• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.12 no.3
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• pp.125-132
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• 2007

We estimated the distribution of predator-prey interaction strengths for 12 species of herbivores (including amphipods, isopods, gastropods, and sea urchins) and made a regression model that may be applicable to other species. Laboratory experiments were used to determine per capita grazing rate (PCGR; g seaweeds/individual/day). Relationship between the biomass of individual grazers and fourth-root transformed PCGR was fitted to power curve ($y=0.2310x^{0.3290}$, r=0.8864). This finding supported that the grazing efficiency was not even as individual grazers increase in size (biomass). Therefore, the biomass-normalized PCGR was estimated and revealed that smaller size herbivores were more effective grazers. Grazing impact considering density of each taxon was calculated. The sea hare Aplysia kurodai had greatest grazing impact on the seaweed bed and the sea urchin Strongylocentrotus nudus and S. intermedius were ranked in descending order of the impact. The amount of seaweed grazed by the amphipod Elasmopus sp. (>4,000 $ind./m^2$) and Jassa falcata (>2,000 $ind./m^2$) were 3.435 and $1.697mg/m^2/day$ respectively. The combined grazing amount of herbivores was $5,045mg/m^2/day$ in the seaweed bed. Although sea hare and sea urchin had strong impacts on seaweeds, the effects of dense, smaller species could not be seen as negligible. Surprisingly, the calculated grazing potential of sea urchins with a mean density of 3 $ind./m^2$ exceeded the mean production of seaweed cultured in domestic coastal waters in Korea (ca., 5 ton/ha). Small crustaceans were also expected to consume up to 16% of the seaweed production if their densities were rising under weak predation conditions. Considering that the population density of herbivores are strongly controlled by fish, human interference like overfishing may have strong negative effects on persistence of seaweeds communities.

• ALGAE
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• v.30 no.2
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• pp.139-146
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• 2015

Urchin barrens have been a major issue of rocky coastal ecosystems in temperate regions. In South Korea, the east coast and Jeju Island have especially been a focus because the area of barren ground increases in spite of continual efforts to install artificial reefs. This study approached the urchin barrens issue in South Korea, by focusing on a correlational analysis of urchin and macroalgal abundance. Urchin density and algal species coverage were obtained using a quadrat image analysis. Subtidal sites were then classified into three groups according to the average densities of urchins to evaluate the characterization of the macroalgal community: no urchin (NU) zone; transition (TR) zone, $4inds.\;m^{-2};$ and urchin (UR) zone, ${\geq}8inds.\;m^{-2}$. The average urchin density in the study site was $4.7inds.\;m^{-2}$ and 57 macroalgal species were found in the study site. From the NU zone to UR zone, total species number, species diversity index and evenness gradually decreased, whereas the dominance index increased. The algae species with negative correlations were Grateloupia divaricata, Polysiphonia morrowii, Chondracanthus intermedius, Delesseria violacea, Desmarestia viridis; and those with positive correlations were the crustose corallines, Sargassum horneri. Other species were not significantly correlated with urchin density. The significant correlations indicate that the abundance of some macroalgal species is proportionally regulated by sea urchin density. This study also shows how macroalgal vegetation changes in response to an urchin's density gradient in a natural condition; and there is a TR zone that existed with respect to an intermediate level of algal abundance.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.13 no.8
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• pp.3785-3791
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• 2012

Dissolved oxygen is one of the most important factors controlling growth in aquatic organisms. Hypoxia is generally defined as dissolved oxygen less than 2.8 mg $O_2/L$ (equivalent to 2 mL $O_2/L$ or 91.4 mM). Therefore, hypoxia zone can cause a serious problem in marine ecosystem. In this study, to investigate embryotoxic (fertilization and embryo development rates) effects of hypoxia on sea urchin Strongylocentrotus nudus were exposed to dissolved oxygen levels of 7.6 mg $O_2/L$ (normoxia) and 1.8 mg $O_2/L$ (hypoxia) for 2 days at $15^{\circ}C$ and 33 ‰. Also, Expression levels of stress related gene (HSP70) and antioxidant related gene (glutathione reductase) in the sea urchins exposed to hypoxia were confirmed by Immunoblotting and RT-PCR analysis. In results, we showed that developmental rates were dramatically reduced in hypoxia condition. Molecular analysis demonstrated that higher HSP70 (5.5 fold) and glutathione reductase gene (2.79 fold) were present in the sea urchin exposed to hypoxia. Our results suggested that hypoxia can cause the abnormal development and elicits a stress and antioxidant response on sea urchin.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.45 no.3
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• pp.262-270
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• 2012

