (Tridacnidae) ii) Small individual flatworms*10 are often found on have a well-developed, beautifully colored mantle the surface of reef-building corals. The size of the con­taining large numbers of zooxanthellae, and they flatworms range between 0.5 and 3 mm. They have generally occur on sea bottoms with sufficient light. very thin, egg-like, round bodies with tapering heads. Heart cockles (Corculum cardissa) also have zooxan­ There are no visible internal organs. The flatworms thellae, but differ from giant clams in that they in­ are brown and hence, are easily overlooked on the habit sunny reef flats. coral surface. How­ever, they may become obvious in v) Aeolid nudibranchs occurring near coral colonies the field when they aggregate and fully cover the have zooxanthellae in their cerata. They also show surface of a coral colony*. The surface of such a positive phototaxis. coral colony turns a pale color. There are numerous vi) Cultured zooxanthellae tend to aggregate in the zooxanthellae inside the flatworm bodies. Zooxanth­ light. ellae near the body surface have a normal shape, but those in deeper parts of the body have relatively As described above, zooxanthellate animals show large diameters and appear to be in the process of positive phototaxis. The biological/physiological 40 pro­cesses involved in phototaxis are unclear at this 21. Phototaxis as a factor in determining the stage, but I can state that they are somehow related to life form of reef-building corals the presence of zooxanthellae. I previously hypoth­ As described in the last paper (Kawaguti 1937)Ref24, esized that all reef-building corals harboring zoo­ phototaxis is the major factor determining the life xanthellae exhibit positive phototaxis. Here, I would form of reef-building corals. However, Mr. Abe and like to extend this hypothesis to “all zooxanthellate­ Mr. Motoda have claimed that water flow is the animals exhibit positive phototaxis.” primary factor. In order to compare the importance of these factors, I conducted a field experiment. * I thought that the flatworm was taxonomically Skeletal regeneration and growth of branch pieces close to Convoluta roscoffensis reported by Keeble of Acropora palawensis, A. hyacynthus, Acropora and GambleRef22. However, according to Dr. Kojiro sp. and Anacropora spinosa. were observed with Kato+8, Ref23, the flatworm might belong to the genera incubator jars. A rectangular plate with a small hole Haplodiscus or Proporus, which are more primitive was fixed to the bottom of each glass jar (10 cm in than Convoluta. I am grateful for Dr. Kato’s sugges­ diameter and 18 cm in depth). The surfaces of some tion. jars were completely­ painted with black enamel to block light penetration (dark jars), whereas others *10 Translators’ Note: Currently described as Acoelomorpha were not (light jars). A coral branch was tied with a Ref18 Kawaguti S (1937) On the physiology of reef­corals. II. string to the plate on the bottom of each jar. The The effect of light on colour and form of reef corals. position of the knots was changed to vary the angles Palao Trop Biol Stat Stud 12: 199-208 or Kawaguti of the coral branches (i.e., some coral branches were S (1937) On the physiology of reefcorals. III. upright, whereas others were either horizontal or Regeneration and phototropism in reef corals. Palao hanging down). The jars with coral branches were Trop Biol Stat Stud 12: 209-216, 2 plates or Kawaguti then suspended­ underwater at a depth of 1 m. The S (1943) Further studies on the phototaxis and mouths of all jars faced downward, so that the coral regeneration of reef corals. Trans Nat Hist Soc branches were hanging from the bottom of the jars. Formosa 33: 285-297 (in Japanese) This experimental setup allowed different combina­ Ref19 Kawaguti S (1941) Reason for life of Cassiopea tions of light and water-flow direction to be applied inhabiting the reef flat. Science of the South Sea to the coral branches. Coral branches sus­pended near (Kagaku Nanyo). 