Yeon Gyu Lee

Postglacial Sea-Level Change of the Korean Southern Sea Shelf

Abstract Molluscan shells were sampled from 31 localities in the South Sea shelf (26 in the southeastern continental shelf and 5 in the southwest sea) to understand the sea-level changes and molluscan thanatocoenoses after the last glacial maximum (LGM). At the southeastern continental shelf, 13,074 shell remains were classified into 119 genera and 170 species (Bivalvia: 73 genera and 105 species; Gastropoda: 43 genera and 60 species; Scaphopoda: 3 genera and 5 species). Cluster analyses were used to group the species into 12 assemblages (Glycymeris–Ventricoloidea–Phacosoma [GVPA], Glycymeris–Paphia–Pitar [GPPA], Glycymeris–Cryptopecten [GCA], Glycymeris–Ventricoloidea–Cryptopecten [GVCA], Pecten–Pitar, Ostrea–Limopsis, Dentalium, Nuculana–Cranulilimopsis, Lucinoma–Glycymeris, Pecten–Acila–Siphonalia, Glycymeris, and Buccium), among which the Glycymeris fauna (GVPA, GPPA, GCA, GVCA) occurred at 11 stations, mainly around Tsushima Island on the South Korean shelf. Radiocarbon dates between late Pleistocene and Holocene were determined for 47 dominant and specific species, which were sampled from 24 stations of the South Sea. Fortunately, the habitats of the molluscan species were depth sensitive, allowing for the discrimination of samples into depth-limited age groups. These groups suggested that the sea level fell by about 150–160 m about 15,000 years ago (during LGM), allowing a land bridge to form between the Korean peninsula and Japan. Subsequently the sea rose approximately 60 m about 9000 years ago. Sea level remained at 50–60 m until about 4000–5000 years ago. About 3000–4000 years ago sea level rose to about 10–20 m (below present) and has remained there to the present. Glycymeris fauna were created on the southeastern shelf about 6000 years ago, whereas Arca fauna prospered in the southwestern sea area about 2000–3000 years ago when the sea level was 10–20 m below present.

Ecotoxicological evaluation of tributyltin toxicity to the equilateral venus clam, Gomphina veneriformis (Bivalvia: Veneridae)

Tributyltin (TBT) is the most common pesticide in marine and freshwater environments. To evaluate the potential ecological risk posed by TBT, we measured biological responses such as growth rate, gonad index, sex ratio, the percentage of intersex gonads, filtration rate, and gill abnormalities in the equilateral venus clam (Gomphina veneriformis). Additionally, the biochemical and molecular responses were evaluated in G. veneriformis exposed to various concentrations of TBT. The growth of G. veneriformis was significantly delayed in a dose-dependent manner after exposure to all tested TBT concentrations. After TBT was administered to G. veneriformis, the gonad index decreased and the sex balance was altered. The percentage of intersex gonads also increased significantly in treated females, whereas no intersex gonads were detected in the solvent control group. Additionally, intersex gonads were detected in male G. veneriformis specimens exposed to relatively high TBT concentrations (20 μg L⁻¹). The filtration rate was also reduced in a dose-dependent manner in TBT-exposed G. veneriformis. We also noted abnormal gill morphology in TBT-exposed G. veneriformis. Furthermore, increases in antioxidant enzyme activities were observed in TBT-exposed G. veneriformis clams, regardless of dosage. Vitellogenin gene expression also increased significantly in a dose-dependent manner in G. veneriformis exposed to TBT. These results provide valuable information regarding our understanding of the toxicology of TBT in G. veneriformis. Moreover, the responses of biological and molecular factors could be utilized as information for risk assessments and marine monitoring of TBT toxicity.

Sequential hermaphroditism in Manila clam Ruditapes philippinarum (Bivalvia: Veneridae)

The rate of sex reversal in the Manila clam Ruditapes philippinarum was 19.0%. The male to female sex reversal ratio was 21.1%, which was higher than the female to male sex reversal ratio of 12.9%. Based on our results, R. philippinarum is confirmed to be a sequential hermaphrodite.