Seaweeds provide habitats in which marine animals can spawn and develop, and serve as a food supply for algaegrazing species such as sea urchins and abalone. Recently, seaweed species have disappeared from coastal ecosystems, leaving barren ground, defined as habitats that have lost their algae forests and where coralline algae containing calcium carbonate components have become encrusted on rocks. The biological causes of barren ground include grazing by herbivores and excessive seaweed harvest. The environmental harm caused by the spread of barren ground includes accelerated eutrophication following the reduction in seaweed, which plays an important role in oceanic purification. In the present study, we identified the relationships between various seaweed species and the occurrence of barren ground. Subtidal benthic macroalgal flora and community structure were observed seasonally on barren ground along vertical transects of rocky shores of Bihwa, Samchuck, and the east coast of Korea from February to November 2006. Fifty-eight seaweed species were identified, including 7 green, 15 brown, and 36 red algae species. There were between 6 and 28 species among seasons. Over the whole study period, average seaweed biomass (g wet wt $m^{-2}$) was 241.90 g, with a seasonal range of 25.26 to 760.34 g. Seaweed biomass declined with increasing seawater depth and ranged between 91.26 and 422.08 g. The vertical distribution of algae was characterized by Undaria pinnatifida and Sargassum honeri at 5 m, S. honeri and U. pinnatifida at 10 m, and U. pinnatifida and Agarum clathratum at 15 m depth. Seasonal patterns in community indices were not found. Community indices showed different patterns along vertical shoreline gradients; the dominance index increased but the richness, evenness, and diversity indices decreased with seawater depth. Sea urchin density was 8 to 24 individ. $m^{-2}$ in Bihwa. These urchin populations had significantly aggregated spatial patterns and recurrent destructive grazing appeared to be occurring.

• Proceedings of the Materials Research Society of Korea Conference
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• 2009.11a
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• pp.33.1-33.1
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• 2009

To date, nanostructured tungsten oxides with a variety of stoichiometries, such as WO3, WO2.9, W18O49, and WO2, have been prepared, because they are promising candidates for applications such as gas sensors, photocatalysts, electrochromic devices, and field emission devices. Among them, W18O49 and WO2 have been widely studied due to their outstanding chemical sensing, catalytic, and electron emissive properties. Here we report, for the first time, a one-pot solution-phase route to synthesizing a novel composite hierarchical hollow structure without adding catalysts, surfactants, or templates. The products, consisting of a WO2 hollow core sphere surrounded by a W18O49 nanorod shell (yielding a sea urchin-like structure), were generated as discrete structures via Ostwald ripening. To our knowledge, this type of composite hierarchical core/shell structure has not been reported previously. The morphological evolution and the detailed growth mechanism were carefully studied. We also demonstrate that the size of the hollow urchins is readily tunable by controlling the reactant concentrations.Interestingly, although bulk tungsten oxides are weakly paramagnetic or diamagnetic, the as-prepared products show unusual ferromagnetic behavior atroom temperature. The urchin structures also show a very high Brunauer-Emmet-Teller (BET) surface area, suggesting that they may potentially be applied to chemical sensor or effective catalyst technologies.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.44 no.4
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• pp.397-402
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• 2011

We surveyed the bycatch and discard of the shrimp-pot fishery in Hokkaido, Japan, three times during the major fishing period in September 2005. The surveyed catches were analyzed to separate bycatch, discard, and landings. To analyze bycatch and discard, we randomly selected 2 shrimp pots from each of 7 sets, for a total of 14 pots per survey. The total bycatch and discards from the rest of the shrimp pots were also analyzed in each survey. The total catch averaged 12 species. Coonstripe and pink shrimp catches averaged 74.7 kg/haul and 12.7 kg/haul, respectively. The weight of the bycatch averaged 33.4 kg/haul. The bycatch consisted mainly of snail fishes(5.1%), brittle stars(5.0%), and short-spined sea urchins(4.1%). Our analysis showed that the ratio of discard was 0.38, the rate of the discard was 27.4%, and the discard per unit effort was 33.4 kg/haul. The Hokkaido shrimp-pot fishermen discarded all of the bycatch except shrimps. Hence, the weight of the bycatch was equal to the weight of the discard. Our results comprise preliminary data that can be used to find ways to reduce bycatch and discard in the shrimp-pot fishery.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.18 no.4
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• pp.363-368
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• 1985

Tagged and untagged sea urchins, Hemicentrotus pulcherrimus (A. Agassiz) were reared for 84 days in the laboratory, Vinyl tape and trapall paper were used as tag materials. The natural mortality, mortality by predation and shedding rate of tags of the tagged groups were examined, and the results were compared with those of untagged control group. The results of Chi-square test of natural mortality between tagged and control groups were very significative, however, the comparison between the two tagged groups was insignificative. No effect of tag attachment seems to be present at the point of natural predation by starfish, and $x^2-test$ between two the tagged groups on the loss rate of tags showed also insignificance. The mortality shortly after tagging seems to be negligible, and the distinct decreasing effect on growth due to tag attachment was not revealed because of insufficient individuals and rearing periods.

