Research Institute, Meio University Nago, Okinawa, JAPAN

soken1@mail.meio-u.ac.jp

　

Sudden increase in population of the crown-of-thorns starfish (Acanthaster planci) started in 1969 at the central western coast of Okinawa Island, Japan. Since then, island wide surveys for A. planci were conducted six times, in 1972, 1976, 1984, 1987, 1992 and 1998. The starfish population first established in 1969 in the central western coast of Okinawa Island gradually spread northward and southward along the longer axis of island, and reached the eastern coast sometime before 1984. By this time, corals of the eastern coast were all devastated, with those of the western coast recovered by this time but not to the original level.

　

Corals of the eastern coast have not recovered until present. Probably due to this low coral coverage, almost no A, planci has been present in the eastern coast after 1984. Although the coral coverage remained at the intermediate level until 1987 and to the higher level at many points in 1992 in the western coast, A. planci population continuously decreased except at some scattered places where higher density was maintained. The places where higher population density was found in 1998 were those places where higher coral coverage was found in 1992, indicating that corals then stimulated A. planci to aggregate at these places.

　

　

Institute of Oceanic Research and Development, Tokai University Shimizu, Shizuoka, JAPAN

yokochi@scc.u-tokai.ac.jp

　

Outbreaks of Acanthaster planci have occurred in various parts of the Indo-Pacific region since the late 1950s. A number of control programs have been attempted, but although some small-scale control programs have been successful, no large-scale programs have been. The largest control program to date was that for the Ryukyus, where tremendous amounts of money and labor were invested, but the program was considered a failure. One of the factors that contributed to the failure of the program was the delay in its initiation; the control program started only after A. planci was observed causing heavy coral mortality, and the system for funding such projects was based on submitting proposals for the following year.

　

Advanced warning is the key factor in the success of control programs. Monitoring the recruitment of algae-eating juvenile starfish is an efficient predictor of A. planci outbreaks. The juveniles can be found by visual searches, using the feeding scars that they leave on coralline algae as a clue to their location. Individual scars are circular, and they are usually grouped or overlapping. Fresh feeding scars are white, while recent scars are greenish. The juveniles are usually found near the greenish scars. Juvenile recruitment should be monitored on reef slopes or on the floors of grooves or channels at depths of 2 to 10 m, where dead coral rubble encrusted with coralline algae is deposited. In Okinawa, the best time for monitoring is from late autumn to early winter, because at this time the juveniles are around 10 mm in diameter, and the feeding scars are sufficiently large to find visually. Subsequently, the juveniles gradually switch their diet to coral and begin to disperse.

　

When heavy recruitment of juvenile starfish occurs and an outbreak is expected, a control program should be arranged. Since A. planci reaches sexual maturity at the end of its second or third year, monitoring can provide a one- or two-year lead-time in which to arrange and institute a control program in a timely manner.

　

　

Department of Tourism, Faculty of International Studies, Meio University Nago, Okinawa, JAPAN

　

Large scale coral bleaching, extended from the Ryukyus to the southern Kyushu in Japanese water, owing to high seawater temperature occurred in 1998. In this study, the authors showed population fluctuations of Acanthaster planci before and after this bleaching event, and tried to explain the reason of these fluctuations in relation with this event. A. planci, one of the strongest coral predators, prefers to prey on Acroporidae corals. Acroporidea corals were easy to bleach and the most of them died from the bleaching. Thus, it is easy to believe that the decrease of A.planci in the year of coral bleaching is owing to the lack of Acroporidea corals as food of A. planci. The data of exterminations at the Busena Cape, however, showed decreases began at mid-June when seawater temperature began to rise, and when it was about three month before the extensive death of Acroporidea. The adult A. planci has a very narrow tolerance for temperature, and water temperature about 30℃ has a very big effect on its behavior. Therefore, one could consider the abnormally high seawater temperature started in mid-June, 1998, as the immediate cause for the sudden decrease in the number of extermination at the Busena Cape in 1998 and shortage of food for A. planci due the death of coral afterward ofbleaching as the less immediate cause.

　

Key word: Acanthaster planci, coral bleaching, population fluctuations, seawater temperature

　

　

¹Yaeyama Marine Park Research Station Taketomicho, Okinawa, JAPAN

ueno_kuroshima@hotmail.com

　

²Kushimoto Marine Park Research Station Kushimotocho, Wakayama, JAPAN

ykote@skyblue.ocn.ne.jp

　

Outbreak of crown-of-thorns starfish (COTS) had already begun in the Yaeyama Islands, the southern Ryukyus when Marine Parks Center of Japan carried out the first survey in 1972. The high-density aggregation existed at Hatoma Is. and then localized population was observed in the southeastern part of Sekisei Lagoon between Ishigaki and Iriomote Islands in 1974. COTS spread over the whole lagoon in the beginning of 1980s. After the outbreaks ended, 10 years later, the high coral coverage area was left only at the northwestern part of the lagoon. And about 1.6 million individuals of COTS were exterminated from the Yaeyama area during 1974- 1993. Yaeyama Marine Park Research Station continues to monitor distributions of COTS and coral coverage in Sekisei Lagoon once a year from 1983. During the past decade several COTS were observed in each monitoring and reef-building corals were recovering rapidly.

　

However, the result of the monitoring in 2001 show that COTS were increasing since they were seen at 9 stations (14 individuals) among the all 102 stations. These 6 stations (11 individuals) were located in the southeastern part of Sekisei Lagoon. Further more, small individuals were found in most survey sites from the results of population survey of COTS at Kuroshima Is. But the each population density was still low, and one population was almost consisted of the second years old individuals. These results may give the indication of population outbreak once more in the near future.

　

　

¹Institute of Oceanography Nha Trang, VIETNAM

　

²IUCN Hon Mun MPA pilot project Nha Trang, VIETNAM

　

Coral reefs are considered as key habitats in the shallow waters of Nha Trang bay. These reefs are biodiverse, showing strong biogeographic affinity with Indo-Pacific center of biodiversity. They play very important roles in maintaining livelihood of the communities in the islands and nearby coastal areas, and in tourist development of the city. The coral reefs of the bay are suffering impacts such as destructive fishing, overexploitation, river discharge, nutrient enrichment and uncontrolled tourism, crown of thorns starfish. Coral reef monitoring data (ReefCheck and GCRMN) collected since 1998 showed increasing trends in the density and distribution of crown of thorns starfish. They were uncommon and rare in 1998 - 1999, increasing in abundance to outbreak level in 2001 (20 individuals 400 m-2 transect, equivalent to 500 starfish ha-1). In 2002, the starfish were distributed on most reef areas of Nha Trang bay, causing significant reduction in coral cover and likely changes of coral species composition. Size structure and reproductive status of the population will be described. At present, this is only known starfish outbreak in Vietnam waters. Causes of the outbreak are not known, although overexploitation of fisheries has depleted known predators of the starfish. Provincial authorities and the MPA support expanding diver tourism and other ecotourism operations depending on the remaining corals. As part of the new MPA management program a starfish control exercise was undertaken with starfish from the outbreak population removed from the MPA. In the longer term, the strategy of marine environmental management should aim toward restoring these predator populations for ecological sustainability.