Growth dynamics of the deep-water Asian eelgrass, <Emphasis Type="Italic">Zostera asiatica</Emphasis>, in the eastern coastal waters of Korea

Among the seagrasses that occur along the coast of Korea, Zostera asiatica inhabits the deepest depth; however, to date, there is limited information on its ecology. This study presents the first quantitative data on the seasonal growth dynamics of Z. asiatica in Korea. We measured seasonal growth and morphological characteristics, as well as environmental factors, including underwater irradiance, water temperature, salinity and nutrient concentrations of the water column and sediment pore water, bimonthly from July 2012 to May 2015. Underwater irradiance showed clear seasonal trends, increasing in the spring and summer and decreasing in the fall and winter, ranging from 2.4 ± 0.2 mol photons m^-2 d^-1 in November 2012 to 12.8 ± 1.3 mol photons m^-2 d^-1 in July 2014. Water temperature also followed a strong seasonal trend similar to underwater irradiance, ranging from 9.8 ± 0.1°C in January 2013 to 20.5 ± 0.2°C in September 2013. Nutrient availability fluctuated substantially, but there was no evidence of distinct seasonal variations. Shoot density, biomass, leaf productivity, and morphological characteristics of Z. asiatica exhibited significant seasonal variations: maximum values of these variables occurred in summer, and the minima were recorded in winter. Total shoot density was highest (218.8 ± 18.8 shoots m^-2) in July 2012 and lowest (106.3 ± 6.3 shoots m^-2) in January 2013. Total biomass ranged from 182.6 ± 16.9 g dry weight (DW) m^-2 in January 2015 to 310.9 ± 6.4 g DW m^-2 in July 2014.Areal leaf production was highest (4.9 ± 0.0 g DW m^-2 d^-1) in July 2012 and lowest (1.4 ± 0.2 g DW m^-2 d^-1) in January 2013. The optimum water temperature for the growth of Z. asiatica was between 16-19°C. Growth of Z. asiatica was more strongly correlated with underwater irradiance than water temperature, suggesting that light is the most important factor determining seasonality of Z. asiatica at the study site.     

GNSS integration with vision-based navigation for low GNSS visibility conditions

In urban canyons, buildings and other structures often block the line of sight of visible Global Navigation Satellite System (GNSS) satellites, which makes it difficult to obtain four or more satellites to provide a three-dimensional navigation solution. Previous studies on this operational environment have been conducted based on the assumption that GNSS is not available. However, a limited number of satellites can be used with other sensor measurements, although the number is insufficient to derive a navigation solution. The limited number of GNSS measurements can be integrated with vision-based navigation to correct navigation errors. We propose an integrated navigation system that improves the performance of vision-based navigation by integrating the limited GNSS measurements. An integrated model was designed to apply the GNSS range and range rate to vision-based navigation. The possibility of improved navigation performance was evaluated during an observability analysis based on available satellites. According to the observability analysis, each additional satellite decreased the number of unobservable states by one, while vision-based navigation always has three unobservable states. A computer simulation was conducted to verify the improvement in the navigation performance by analyzing the estimated position, which depended on the number of available satellites; additionally, an experimental test was conducted. The results showed that limited GNSS measurements can improve the positioning performance. Thus, our proposed method is expected to improve the positioning performance in urban canyons.     

Evaluating Hyperspectral Imager for the Coastal Ocean (HICO) data for seagrass mapping in Indian River Lagoon,FL

Differentiation between benthic habitats, particularly seagrass and macroalgae, using satellite data is complicated because of water column effects plus the presence of chlorophyll-a in both seagrass and algae that result in similar spectral patterns. Hyperspectral imager for the coastal ocean data over the Indian River Lagoon, Florida, USA, was used to develop two benthic classification models, Slope_RED and Slope_NIR. Their performance was compared with iterative self-organizing data analysis technique and spectral angle mapping classification methods. The slope models provided greater overall accuracies (63–64%) and were able to distinguish between seagrass and macroalgae substrates more accurately compared to the results obtained using the other classifications methods.     

