Coastal Waters Of South Korea Research Articles

Experimental Study of Cavitation Damage to Marine Propellers Based on the Rotational Speed in the Coastal Waters

Cavitation in a propeller causes erosion, accelerating corrosion, and tearing off blades in severe cases. Despite the maintenance requirements caused by cavitation, few studies have investigated the cavitation resistance of small ship propellers. Therefore, in this study, these characteristics were investigated through a demonstration test in the coastal waters of South Korea. Cavitation erosion characteristics were analyzed according to the low- and high-rotational speed of the propeller, and the weight was measured every 10 h for 100 h of sailing. The erosion pits were qualitatively compared through liquid penetrant testing (PT) and quantitatively compared by image processing with color edge detection. The results showed that propeller weight loss at high speed was double that at low speed. The cavitation erosion exhibited one cycle each of incubation, acceleration, deceleration, and steady state at low speed, while the acceleration and deceleration periods repeated at high speed. According to PT and color edge detection, the concentration of pits in the low- and high-speed conditions increased towards the trailing and leading edges, respectively. Further, in the radial direction, the trend was similar in both conditions, and the largest number of pits were detected in the region of 0.7–0.9R, where R is the propeller radius.

Determination of spatial and individual variations in the dietary composition of Pennahia argentata in coastal waters of South Korea using metabarcoding and morphological analyses

Understanding the feeding ecology of dominant fish species can be accomplished by considering on spatial and individual variations in prey composition. This study aimed to characterize the diet and feeding habits of Pennahia argentata (silver croaker, a common sciaenid fish in the southern coastal seas of Korea) by analyzing the gut contents of individuals. Morphological and metabarcoding identifications were applied to 92 and 94 gut samples collected from four stations in Gwangyang Bay in September 2018, respectively. P. argentata was the dominant species at all stations. The most common prey species was shrimp, as determined by both morphological (38.8%F) and metabarcoding (233.3%F) analyses. The phylum-level dietary profiles were similar among the individuals at different sites, but the species-level dietary profiles varied among the individuals at different sites and were distinguished by the read abundance of Oratosquilla oratoria (mantis shrimp) and Aliaporcellana sp. (crab). P. argentata is mostly generalized and mixed in its feeding habit, with varying frequencies of occurrence of two important prey items, O. oratoria and Aliaporcellana sp., and degrees of specialization on several items among the sites and size groups. Regardless of the relatively small spatial scale, the DNA metabarcoding analyses identified compositional variations in the gut contents of P. argentata. These variations appeared to be associated with water quality variables (total organic carbon, total nitrogen, and total phosphorus) and individual characteristics (body length and weight), but not with fish community traits (diversity, dominance, and evenness). Our results demonstrate the usefulness of gut content eDNA analyses for evaluating biodiversity in fish diets and the describing feeding strategies of fish.

The occurrence of two non-indigenous Conopeum (Bryozoa: Cheilostomata) species in the coastal waters of South Korea

The occurrence of two non-indigenous Conopeum (Bryozoa: Cheilostomata) species in the coastal waters of South Korea

Taxonomy of four scuticociliates(Protozoa: Ciliophora) from coastal waters of South Korea

Taxonomy of four scuticociliates(Protozoa: Ciliophora) from coastal waters of South Korea

Zooming on dynamics of marine microbial communities in the phycosphere of Akashiwo sanguinea (Dinophyta) blooms.

