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Atsugi, Japan

Nakamura M.,Okinawa Institute of Science and Technology | Nakamura M.,Tokai University | Kumagai N.H.,Japan National Institute of Environmental Studies | Sakai K.,University of Ryukyus | And 3 more authors.
Marine Ecology Progress Series | Year: 2015

We compared spatial variability in recruitment patterns between acroporid corals and the predatory crown-of-thorns starfish Acanthaster planci along the Onna village coast of Okinawa Island, Japan. Our objective was to understand population dynamics of both predator and prey. To quantify recruitment, we established artificial recruitment plates for acroporid corals and conducted quadrat surveys for juvenile A. planci at 7 sites. We also examined distributional patterns of adult populations of both species and observed surface currents during larval dispersal periods using GPS-equipped surface drifters. Acroporid recruits typically arrived in greater numbers at more northern sites. Despite high variability, A. planci recruits displayed similar spatial patterns. Drifter trajectories suggest that these spatial recruitment patterns are probably driven by near-shore currents in the summer. Moreover, current data imply a complicated metapopulation relationship in this region, especially for A. planci, new recruits of which may mainly originate outside of the Onna area. Meta - population dynamics within the study area and among surrounding regions must be explained by the complex surface current circulation, because simpler explanations involving only the Kuroshio Current do not adequately describe the relationship between these populations. © Inter-Research 2015. Source


Okubo N.,Japan Society for the Promotion of Science | Yamamoto H.H.,Okinawa Churaumi Aquarium | Nakaya F.,Ochanomizu University | Okaji K.,Coralquest Inc.
Biological Bulletin | Year: 2010

In the late 1990s, the once prolific populations of the coral Acropora intermedia surrounding Okinawa, Japan, dramatically declined because of thermal stress, bleaching caused by heat stress, and consequent mortality. Before the bleaching event, 72 fragments (about 15 cm in length) were collected and transferred to the Okinawa Churami Aquarium. Through growth and repeated fragmentation, these original fragments developed into about 100 colonies that spawned from 1999 to 2009. In this study, we compared gametogenesis, fertilization, survival, and O2 consumption in cultured and wild colonies of A. intermedia and their offspring. Cultured A. intermedia had larger oocytes and higher fertilization and survival rates than samples from wild colonies. O2 consumption of cultured embryos was similar to that of wild embryos. These results suggest that cultured A. intermedia and their offspring are as viable as wild colonies. Aquaria can play a role in the conservation of endangered corals, and their cultured colonies could be used to re-establish devastated species on the Okinawa reefs. Source


Fabricius K.E.,Australian Institute of Marine Science | Okaji K.,Coralquest Inc. | De'ath G.,Australian Institute of Marine Science
Coral Reefs | Year: 2010

Population outbreaks of the coral-eating crown-of-thorns seastar, Acanthaster planci, continue to kill more coral on Indo-Pacific coral reefs than other disturbances, but the causes of these outbreaks have not been resolved. In this study, we combine (1) results from laboratory experiments where larvae were reared on natural phytoplankton, (2) large-scale and long-term field data of river floods, chlorophyll concentrations and A. planci outbreaks on the Great Barrier Reef (GBR), and (3) results from A. planci-coral population model simulations that investigated the relationship between the frequency of outbreaks and larval food availability. The experiments show that the odds of A. planci larvae completing development increases ~8-fold with every doubling of chlorophyll concentrations up to 3 μg l-1. Field data and the population model show that river floods and regional differences in phytoplankton availability are strongly related to spatial and temporal patterns in A. planci outbreaks on the GBR. The model also shows that, given plausible historic increases in river nutrient loads over the last 200 years, the frequency of A. planci outbreaks on the GBR has likely increased from one in 50-80 years to one every 15 years, and that current coral cover of reefs in the central GBR may be 30-40% of its potential value. This study adds new and strong empirical support to the hypothesis that primary A. planci outbreaks are predominantly controlled by phytoplankton availability. © 2010 Springer-Verlag. Source


Nakamura M.,Okinawa Institute of Science and Technology | Okaji K.,Coralquest Inc. | Higa Y.,Onna Village Fisheries Cooperative | Yamakawa E.,Okinawa Environment Science Center | Mitarai S.,Okinawa Institute of Science and Technology
Marine Biology | Year: 2014

Boom and bust dynamics are a prominent characteristic of the crown-of-thorns starfish (Acanthaster planci) populations. Outbreaking starfish populations damage coral communities extensively and then often disappear quickly. In contrast, Onna village, on the central west coast of Okinawa Island, Japan, has been experiencing chronically high population densities of A. planci for decades. In this study, we examined spatial and temporal population dynamics of A. planci along the coast of Onna village, using removal data gathered over 24 years by a local fisheries cooperative. The results demonstrate that A. planci populations along the Onna coast often experienced high densities prior to 2003 and that recently, populations have again been increasing drastically. Size-frequency distributions suggest multiple, successive recruitment, as one of the driving factors maintaining A. planci populations in this location. Moreover, within the Onna area, the timing of outbreak peaks varied among different locations, showing a northward progression. © 2014 Springer-Verlag Berlin Heidelberg. Source


Yasuda N.,Japan National Research Institute of Fisheries And Environment of Inland Sea | Ogasawara K.,Okinawa Environmental Research and Technology Center | Kajiwara K.,Miyakojima City Office | Ueno M.,Yaeyama Fishermens Association Ishigaki | And 6 more authors.
Plankton and Benthos Research | Year: 2010

Chronic outbreaks of the coral eating crown-of-thorns starfish (Acanthaster planci) have devastated coral communities throughout the Ryukyu Islands in the past four decades. Since A. planci has high fecundity and long larval duration, knowledge of reproductive timing and larval dispersal are keys to understanding mechanisms of successive recruitment and consequent outbreaks of adults. As the first step to acquiring this knowledge, we monitored water temperature and peak spawning periods using gonad observation. A total of 379 A. planci specimens were collected from May to September in 2004 at five latitudinally different locales in the Ryukyu Islands. Peak spawning, at which starfish gonads rapidly shrunk in size, was first observed in late May in Ishigaki Island, the southernmost sampling site. Then spawning time was progressively delayed with increasing latitude, ie. from mid to late June in Miyako Is., late June to mid July in Kerama Is., late July in Okinawa Is. and Amami Ohshima Is. When we started the survey in May, some A. planci had already started spawning, though not at Amami Ohshima. The peak spawning time in every locality coincided with the time when the water temperature exceeded 28°C. Accordingly, we can predict the approximate peak for spawning by monitoring water temperatures throughout the Ryukyu Islands. The information will be useful for: (1) numerical simulations predicting larval dispersal pathways by particle tracking through provision of the input parameter for the timing of larval release, (2) selecting times for larval sampling in the field in empirical early life history studies. © The Japanese Association of Benthology. Source

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