Effect of abalone farming on sediment geochemistry in the Shallow Sea near Wando, South Korea

Wando County has grown up to 93% of the total abalone produced in South Korea since the late 1990s; however, this production has been decreasing in recent years. The objectives of this study were to understand the potential contamination risks of abalone farming and to examine the influence of intensive abalone farming on sediment quality by analyzing grain-size composition, organic matter (total organic carbon (TOC), total nitrogen (TN), total sulfur (TS)) and heavy metal content, pH, and 210Pb geochronology. The results of organic matter analysis from surface and core sediment (length: 64 cm) showed that the area around the abalone farm had oxic marine-to-brackish conditions, but that the area directly below an abalone cage (location 7) had reductive conditions, with a C/S ratio of ~2. The average TN levels in the surface and core sediments were 0.25% and 0.29%, respectively, and this was predominantly due to the use of seaweed for feed. The low sediment pH (surface, 7.23; core, 7.04), indicates that acidification of the bottom sediment has gradually increased since the initiation of abalone farming and is likely due to the continuous accumulation of uneaten feed and feces. Heavy metal pollution was not apparent based on the examination of EF and Igeo, although the excess metal flux of Ni, Pb, Cu, Co, As, and Cd increased toward surface of the sediment core. These sediment changes may be caused by the rapid accumulation (sedimentation rate: 1.45 cm/year) of sludge discharged from the abalone farm and may be controlled by tidal currents, physiography, water depth, and tidal ranges.

Effects of hypoxia caused by mussel farming on benthic foraminifera in semi-closed Gamak Bay, South Korea

Seawater monitoring and geochemical and benthic foraminiferal analysis of sediments were conducted to identify the effects of hypoxia created by a mussel farm on benthic foraminifera in a semi-closed bay. Extremely polluted reductive conditions with a high content of organic matter (OM) at >12.0% and oxygen minimum zones (OMZs) with dissolved oxygen (DO) <0.4mg∙L(-1) were formed below the mussel farm in the northwest area of Gamak Bay, and gradually diffused toward the south. Highly similar patterns of variation were observed in species diversity, abundance frequency, and benthic foraminiferal assemblage distributed from Elphidium subarcticum-Ammonia beccarii in the northwest area through E. subarcticum-A. beccarii-Trochammina hadai, E. subarcticum-A. beccarii-Elphidiumclavatum, and E. clavatum-Ammonia ketienziensis in the southern area. These phenomena were caused by hydrodynamics in the current water mass. It was thought that E. subarcticum is a bioindicator of organic pollution caused by the mussel farm.

Effects of Heavy Rainfall on Sedimentation in the Tidal Salt Marsh of Suncheon Bay, South Korea

ABSTRACT Lee, Y.G.; Kim, S.; Jeong, D.U.; Kim, J.K., and Woo, H.J., 2013. Effects of heavy rainfall on sedimentation in the tidal salt marsh of Suncheon Bay, South Korea. Tide observations, geographic surveys, sediment composition, and sediment accretion rate monitoring were conducted to investigate the relationship between general pattern changes and control factors of the accretion rate at 10 localities of the tidal salt marsh of Suncheon Bay over 2 years (June 2007–May 2009). The substrate sediments of the tidal salt marshes that are distributed between the mean sea level and the high water of ordinary spring tide are mainly composed of silt (37.98%) and clay (60.45%) and have a high average annual accretion rate of 28.88 mm/y. The high substrate sedimentation of tidal salt marshes is caused by: (1) a high concentrated suspended sediment supply from the tidal flat; (2) considerable marsh grass vegetation; (3) undeveloped tidal salt marsh creek; and (4) marsh elevation distributed between the mean sea level and the high water of ordinary spring tide. The variation in patterns of the average monthly accretion rate can be divided into three stages: the low stage (June 2007 to February 2008) was the period of lowest accretion rate over 2 years and consistently measured between 5.35 mm and 12.40 mm, averaging out to 8.89 mm that period. The recovery stage (March 2008 to October 2008) was a period of rapid increase in accretion rate and measured from 14.93 mm to 49.47 mm with an average of 33.02 mm. The high stage (November 2008 to May 2009) was a period of high deposition in accretion rate, and measured between 46.67 mm and 53.38 mm, averaging to 49.83 mm. These three stages were formed and changed by heavy rainfall brought about by typhoons in the summer season of Korea and undeveloped tidal salt-marsh creek system. It was confirmed that heavy rainfall may significantly alter the sediment flux within the marsh system in this study.