Characterizing ecological relationships between viruses, bacteria and phytoplankton in the ocean is critical to understanding the ecosystem; however, these relationships are infrequently investigated together. To understand the dynamics of microbial communities and environmental factors in harmful algal blooms (HABs), we examined the environmental factors and microbial communities during Akashiwo sanguinea HABs in the Jangmok coastal waters of South Korea by metagenomics. Specific bacterial species showed complex synergistic and antagonistic relationships with the A. sanguinea bloom. The endoparasitic dinoflagellate Amoebophrya sp. 1 controlled the bloom dynamics and correlated with HAB decline. Among nucleocytoplasmic large DNA viruses (NCLDVs), two Pandoraviruses and six Phycodnaviruses were strongly and positively correlated with the HABs. Operational taxonomic units of microbial communities and environmental factors associated with A. sanguinea were visualized by network analysis: A. sanguinea–Amoebophrya sp. 1 (r = .59, time lag: 2 days) and A. sanguinea–Ectocarpus siliculosus virus 1 in Phycodnaviridae (0.50, 4 days) relationships showed close associations. The relationship between A. sanguinea and dissolved inorganic phosphorus relationship also showed a very close correlation (0.74, 0 day). Microbial communities and the environment changed dynamically during the A. sanguinea bloom, and the rapid turnover of microorganisms responded to ecological interactions. A. sanguinea bloom dramatically changes the environments by exuding dissolved carbohydrates via autotrophic processes, followed by changes in microbial communities involving host‐specific viruses, bacteria and parasitoids. Thus, the microbial communities in HAB are composed of various organisms that interact in a complex manner.

Risk screening of the potential invasiveness of non-native marine fishes for South Korean coastal waters

Risk screening tools are being increasingly used to identify the potential invasiveness and associated risks of non-native species. In this study, the Aquatic Species Invasiveness Screening Kit was used to evaluate the invasiveness risks of extant and horizon non-native marine fish species for the coastal waters of South Korea. In total, 57 marine fish species were screened and the threshold scores for the Basic Risk Assessment (BRA) and the BRA + Climate Change Assessment (BRA+CCA) (5.5 and 1.5, respectively) reliably distinguished those species carrying a high risk of invasiveness from those carrying a low to medium risk. For both the BRA and BRA+CCA, common lionfish Pterois miles was the highest-scoring species, followed by white perch Morone americana, red drum Sciaenops ocellatus, marbled spinefoot Siganus rivulatus and redcoat Sargocentron rubrum. The outcomes of this study will contribute to the management of non-native marine fish species for the conservation of the native ecosystems in the coastal waters of South Korea.

First Record of the Olive Ridley Sea Turtle Lepidochelys olivacea (Reptilia: Testudines: Cheloniidae) from South Korea

We report Lepidochelys olivacea from coastal waters of South Korea for the first time on the basis of two specimens (one male and one female) whose taxonomic identities were verified on morphological and molecular grounds. Four species of sea turtles, Dermochelys coriacea, Chelonia mydas, Caretta caretta, and Eretmochelys imbricata. have been recorded from South Korean waters, and present findings add another species to the sea turtle fauna of this region.

The complete mitochondrial genome of Gruberia lanceolata (Gruber, 1884) Kahl, 1932 (Ciliophora: Heterotrichea)

The ciliate Gruberia lanceolata (Gruber, 1884) Kahl, 1932 belonging to the class Heterotrichea was sampled from the coastal waters of South Korea. The complete mitogenome in its linear form and large size (∼40 kb) was obtained. It consisted of 27 protein-coding genes (PCGs), two ribosomal subunit RNA (rRNA) genes, four transfer RNAs (tRNAs), and ten unclassified open reading frames (ORFs). Their telomeric structures were capped, with repeat regions at both ends. We analyzed its phylogenetic tree using the data of its respiratory chain complex I genes. It can be suggested that the complete mitochondrial genome of G. lanceolata can be recorded as a new class of the mitogenome.

Atmospheric Trace Gas (NO2 and O3) Variability in South Korean Coastal Waters, and Implications for Remote Sensing of Coastal Ocean Color Dynamics

