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南太平洋海域調査研究報告
OCCASIONAL PAPERS

No.58（2017 年 3 月）
No.58（March 2017）

Species Diversity of Hexacorallia
around the Satsunan Islands, Japan
FUJII Takuma
Research Center for the Pacific Islands, Kagoshima University

Abstract
The Satsunan Islands, in the middle to the north of the Ryukyu Islands, Japan, are located in an
important location for biogeography, as there is a shift of marine fauna in this region from subtropical totemperate. However, few have studied about marine biodiversity of this region for many taxa, withexceptions such as fishes. In this report, the biogeographic relations between the Coral Triangle region ofhighest marine diversity, and the Satsunan Islands, using previous reports related to species diversity of
subclass Hexacorallia are reviewed. In the near future, it is strongly needed to more clearly reveal the
species diversity of order Hexacorallia within the Satsunan Islands, a region of ecological variety, based on
thorough and taxonomical surveys.
Keywords: biogeography, ecological variety, ecozone, Scleractinia, Zoantharia

Suborder Hexacorallia
Class Anthozoa, currently consisting of 3 subclasses; Hexacorallia, Octocorallia andCeriantharia, is characterized by a lack of the medusa stage in their life cycles. Anthozoans
are common organisms that are widely distributed in various marine environments fromshallow to deep, from the equator to the polar region. The phylogenetic relationships within
Anthozoa are not yet resolved. Compared to the other two suborders, inter-order level
phylogeny within the subclass Hexacorallia is still under revision (DALY et al. 2007, STAMPAR
et al. 2014). Octocorallia is characterized by eight plumate tentacles and eight complete
mesenteries inside the body cavity. Ceriantharia, recently promoted to subclass from an order
within subclass Hexacorallia, is characterized by a nest tube formed utilizing a specialized
nematocyst, and unpaired, coupled mesenteries in the body cavity. In contrast to the twoeasily definable subclasses, Hexacorallia is a less coherent taxon. The morphological andecological features within the subclass are very varied compared to the other subclasses. The
synapomorphys of hexacorallians are considered to be the appearance of spirocysts, a type ofnematocyst, and the first six mesenteries in the development of polyps.

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Currently, subclass Hexacorallia consists of five orders; Scleractinia, Corallimorpharia,
Actiniaria, Zoantharia and Antipatharia. It has been estimated that there are around 4,000
species contained within this subclass in a previous study (DOUMENC and VAN PRAET 1987).
However, as well as the other marine invertebrates, the development of the analyticaltechniques have provided more and more discoveries of new taxa (e.g., studies for order
Zoantharia: REIMER and FUJII 2017), and reconstructions of taxonomy have been performed(e.g., studies for order Scleractinia: FUKAMI et al. 2008, KITAHARA et al. 2010). In the orders
Corallimorpharia, Actiniaria and Antipatharia, the accumulation of basal knowledge of
species diversity is still required.

The Coral Triangle and the Satsunan Islands
The “Coral Triangle”, an area of Southeast Asia between Malaysia, the Philippines,
Indonesia and Papua New Guinea, is considered to be the center of the coral reef region, andthe center of maximum marine biodiversity. Recently, the global patterns of biodiversity withvarious parameters such as species richness, uniqueness, or threats for major marineorganisms have been discussed and analyzed for this region. However, further basal studies
are required to properly estimate detailed biogeographical patterns. Most previous studies
were focused on only major taxa, such as fish, snails, zooxanthellate corals, or lobsters, andthe information on the border areas of the Coral Triangle is seriously deficient (e.g.,
HOEKSEMA 2007, ROBERTS et al. 2002).
The Ryukyu Islands are at the northern edge of the Coral Triangle, and are considered as
one of the highest centers of marine bio-endemism (ROBERTS et al. 2002). Moreover, theSatsunan Islands are an important area to study the gradient of marine biodiversity fromsubtropical to temperate zones following the Kuroshio Current. The Ryukyu Islands are thesouthern chain of islands in Japan, from the east side of Taiwan to the Osumi Islands, andspans from the subtropical to temperate zone. The Ryukyu Islands, or even the Nansei Islands,
span over two prefectures, Okinawa and Kagoshima. The northern part is called the Satsunan
Islands of Kagoshima Prefecture (TOYAMA 2009). From a biogeographical point of view, theSatsunan Islands extend into two regions as well; the Palearctic and Indomalaya ecozones.
The border between these two ecozones, designated as Watase line, is crossed on Tokara Strait
where is between Kodakarajima Island and Akusekijima Island. The border of thebiogeographical ecozones was decided based on the terrestrial organisms, and it’s still
doubtfully if it can be applied to the marine benthic fauna. For example, the northernmost
coral reef region is considered to be around Tanegashima Island (approx. N30° 21’ to N 30°51’), where in the areas where the average sea surface temperature of the coldest month isgreater than 18°C (YAMANO 2009). Either way, the Satsunan Islands possibly having high33
Species Diversity of Hexacorallia around the Satsunan Islands, Japan

