Man Chang

Spatial and Temporal Trends in Water Quality in Response to Sewage Discharge in Masan and Hangam Bays, Korea

Abstract This study investigated the spatial and seasonal variations of nutrients, chlorophyll-a (Chl-a), particulate organic carbon, and dissolved oxygen at four stations around Masan Bay from February 2004 to February 2006. Nutrients showed large spatial and seasonal variations in the study area. Dissolved inorganic nitrogen and dissolved silicate concentrations were highest at inner Masan Bay, which was ascribed to the largest inputs of both nutrients from the lands among four stations. Dissolved inorganic phosphorus concentrations are highest at Hangam Bay, where a fertilizer plant caused serious soil pollution with the by-products of phosphate rocks. The extremely high Chl-a concentrations (>60 µg L−1) were observed at inner Masan Bay in July and attributed to the plentiful nutrients, high water stability, and longer residence time at this area during summer. Surface Chl-a concentrations displayed large seasonal variations at all stations, with high values in summer and low values in fall and winter. The lower Chl-a concentrations in fall and winter may be due to strong vertical mixing, which could transport phytoplankton below the euphotic depth, and as a result, constrained phytoplankton growth. Particulate organic carbon–to–Chl-a ratios varied from 59.8 to 121, with large spatial variation and small seasonal change. Hypoxia (<2 mg L−1) was observed at inner and outer Masan and Hangam bays during summer. Outer Masan Bay showed more severe hypoxia than inner Masan Bay in summer 2004 and 2005, which was probably because of the higher organic contents at the bottom sediments and deeper water depth. Despite construction of the Masan and Jinhae wastewater treatment plants, Masan and Hangam bays still received high loading of nutrients, and serious eutrophication was still observed at these bays.

Effect of Thermal Stratification and Mixing on Phytoplankton Community Structure in the Western Channel of the Korea Strait

The profile of a fixed site at station M (34.77˚N, 129.13˚E) in the Korea Strait was studied from March 2006 to February 2007. The aim was to understand the relationship between the annual thermal stratification pattern and seasonal variation in phytoplankton community structure. Physicochemical factors including temperature, salinity and nutrient concentrations, which strongly influence the proliferation and diversity of phytoplankton, were measured. The study period was divided into three due to the characteristic of thermohaline structures; mixed Ⅰ (March-May 2006), stratified (June-November 2006) and mixed Ⅱ (December 2006-Feburuary 2007). Diatoms dominated during the mixed Ⅰ (89%) and Ⅱ (48%) periods, while nanoplankton group occupied over 83% of total population during the stratified period. The dominant species during the mixed Ⅰ and Ⅱ was Chaetoceros socialis (47% and 29%, respectively), while during the stratified period Gyrodinium sp. (4%) was the most dominant. Averaged total chl a concentrations during the mixed Ⅰ and Ⅱ periods were 0.61 ㎎ m?³ and 0.72 ㎎ m?³, respectively, which were at least two-fold higher than that during the stratified period (0.30 ㎎ m?³). The vertical mixing and convection process of the water column induced nutrient supply from the bottom layer to the euphotic zone. It also led to the dominance of diatoms during the mixed periods, whereas small phytoplankton prevailed over large phytoplankton as stratification blocked the upward movement of nutrients to subsurface during the stratified period. During the mixed Ⅰ and Ⅱ periods, microplanktonic chl a dominated concentrations (50% and 48%, respectively), while picoplanktonic chl α occupied over 37% of total chl a during the stratified period.

Effects of Hypoxia on the Fertilization and Early Development of Sea Urchin, Strongylocentrotus nudus

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 (equivalent to 2 mL 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 (normoxia) and 1.8 mg (hypoxia) for 2 days at 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.

Evaluation of rapid cell division in non-uniform cell cycles.

To better understand the mechanisms of development of harmful algal blooms (HABs), accurate estimates of species‐specific in situ growth rates are needed. HABs are caused by rapid cell division by the causative microorganisms. To accurately estimate the in situ growth rates of harmful algae having non‐uniform and/or irregular cell cycles, we modified a standard equation based on the cell cycle, and calculated the in situ growth rate to describe the process of bloom development in nature. Sampling of a developing bloom of Heterosigma akashiwo in Pohang Bay, Korea, was conducted every 3 h from 15:00 on August 2 to 07:00 on August 4, 2006. The amount of H. akashiwo DNA was measured using flow cytometry following tyramide signal amplification‐fluorescence in situ hybridization. On August 2, the percentage of G1 phase cells decreased from 15:00 to 19:00 then increased until 22:00; it then decreased until 07:00 on August 3, followed by an increase to 10:00. This indicates the ability of the cells in nature to undergo more than one round of division per day. During the following night two rounds of division did not occur. The in situ growth rates estimated using the modified equation ranged from 0.31 to 0.53 d−1. We conclude that the use of this equation enables more accurate estimates of bloom formation by rapidly dividing cells.

