Southern Yellow Sea Research Articles

Effects of Yellow Sea Cold Water Mass on marine nematodes based on biological trait analysis

The Yellow Sea Cold Water Mass (YSCWM) is a seasonal hydrological phenomenon with significant effects on benthic animals. Based on a range of biological traits, including feeding type, tail shape, adult body length, body shape and life history (c-p value), the biological trait analysis (BTA) of marine nematodes in the southern Yellow Sea was studied in June 2003 (summer) and January 2004 (winter) in order to reveal the effects of YSCWM on benthic animals. In terms of biological traits composition of marine nematode assemblages, results of ANOSIM showed that there were no significant differences among sites inside the YSCMW area. However, for spatial distribution, marine nematode assemblages showed significant differences between sites inside and outside of the YSCWM area in terms of body shape, as there was higher percentage of nematodes with slender body shape while lower percentage with stout and long thin body shape at the sites inside the YSCWM area. Results of BIOENV analysis showed that water depth and sediment silt-clay percentage were the most important factors contributed to the differences of biological traits of marine nematode assemblages in summer, while sediment phaeophorbide content best explained the differences of marine nematode assemblages in winter. The existence of the YSCWM may provide a stable environment for marine nematode assemblages, keeping them in a continuous state during the seasonal changes. The higher percentage of nematodes with slender body may be the response to the YSCWM.

A study of the environmental factors influencing the growth phases of Ulva prolifera in the southern Yellow Sea, China

Macroalgal blooms of U. prolifera in the southern Yellow Sea (SYS) have become an ecological disaster. In this study, we attempt to explore the influence of environmental factors and human activity on the annual development of U. prolifera during 2011–2016, combining geostationary ocean color imager images and monitored environmental factors. Blooms of U. prolifera were mainly distributed in the central SYS, drifting from the southern Yellow Sea Radial Sand Ridges. Three growth phases were defined (initial phase, outbreak phase and dissipation phase) to facilitate analysis of the relationship between the environmental factors and growth conditions of U. prolifera. Seaweed cultivation, sea surface temperature (SST) and available radiation influenced the algal biomass during the initial phase; the seawater transparency, precipitation and wind activity affected the algae during the outbreak phase; and SST, intense radiation and cleanup operations increased the rate of algal extinction in the dissipation phase.

Characteristics of phytoplankton assemblages in the southern Yellow Sea, China

The characteristics of phytoplankton assemblages were analyzed by the Utermöhl method in the southern Yellow Sea in summer, 2008. A total of 113 species (including varieties and forms), belonging to 51 genera and 3 phyla, were identified. Diatom was the most dominant group. The dominant species included Eucampia zoodiacus, Leptocylindrus danicus, Chaetoceros affinis, Thalassionema nitzschioides, Skeletonema costatum, Paralia sulcata and Chaetoceros tortissimus, which were eurytopic and temperate species. The cell abundance of phytoplankton ranged from 0.04 to 620.08 cells·mL−1 with an average of 27.52 cells·mL−1. Horizontally, the cell abundance showed a decreasing trend from the south to the north. In terms of vertical distribution, the values in surface and subsurface water layers were higher than those in bottom water layers. Results of correlation analysis showed that phytoplankton cell abundance was positively correlated with water temperature, ammonia and nitrite concentrations, and negatively correlated with salinity and silicate concentration.

Safety and quality of the green tide algal species Ulva prolifera for option of human consumption: A nutrition and contamination study

This study sampled U. prolifera and surface seawater from the same locations where green tide broke out in the southern Yellow Sea, in both the year 2016 and 2017. The revealed nutritive components of U. prolifera samples characterized U. prolifera as a high-protein, high-Fe, high ratio of unsaturated lipid acids and low-fat seaweed food, with an ideal ratio of essential and nonessential amino acids. The concentrations and health risk assessment of major micropollutants (heavy metals, pesticides and polycyclic aromatic hydrocarbon (PAHs)) in U. prolifera were also analyzed, respectively. The results showed that the Target Hazard Quotient values of five heavy metals (<1.0 × 10−1) and the total hazard index of 13 pesticides (<1.5 × 10−8) were lower than the unity, respectively, and the incremental lifetime cancer risk values of PAHs (<7.4 × 10−7) were lower than the USEPA limit (1.0 × 10−6). It suggested that consuming U. prolifera is safe as a food-source option, with PAHs causing relatively higher risks. PAHs from the sites closer to the shore were also found more originated from pyrolysis. We further confirmed the PAH congeners were partly in equilibrium between seawater and U. prolifera. It suggested the possibility that the food safety-risk turned to be above the USEPA limit was not high regardless of the sample collecting time. However, the sources of PAHs and their contributions to the accumulation in U. prolifera need further investigation. This study favored that U. prolifera of the green tide from the southern Yellow Sea has a potential for a nutritious-food production.