3: 177-178 (in Japanese) the jars were considered as controls. Ref20 Loeb J (1893) Uber kilnstliche Umwandlung positiv Coral branches in the light jars regenerated and heliotropischer Tiere in negativ heliotropische und grew in the same manner as the controls. Most of the umgekehrt. Pflug Arch ges Physiol 53: 81-107 coral branches in the dark jars died or became pale Ref21 Yonge CM (1936) Mode of life, feeding, digestion and brown, probably due to insufficient light, as reported symbiosis with zooxanthellae in the Tridacnidae. Sci in the previously (Report no. 2 in this issue). These Rep Great Barrier Reef Exp 1: 283-321 results can ensure the hypothesis that light intensity Ref22 Keeble F, Gamble FW (1907) The origin and nature of or phototaxis is the primary factor determining the the green cells of Convoluta roscoffensis. Quart J regeneration, growth, and the life form of reef- microsc Sci 51: 167-219 building corals. Ref23 Kato K personal communication Ref24 Kawaguti S (1937) On the physiology of reef corals. III. Regeneration and phototropism in reef corals. 41

Palao Trop Biol Stn Stud 1: 209-216 These zooxanthellae are expelled from stressed corals. In the case of Fungia, seawater in a bowl 22. Pseudo-planula of Acropora turns light brown and subsequently, zooxanthellae The condition of a small colony of Acropora gradually settle on the bottom. Based on these ob­ began deteriorating when the weather became warm servations, it was assumed that the specific gravity of in April. The coral colony had been kept in an zooxanthellae is greater than that of seawater. aquarium for nearly five months. A large part of the I measured the specific gravity of zooxanthellae coenosarc had died, and a white skeleton had ap­ using the following methods. Samples of reef- peared, but the polyps were still alive. I observed building corals were collected at Keelung (Taiwan) tentacles emerging from a coral calice attached to the and were transferred to an aquarium in the laboratory wall of the aquarium. It was very tiny, but its mor­ of Taihoku Imperial University. Corals were exposed phology was that of a complete juvenile coral polyp. to 37ºC seawater for a few minutes and then kept in I believe that the juvenile was somehow released an aquarium at room temperature. Several hours from live tissues of the coral colony. I would call it a later, zooxanthellae expelled from the corals were “pseudo-planula,” since its development was differ­ collected and rinsed with clean seawater. The zoo­ ent from that of larvae. It has not yet been confirmed xanthellae were suspended in seawater-sucrose solu­ whether such pseudo-planulae have the ability to tions of various concentrations and centrifuged at grow into a new colony in a similar way as larvae. 2,800 rpm for either 5 min or 20 min. The results are However, this is quite likely if environmental con­ summarized in Table 10. These pro­cedures were run ditions are favorable, because the pseudo-planula at 25ºC. actually secreted a new calcium carbonate skeleton. The specific gravity of the zooxanthellae was between 1.130 and 1.220, with an average of 1.150- 23. Specific gravity of zooxanthellae 1.160. These values are greater than the average When a branch of Acropora was placed for a day specific gravity of seawater, and this is the reason in a wash bowl in the laboratory, zooxanthellae were that zooxanthellae settle on the bottom of a wash found to settle on the bottom, as if they form a thread bowl. I hypothesized that zooxanthellae could exist from the broken end of the branch to the bottom. freely in seawater (Report no. 14 in this issue) and