marine biodiversity from ecological, species to genetic levels. Previously some faunal reportson the major taxa of marine organisms were published only on some part of the islands (e.g.,
fish: MOTOMURA 2016).

Faunal Reports on Subclass Hexacorallia from the Satsunan Islands
The order Scleractinia, generally called stony corals, is one of the key taxa in the coral
reef region. More than half of the approximately 1,400 species of this order are symbiotic
with photosynthetic brown algae and known as reef-building corals or zooxanthellate corals(CAIRNS 1999). Zooxanthellate corals have important ecological roles in shallow warm waters
as the primary producers and constructing complex physiological structures on the sea floor
that providing various spaces to live for other organisms. Because not only of their ecologicalbut also of the economic importance, recently the scleractinian species have become to bemuch studied regarding their species diversity for ecological monitoring, particularly by local
administrative agencies and civilian organizations (see THE JAPANESE CORAL REEF SOCIETY
and MINISTRY OF THE ENVIRONMENT 2004). Unfortunately, it is often difficult to access todetails of such reports and to recognize if the surveys were carried out scientifically or not.
A field guidebook edited by VERON (2000) may be the most widely used material toidentify zooxanthellate corals in recent years, and currently a beta version of the associatedweb database has been updated (VERON et al. 2016). Based on this database (2016), 369
species of zooxanthellate scleractinian corals have been listed in “Ryukyu Islands North”
region (=from Okinawajima Island and the Kerama Islands to the Tokara Islands), and 218
species in the “Kyushu South-east” region (=from the Osumi Islands to the Koshiki Islands,
southern Kyushu Island and east coast of Kyushu Island). However, these list contain someuncertain information as the distribution was reported based either or both on specimens or insitu photographs clearly identified combined with possibly distributed species in which the
distribution was estimated but currently no records exist. Thus, although there are no doubtsthat this field guide and database are valuable in the preliminary identification and estimationof biogeographical patterns, these data should treat carefully and with caveats for scientificstudies.
Within the Satsunan Islands, SUGIHARA et al. (2015) reported 161 species ofzooxanthellate scleractinian corals from Tanegashima Island in the Osumi Islands. Although
this work is an open access electronic field guide book and there is an absence of descriptionsof voucher specimens, it can be considered to be a valuable distributional report as themethodology of identification and the traceability of the taxonomy were clarified. YABE andSUGIYAMA (1935) and SUGIYAMA (1937) reported 63 zooxanthellate scleractinian corals
species from the Amami Islands and UTINOMI (1956) reported 15 species from the Tokara