Microanatomy and ultrastructure of the foot of the infaunal bivalve Tegillarca granosa (Bivalvia: Arcidae)

In this study, the morphology and ultrastructure of the foot of Tegillarca granosa was compared with the bivalves from different habitats. The sediment of habitat of T. granosa is mostly a mixture of sand (68.93%) and mud (24.12%). The foot is wedge-shaped with multiple projections on the surface and covered with ciliary tufts. The epithelial layer is simple and composed of ciliated columnar epithelia and mucous cells. Although the mucous cells are distributed mostly in the epithelial layer, they are developed even in the connective tissues and muscle layers, and the mucous cells mostly contain acidic carboxylated mucosubstances. From the TEM observation, secretory cells are classified into three types. Type A secretory cell has a goblet form and is most widely distributed among the three types. Type B secretory cell has an oval form and the secretory granule has fibrous substance. Type C secretory cell has an elongated elliptic form and membrane-bounded secretory granules. The muscle fiber bundles are composed mainly of smooth muscle fibers. The smooth muscle fibers can be divided into two types. Type A muscle fibers have evenly distributed thick microfilaments between the thin microfilaments of cytoplasm. Type B muscle fiber has cluster of condensed microfilaments in the medulla cytoplasm while the cortical cytoplasm has loose distribution of thin microfilaments.

Effect of abalone farming on seawater movement and benthic foraminiferal assemblage of Zostera marina in the inner bay of Wando, South Korea

Tidal current survey as well as geochemical and benthic foraminiferal analyses of sediment cores were conducted in an abalone farm and a Zostera bed to understand the degree to which the abalone farm facilities installed along a channel in a shallow sea affect the benthic environment and ecology. In the abalone farm, Ammonia beccarii-Pseudoparrella naraensis-Elphidium somaense-Rosalina globularis-Trochammina hadai and P. naraensis-E. somaense-A. beccarii-T. hadai assemblages appeared owing to an increase in the total nitrogen content from the biodeposits. The Zostera bed consisted of A. beccarii-P. naraensis-Buccella frigida-T. hadai assemblage owing to the gradual expansion of a brackish shallow-water environment by the rapidly decreasing current speed, and it may have flourished. Moreover, the total sulfur, Zn, Cr, and Cu contents in the sediments decreased remarkably more than those of the pre-abalone farming did, caused by the vigorous activity of Zostera marina physiology.

Gonadal Development and Reproductive Cycle of Cultured Abalone, Haliotis discus hannai (Gastropoda: Haliotidae) in Korea: Implications for Seed Production

ABSTRACT The objective of this study was to examine gonad development and reproductive cycle of the abalone Haliotis discus hannai at three main abalone aquaculture farms (Uljin, Wando, and Jeju Island) in Korea to obtain information on artificial seed production. The sex ratio (female:male) was approximately 1:1 without significant difference among the three regions or between females and males. Average gonad index was the highest during July in Uljin and Jeju Island and during August in Wando. There was no definitive seasonal change in condition index and meat weight index throughout the year in the three regions. The gonad of H. discus hannai displayed seasonal change histologically, thereby enabling us to distinguish the following stages: inactive (November–December), early active (January–March), late active (March–April), ripe (May–July), spent (August–October), and degenerative (October–November). The main spawning period of H. discus hannai was determined to be during September–October in Uljin and Wando, and August–September in Jeju Island.

Implication of salt marsh foraminiferal assemblages in Suncheon Bay, South Korea

Analyses of the compositions of benthic foraminifera and sediment, observations of tidal level and salinity, and a geographic survey of the tidal salt marsh in Suncheon Bay were conducted to examine the vertical distribution of foraminifera and evaluate their potential use for sea level studies. The salt marsh is composed mainly of fine-grained silty clay sediment and its salinity is below approximately 11 psu. The tidal current flows in the southwest-tonortheast direction with an average velocity of 26.57 cm/s. A total of 33 species of foraminifera (17 agglutinated and 16 calcareoushyaline) belonging to 24 genera was identified. The species diversity (1.1 on average) was relatively low. Dominant species were Ammonia beccarii, Miliammina fusca, Haplophragmoides wilberti, and Jadammina macrescens. Calcareous foraminifera (29.5%) were dominantly represented by the Ammonia beccarii assemblage, which characterized the region between mean tide level and mean low high water (MLHW). Agglutinated species (70.5%) were represented mostly by Miliammina fusca, Miliammina fusca-Haplophragmoides wilberti, and Haplophragmoides wilberti assemblages, which characterized the MLHW–mean high water (MHW), MHW–mean highest high water (MHHW), and MHHW–Approx. highest high water tide levels, respectively. In particular, the Haplophragmoides wilberti assemblage is believed to represent the highest elevation zone of foraminifera in the salt marshes of Suncheon Bay and is considered to be a reliable indicator of sea level as a result of its narrow vertical range.