Kun-Seop Lee

Effect of in situ light reduction on the maintenance, growth and partitioning of carbon resources in Thalassia testudinum banks ex König

Abstract The effects of in situ light reduction on the subtropical seagrass, Thalassia testudinum Banks ex Konig, in Corpus Christi Bay, Texas were examined from April 1993 to August 1994. The annual quantum flux at the seagrass canopy level was 5207 mol · m−2 · yr−1 or 46% of surface irradiance (SI) compared with two manipulated treatments that reduced underwater light to 1628 mol · m−2 · yr−1 (14% SI) and 864 mol · m−2 · yr−1 (5% SI). All plants subjected to 5% SI died after 200 days and over 99% of the plants receiving 14% SI died by the end of the experiment (490 days). Blade widths of plants in the control groups ranged from 6.4 to 7.0 mm, but decreased within months to 4.7 mm in both treatment group as a result of light reduction. Leaf production rates were significantly higher in control plants compared to plants within the 14 and 5% SI treatment groups, with all plants showing a seasonal trend of high productivity in July and low productivity in April. Blade chlorophyll (chl) concentrations increased, while the chl a-b ratio decreased with reduced light level. Soluble carbohydrate carbon content of controls was highest in rhizomes (102–152 mg C · g−1 dry wt.) and was relatively low in leaves (50–66 mg C · g−1 dry wt.) and in roots (57–74 mg C · g−1 dry wt.). In both light treatment groups, rhizome carbohydrate carbon content was 50% lower and leaf carbohydrate carbon content was about 15% lower than in controls, while the root carbon content did not differ significantly between the treatment groups and the controls. Ammonium and sulfide concentrations of pore water in the shaded cages were significantly higher than in control cages. We conclude that indices of shoot density, blade width, leaf growth, chl a:b ratio and blade chlorophyll content may be important early warning indicators of chronic underwater light stress in T. testudinum. A quantum flux of 1628 mol · m−2 · yr−1 (14% SI) was insufficient to maintain a positive carbon balance in T. testudinum in this bay system.

Diurnal changes in pore water sulfide concentrations in the seagrass Thalassia testudinum beds : the effects of seagrasses on sulfide dynamics

The dynamics of the seagrass-sulfide interaction were examined in relation to diel changes in sediment pore water sulfide concentrations in Thalassia testudinum beds and adjacent bare areas in Corpus Christi Bay and lower Laguna Madre, Texas, USA, during July 1996. Pore water sulfide concentrations in seagrass beds were significantly higher than in adjacent bare areas and showed strong diurnal variations; levels significantly decreased during mid-day at shallow sediment depths (0-10 cm) containing high below-ground tissue biomass and surface area. In contrast, diurnal variations in sediment sulfide concentrations were absent in adjacent bare patches, and at deeper (>10 cm) sediment depths characterized by low below-ground plant biomass or when the grasses were experimentally shaded. These observations suggest that the mid-day depressions in sulfide levels are linked to the transport of photosynthetically produced oxygen to seagrass below-ground tissues that fuels sediment sulfide oxidation. Lower sulfide concentrations in bare areas are likely a result of low sulfate reduction rates due to low organic matter available for remineralization. Further, high reoxidation rates due to rapid exchange between anoxic pore water and oxic overlying water are probably stimulated in bare areas by higher current velocity on the sediment surface than in seagrass beds. The dynamics of pore water sulfides in seagrass beds suggest no toxic sulfide intrusion into below-ground tissues during photosynthetic periods and demonstrate that the sediment chemical environment is considerably modified by seagrasses. The reduced sediment sulfide levels in seagrass beds during photosynthetic periods will enhance seagrass production through reduced sulfide toxicity to seagrasses and sediment microorganisms related to the nutrient cycling.