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Islands based on vouchered specimens in public museums. However, these older reports were
simply the results of elementary surveys in each reports, and asides from the TanegashimaIsland data, these reports are too old to be treated as information on the current species
diversity around the Satsunan Islands region. Thus, there is an overall lack of basal
information on coral species diversity in the Satsunan Islands.
The Zoantharia is the other hexacorallian order in which recently the studies on species
diversity have been advanced as much as the order Scleractinia. This order, often calledcolonial sea anemones or sand-encrusting sea anemones, is characterized by a specialized
bilateral mesenterial arrangement. This order is as large as Scleractinia, consisting of around
300 species, and the fact that almost all the species have no hard tissues such as a skeleton orsclerites had limited the progress of taxonomy in the past. However, molecular techniques
have helped to sort out the taxonomy and advanced biogeographical research. Previously, 13
zoantharian species were recorded from the Satsunan Islands region based on voucher
specimens or the descriptions of in situ observation, with 9 zooxanthellate species and 4
azooxanthellate species (see REIMER and FUJII 2017). Zooxanthellate zoantharians are
considered to occupy a similar niche with zooxanthellate corals and assuming the ecologicalrole as the primarily producer in the coral reef ecosystems, although they have no skeletal
tissues to construct the new structures on the sea floor. ONO et al. (2008) revealed the
distribution patterns of 9 zooxanthellate zoantharian species in the Satsunan Islands, showing
decreasing species richness from south to north.
The other hexacorallian orders; Corallimorpharia, Actiniaria and Antipatharia, have beenstudied little regarding the species diversity around the Ryukyu Islands region. There is no
doubt that these orders also have high species diversity around not only the Satsunan Islands
but also in the whole Ryukyu Islands, as there are many photographs on field guides (e.g.,
SHIRAI 1977, UCHIDA and SOYAMA 2001). The preliminary results of this author’s informal
survey suggest the distribution of 7 species including 2 previously unrecorded species ofzoantharias around Takarajima Island, the Tokara Islands (FUJII 2016). Thus, it is easy toestimate that the species diversity of Hexacorallia is higher than has been previously reported
within this region, particularly given that Takarajima Island is a comparatively small islandand the eco-habitats for hexacorallian species are less varied within the Satsunan Islands.
In the near future, it will be strongly required to more clearly reveal the species diversityof order Hexacorallia not only within the Coral Triangle, the region of highest marine
biodiversity, but also within the Satsunan Islands, a region of ecological variety, to report
representatively based on the thorough field and taxonomic surveys utilizing identification
with voucher specimens.

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Species Diversity of Hexacorallia around the Satsunan Islands, Japan

References
CAIRNS, S. D. 1999. Species Richness of Recent Scleractinia. Atoll Research Bulletin, 459:
1–46.
DALY, M., BRUGLER, M. R., CARTWRIGHT, P., COLLINS, A. G., DAWSON, M. N., FAUTIN, D. G.,
FRANCE, S. C., MCFADDEN, C. S., OPRESKO, D. M., RODRIGUEZ, E., ROMANO, S. L. and
STAKE, J. L. 2007. The Phylum Cnidaria: A Review of Phylogenetic Patterns andDiversity 300 Years after Linnaeus. Zootaxa, 1668: 127–182.
DOUMENC, D. A. and VAN PRAET, M. 1987. Ordre des Actiniaires, ordre desPtyochodactiares, Ordre des Corallimorphares (Order Actiniaria, Order Ptychodactira
and Order Corallimorpharia). In: Traite de Zoologie, Tome III, Fasicule 3, Cnidaries
Anthozoaires (Treaty of Zoology, Volume III, Fasicule 3, Cnidarians Anthozoans) (Ed.
GRASSE, P. P.), 257–401, Masson, Paris, France (in French).
FUJII, T. 2016. Satsunan Shotou ni okeru Sunaginchakumoku oyobi Isoginchakumoku no
Tayousei (Preliminary Report of Diversity of Orders Zoantharia and Actiniaria in theSatsunan Islands, Kagoshima). Occasional Papers (Kagoshima University ResearchCenter for the Pacific Islands), 57: 87–88 (in Japanese).
FUKAMI, H., CHEN, C. A., BUDD, A. F., COLLINS, A., WALLACE, C., CHUANG, Y., CHEN, C.,
DAI, C., IWAO, K., SHEPPARD, C. and KNOWLTON, N. 2008. Mitochondrial Nuclear Genes
Suggest that Stony Corals Are Monophyletic but Most Families of Stony Corals Are Not(Order Scleractinia, Class Anthozoa, Phylum Cnidaria). PLoS One, 3: e3222.
HOEKSEMA, B. W. 2007. Delineation of the Indo-Malayan Centre of Maximum Marine
Biodiversity: The Coral Triangle. In: Biogeography, Time and Place: Distributions,
Barriers, and Islands (Ed. RENEMA, W.), 117–178, Springer, Amsterdam, Netherlands.
KITAHARA, M. V., CAIRNS, S. D., STOLARSKI, J., BLAIR, D. and MILLER, D. J. A. 2010.
Comprehensive Phylogenetic Analysis of the Scleractinia (Cnidaria, Anthozoa) Based on
Mitochondrial CO1 Sequence Data. PLoS One, 5: 1–9.
MOTOMURA, H. 2016. The Ichthyofauna of Yoron-Jima Island in the Southern Extremity of
the Amami Islands, Japan, Including Comparisons with Similar Nearby Regions. In: The
Amami Islands: Culture, Society, Industry and Nature (Eds. KAWAI, K., TERADA, R. and
KUWAHARA, S.), 71–78, Hokuto Shobo Publishing, Tokyo.
ONO, S., REIMER, J. D. and TSUKAHARA, J. 2008. Ecological Survey of Zooxanthellate
Zoanthid Diversity (Hexacorallia: Zoantharia) from Kagoshima, Japan. Kuroshio
Biosphere, 4: 9–24.
REIMER, J. D. and FUJII, T. 2017. Zoantharia (Cnidaria: Anthozoa: Hexacorallia) Diversity
Research in Japan: Current State and Future Trends. In: Species Diversity of Animals inJapan (Eds. MOTOKAWA, M. and KAJIHARA, H.), 383–399, Springer Japan, Tokyo, Japan.