• The Korean Journal of Malacology
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• v.22 no.2
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• pp.167-173
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• 2006

The embryos of marine bivalves have been commonly used in bioassays for quality assessments of marine environments. Although several standard protocols for the developmental bioassay of bivalves have been proposed, only a few trials for application of these protocols in environmental assessments or for the development of a new protocol with Korean species have been conducted. As such, there is a strong need to establish standard bioassay protocols with bivalves commonly found in Korean waters. To determine the sensitivity of Mytilus galloprovincialis to establish a standard bioassay, their fertilized eggs were exposed to six metals (Ag, Cd, Cr, Cu, Ni, and Zn). The order of biological impact was Ag > Cu > Ni > Zn > Cr > Cd and their lowest observed effective concentration were 5, 16.4, 25.4, 142, 187 and 1,500${\mu}g/l$, respectively. The proportion of normal larvae appeared to decrease linearly with the logarithm of each toxicant concentration within the tested range. The average values of median effective concentrations $(EC_{50})$ from the triplicate experiments for Ag, Cd, Cr, Cu, Ni, and Zn were 6.8, 1,797, 786, 16.6, 68.1, and 139.2${\mu}g/l$, respectively. There was a more than 100-fold difference in $EC_{50}$ values of Cu and Cd. The value of $EC_{50}$ or median lethal concentration of Cu was within the range observed for other bivalve developmental bioassays. The overall sensitivity of M. galloprovincialis in the present developmental bioassay was also similar to that of other marine organisms commonly used in aquatic bioassays (e.g. sea urchins, oysters). Hence, the bioassay using the embryo of M. galloprovincialis is considered to be a useful tool to monitor and evaluate the quality of marine aquatic environments.

• Journal of the Korean Society for Marine Environment & Energy
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• v.9 no.4
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• pp.243-252
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• 2006

Influence of the increasing carbon dioxide concentration in seawater on various marine organisms is assessed in this article with regard to the impacts of anthropogenic $CO_2$ introduced into surface or deep oceans. Recent proposals to sequester $CO_2$ in deep oceans arouse the concerns of adverse effects of increased $CO_2$ concentration on deep-sea organisms. Atmospheric introduction of $CO_2$ into the ocean can also acidify the surface water, thereby the population of some sensitive organisms including coral reefs, cocolithophorids and sea urchins will be reduced considerably in near future (e.g. in 2100 unless the increasing trend of $CO_2$ emission is actively regulated). We exposed bioluminescent bacteria and benthic amphipods to varying concentrations of $CO_2$ and also pH for a short period. The ${\sim}l.5$ unit decrease of pH adversely affected test organisms. However, amphipods were not influenced by decreasing pH when HCl was used for the seawater acidification. In this article, we reviewed the biological adverse effects of $CO_2$ on various marine organisms studied so for. Theses results will be useful to predict the potential risks of the increase of $CO_2$ concentrations in seawater due to the increase of atmospheric $CO_2$ emission and/or sequestration of $CO_2$ in deep oceans.

• Journal of Aquaculture
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• v.13 no.2
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• pp.129-135
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• 2000

Genetic variabilities of local populations of Anthocidaris crassispina and Hemicentrotus pulcherrimus were analysed by random amplified polymorphic DNA (RAPD) technique with phenotypic variabilities in timing of gonadal maturation, reproductive output and size of individuals in Cheju. H, pulcherrimus, collected from 4 locations during March 1997, indicated that Daepo individuals were significantly smaller than that at Hamdok, Wimi site A and Wimi site B (ANOVA, p>0.001). Gonodal-somatic index (GSI) of the Wimi site B population was significantly higher than that of three other locations (ANOVA, P>0.0001). An ANOVA test conducted on test size of A. crassispina, harvested from six different locations of Cheju during June 1997, indicated that the size of individuals from Pophwan was significantly smaller (P>0.0001) than that from five other locations. GSIs of urchin m Wimi and Hanlim were significantly higher than that from Pohwan and Oedo (ANOVA, p>0.0001). Genetic similarity, calculated from k13 primer analysis of total DNA, among the six different populations of A. crassispina varied from 0.67 to 0.92, and the values for H. pulcherrimus from 0.60 to 0.73; thus there was no genetic variation among different populations of the same species. Therefore, the populations are genetically homologous and the observed phenotypic variabilities were possibly associated with water temperature and food.