Textures, provenances and structures of sediment in the inner shelf south of Shandong Peninsula, western South Yellow Sea

Although many studies have been performed on the mud wedge in the distal part of the Yellow River subaqueous delta, little is known about the southwestern terminus of the Yellow River mud wedge in the inner shelf of the Southern Yellow Sea (SYS). We use ∼3000 km of high-resolution subbottom seismic profiles, 147 surficial sediment samples, as well as 30 fluvial sediment samples to study sediment textures, provenance and structures in the inner shelf in western SYS. Our results show that sediment in the inner shelf south of Shandong Peninsula can be categorized into multiple types, including sand, silt, sandy silt, muddy sand, mud, gravel mud and others. About 60% of the study area is covered by silt and sandy silt. Assuming a finer texture of sediment from Yellow River and a relatively coarser one for sediment from local small rivers, our results reveal at least two contrasting sediment sources. East of the Laoshantou Headland, on the southern coast of the peninsula, the sediment is mainly from the Yellow River. Holocene sediment deposition reaches about 15 m thickness in water depths of ∼10 m. The homogeneous surficial sediment pattern is mainly controlled by the Yellow Sea Coastal Current, the Yellow Sea Warm Current, as well as local currents. However, west of Laoshantou Headland, sediment from local small rivers draining the peninsula plays a more important role. Over there the Holocene mud wedge is no more than 5-m thick, and is re-worked by strong tides and longshore currents. The seaward extension of Laoshantou Headland the southern peninsula seems to act as an effective sediment trap, aiding the accumulation of sediment carried by longshore currents. This new study delineates the western boundary of Yellow River subaqueous delta and helps better quantify sediment budget in the Yellow Sea. It also shed light on the sedimentation interplay of large rivers with local small rivers on many epicontinental shelves and passive margins around the world.

Tracking the phenology and expansion of Spartina alterniflora coastal wetland by time series MODIS and Landsat images

Accurate information on phenology of Spartina alterniflora is basic for observing its growing condition in native and invasive places. Remote sensing (RS) can be used to analyse and monitor vegetation at a large spatial and long time scale. In this study, RS is used to explore phenology of coastal wetland vegetation (Reed, Suaeda salsa and Spartina alterniflora) based on time series data of four spectral indices (SI): Normalized Difference Vegetation Index (NDVI); Enhanced Vegetation Index (EVI); Land Surface Water Index (LSWI) and Modified Normalized Difference Moisture Index (mNDWI). These SIs were calculated based on Moderate Resolution Imaging Spectroradiometer (MODIS) and Land Satellite (Landsat) images, respectively. Phenology (including growing season and non-growing season) of Spartina alterniflora based on SIs to track its dynamic expansion since it invaded in southern Yellow Sea (Jiangsu, Yancheng), China through observing Landsat sub-pixels in per MODIS pixel. We also developed a new phenology-based algorithm to identify Spartina alterniflora from 1984 to 2015. The results show that Spartina alterniflora has a longer growth circle (around 286 days in a year) and higher productivity (about 0.6–0.8 NDVI) than the other salt marsh vegetation. The way of observing vegetation phenology on RS, and then developing a new phenology-based algorithm to track coastal wetland including invasive species—like Spartina alterniflora can support the studies of biological expansion, coastal wetland biodiversity conservation, and even global carbon cycling and climate change further.

Spatio-temporal patterns of Ulva prolifera blooms and the corresponding influence on chlorophyll-a concentration in the Southern Yellow Sea, China

