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Choi Y.-U.,Korea South Pacific Ocean Research Center | Park M.,Kookmin University | Lee K.-W.,Korea South Pacific Ocean Research Center | Oh C.,Global Bioresources Research Center | Park H.-S.,Korea South Pacific Ocean Research Center
Ocean Science Journal | Year: 2014

This study was conducted to investigate the reproductive characteristics of the humbug damselfish, Dascyllus aruanus, through the measurement of gonadosomatic indices (GSI) and histological examination of the gonads. Fish were collected from Chuuk Lagoon, Micronesia (7°27′N; 151°53′E), between August 2009 and July 2010. Overall, the functional sex ratio was approximately 1:1; however, there was a female bias in the smaller size range (35–40 mm standard length [SL]) and male bias in the larger size range (45–60 mm in SL). The process of oocyte development exhibited a group synchronous pattern, from the vitellogenic phase oocytes in the gonads following the two clutches of oocytes, as the primary growth stage and yolk vesicle stage. The testis with an ovarian lumen exists as a central slit, and the sperm ducts extend into the medial hilar region of the gonads, indicating that males of D. aruanus have a secondary testis of protogynous species. Monthly variations in the GSI and evolution of gonad status indicated that reproductive activity in this species occurs throughout the year in Chuuk Lagoon, Micronesia. © 2014, Korea Ocean Research & Development Institute (KORDI) and the Korean Society of Oceanography (KSO) and Springer Science+Business Media Dordrecht.

Kim T.,Korea South Pacific Ocean Research Center | Park H.-S.,Korea South Pacific Ocean Research Center
Ocean and Polar Research | Year: 2013

The coral symbiotic algae zooxanthellae is often expelled from the host as the host coral is under physiological stress, causing the coral to turn completely white. Such coral bleaching events are occurring more frequently with the increase in the global warming, ocean acidification and increased level of anthropogenic impacts such as eutrophication. In the present study, we investigated the effects of inorganic nutrients including ammonium, nitrate, phosphate and elevated water temperature on the symbiotic zooxanthellae density in the fragment of branching coral Acropora nobilis. Zooxanthellae density in the host coral decreased 8 hrs after the experiment at a given elevated water temperature (32oC, p < 0.05). In contrast, no clear coral bleaching or decrease in the symbiotic algae density was observed from the branching coral exposed to a normal water temperature of 30oC and high levels of nutrients such as 20 μM of NH4Cl, 20 μM of NaNO3 and, 10 μM KH2PO4. Accordingly, the data indicated high water temperature is one of the stressful factors to cause bleaching in A. nobilis, whereas the high levels of nutrients is not a factor. It is believed that the results obtained in the present study are useful as baseline information in the management of the coral reefs.

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