Ok Hwan Yu

The first record of two demersal calanoid copepods, Pseudodiaptomus poplesia and P. nihonkaiensis in Korea, with remarks on morphology of the genital area

The demersal calanoid copepods Pseudodiaptomus nihonkaiensis Hirakawa, 1983 and P. poplesia (Shen, 1955) are redescribed from Korean waters. Using scanning electron microscopy, we examine the morphology of the female genital systems of four species of Pseudodiaptomus (P. inopinus, P. marinus, P. nihonkaiensis and P. poplesia), revealing interspecific differences. The zoogeography of these four species is discussed.

LIFE HISTORY AND REPRODUCTION OF JASSA SLATTERYI (AMPHIPODA, ISCHYROCERIDAE) ON A SEAGRASS BED (ZOSTERA MARINA L.) IN SOUTHERN KOREA

Abstract The life history and reproduction of the amphipod Jassa slatteryi were investigated monthly for one year on a seagrass bed (Zostera marina L.) in Gwangyang Bay, southern Korea. The standing crop of seagrass showed two peaks in spring and fall. Population dynamics of J. slatteryi was closely correlated with the standing crop of seagrass, suggesting that there is biological interaction between these two species. The life-history pattern was annual and iteroparous with two principal periods of juvenile recruitment during the year; in spring (March to May) and fall (October to December). Overall sex ratio was female-biased. The mean body length of adults and brood size was larger in the spring breeding period than in the fall. There was a positive relationship between the brood size and body length of ovigerous females. The mean egg volume was more than 0.03 mm3 in fall breeding periods, but in other periods it was less than 0.03 mm3. Egg volume was positively related to body length of ovigerous females. At any given female size, egg volume was significantly higher in the fall than in the spring, whereas brood size in the spring was significantly larger than that in the fall. The reproductive output of females was much greater in the fall than that in the spring, suggesting higher reproductive effort during the fall breeding period.

Influence of Environmental Variables on the Distribution of Macrobenthos in the Han River Estuary, Korea

We compared environmental effects on the macrobenthic community of the Han River Estuary in summer, when freshwater input from the Han River increased, and in spring, when freshwater input decreased. Field samples were taken from the upper region of the Shingok reservoir to the southern area of Ganghwado at 18 sampling sites after rainy (August 2006) and dry (March 2007) seasons. Macrobenthic fauna were collected using a Van Veen Grab (0.025 m2 and 0.1 m2) and environmental factors were measured simultaneously. Dominant species of macrobenthic fauna and the macrobenthic community were divided into two areas, the area of the Han River with no salinity (< 0.1 psu) and the southern part of Ganghwado with salinity (> 20 psu). The dominant species Byblis japonicus appeared at Junruri in the dry season. The distributions of two polychaetes, Hediste japonica and Nephtys caeca, were divided into the lower and upper areas of the Singok submerged weir. BIO-ENV (the matching of biotic to environmental patterns) analysis revealed that salinity was the most important factor affecting macrobenthic communities in the Han River Estuary, with other factors such as sediment grain size, bottom dissolved oxygen, and total organic carbon of sediment being secondary.

Interactive Effects of Increased Temperature and pCO 2 Concentration on the Growth of a Brown Algae Ecklonia cava in the Sporophyte and Gametophyte Stages

To examine the effects of increased CO₂ concentration and seawater temperature on the photosynthesis and growth of forest forming Ecklonia cava (Laminariales, Phaeophyta), sporophytic discs and gametophytes were cultured under three pCO₂ concentrations (380, 750, 1000 ppm), four temperatures (5, 10, 15, 20℃ for sporophytes; 10, 15, 20, 25℃ for gametophytes), and two irradiance levels (40, 80 μmol photons m ?2 s ?1 ) for 5 days. Photosynthetic parameter values (ETR max , E k , and α) were generally higher as sporophytic discs were grown under low temperature and increased CO₂ concentration at 750 ppm. However, photosynthesis of Ecklonia sporophytes was severely inhibited under a combination of high temperature (20℃) and 1000 ppm CO₂ concentration at the two photon irradiance levels. The growth of gametophytes was maximal at the combination of 380 ppm (present seawater CO₂ concentration) and 25℃. Minimal growth of gametophytes occurred at enriched pCO₂ concentration levels (750, 1000 ppm) and high temperature of 25℃. The present results imply that climate change which is increasing seawater temperature and pCO₂ concentration might diminish Ecklonia cava kelp beds because of a reduction in recruitments caused by the growth inhibition of gametophytes at high pCO₂ concentration. In addition, the effects of increased temperature and pCO₂ concentration were different between generations - revealing an enhancement in the photosynthesis of sporophytes and a reduction in the growth of gametophytes.