The world's largest macroalgal blooms (MABs) caused by the Ulva prolifera outbreaks have occurred every summer since 2007 in the Southern Yellow Sea, China. Accumulating evidence showed that MABs may deteriorate the regional marine environment and influence the growth of some primary producers such as phytoplankton. In this study, we investigated the spatio-temporal patterns of U. prolifera green tides and chlorophyll-a concentration in the Southern Yellow Sea in 2015 using satellite images obtained from HJ-1 CCD, MODIS, and GOCI. The correlation between the distributions of U. prolifera abundance and chlorophyll-a concentration was analyzed quantitatively by setting up a series of 5 × 5 km experimental grids, and we also discussed the possible mechanisms about the influence of U. prolifera blooms on the other floating microalgae. The results showed that the development of U. prolifera blooms in the Southern Yellow Sea in 2015 could be featured as “appearance – development – outbreak – decline – disappearance”, while the concentration of chlorophyll-a showed “increase – sharp decline – slow recovery – stabilization” from April to August. We also found that the concentration of chlorophyll-a had the following relationships with U. prolifera temporally: (1) the concentration of chlorophyll-a increased with the growth of U. prolifera from April to mid-May; (2) the chlorophyll-a concentration decreased sharply with the dramatically increased coverage of U. prolifera in June; and (3) the chlorophyll-a concentration slowly recovered and finally stabilized as U. prolifera decreased in July. Generally, there was a negative correlation between the occurrence of U. prolifera and chlorophyll-a concentration in the Southern Yellow Sea, China. Our results showed that the outbreak of U. prolifera does have a certain impact on the growth and reproduction of planktonic microalgae, and it suggests that U. prolifera blooms have potentially altered the ecological balance in the coastal waters of the Southern Yellow Sea.

Microplastic pollution in sediments from the Bohai Sea and the Yellow Sea, China

Microplastics are one of the most significant pollutants in the marine environment and accumulate in sediments all over the world. To assess the pollution level in the marine environment in China, the distribution and abundance of microplastics in sediments from the Bohai Sea and the Yellow Sea were investigated in this study. The sediment samples were collected from 72 different sites in the Bohai Sea and the Yellow Sea. Microplastics were separated from sediment through density flotation and categorized according to shape and size under a microscope. Additionally, polymer types were identified using Fourier-Transform Infrared Micro-spectroscopy (μ-FT-IR). Our study demonstrated that microplastics were consistently found in all samples, which emphasized their extensive distribution throughout the Bohai Sea and the Yellow Sea. The average microplastic abundance was 171.8, 123.6 and 72.0 items per kg of dry weight sediment for the Bohai Sea, Northern Yellow Sea and Southern Yellow Sea, respectively. Among the sampled microplastics, fiber (93.88%) and small microplastics (<1000 μm) (71.06%) were the most frequent types. Fourier transform infrared microspectroscopy (μ-FT-IR) analysis determined that the main types of microplastics were rayon (RY), polyethylene (PE) and polyethylene terephthalate (PET). Our results highlighted the widespread distribution of microplastics in sediments from the Bohai Sea and the Yellow Sea and provided useful information for evaluating the environmental risks of microplastics in China.

Analysis of the effective observation of ocean color satellites of the Yellow and East China Seas

ABSTRACTBased on long time series of merged ocean color products (2003–2016) from the ESA GlobColour dataset, spatial and temporal distributions on effective observation days of ocean color satellites of the Yellow and East China Seas are analyzed. The results show that the average number of effective observation days for the region is 51 ± 6.8 days per year. Large numbers of such days appeared for the West Korea Bay and western Liaodong Bay, at 100 ± 8.3 days per year. Small numbers of days appeared for the southwestern southern Yellow Sea, northwestern East China Sea, and the branch of Kuroshio Current region, at 40 ± 10.1 days per year. Effective observation days of the Yellow and East China Seas had strong seasonal characteristics. The Bohai Sea, northern Yellow Sea, and southern Yellow Sea had two peaks in March and October. The East China Sea had a single peak in July. A lack of effective observation reduces the quality of monthly ocean color products, with greater than 15% bias if the monthly data are averaged from 3 days and 30% bias if the monthly data are from 1 day only.

Evolution of the Southern Yellow Sea Cold Water Mass during the last 7 kyr from benthic foraminiferal evidence

