[in Japanese]

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Coral reef functions provide ecological, social and economic benefits to coastal communities. Thus, the role of linkage between ecological and socioeconomic information is increasingly recognized in the decision-making process of sustainable coral reef management. Under the circumstances, socioeconomic value of coral reefs among coastal communities, namely Akajima Island, was evaluated. For the evaluation, a questionnaire survey was conducted with the local people. The result shows that most of the local people are highly dependent on coral reef ecosystems for their living. However, coral reefs are degraded by natural and human induced stresses, and the local people are well aware of those stresses. Their willingness to pay, 8,153 JP¥ (about 75 US$) per person per year, shows significant socioeconomic value of the coral reef ecosystems. The local people consider the need for management approaches preserving the coral reefs, and they are specifically willing to participate in community-based management. For that reason, it is essential for decision makers to establish a stakeholder network that is centered on the local community and provide them clear approaches on coral reef management.

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We found the two morphological types (corallite-wall separate type and corallite-wall fusion type) in Montastraea valenciennesi in Wakayama, southern Honshu, Japan. In this study, we investigated whether these types are the morphological variations within a single species or between separate species, using cross breeding experiments. The results clearly showed that these two types were reproductively isolated, suggesting that these two types should be treated as different species, respectively. However, we could not determine which of the morph-types is true M. valenciennesi, in absence of the examination of type specimen.

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Three types of the morphological variations were found in the living colonies of Acanthastrea hemprichii, which species is common near shore in Wakayama Prefecture. We had the cross experiments using these three types on July 26 and 27 in 2008 to clarify whether they were interor intraspecific morphological variations. The results showed that all crosses among these three types had the high fertilization rates (more than 70%) with similar to the crosses within types. Considering that their skeletal morphologies are not different among types, we concluded that these three types were the intra-specific variations.

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Kushimoto, the southernmost part of Honshu, Japan is strongly influenced by the Kuroshio Warm Current, where hermatypic corals are abundant in spite of its high latitude location of 33°N. Kushimoto has been known as a habitat of tabular-type Acropora coral communities in Honshu for a long time, and this characteristic has been continued essentially without dramatic change until recently. The change of the coral communities in both quantity and quality has been gradually recognized since the middle of the 1990s. The quantitative change consists of reduction of coverage from a peak in 2000 with the state of low coverage continuing for the last five years. The qualitative change includes increased species diversity by recruits of many tropical coral species that were not previously recorded in Kushimoto, and replacement of dominant species by the newcomers. It is suggested that these changes of coral communities were caused by a warm water temperature phenomenon that has continued since the 1990s.

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Hermatypic coral communities were quantitatively described along a latitudinal gradient from Koshiki-jima Islands (Kagoshima Prefecture) to Oki Islands (Shimane Prefecture) in western part of the mainland Japan in 2002-2009. In this region, most coral communities with relatively high coverage and species diversity occurred on hard substrates shallower than 10m at small and turbid baymouths protected from severe wave actions. Their habitats gradually shifted into two different environments with increasing latitudes; (1) shallower and sheltered areas inside small bay, and (2) deeper slopes ranging in depth from 15 to 20m near an offshore but semi-sheltered environment. Subtropical Acropora species A. hyacinthus with a tabular form and A. muricata with a branching form, and Pavona decussata with vertical plates were dominant at Kamikoshiki-jima in Koshiki-jima Islands. Coral communities near an offshore environment at Fukue-jima and Wakamatsu-jima in Goto Islands (Nagasaki Prefecture) were characterized by temperate and tabular Acropora (A. glauca, A. solitaryensis and A. japonica), whereas those in a semi-sheltered environment were dominated by temperate and branching Acropora tumida and A. pruinosa and/or encrusting to massive species such as Leptastrea pruinosa, Mycedium elephantotus and Hydnophora exesa. There occurred no tabular Acropora species at Iki and Tsushima Islands (Nagasaki Prefecture), where massive Favia spp., foliaceous to encrusting Echinophyllia spp. and Lithophyllon undulatum were dominant. Only three species (Massive to encrusting Oulastrea crispata, Alveopora japonica and Psammocora profundacella), which formed sparse populations were found at Oki Islands. The latitudinal changes in coral communities from west Kyushu to Oki Islands can be correlated well with the decrease in sea surface temperature (SST) that is also related to the warm Tsushima current, a branch of Kuroshio Current. Thus, it is important to monitor these coral communities in order to clarify changes in a coastal (shallow-water) ecosystem in this region because the increase in SST is expected in the near future as the global warming progresses.

