• ALGAE
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• v.19 no.3
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• pp.201-205
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• 2004

An ectoparasitic din flagellate infesting plank tonic chaetognath, Sagitta crassa Tokioka was found, for the first time, from Korean coasts. In order to identify the species, we investigated detailed morphology of the din flagellate using Nomarski interference optics as well as epifluorescent microscopes. The parasitic din flagellate consists of an oval to rod-shaped cell with a peduncle, by which the organism attaches to the host. The cell is covered with polygonal thecal plates. The nucleus displays two different shapes according to cell cycle stages: in young trophont the nucleus is elongated and shows typical din flagellate nucleus (dinokaryon), while in matured trophont, the nucleus is dome-shaped and non-dinokaryotic. The peduncle is variable in length and is ornamented with the longitudinal striations. All these characteristics point to identity that the ectoparasitic din flagellate infecting Sagitta crassa in Korean coasts is Oodinium inlandicum Horiguchi et Ohtsuka, originally described from the Seto Inland Sea of Japan. Relationship between prevalence and host sizes differed from those in Japan.

• Ocean and Polar Research
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• v.38 no.1
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• pp.35-46
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• 2016

To understand the diet of chaetognaths, the gut content and fatty acid trophic makers (FATMs) of Sagitta crassa and S. nagae, which are the most predominant species of chaetognath in the Yellow Sea, were analyzed. Gut contents of the two species examined by microscopic analysis revealed that copepods are the major components of the diet (> 70% of gut contents) and there was no significant changes in the gut contents of two species collected in spring and summer season. Although 16:0, 20:5(n-3) (Eicosapentaenoic acid) and 22:6(n-3) (Docosahexanoic acid), which are known as phytoplankton FA markers, were the most dominant among the fatty acids in both chaetognath species, the detection of copepod FA markers, 20:1(n-9) (Gadoleic acid) and 22:1(n-11) (Cetoleic acid), provided evidence that their food sources include copepods. These results suggest that S. crassa and S. nagae are carnivores and mainly feed on copepods in the Yellow Sea.

• Journal of the korean society of oceanography
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• v.38 no.4
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• pp.211-215
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• 2003

A huge freshwater reservoir (ca. 12,000 ha) will be created when the construction of a 33­km dike on a huge mud flat of the Saemankeum areas is established. A large quantity of freshwater will emerge to the adjacent sea from the reservoir through two big gates. Marine organisms outside the dike are expected to frequently experience low salinity waters. To investigate the salinity effects on the dominant metazooplankton in the coastal waters off Saemankeum areas, we measured the survival (Survival 1H and Survival 24H) of 11 different taxa (the copepods Acartia omorii, A. pacifica, Calanus sinicus, Centropages abdominalis, Paracalanus indicus, Pseudodiaptomus inopinus, Tortanus forcipatus, and a hydromedusa, and barnacle nauplius, polychaeta larva, and a chaetognath Sagitta sp.) at salinities of 0, 5, 10, 15, 20, 25, 30, 35, and 40 psu when the organisms were exposed for 1 and 24 h, respectively. Survival 1Hs of P. inopinus and barnacle nauplius were 100% between 5 and 35 psu, while they were 0% at salinities of 0 and 40 psu. Survival 1Hs of A. omorii and A. pacifica, P. indicus, T. forcipatus, and polychaeta larva were 100% at $salinities\;\geq\;10$ psu, while they were 0% at lower salinities. Survival 1Hs of a hydromedusa and Sagitta sp. were 100% at $salinities\;\geq\;15$ psu, while they were 0% at lower salinities. Survival 1H of C. abdominalis and C. sinicus was 100% at $salinities\;\geq\;20$ psu, while they were 0% at lower salinities. Survival 24Hs of A. omorii, A. pacifica, C. abdominalis, barnacle nauplius, and polychaeta larva were the same as Survival 1 Hs at the same salinity, while those of the other metazooplankton were lower than Survival 1Hs. The results of the present study suggest that low salinity water emerging from big gates may cause the death of the metazooplankton, but the salinities at which death of the metazooplankton occurs may differ by species.

• Journal of the Korean Society of Marine Environment & Safety
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• v.26 no.5
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• pp.493-505
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• 2020

Food web structures in the lower trophic levels of the seas around the Korean peninsula were investigated in August 2019 using stable isotopes. There were variable ratios of the carbon (-26.18 ~ -20.61 ‰) and nitrogen stable (5.36 ~ 15.20 ‰) isotopes in the particulate organic matter (POM). Most of the organisms ingested micro-POM as a major food source, but this varied spatially. The chaetognaths (3.40 ± 0.61) occupied the highest trophic level. The isotope mixing model showed that the proportions (13 ~ 51 %) of some organisms (i.e., copepods and euphausiids) reflected the relative contributions as major food sources for chaetognaths at each site.