Factors Controlling Seagrass Revegetation onto Dredged Material Deposits: A Case Study in Lower Laguna Madre, Texas

Abstract Our objective was to evaluate the influence of water quality and sediment chemistry on the survival and growth of Halodule wrightii transplanted onto unconsolidated dredged materials in Lower Laguna Madre, TX. Subsequent to transplanting activities, we measured environmental conditions and seagrass parameters at transplant and natural beds over a 1-yr period. Although water quality characteristics at the transplant and comparison sites were compatible with seagrass growth, transplants failed to survive for more than a few months. Seagrasses at natural sites received high light (>6000 mols m−2 y−1) and exhibited typical patterns of annual growth, biomass and density as well as sediment chemical parameters. In contrast, the estimated annual quantum flux of 2500 to 3200 mols m−2 y−1 at the transplant sites was near the minimum light requirements for H. wrightii. The marginal light environment was a consequence of high turbidity from wind-driven sediment resuspension. Sediment erosion at the transplant site also resulted in a 30 cm increase in water depth. Sediment NH4+ concentrations at the transplant sites were at or above the maximum values for Texas seagrasses (up to 600 µM). Although NH4+ is generally considered a nutrient, recent evidence suggests that moderate to high NH4+ concentrations can be toxic to below ground tissues. We hypothesize that substrate loss, chronic stress from elevated sediment NH4+ levels coupled with minimal light caused the demise of the H. wrightii transplants. Consequently, this work illustrates the importance of site history and sediment bio-geochemistry as factors that control the success of seagrass transplanting efforts.

Species Composition of the Epiphytic Diatoms on the Leaf Tissues of Three Zostera Species Distributed on the Southern Coast of Korea

The epiphytic diatom flora living on leaf tissues of Zostera marina, Z. japonica and Z. caespitosa at three study sites (Dadae, Gabae, and Jangmok) located in Geoje Island has been examined from July 2001 to March 2002 bimonthly. Total 81 species in 26 genera of diatoms have been observed on leaf tissues of the 3 Zostera species throughout the present study. Cocconeis spp. were predominant on Z. japonica, whereas Navicula spp. and Nitzschia spp. were predominant on Z. marina and Z. caespitosa. The community structure of the diatom assemblages varied according to the seagrass species. Species compositions of epiphytic diatoms appear to be closely related to morphology and lifespan of seagrasses.

Growth Dynamics and Carbon Incorporation of the Seagrass, Zostera marina L. in Jindong Bay and Gamak Bay on the Southern Coast of Korea

Since seagrasses in the coastal and estuarine ecosystems achieve high levels of production, they require high inorganic carbon and nutrient incorporation. Thus, seagrasses may play a significant role in carbon and nutrient cycling in the coastal and estuarine ecosystems. To examine growth dynamics of Zostera marina L. environmental factors such as underwater irradiance, water temperature, and salinity, and biological parameters such as shoot density, biomass, shoot morphology, and leaf productivity were measured in two bay systems (Jindong Bay and Gamak Bay) on the southern coast of Korea. While underwater irradiance did not show distinct seasonal trend, water temperature at both sites exhibited clear seasonal trend throughout the experimental period. Shoot density increased dramatically during winter due to the increased seedlings through germination of seeds in Jindong Bay and due to the increased lateral shoots in Gamak Bay. Eelgrass biomass increased during winter and decreased during summer. Maximum biomass in Jindong Bay and Gamak Bay was 250.2 and 232.3 g dry weight m ‐2 , respectively. Carbon incorporation into the eelgrass leaf tissues was estimated from productivity and leaf tissues carbon content. The calculated annual carbon incorporations at the Jindong Bay and Gamak Bay sites were 163 and 295 g C m ‐2 y ‐1 , respectively. This high carbon incorporation into seagrass tissues suggests that seagrass habitats play an important role as a carbon absorber in the coastal and estuarine ecosystems.

Selection of the Optimal Transplanting Method and Time for Restoration of Zostera marina Habitats

【Seagrass bed is an important component in coastal and estuarine ecosystems, providing food and shelter to a wide variety of fauna. Recently, seagrass coverage has declined significantly due to anthropogenic influences such as reclamation, dredging, and eutrophication and consequently, necessity of seagrass habitat restoration is rising. Transplantation experiments with Zostera marina using TERFS, staple method, and shell method have been conducted at Dadae Bay, Kosung Bay and Jindong Bay on the south coast of Korea to select an optimal transplanting method for restoration of Z. marina habitat. Three experimental sites located at the vicinity of natural Z. marina beds with an average water depth of about 4m. Z. marina plants, which were collected from donor bed in Koje Bay were also transplanted at 7 different time from October 2003 to July 2004 to find appropriate transplanting time. Density of Z. marina was monitored monthly at both transplanted areas and natural beds. Transplantation using the staple method showed the highest survival rate of transplant. Shell method was also an effective transplanting method at muddy areas in Kosung Bay and Jindong Bay, but not suitable at sandy areas in Dadae Bay. These results suggest that sediment composition of transplanting areas should be considered for the selection of the optimal transplanting method. Z. marina transplanted during fall usually showed the highest survival rate, while most Z. marina plants transplanted in summer died due to high lethal temperature during this period.】