Coastal environments are highly dynamic, and are characterized by short-term, local-scale variability in atmospheric and oceanic processes. Yet, high-frequency measurements of atmospheric composition, and particularly nitrogen dioxide (NO2) and ozone (O3) dynamics, are scarce over the ocean, introducing uncertainties in satellite retrievals of coastal ocean biogeochemistry and ecology. Combining measurements from different platforms, the Korea-US Ocean Color and Air Quality field campaign provided a unique opportunity to capture, for the first time, the strong spatial dynamics and diurnal variability in total column (TC) NO2 and O3 over the coastal waters of South Korea. Measurements were conducted using a shipboard Pandora Spectrometer Instrument specifically designed to collect accurate, high-frequency observations from a research vessel, and were combined with ground-based observations at coastal land sites, synoptic satellite imagery, and air-mass trajectory simulations to assess source contributions to atmospheric pollution over the coastal ocean. TCO3 showed only small (<20%) variability that was driven primarily by larger-scale meteorological processes captured successfully in the relatively coarse satellite imagery from Aura-OMI. In contrast, TCNO2 over the ocean varied by more than an order of magnitude (0.07–0.92 DU), mostly affected by urban emissions and highly dynamic air mass transport pathways. Diurnal patterns varied widely across the ocean domain, with TCNO2 in the coastal area of Geoje and offshore Seoul varying by more than 0.6 DU and 0.4 DU, respectively, over a period of less than 3 h. On a polar orbit, Aura-OMI is not capable of detecting these short-term changes in TCNO2. If unaccounted for in atmospheric correction retrievals of ocean color, the observed variability in TCNO2 would be misinterpreted as a change in ocean remote sensing reflectance, Rrs, by more than 80% and 40% at 412 and 443 nm, respectively, introducing a significant false variability in retrievals of coastal ocean ecological processes from space.

Efficient placement models of labyrinth-type artificial concrete reefs according to wake volume estimation to support natural submerged aquatic vegetation

The present study presents efficient placement models of labyrinth-type artificial concrete reefs (LT-ACRs) to support natural submerged aquatic vegetation beds or enhance macrophyte beds [Undaria pinnatifida (Harv.) Suringar, Laminaria sp., Ecklonia stolonifera Okamura, and Sargassum fulvellum (Turner) C. Agardh] in the coastal waters of South Korea. To reach an efficient solution, wake regions were obtained for 12 LT-ACR placement models using the element-based finite volume method and wake volume concept. The optimal flatly distributed placement models were identified in intervals between neighboring reefs (i.e., longitudinal width: 1 m ≤ W1 ≤ 3 m; transverse width: W2 = 5 m), which resulted in wake volumes of 43.8, 38.5, and 39.5 m3. The optimal models are regarded as more efficient than the maximum wake volume case because their geometries sustain the intervals between neighboring reefs. Overall, labyrinth-type artificial concrete reefs are efficient because they have relatively wide surfaces and small drag coefficients, and their optimal placement models satisfy Korean practices, which dictate that the intervals should not exceed 5 m. However, the hydrodynamic and economic pros and cons of intervals >5 m were not assessed in the present study.

Distribution of Human Norovirus in the Coastal Waters of South Korea.

The presence of human norovirus in the aquatic environment can cause outbreaks related to recreational activities and the consumption of norovirus-contaminated clams. In this study, we investigated the prevalence of norovirus genogroups I (GI) and II (GII) in the coastal aquatic environment in South Korea (March 2014 to February 2015). A total of 504 water samples were collected periodically from four coastal areas (total sites = 63), of which 44 sites were in estuaries (clam fisheries) and 19 were in inflow streams. RT-PCR analysis targeting ORF2 region C revealed that 20.6% of the water samples were contaminated by GI (13.3%) or GII (16.6%). The prevalence of human norovirus was higher in winter/spring than in summer/fall, and higher in inflow streams (50.0%) than in estuaries (7.9%). A total of 229 human norovirus sequences were identified from the water samples, and phylogenetic analysis showed that the sequences clustered into eight GI genotypes (GI.1, 2, 3, 4, 5, 6, 7, and 9) and nine GII genotypes (GII.2, 3, 4, 5, 6, 11, 13, 17, and 21). This study highlighted three issues: 1) a strong correlation between norovirus contamination via inflow streams and coastal areas used in clam fisheries; 2) increased prevalence of certain non-GII.4 genotypes, exceeding that of the GII.4 pandemic variants; 3) seasonal shifts in the dominant genotypes of both GI and GII.

The estimation of derelict fishing gear in the coastal waters of South Korea: Trap and gill-net fisheries

This study estimates the gross quantity of discarded fishing traps and gill-nets in the coastal waters of South Korea. Using regression analysis it is estimated that 11,436t of traps and 38,535t of gill-nets are abandoned annually. Experts on marine debris recommend replacement of traditional fishing gears with eco-friendly designs and establishment of incentive programmes for the fishermen in order to promote eco-friendly gear designs.