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[in Japanese]

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[in Japanese]

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Larval recruitment plays an important role in determining the structure and dynamics of coral communities. We examined the recruitment pattern of scleractinian corals using artificial substrates at three sites of high-latitude coral communities along the coast of southwestern Shikoku, Japan. At each site, 8 or 10 settlement plate pairs were deployed for 2 months at 1to 2-month intervals for 2 years. Coral recruitment was observed on settlement plates deployed from May to September. Recruit densities were highest in July-September 2007 and June-August 2008, with 1.7 and 2.1 recruits per plate pair, respectively. Recruitment was dominated by Pocilloporidae, which accounted for 72.1% of the total recruits, while Poritidae and Acroporidae represented 12.6% and 6.0%, respectively. This was inconsistent with the coral community structure in the study area. Each taxonomic group exhibited a distinct recruitment pattern. Pocilloporidae recruited between May-July and September-November, mostly in the early half of those periods, which corresponded to times of observed larval releases in the study area. Poritidae also recruited in the same period, with no apparent peak. Acroporidae recruited over a relatively short period from July to August, which corresponded to the observed period of their spawning in the study area. Larval coral recruitment in the study area was characteristic of high-latitude coral communities in having lower settlement rates and a higher proportion of Pocilloporidae to total recruits than do Pacific coral reef communities.

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We conducted oxygen and carbon isotopic analyses for Favia coral skeletons collected from Iki island, Japan, where the northernmost coral reef in the world occurs. Two skeletal structures, theca wall and columella in the single corallite were analyzed separately and compared with metrological factors during the growth period. The result suggested that two skeletal structures formed in different timing, and the isotopic signals in theca walls could be a more faithful environmental recorder such as past sea surface temperatures and insolation. Further investigations about selective sampling for chemical analysis based on skeletal growth mechanisms should be done prior to use the high-latitude Favia corals as a paleoenvironmental proxy.

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Reef building corals in temperate region could be a powerful tool for reconstructing climatic/environmental changes such as global warming and ocean acidification. To demonstrate the possibility of high latitude corals for reconstruction of paleoenvironments, we analyzed oxygen and carbon isotopes in core specimens of living massive colony, Porites lutea, taken from Tatsukushi Bay, Kochi prefecture, Japan. Isotopic variations were compared with the coral skeletology deduced from X-ray photographs and luminescence bands. Comparing with observed sea surface temperature (SST), oxygen isotope profile showed the lack of geochemical records during low temperature. This result was corresponding with the occurrences of high density bands, low skeletal extension rate, and low calcification rate in winter. Annual averages of carbon isotopes increased from 2001 toward 2008 and coral luminescence bands observed in the period from 2001 to 2005. These results suggested that the calcification significantly decrease or cease in low temperature. Coral in this study recorded the local history of marine environments at Tatsukushi Bay caused by terrestrial inputs due to heavy rainfall event occurred in 2001. Coral isotopic compositions and skeletal structure were sensitive to response on SST changes. Future analysis using the full length of coral cores could be expected to capture both global environmental changes and local history at Tatsukushi Bay.

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Although various monitoring studies have conducted for corals in seas close to Japan since 1970’s, the outputs were compiled in different formats, and therefore, intercomparison of the results was extremely difficult. In this study, we collected numerous bulletin reports and monitoring data on coral cover (percentage of corals relative to whole substrate), developed a database in a unified format, and analyzed the database. Our study suggests that time series of coral cover is substantially different among oceanic regions close to Japan. Further analyses of controlling factors on coral cover such as the water temperature and counter-pest density using the database are anticipated to allow us to evaluate more quantitatively the influence of the stress factors on coral cover in each oceanic region.

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Global warming and associated increases in water temperature is considered to be a crucial factor for future corals, by inducing coral habitat migration toward higher latitudes and intensifying chances for coral bleaching and death. Using projected monthly-mean sea surface temperature in the 21^st century, we quantitatively evaluate the potential effects of global warming on corals in seas close to Japan. Our result shows that the temperature-determined northern limit of subtropical coral reefs, which is currently located in the southern Kyushu, is expected to migrate northward, up to the northern Kyushu, and that the northern limit of coral habitat, currently located in Niigata and Chiba Prefectures, is estimated to go up to Aomori and Iwate Prefectures, by the end of the 21^st century. In the Ryukyu Islands, on the other hand, both frequency and area of coral bleaching or death are expected to be intensified. Particularly, intermittently experienced high water temperatures which result in bleaching or death of present-day corals, will appear perpetually in the latter half of the 21^st century.

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