Table 10 Specific gravity of zooxanthellae measured by sucrose differential centrifugation 42 demonstrated that they were actually free-living same length as that of the body (Fig. 11). It also had (Report no. 24). The difficulty in finding naturally a wavy flagellum surrounding the center part of the occurring zooxanthellae­ in a seawater column may body. When the wavy flagellum was extended, its be due to their small size and specific gravity. length was slightly longer than that of the other flagellum. The wavy flagellum was also thinner than 24. Zooxanthellae in reef-building corals are the other flagellum. The morphology of the zoo­ Gymnodinium sp. (Dinoflagellata) (continua­ xanthella was similar to that of the Dinoflagellata tion of “14. Culturing of zooxanthellae”) Gymno­dinium sp. The zooxanthella may be tenta­ I have succeeded in culturing zooxanthellae using tively identified as Gymnodinium sp. until further a method similar to that reported previously (Report tax­onomic studies are conducted. no. 14 in this issue). I collected a colony of Acropora Isolated zooxanthellae seem to be capable of cell at Keelung and brought it back to the laboratory at division regardless of their body shape and motility. Taihoku Imperial University. The coral colony was Mushroom-shaped zooxanthellae undergoing cell divided into some pieces and placed in a 2-L division were often observed (3 in Fig. 10). A moving container for a few days. A small branch tip (ca. 3 g) zooxanthella occasionally became still and changed was collected and rinsed well with culture medium its body shape, as do zooxanthellae do in corals. (Miquel-Allen solution), and crushed with a hammer These zooxanthellae are also capable of cell division. on a clean marble plate. The broken fragments were Thus, zooxanthellae of reef-building corals, re­ transferred to a beaker containing 30 mL of culture ferred to as Gymnodinium sp., are demonstrated to me­dium and mixed vigorously. After the skeleton maintain life outside of their hosts. Therefore, ex­ and large tissue settled on the bottom, a few drops of isting perspectives on the relationships between zoo­ supernatant were added to test tubes containing xanthellae and corals must be reconsidered. 10 mL of culture medium. Clean test tubes with fresh Yonge and Nicholls (1931)Ref25 suggested that zoo­ medium were inoculated­ every 4-6 weeks. xanthellae were likely to be transmitted from adult Freshly collected zooxanthellae usually settle on corals to larvae after fertilization for the following­ the bottom of a container, because the specific reasons: zooxanthellae were found only within the gravity of the cell is greater than that of seawater. cells of corals and zooxanthellae were found within Eventually, isolated zooxanthellae become motile. planulae, but not within either unfer­tilized eggs or This took approx­imately 10 h in the case of the natural seawater. This raises the question of how reddish-brown zooxanthellae from Acropora corym­ corals transmit zooxanthellate cells to their fertilized bosa. The zooxan­ ­thellae began rotating clockwise. eggs. I believe that the re­lationship between corals Some moved around in a circle with a radius slightly and zooxanthellae is not as strong as Yonge and larger than their body size. Many zooxanthellae then Nicholls suggested. Zooxanthellae are probably began moving vertically in the culture medium. The released from coral cells and transmitted to planulae zoo­xanthella cell appeared round from the top (Fig. via a free-living stage. This process should take 10). Actively moving cells had elongated oval place within coral tissues, but zooxanthellae may shapes, whereas inactive cells were spherically also be transmitted between coral colonies. WilsonRef26 shaped. Actively moving cells often rested for a reported that zooxanthellae were not con­tained in the short time. In contrast, inactive cells began moving eggs of Maeandra areolata. It was considered that suddenly. When I observed a moving zooxanthella in zooxanthellae enter the bodies of larvae through the detail, I observed a flagellum of approximately the epithelia and then move to the endothelia. It was also 43

Fig. 10 Cultured zooxanthellae. Most cells are in the motile stage; (1, 2) side views of a cell and (3) a cell undergoing longi­tudinal cell division (ca. ×1600)