The Southern Yellow Sea Cold Water Mass (YSCWM) is closely related to the modern circulation system of the east China shelf seas, which has significantly influenced regional marine environmental changes. The study of the Holocene evolution of the YSCWM will greatly improve our understanding of the mechanisms of regional environmental change. Benthic foraminifera are sensitive to bottom water environmental changes and can serve as useful indicators in bottom water environmental reconstruction. In this study, benthic foraminifera were analyzed in core N02 from the northwestern margin of the southern Yellow Sea Mud to decipher the phase evolution of the YSCWM during the last 7 kyr. Benthic foraminifera census counts and Q-mode factor analysis indicate that the Holocene sedimentary environment can be divided into three stages: From 6.9–5.0 ka, the fauna was dominated by Ammonia ketienziensis, indicating that the YSCWM was at its strongest during the last 7 kyr, while the Yellow Sea Coastal Current (YSCC) had a weak influence on the bottom water of the study area. From 5.0–2.9 ka, the relative abundance of Hanzawaia nipponica remarkably increased while the abundance of A. ketienziensis decreased significantly, reflecting that the strength of the YSCWM was relatively weak and the range of the YSCWM might have contracted. The influence of the YSCC on the bottom water might have slightly increased, although its influence was still weak during this time. A notable increase in low-temperature and low-salinity species, such as Protelphidium tuberculatum and Buccella spp. has occurred since 2.9 ka, indicating that the YSCC has had a strong influence on bottom water during this period, while the strength of the YSCWM has been at its weakest during the last 7 kyr. Generally, the influence of the YSCWM and the YSCC on the bottom water properties of the study area show an obvious seesaw pattern, with one’s influence increasing while the other’s influence decreases and vice versa. The fluctuations in the strength of YSCWM during the Holocene may be caused by the different effect allocations of regional climatic factors (i.e. El Nino Southern Oscillation, East Asian Winter Monsoon, summer insolation in the northern hemisphere, etc.) acting on the circulation system during different periods.

Eukaryotic Micro-plankton Community Diversity and Characteristics of Regional Distribution in the Yellow Sea by ITS High-throughput Sequencing

Eukaryotic micro-plankton plays a key role in the marine biotic community and in maintaining the stability of the marine ecosystem. In order to determine the diversity and characteristics of eukaryotic micro-plankton in the Yellow Sea, Illumina high-throughput sequencing, based on gene markers of ITS, was conducted. An analysis of the relationship between community structure and environmental factors was conducted as well. The results are summarized in the following. ① Various of species of fungi, phytoplankton, and zooplankton were obtained by high-throughput sequencing technology; for OTUs, the order is fungi > phytoplankton > zooplankton, and for reads, the order is fungi > zooplankton > phytoplankton. ② In different waters, species abundance and diversity differed from each other. The Ace index and Chao1 index demonstrated an ordering of southern Yellow Sea > northern Yellow Sea > northern East Sea > Cold Water Mass; however, for the Simpson index and Shannon-Wiener index, the tendency followed the order of northern East Sea > northern Yellow Sea > southern Yellow Sea > Cold Water Mass. Species abundance and diversity in the Cold Water Mass were lowest. ③ The reads and OTUs of fungi, phytoplankton, and zooplankton increased as temperature rose. The reads and OTUs of fungi increased as salinity increased, while there was an opposite trend for phytoplankton and zooplankton. Latitude was another significant factor. In the range of 30° to 40° north latitude, the Shannon-Wiener index for fungi and zooplankton indicated an increasing tendency with an increase in latitude, while the Shannon-Wiener index for phytoplankton showed an opposite trend. With a greater distance from the coast, the Shannon-Wiener index of fungi, phytoplankton and zooplankton was lower. This is the first study that amplifies the use ITS in the research of marine eukaryotic micro-plankton, giving an enriched understanding of eukaryotic micro-plankton. The feasibility of applying high-throughput sequencing technology in the sea is proven, and this will provide a reference for other researchers.

Changes in fish diversity and community structure in the central and southern Yellow Sea from 2003 to 2015

The central and southern Yellow Sea is an important overwintering ground for many fish species in the Bohai Sea and Yellow Sea. For better understanding the status of the fish community after years of heavy exploitation, variations in fish community structure and diversity were analyzed using data from bottom trawls during 2003–2015. Five fish assemblage indices all showed fluctuations without clear trends from 2003 to 2015, yet there were strong positive and significant correlations ( P 0.05); there were also no significant differences between the slope of the size-spectra and fishing effort. The catch per unit effort and mean individual weight analyses of the whole fish assemblage both showed a significantly decreasing trend over time. Overall, the results showed that the fish community structure in the central and southern Yellow Sea was relatively stable from 2003 to 2015 and the study could be used as a reference for supporting ecosystem-based fishery management.