Effect of temperature on changes in size and morphology of the marine diatom, Ditylum brightwellii (West) Grunow (Bacillariophyceae)

The objective of the present study was to assess size and morphological changes in response to temperature in the marine diatom, Ditylum brightwellii (West) Grunow, using ecological, morphological and physiological approaches. D. brightwellii has two distinct cell morphologies: prism (large-sized cell) and cylinder types (small-sized cell). In the coastal waters of South Korea, the prism type was found to be present at high frequency at low temperatures, whereas the cylinder type was predominant at high temperatures. Other environmental factors did not affect the presence of either cell type significantly. In growth experiments to determine the effect of temperature on the size of D. brightwellii, the abundance of the prism type increased at low temperature, but the abundance of the cylinder type increased at high temperature. These results are important for understanding temperature-induced size and morphological changes in D. brightwellii, and their potential role as an adaptive strategy.

Morphological Characteristics of Four Species in the Genus Skeletonema in Coastal Waters of South Korea

Most Skeletonema species have been identified under the name of S. costatum. To assess the morphological species diversity in the genus Skeletonema, we surveyed the nine localities in the coastal waters of South Korea. The light microscopy (LM) and scanning electron microscopy (SEM) observations in this study showed that ultrastructural features of genus Skeletonema discriminated among four species: S. dohrnii Sarno & Kooistra, S. marinoi Sarno & Zingone, S. subsalsum (Cleve) Bethge, and S. tropicum Cleve. In S. dohrnii, cell diameters were 3-6 μm and the pervalvar axes were 13-19 μm. One or two partial chloroplasts were visible in a cell. Cells of S. marinoi were 4-10 μm and the pervalvar axes were 8-18 μm. Each cell contained one chloroplast. Cells of S. subsalsum which contained 1-2 chloroplasts were 8-13 μm and the pervalvar axes were 11-20 μm. Cells of S. tropicum were 10-18 μm and the pervalvar axes were 4-9 μm. 2-4 chloroplasts were seen in each cell. Tip width of fultoportula in S. dohrnii and S. marioni was flared and flat, but that in S. subsalsum and S. tropicum was narrow. Morphological groups among them, S. dohrnii and S. marinoi were the most widely distributed in all seasons, while S. tropicum was only occurred in a summer season.

Forest fire ash impact on micro- and macroalgae in the receiving waters of the east coast of South Korea

Mountain forest fire ash flushed into the eastern coastal waters of South Korea is known to contain cadmium as one of its significant constituents. To study its impact, two representatives of the micro- and macroalgal communities, Ulva pertusa and Nannochloropsis oculata, were exposed to the concentration range of Cd indicated from the forest fire localities. At low concentrations of 0.224–0.448 mg L −1, a 20% reduction in growth rate of N. oculata was observed. Chlorophyll a pigment concentration was proportionate to the growth reduction while at higher concentrations (1.792 mg L −1) pigments were completely leached. In the macrophyte U. pertusa, a similar trend of pigment leaching was observed. Bioaccumulation factors obtained for these rapidly growing algal species revealed excessive bioconcentration of Cd. Variations in the concentration of Cd among the samples collected along the Korean coast clearly indicated the additional source of metal influx from the forest fires.

TBT toxicity on the marine microalga Nannochloropsis oculata

Commercial antifouling formulations containing TBT are the major source of organotin contamination in coastal waters. In view of the persisting TBT residues (13 ng Sn l −1) in the coastal waters of South Korea, an attempt has been made to evaluate the growth response and biochemical composition of laboratory-cultured Nannochloropsis oculata to TBT toxicity. It is evident that the persisting concentration level of TBT is high enough to cause adverse effect on the microalgal species. The EC 50 (24 h) was found to be at 0.89 nM level of TBT for this marine eustigmatophyte N. oculata. Photosynthetic pigment content was significantly affected. At elevated TBT concentrations of 1.0 nM, especially pronounced changes in biochemical composition was found. TBT tolerance of N. oculata and its growth as well as biochemical responses are discussed.