reported that the larvae of Euphyllia glabrescens have zooxanthellae within their epithelia in the early de­velopmental stages. Here I review the current status of zooxanthellae taxonomy. BrandtRef27 reported that an isolated radio­ larian zooxanthella cell released a zoospore having two flagella. Brandt believed that the morphology of the zoospore corresponded to the description of Exuviaella marina found in Radiolaria by Cienkowski (1880)Ref28. Fig. 11 Zooxanthellar cells at the motile stage Oltmanns (1923)Ref29 suggested that coral zooxanth­ ellae belong to the phytoflagellate family Crypto­ Ref30 chrysi­daceae. However, Gardiner (1931) reported sites. that zooxanthellae belong to the phytoflagellate Zooxanthellae change their morphology and pro­ order Cryptomonadina.­ These reports appear to be perties according to their host animal. The finding Ref27 based on Brandt (1885) . In contrast, Hovasse and that zooxanthellae of reef-building corals are tax­ Ref31 Ref32 Teissier (1923) and Hovasse (1937) suggested onomically distinct from the Radiolaria is very in­ that the morphology of coral zooxanthellae nuclei teresting. Further research on the taxonomy of zoo­ was comparable to that of the dinoflagellate Peri­ xanthellae is needed, because current knowledge is dinien, though they did not observe isolated zoo­ based only on the research of BrandtRef27. xanthellae. Their reports were based on the research Ref33 by Chatton (1920) on Peridinien copepod para­ Ref25 Yonge CM, Nicholls AG (1931) Studies on the 44

physiology of corals IV. The structure, distribution i) The algae mostly grow near the boundary between­ and physiology of the zooxanthellae. Sci Rep Great live coral tissue and the skeleton. The algae may Barrier Reef Exp 1: 6-140 favor moderate light conditions under coral tissues, Ref26 Wilson HV (1888) On the development of Mani­eina but this also may have many advantages for the areolata. J Morphol 2: 191-253 uptake of nutritious compounds. A prominent Ref27 Brandt K (1885) Die koloniebildenden Radiolarien­ example can be found in Psammocora exessa. When (Sphaerozoëen) des Golfes von Neapel und der a branch is fractured, dark green bands of the algae angren­zenden Meeresabschnitte. Fauna und Flora can be seen inside the skeleton (Fig. 14). These des Golfes von Neapel. Monograph 13: 65-71 bands are located approximately 2 mm from the Ref28 Cienkowski L (1881) An account on the White Sea brown coral tissue. Under a microscope, the algal excursion in 1880. Proc St-Petersb Imp Soc Nat 12: filaments are observed to cover the surface of the 130-171 (in Russian) skeleton. * The reference for “Cinekowski (1880)” in the main text ii) Although precise observation is difficult as a may intended to refer this article result of the complexity of the coral skeleton, no Ref29 Oltmanns FR (1923) Morphologie und Biologie der hole or groove is observed on the skeletal surface Algen. III. Band, Jena, Verlag von Gustav Fischer. pp. 502-514 Ref30 Gardiner JS (1931) Coral Reefs and Atolls. London: Macmillan, New York, 181 pp Ref31 Hovasse R, Teissier G (1923) Sur la position systém­ atique des Xanthelles. Bull Soc Zool Fr 48: 146-150 Ref32 Hovasse R (1937) Les zooxanthelles sont des dino­ flagelles. Compt Rend Acad Sci Paris 206: 1015 Ref33 Chatton E (1920) Les Péridiniens parasites: morph­ ologie, reproduction, éthologie. Arch Zool Exp Gen 59: 1-475 Fig. 12 Filamentous green algae growing in agar, 25. Parasitic green algae living in reef-build­ inoculated from the skeleton of Acropora (×60) ing corals Filamentous green algae are often parasitic on the skeletons of reef-building corals (Figs. 12, 13). Many re­searchers are aware of the algae and have discussed its role, but there are only a few published reports (Hiro 1939)Ref34. To date, it has been assumed that green algae dissolve and destroy coral skeleton. However, based on my observations on the relationships of the algae with corals, I have a different view on the role of the algae. The algae probably utilize organic matter without dissolving a large amount of the coral Fig. 13 Filamentous green algae. Magnified image skeleton. There are three reasons for this: of Fig. 12 (ca. ×260) 45

light-green filamentous algae are found on the surface of the skeleton. The algae do not appear to form branches.