Expression of Mycosporine-like Amino Acids Biosynthetic Genes in the Chlamydomonas sp. Exposed to Radiofrequency

Mycosporine-like amino acids (MAAs) are UV-absorbing substances, and diverse marine organisms have the evolved the capacity to diminished the direct and indirect damaging effects of environmental ultraviolet radiation by synthesis and accumulation of MAAs. In this study, we manufactured a radiofrequency (RF) generation device and applied to microalgal culture. 0.35±0.05 mHz of RF was supplied to culture vessel for Chlamydomonas sp. and samples were harvested at the designated time intervals (1, 0.5, 1 and 2 hr). MAAs biosynthetic genes, dehydroquinate synthase homolog (DHQS-like) and nonribosomal peptide synthetase homolog (NRPS-like), were cloned from Chlamydomonas sp. and their gene expressions under the RF exposure were analyzed using qRT-PCR. DHQS-like and NRPS-like gene expressions of Chlamydomonas sp. exposed to RF were increased 1.46 and 1.19 fold at 1 hr, respectively. These results means that DHQS-like and NRPS-like genes can be good biomarker candidates for diagnosis of MAAs biosynthesis in the Chlamydomonas sp.

Expressed Sequence Tag Analysis of Toxic Alexandrium tamarense and Identification of Saxitoxin Biosynthetic Genes

Expressed sequence tag (EST) library was constructed from A. tamarense. Base sequences of EST clones were analyzed and saxitoxin biosynthesis-related genes were cloned. Sequences of 827 clones were analyzed and 564 EST were functionally clustered using Blast searches against GenBank. Main genes in the EST had functions on cellular organization, cell metabolism, energy, cell cycle and DNA processing, cellular transport and transport, cell rescue, defense, death and aging, and transcription. Moreover, expression of S-adenosylmethionine synthetase and H2A histone family genes were increased in the toxic A. tamarense. These results show that two genes could be a good biomarkers for the detection of saxitoxin biosynthesis in the A. tamarense.

Production of antibodies for saxitoxin analysis and sensitivity analysis of anti-saxitoxin antiserum

Abstract The most essential but missing components to understand and use toxic substances from marine microalgae are developing the fast, easy and economical determining technology for detecting it. In this paper we produced the antibodies against saxitoxin (STX). Mariculture keyhole limpet hemocyanin (mcKLH) and ovalbumin (OVA) were used as carrier proteins. mcKLH-STX conjugates were injected into the peritonial cavity of BALB/c mouse for immunization. After bleeding from mouse, anti-STX antiserum was isolated. Indirect enzyme-linked immunosorbent assays (ELISA) was performed to determine antiserum titer using the microtiter plate coated with free STX and OVA-STX. A goat anti-mouse IgG-phosphatase conjugate was used as secondary antibody to enable chromogenic reaction. Reactions of anti-STX antiserum were very specific on the OVA-STX and free STX. Sensitivity of anti-STX antiserum on STX was very high and STX detection limit was to be 64.9 ng/kg for indirect ELISA. Key Words : Saxitoxin, Immunization, Antiserum, ELISA

Extraction of anti-microalgal material from Laminaria spp. and effect of oligo-alginate derivatives on membrane potential.

Abstract Oligo-alginate derivatives were extracted from brown algae and its antimicroalgal effects and reaction mechanism were investigated. Oligo-alginate derivatives were produced from sequential hydrolysis of high molecular weight alginate by treatment of 2 N HCl and 1% H 2 O 2. Antimicroalgal activity of extracts was proportional to reaction time and activitywas highest at 4 hrs. When oligo-alginate derivatives were treated to Akashiwo sanguinea and Cochlodinium polykrikoides ,mobilities of cells were ceased. A. sanguinea cells were crushed and plasmolysis was induced in C. polykrikoides cells.To investigate the action mechanism of oligo-alginate derivatives, changes of intracellular (pHi) and extracellular pH (pHe)were determined in the microalgal cells exposed to 0.05% of oligo-alginate derivatives. pHi was decreased about 0.3 unitand pHe was increased about 0.9 unit. These results suggested that change of membrane potential by oligo-alginate derivatives could led to microalgal cell death.