Effects of the Loess Coating on Seed Germination and Seedling Growths of the Eelgrass, Zostera marina

Seagrass bed is an important component in coastal and estuarine ecosystems, providing food and habitats to a wide variety of marine organisms. Recently, seagrass coverage has declined significantly due to anthropogenic impacts such as cultural eutrophication and reclamation, and thus efforts are under way to prevent further losses and restore disturbed seagrass habitats worldwide. Seagrass transplantation techniques for habitat restoration include vegetative and seed-based methods. Seagrass seeds can be collected easily, and sowing seeds is an economically effective method for large-scale restoration. However, large numbers of seed can be lost by seed predation and physical disturbance in the planting areas. In the present study, Zostera marina seeds were coated with loess to reduce seed loss by predation and sweeping away by the water currents, and germination rates of coated seeds and seedling growth were examined to assess the feasibility of the seed-coating method for large-scale restoration. Germination rate of the coated seeds with loess was significantly higher than that of the uncoated seeds. Additionally, seedling growths were not significantly different between the coated and the uncoated seeds. These results suggest that coating of eelgrass seeds with loess enhances success of seed germintion with no harmful effects on seedling growth. Therefore, the seed coating method using loess may be an effective and applicable seedbased transplanting technique for large-scale restoration.

Genetic identification and evolutionary trends of the seagrass Halophila nipponica in temperate coastal waters of Korea

Although seagrass species in the genus Halophila are generally distributed in tropical or subtropical regions, H. nipponica has been reported to occur in temperate coastal waters of the northwestern Pacific. Because H. nipponica occurs only in the warm temperate areas influenced by the Kuroshio Current and shows a tropical seasonal growth pattern, such as severely restricted growth in low water temperatures, it was hypothesized that this temperate Halophila species diverged from tropical species in the relatively recent evolutionary past. We used a phylogenetic analysis of internal transcribed spacer (ITS) regions to examine the genetic variability and evolutionary trend of H. nipponica. ITS sequences of H. nipponica from various locations in Korea and Japan were identical or showed very low sequence divergence (less than 3-base pair, bp, difference), confirming that H. nipponica from Japan and Korea are the same species. Halophila species in the section Halophila, which have simple phyllotaxy (a pair of petiolate leaves at the rhizome node), were separated into five well-supported clades by maximum parsimony analysis. H. nipponica grouped with H. okinawensis and H. gaudichaudii from the subtropical regions in the same clade, the latter two species having quite low ITS sequence divergence from H. nipponica (7–15-bp). H. nipponica in Clade I diverged 2.95 ± 1.08 million years ago from species in Clade II, which includes H. ovalis. According to geographical distribution and genetic similarity, H. nipponica appears to have diverged from a tropical species like H. ovalis and adapted to warm temperate environments. The results of divergence time estimates suggest that the temperate H. nipponica is an older species than the subtropical H. okinawensis and H. gaudichaudii and they may have different evolutionary histories.

Seasonal Changes in the Carbon and Nitrogen Contents of Zostera marina Populations in the Intertidal and Subtidal Zones of the Seomjin Estuary, Korea

1 , respectively. Eelgrass leaf N content decreased from March to August and increased from September to February in the subtidal zone, whereas these trends were not observed in the intertidal zone. Eelgrass rhizome C content increased from April to September and decreased from October to March in the subtidal zone, whereas those tendencies were not recorded in the intertidal zone. Eelgrass rhizome C:N ratios showed a strong reverse trend to leaf C:N ratios in the subtidal zone, but these tendencies were not observed in the intertidal zone. The effects of exposure appeared to cause no seasonal trend in eelgrass tissue C and N content or C:N ratios in the intertidal zone in the Seomjin Estuary.