Reprint of Mechanisms of maintaining high suspended sediment concentration over tide-dominated offshore shoals in the southern Yellow Sea

An understanding of the dynamics and behaviors of suspended sediments is vital in analysis of morphological, environmental, and ecological processes occurring in coastal marine environments. To study the mechanisms of maintaining high suspended sediment concentrations (SSCs) on a tide-dominated offshore shoal, we measured water depths, current velocities, SSCs, wave parameters and bottom sediment compositions in the southern Yellow Sea. These data were then used to calculate bottom shear stresses generated by currents (τc), waves (τw), and wave–current interactions (τcw). SSCs time series exhibited strong quarter-diurnal peaks during spring tides, in contrast to the semidiurnal signal during neap tides. A Fourier analysis showed that suspended sediment variations within tidal cycles was mainly controlled by resuspension in most stations. There existed relatively stable background SSCs (maintaining high SSCs among tidal cycles) values at all four stations during both windy (wind speed > 9.0 m/s) and normal weather conditions (wind speed < 3.0 m/s). The background SSCs had strong relationship with spring/neap-averaged τcw, indicating background SSCs were mainly controlled by mean bottom shear stress, with a minimum value of 0.21 N/m2. On account of the strong tidal currents, background SSCs of spring tides were greater than that of neap tides. In addition, on the base of wavelet, statistics analyses and turbulence dissipation parameter, background SSCs during slack tide in the study area may be maintained by intermittent turbulence events induced by a combined tidal current and wave action.

Differences in planktonic ciliate spatial distribution in spring and autumn in the southern Yellow Sea

Seasonal variation of marine plankton spatial distribution is important in understanding the biological processes in the ocean. In this study, we studied spatial distribution of planktonic ciliate abundance and biomass in the central deep area (station depth greater than 60 m) and the coastal shallow area (station depth less than 60 m) of the southern Yellow Sea (32°–36.5°N, 121°–125°E) in spring (April) and autumn (October–November) of 2006. Our results showed that both ciliate abundance and biomass in the surface waters were higher in spring ((1 490±2 336) ind./L; (4.11±7.81) μg/L) than in autumn ((972±823) ind./L; (1.11±1.18) μg/L, calculated by carbon). Ciliate abundance and biomass in the surface waters of the coastal shallow area were similar in spring and autumn. However, in the central deep area, those values were much higher in spring ((1 878±2 893) ind./L; (5.99±10.10) μg/L) than in autumn ((738±373) ind./L; (0.74±0.76) μg/L). High values of ciliate abundance and biomass occurred in the central deep area in spring and in the coastal shallow area in autumn. Mixotrophic ciliate Laboea strobila was abundant in the central deep area in spring, when a phytoplankton bloom occurred. However, in autumn, L. strobila was abundant in the coastal shallow area. Boreal tintinnid Ptychocyli obtusa was found in spring. Both L. strobila and P. obtusa were concentrated in the surface waters when their abundance was more than 1 000 ind./L. Peaks of these species were in the subsurface waters when their abundance was less than 400 ind./L. This study showed that both high abundance and biomass of ciliates occurred in different areas in southern Yellow Sea seasonally.

A UAV and S2A data-based estimation of the initial biomass of green algae in the South Yellow Sea

Previous studies have shown that the initial biomass of green tide was the green algae attaching to Pyropia aquaculture rafts in the Southern Yellow Sea. In this study, the green algae was identified with unmanned aerial vehicle (UAV), an biomass estimation model was proposed for green algae biomass in the radial sand ridge area based on Sentinel-2A image (S2A) and UAV images. The result showed that the green algae was detected highly accurately with the normalized green-red difference index (NGRDI); approximately 1340 tons and 700 tons of green algae were attached to rafts and raft ropes respectively, and the lower biomass might be the main cause for the smaller scale of green tide in 2017. In addition, UAV play an important role in raft-attaching green algae monitoring and long-term research of its biomass would provide a scientific basis for the control and forecast of green tide in the Yellow Sea.

Seasonal and Spatial Changes in Trichodesmium Associated With Physicochemical Properties in East China Sea and Southern Yellow Sea

AbstractTrichodesmium is broadly distributed and occasionally blooms in the East China Sea (ECS) and southern Yellow Sea, where it contributes to local N and C budgets. However, its population structure, spatiotemporal distribution, controlling factors, and N2 fixation remain poorly documented. Here we provide high spatial resolution data sets of Trichodesmium during the four seasons of 2011–2012 using water‐ and net‐collected methods. The net‐collected method captures colonial trichomes of Trichodesmium effectively but results in an underestimation of free trichomes. Colonies are rarely observed and occur only on the ECS shelf, which are easily missed in water‐collected samples. Depth‐integrated densities of Trichodesmium were found to be significantly higher in warm seasons than in cold seasons. Maximum densities in the water column were generally found at depths of 10–50 m. Trichodesmium thrives on the oligotrophic, warm, offshore ECS shelf (controlled by the Kuroshio and Taiwan Warm Current), but restrains in the cold southern Yellow Sea and the eutrophic, inshore ECS. Seasonal and spatial variations in Trichodesmium are closely correlated with physicochemical properties (mainly temperature and P), which are primarily controlled by circulation alteration and water mass movement. The N2 fixation rates of Trichodesmium in the ECS in summer and autumn (&gt;20°C) are roughly estimated at 17.1 and 41.7 μmol N m−2 d−1 under nonbloom conditions, which potentially contribute to 81% and 57% of biological N2 fixation, respectively. Compared with historical data since the 1970s, Trichodesmium densities have increased considerably in all seasons, and the distribution boundary has shifted northward under regional warming and hydrological changes.