36
FUJII Takuma

ROBERTS, C. M., MCCLEAN, C. J., VERON, J. E., HAWKINS, J. P., ALLEN, G. R., MCALLISTER,
D. E., MITTERMEIER, C. G., SCHUELER, F. W., SPALDING, M., WELLS, F., VYNNE, C. and
WERNER, T. B. 2002. Marine Biodiversity Hotspots and Conservation Priorities for
Tropical Reefs. Science, 295: 1280–1284.
SHIRAI, S. 1977. Genshoku Okinawa Kaichuu Doubutsu Seitai Zukan (Underwater Animal
Ecology of Okinawa), 636 pp., Shinsei Tosho, Okinawa, Japan (in Japanese).
STAMPAR, S. N., MARONNA, M. M., KITAHARA, M. V., REIMER, J. D. and MORANDINI, A. C.
2014. Fast-Evolving Mitochondrial DNA in Ceriantharia: A Reflection of Hexacorallia
Paraphyly? PLoS One, 9: e86612.
SUGIHARA, K., NOMURA, K., YOKOCHI, H., SHIMOIKE, K., KAJIWARA, K., SUZUKI, G., ZAYASU,
Y., DEWA, N., FUKAMI, H., KITANO, Y. F., MATSUMOTO, H., MEZAKI, T., NAGATA, S.,
TACHIKAWA, H. and KIMURA, T. 2015. Nihon no Yusousei Ishisangorui Tanegashimahen(Zooxanthellate Scleractinian Corals of Tanegashima Island, Japan), 197 pp., Center for
Environmental Biology and Ecosystem Studies, National Institute for Environmental
Studies, Ibaraki, Japan (in Japanese).
SUGIYAMA, T. 1937. Honpou Engan Sangen Zoushou Sango ni tsukite (On the Recent Reef
Corals Occurring in the Coast of Japan), 60 pp., Contribution of Institute of Geology andPaleontology, Tohoku University, Sendai, Japan (in Japanese).
THE JAPANESE CORAL REEF SOCIETY and MINISTRY OF THE ENVIRONMENT 2004. Coral Reefs
of Japan, 358 pp., Ministry of the Environment, Tokyo, Japan.
TOYAMA, M. 2009. Ryuukyuu Rettou no Meishou ni Kansuru Memo (A Note on the Names of
the Ryukyu Islands). Bulletin of the Historiographical Institute, 37: 59–68 (in Japanese).
UCHIDA, H. and SOYAMA, I. 2001. Isoginchaku Gaido Bukku (Sea Anemones in Japanese
Waters), 157 pp., Hankyu Communications, Tokyo, Japan (in Japanese).
UTINOMI, H. 1956. Invertebrate Fauna of the Intertidal Zone of the Tokara Islands XIV. Stony
Corals and Hydrocorals. Publications of the Seto Marine Biological Laboratory, 5:339–346.
VERON, J. E. N. 2000. Corals of the World, 3 Volumes, 1381 pp., Australian Institute ofMarine Science, Townsville, Australia.
VERON, J. E. N., STAFFORD-SMITH, M. G., TURAK, E. and DE VANTIER, L. M. 2016. Corals of
the World, version 0.01 (Beta). Retrieved 20 November, 2016, fromhttp://coralsoftheworld.org.
YABE, H. and SUGIYAMA, T. 1935. Geological and Geographical Distribution of Reef-Corals
in Japan. Journal of Paleontology, 9: 183–217.
YAMANO, H. 2009. Nihon ni okeru Sangoshou no Bunpu (Distribution of Coral Reefs inJapan). Bulletin on Coastal Oceanography, 46: 3–9 (in Japanese).