Two new species of the deep-sea genus Neotanais Beddard, 1886 (Tanaidacea: Neotanaididae) from the eastern central Pacific

We describe two new species of deep-water neotanaids collected from the Korea Deep Ocean Study (KODOS) Area in the eastern central Pacific. Neotanais pacificus is distinguished from other species of Neotanais by the following morphological combination: in the female: 1) pereiomere 5 is the longest of the pereiomeres, 2) distal claw of the cheliped fixed finger bulges outward, and the cutting edge descends steeply, 3) the uropod exopod is much longer than first endopodal article, 4) the setal row of the left mandible has bi-serrated setae and plumose seta, 5) the maxilliped endite bears three bipinnate spiniform setae on the inner posterior margin and medially expanded plumose seta on the distal margin, and 6) the propodi of pereipods 1 to 3 bear thick bi-pinnate spiniform setae. The female of N. capillus distinctly differs from other species of Neotanais by the following morphological combination: 1) pereiomeres 4 and 5 are longer than wide, 2) the pleomeres are without midventral spurs, 3) the pleotelson bears fine setules along the distal margin, 4) the maxilliped endite has a very long plumose seta on the distal outer corner and two bipinnate spiniform setae on inner posterior margin, 5) the propodi of pereiopods 1 to 6 have thick bipinnate spiniform setae, and 6) the uropod is shorter than the pleon. In this study, distinct morphological characters differentiating the N. pacificus and N. capillus from other species of Neotanais are given on the basis of detailed descriptions.

Reproductive pattern of the epifaunal amphipodPontogeneia rostrata (Crustacea) on dolsando sandy shore in Korea

Reproductive patterns of an epifaunal amphipod,Pontogeneia rostrata, were studied on Dolsando sandy shore in Korea. The life history pattern was iteroparous, with recruitment mainly occurring from winter to spring. The sex ratio was male-biased, especially during breeding periods. The mean body length of females was significantly larger than that of males. Brood size and egg volume were positively related to the body length of ovigerous females. There was no significant difference in brood size between successive breeding periods, but egg volumes were significantly higher in early winter (December) than in late spring breeding (May and June), increasing the probability of survival to hatching. These traits contribute to more reproductive potential in early winter than in late spring breeding. The mean brood size of epifaunalP. rostrata was larger but the mean egg volume smaller than that of infaunal amphipods in this sampling area. We suggest that reproductive effort for epifaunal species may be proportionally greater than for infaunal species in risky environments.

Spatiotemporal Distribution of Macrobenthic Communities in the Coastal Area of Uljin and Its Relation to Environmental Variables

Although thermal effluent from coastal power plants affects marine ecosystems, few studies have examined the spatiotemporal distribution of macrobenthic communities in a coastal area of Korea with thermal discharge. This study analyzed the species composition and abundance of a macrobenthic community in relation to environmental variables for a period of 1 year. In total 334 macrobenthic faunal species were collected; the mean density was 3,221 ind/㎡. The number of species and the density of macrobenthic fauna increased with distance from the thermal discharge site. Cluster analysis indicated that the macrobenthic community could be divided into two groups: group I in shallow (＞ 30 m deep) and group II in the outer areas (＞ 30 m deep). Group I showed the lowest species density and diversity. Four polychaetes, including Magelona japonica, Spiophanes bombyx, Scolotoma longifolia and Chaetozone setosa, all of which have been dominant species since 1987, exhibited higher mean densities in the area distant from the thermal discharge (the outer and north areas). Conversely, the warm-adapted and opportunistic species, such as the amphipods Urothoe convexa and Mandibulophoxus mai, the bivalve Felaniella sowerbyi, and the polychaete Rhynchospio sp., were more abundant in the thermal discharge region. The results of this study indicate that thermal effluent influences macrobenthic communities in the shallow area, while other environmental variables, such as depth, sediment grain size, and TOC, are more important determinants of the macrobenthic communities in deeper regions (＞ 30 m deep).