Applicability to Korean Marine Clay of the Mobilized Undrained Vane Shear Strength Using Correction Factors

The undrained shear strength normalized by the yield consolidation pressure, su/pc', is presented for four coastal sites: Busan/Gwangyang and Incheon/Gunsan, having the characteristics of high and low plasticity, respectively. The field vane shear strengths, su(FVT), were compared with unconfined compressive strength, qu/2 which has been used as a representative testing method in Korea. Many researchers have suggested that the undrained shear strength normalized by the yield consolidation pressure, su/pc', depends on Ip. However, the undrained shear strength normalized by the yield consolidation pressure, su/pc' is in the range of 0.25–0.35, independently of the plasticity index, Ip except for su/pc' using qu/2 values in the case of soils having a low plasticity, such as Incheon and Gunsan intermediate soils.

Bjerrum's correction factor has been commonly applied to evaluate mobilized undrained shear strength using the field vane test in Korea. However, the corrected undrained shear strengths using Bjerrum's correction factor, including Morris and Williams' method, were considerably underestimated for Korean marine clay when compared with the qu/2 values that have been used as the mobilized undrained shear strength for practical design in Korea.     

Molecular identification of anisakid nematodes third stage larvae isolated from common squid (Todarodes pacificus) in Korea

The occurrence of Genus Anisakis nematode larvae in marine fishes and cephalopods is epidemiologically important because Anisakis simplex larval stage can cause a clinical disease in humans when infected hosts are consumed raw. Common squid (Todarodes pacificus) from Korean waters were investigated for anisakid nematodes infection during 2009～2011. In total, 1,556 larvae were collected from 615 common squids and 732 of them were subsequently identified by PCR-RFLP analysis of ITS rDNA. Depending on the sampling locations, the nematode larvae from common squid showed different prevalence, intensity and species distribution. A high prevalence (P) and mean intensity (MI) of infection were observed in the Yellow Sea (n = 250, P = 86.0%, MI = 5.99 larvae/host) and the southern sea of Korea (n = 126, P = 57.1%, MI = 3.36 larvae/host). Anisakis pegreffii was dominantly found in common squid from the southern sea (127/ 140, 90.7%) and the Yellow Sea (561/565, 98.9%). In contrast, the P and MI of infection were relatively low in the East Sea (n = 239, P = 8.37%, MI = 1.25 larvae/host). A. pegreffii was not found from the East Sea and 52.0% (13/25) of the nematodes were identified as A. simplex. Most of them were found in the body cavity or digestive tract of common squid, which are rarely consumed raw by humans. Considering the differenences in anisakid nematode species distribution and their microhabitat in common squid, it remains unclear whether common squid plays an important role in the epidemiology of human anisakis infection in Korea. Further extensive identification of anisakid nematodes in common squid, with geographical and seasonal information will be necessary.     

Late quaternary paleoceanographic changes in the northeastern Ulleung Basin, East Sea, inferred from variations in biogenic components

Two piston cores (DD09-ST21, DD09-ST39B) from the northeastern Ulleung Basin in the East Sea were obtained to investigate variations in the biogenic components (calcium carbonate, organic carbon) and biogeochemical processes (δ¹³C and δ¹⁵N). The two cores had distinctive characteristics in terms of surface production, preservation and dissolution capacity of carbonate, and redox conditions of bottom-water. Core DD09-ST21 was characterized by an oxygen-depleted condition from 15 ka (MIS 2) to 60 ka (MIS 3). Core DD09-ST39B, on the other hand, showed oxic bottom-water conditions, possibly due to shallow water depth. These two cores with different redox condition showed opposite trends in terms of CaCO₃, TOC, and C₃₇ alkenone concentrations. CaCO₃ and C₃₇ concentrations were higher during the LGM in DD09-ST21 while lower contents were observed in DD09-ST39B in the same period. Moreover, consistently low TOC in DD09-ST39B and higher fluctuation of organic matters in DD09-ST21 may suggest difference in primary productivity, preservation capacity, or a potential dissolution effect. During the Holocene, the surface productivity of both cores increased, probably due to renewed ventilation and vertical mixing in the East Sea. Therefore, this study suggests spatial variation in production and preservation of biogenic components in the two cores since last 50 ka for DD09-ST39B and 80 ka for DD09-ST21 due to difference in environmental conditions such as water depth, bottom-water conditions, surface productivity and preservation.