Variations in macrobenthic community at two stations in the southern Yellow Sea and relation to climate variability (2000–2013)

Decadal variations (2000–2013) in the macrobenthic community of the southern Yellow Sea were investigated based on the analysis of the community at two stations located basically along the 70 m depth contour. Significant decadal variations in community structure were found through cluster analysis, nMDS ordination and one-way ANOSIM. SIMPER analysis showed that the decadal community variations could be roughly attributed to the decrease of two species of Mollusks (Thyasira tokunagai and Nucula tenuis) and the increase of one echinoderm (Ophiura sarsii vadicola), one polychaete (Notomastus latericeus) and one bivalve (Portlandia japonica) at both stations. Redundancy analysis showed that the Pacific Decadal Oscillation and the Southern Oscillation Index were significant climate indices influencing the macrobenthic community structure in the southern Yellow Sea. Most of the species collected in 2000s showed a positive correlation with Pacific Decadal Oscillation at both stations, especially for cold water species Thyasira tokunagai, while most species in 2010s were positively correlated to Southern Oscillation Index, e.g. Portlandia japonica and Notomastus latericeus at station 1 and Sigambra bassi and Aricidea fragilis at station 2.

Pollution levels of DDTs and their spatiotemporal trend from sediment records in the Southern Yellow Sea, China

In order to study the pollution levels and spatiotemporal trend of Dichlorodiphenyltrichloroethanes (DDTs) in the Southern Yellow Sea (SYS), thirty-two surface sediment samples and a sediment core have been analyzed, and our results have been compared with previous reports. DDTs contents in our samples ranged from below detection limit to 5.1ng/gdry weight (d.w.), which presented lower ecological risks in the SYS. Surface sediment results show a seaward increasing trend with high values in the northern region of the central basin of the SYS. Our reconstructed core record and historical data from previous reports reveal an increasing trend from 1905 to 1955 but a decline trend since 1985 for DDTs, which is consistent of the production, usage and banning of DDTs in China. The source identification, based on (DDE+DDD)/DDTs, suggested that aged DDTs were the major contributor, though there were some inputs of fresh DDTs from the usage of 1,1-bis(p-Chlorophenyl)-2,2,2-trichloroethanol (dicofol).

A dataset of macrobenthic mollusks of southern Yellow Sea in summer 2011 &amp;ndash; 2013

A dataset of macrobenthic mollusks of southern Yellow Sea in summer 2011 &amp;ndash; 2013

Mechanisms of SAR Imaging of Shallow Water Topography of the Subei Bank

In this study, the C-band radar backscatter features of the shallow water topography of Subei Bank in the Southern Yellow Sea are statistically investigated using 25 ENVISAT (Environmental Satellite) ASAR (advanced synthetic aperture radar) and ERS-2 (European Remote-Sensing Satellite-2) SAR images acquired between 2006 and 2010. Different bathymetric features are found on SAR imagery under different sea states. Under low to moderate wind speeds (3.1~6.3 m/s), the wide bright patterns with an average width of 6 km are shown and correspond to sea surface imprints of tidal channels formed by two adjacent sand ridges, while the sand ridges appear as narrower (only 1 km wide), fingerlike, quasi-linear features on SAR imagery in high winds (5.4~13.9 m/s). Two possible SAR imaging mechanisms of coastal bathymetry are proposed in the case where the flow is parallel to the major axes of tidal channels or sand ridges. When the surface Ekman current is opposite to the mean tidal flow, two vortexes will converge at the central line of the tidal channel in the upper layer and form a convergent zone over the sea surface. Thus, the tidal channels are shown as wide and bright stripes on SAR imagery. For the SAR imaging of sand ridges, all the SAR images were acquired at low tidal levels. In this case, the ocean surface waves are possibly broken up under strong winds when propagating from deep water to the shallower water, which leads to an increase of surface roughness over the sand ridges.