Characterization of Deep-sea Macrofauna in the Korean Exploration Claim Area in the Clarion-Clipperton Fracture Zone, Northeastern Pacific Ocean

Macrofauna in the Clarion-Clipperton Fracture Zone remain poorly understood, due both to gross undersampling and to the fact that most species collected from the area are new to science. Evaluation of the diversity and species distribution of the benthic fauna in this area is critical to predicting and managing the impacts of manganese nodule mining. In this study, we investigated the distribution of macrofauna to understand the natural variability in the macrobenthic community and, by extension, to establish a baseline for environmental risk assessment. Samples were collected from the KR5 block of the Korea Contract Area, within the abyssal area of the Clarion-Clipperton Fracture Zone in the northeastern Pacific Ocean, by the RV Onnuri from 2012–2014. A total of 36 core samples were examined in the survey, from which we identified 183 macrobenthic species in 25 faunal groups with a mean density of 257 ind/m2. Not taking into account meio-faunal groups such as nematodes and harpacticoid copepods, the highest percentage of individuals was represented by Arthropoda. The dominant species (> 1% of total density) were the tanaids Typhlotanais sp.1, and Akanthophoreus spp. and Stenotanais sp., the isopod Macrostylis sp.1, and the polychaetes Cirratulidae spp. and Levinsenia uncinata. The abundances of the two dominant species, the tanaid Typhlotanais sp1. and isopod Macrostylis sp.1., were positively correlated with total organic carbon (TOC). There were no differences in macrofaunal density and community structure between preserved areas (PRA), the potential benthic impacted site (BIS), and other areas near the BIS. In general, higher diversity was associated with homogeneous environmental conditions, with high nodule coverage (> 50%) and TOC.

Community Structure of Macrobenthos around the Thermal Discharge Area of the Uljin Nuclear Power Plant in the East Sea, Korea

This study analyzed the community structure of macrobenthic organisms in the subtidal area suffering under the influence of thermal discharge from the Uljin nuclear power plant during 2012-2013 and reviewed the temporal change in the faunal composition of the macrobenthic community using data from p...

Erratum to: Effects of environmental and biological conditions on the recruitment and growth of the Manila Clam Ruditapes philippinarum on the West Coast of Korea

The distribution of the Manila clam Ruditapes philippinarum, which is often dominant in intertidal zones, is influenced by both environmental and biological conditions. However, there have been few comprehensive studies on the interactive effects of these two groups of factors. The present study examined the environmental and biological parameters determining the population dynamics of the clams that is a dominant component of the intertidal communities of Euhangri and Padori on the west coast of Korean peninsula. We collected R. philippinarum and other members of the macrobenthos (> 1 mm long) monthly from 0.25 m2 quadrats deployed in the intertidal zones at Euhangri, Taean, and Padori during the period from August 2013 to January 2015. Physicochemical parameters of the water and sediment were measured at the same time. Water temperature and salinity is high and low in the summer to winter, respectively. While mean grain size of the sediment was higher at Euhangri than at Padori, total mean density of R. philippinarum was higher at Euhangri (325 ind./ 0.25 m2 at Padori vs. 194 ind./0.25 m2 at Euhangri). Settled spat (< 10 mm in length) density was much higher at Euhangri than at Padori (132 vs. 12 individuals/0.25m2, respectively). R. philippinarum spats settled down on the sediment at Euhangri in October and grew continually until the following May, when they reached adult size. Spats that settled down at Padori between March and April were not able to reach the adult stage. As the density of the adult population increased, the condition index of individual clams decreased, but as the population density of the spat increased the body condition index increased. The chlorophyll a content of the sediments at Padori exceeded that at Euhangri and decreased as the population of R. philippinarum increased. The shapes of R. philippinarum shells at Euhangri were more prolate than those at Padori, and the condition index at Euhangri exceeded that at Padori, indicating better growth conditions at Euhangri. The condition index and density of R. philippinarum were affected by the amount of chlorophyll a in the water column and in the sediment. The recruitment success of spats was negatively influenced by spat density. We suggest that regulation of habitat conditions for R. philippinarum, including the food supply, will optimize production of these commercial clams.