Ref34 Hiro F (1939) Excavated zone of the margin of lime stone islands. Science of the South Sea (Kagaku Nanyo) 1: 138-146 (in Japanese) Ref35 Duncan PM (1876) Notices of some deep-sea and littoral corals from the Atlantic Ocean, Caribbean, In­dian, New Zealand, Persian Gulf and Japanese & c. seas. Proc Zool Soc London 1876: 428-442 Fig. 14 Fractured section of a branch of Psam­ mocora exessa. The surface is brown because of 26. Causes of forestation on the Rock Islands coral tissue with zooxanthella. (1) The portions One of my first impressions of Palau was of the more than 1-2 mm in depth are white skeletons. densely forested Rock Islands. The Rock Islands are (2) The clear bands in the skeletons are green, due remnants of uplifted coral reefs. All islands have to the existence of parasitic green algae extremely steep slopes and rugged rocky surfaces (see Appendix 3-2). In contrast, many areas of covered by the algae. andesitic Koror Island are barren land covered with iii) There are no signs of skeletal disintegration on red soil. Vegetation in such areas is mainly composed the areas overgrown by the algae. Rather, the skeleton of breadfruit trees and weeds. The only dense forests appears more consolidated by the presence of the are mangroves around coastlines. The climates of algae. When a colony of Porites washed ashore, a these islands are quite similar, but the topography of similar type of algae was growing on the colony the Rock Islands is rather unfavorable for forestation. surface. The colony surface was very robust. There­ Once plants are grown on such islands, there is fore, I presume that some type of chemical reaction sufficient soil for maintaining the forest. However, has altered the strength of the coral skeleton. in the early stages of vegetation, various organic and The characteristics of the algae are quite similar to inorganic compounds­ might have been supplied those of Achlya penetrans described by Duncan from limestone exudates; i.e., dead reef-building (1876)Ref35. Initially, culturing the algae was difficult; coral skeletons. The Rock Islands may be more however, it was successfully cultured using agar fertile than Koror Island. with a small piece of coral skeleton. The algae can I remember that some farmers in Okinawa used also be cultured using Miquel-Allen solution. The the reef-building coral Acropora as a fertilizer. algae can easily enter the skeleton and start growing Seaweeds and small animals caught by trawl nets after inoculation. were commonly used; hence, coral fertilizers were There are various parasitic algae that differ in used only on farms where the soil contained lime­ color and morphology according to the species of stone rubble. reef-building coral. For example, Porites rarely has the green algae described above, but the skeleton of 27. Reef-building corals and petroleum Porites somaliensis occasionally shows light pink Reef-building corals are used for various purposes, coloration. Under microscopic observation, pink or but the major portion used is the skeletons. Organic 46 compounds of corals are seldom used. From my tained about 0.25% wax-like materials. They also previous report (Report no. 26 in this issue), I con­ reported that organic matter was structurally included sidered the possibility that petroleum originated inside inorganic coral skeletons. With this article, I from corals. My thoughts regarding petroleum and realized that my speculation was justifiable. coral also originated from an interesting observation Wax-like materials are known to exist in animal made in Palau in the summer of 1936. I wrote it bodies. Coral skeletons contain various organic mat­ down in my diary on August 7: ter that cannot be removed by either soaking in al­ “I was caught in a heavy squall during field work. cohol or boiling with alkaline solution. This or­ganic I went into the shade of an overhanging rock to hide matter is a wax-like material (Dana 1846)Ref37. Mr. from the rain. As I walked around and looked up, I Akita*11, +9 obtained similar results from his analysis saw a yellow resin-like lump on the limestone of coral skeletons. surface. It was not sticky, but it was rather tough like Accumulated corals could be a source of petro­ gum. It is interesting if reef-building corals are the leum, because the skeletons hold a certain amount of origin of this yellow lump. It makes sense why the organic matter even after the living tissues have Rock Islands are so forested. The origin may be washed away. Thus, the possibility of recovering oil animal fat. Petroleum is thought be originated from from coral reef islands can be debated upon. dead plankton. If so, dead corals could be an origin as well. There may be such petroleum reservoir beds *11 Translators’ Note: “these results obtained by Mr. Akita” between andesitic rocks and limestones. We may be may be found in; Akita YK, Kawaguti S (1948) On the able to find petroleum from tropical oceanic islands. chemical composition of the skeleton of living reef Is there any reservoir?” coral. Acta Zool Taiwan 1: 67-80 I believed that the origin of a potential petroleum Ref36 Bergmann W, Lester D (1940) Coral-reefs and the reservoir in southern Taiwan could possibly be formation of petroleum. Science 92: 452-453 explained by my speculation. I talked about corals Ref37 Dana JD (1846) Zoophytes. In US Explor Exp During and petroleum with some people, but no one was the Years 1838, 1839, 1840, 1841, 1842. Under the Com­ interested. However, Bergmann and Lester (1940)Ref36 mand of Charles Wilkes, U.S.N. Lea and Blanchard, pointed out the possibility that reef-building corals Philadelphia. 7, 740 pp were the origin of petroleum, because corals con­