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The relative importance of different organic matter sources to macrobenthic consumers was investigated at two vegetational habitats ( Phragmites australis and Suaeda japonica) and at a bare intertidal flat in Suncheon Bay in May and August 2010, using stable carbon and nitrogen isotope tracers. The δC of consumers was much narrower in range than that of potential food sources (microphytobenthos, marsh plants, and riverine and marine particulate organic matter), and values were similar between sites. However, cluster analysis based on the consumer's isotope values showed that they are divided according to functional groups rather than habitat type and taxonomical group, suggesting that the exploitation of different dietary sources depends on feeding strategy. Except for two suspension feeders and nonselective deposit feeders at the Phragmites bed, most consumers had similar δC to those of microphytobenthos. An isotopic mixing model calculation revealed the consistent importance of microphytobenthos to the nutrition of benthic invertebrates among wetland habitats in different seasons. In contrast, very little contribution of marsh plant-derived organic matter to consumer nutrition was detected at all sites. Furthermore, our results suggest that the summer monsoon event does not lead to a seasonal shift in dietary sources of consumers in this coastal wetland system. [ABSTRACT FROM AUTHOR]

The article discusses research done on the effect of intertidal groundwater seepage on benthic microalgae and macrofauna in several sites situated in two ecosystems in Korea. The study procedure included the comparison of the biological, physical, and chemical characteristics of the glossy seepage sites with sites that did not feature a visually distinct groundwater discharge. Results indicated the similarity of the pore water chemistry and the sediment properties in three out of four sites. The salinity and the nutrient concentrations of the groundwater seepage in the fourth site were also different from the other sites.

Abstract: The vertical distribution of microphytobenthos (MPB) was investigated in intertidal flats of the Nakdong River estuary over different temporal periods. The MPB biomass were measured as chlorophyll a concentration in the sediment, and monitored at two different depth scales. From August 2006 to August 2007, monthly sampling was carried out at four sites to a depth of 10cm. The vertical distribution exhibited an exponential decline with depth and the slope was closely related to sediment composition and MPB biomass in the surface sediment. The two slightly muddy sand (5–25% mud, <63μm) sites presented similar trends of seasonal variation to a sediment depth of 10cm, and no statistical difference was observed in their initial values and the slope of the exponential curves applied to each data set. The site with higher mud content also had higher surface biomass, and the fitted exponential curve had a larger slope than sites with more sand content. The seasonal variations of phaeo-pigments compared to chlorophyll a revealed higher grazing stress on the MPB in summer at the three slightly muddy sand sites, and low grazing stress all year around at the sand (<5% mud) site. In January, April and October 2007, and January 2008, diurnal sampling was conducted at hourly intervals at one slightly muddy sand site. The investigation in January 2007 which was conducted at 1cm intervals to a depth of 10cm sediment showed the migration mainly existed in the upper 1cm. The other diurnal sampling was undertaken to a 1cm depth at 0.5mm intervals. An evident migratory rhythm was present, with migration up to the surface during daytime emersion and down into deeper sediment during night and high tide submersion. Migrating cells could reach sediments as deep as 6 or even 10mm. When the visible thick biofilms formed, the migratory rhythm changed by keeping higher biomass at the surface even at night and during high tide submersion. Generally, the MPB surface biomass was an important factor in structuring the MPB vertical distribution. The vertical distribution to depths of 10cm was closely related to the sediment composition over the long term, while the MPB migration influenced the vertical distribution over the short term in the top 1cm of the sediment. [Copyright &y& Elsevier]

Abstract: Intertidal microphytobenthos (MPB) were investigated monthly from August 2006 to March 2008 at four different sites in the sand flats of Nakdong River estuary, Korea. Samples of surface sediment (ca. 1cm) were collected, and chlorophyll a was extracted as biomass estimation. Species identification and enumeration were carried out by light microscopy, assisted where necessary by scanning electronic microscopy. Biomass varied between 0.47 and 16.58μgcm−3, abundance changed from 5.25 to 414.75×103 cells cm−3, while the Shannon diversity indexes ranged between 0.69 and 2.35 H′. Thirty-nine MPB taxa were identified, primarily composed of epipelic diatoms, among which Amphora and Navicula were the most abundant genera. Based on the biomass, abundance, species composition and their dynamics, MPB assemblages of sampling sites were grouped into three distinct communities corresponding to their sediment composition characteristics. Multivariate correlation analysis revealed that biomass was positively related to mud and very fine sand, negatively related to fine and medium sand, but not significantly related to environmental factors such as pore water nutrients, light intensity and salinity, which fluctuated rapidly during emersion period. Cluster analysis corroborated the division of MPB communities according to site types on seasonal scales, and also showed seasonality between sites by cluster of all summer groups. Principal component analysis identified that variability in species composition was significantly affected by mud, very fine sand, fine sand, light intensity, and sediment temperature. This study suggests that sediment composition plays an important role in the functioning of intertidal MPB communities in estuarine ecosystems. [Copyright &y& Elsevier]

The article presents a study which aims to quantify the nitrate and ammonium uptake by intertidal microphytobenthos (MPB). It also seeks to determine the association of nutrient concentration, light availability, and migration in the assimilation of dissolved inorganic nitrogen (DIN) by MPB. To assess the nitrate and ammonium uptake kinetics by MPB, 15N stable isotopes technique on cell extracted from the sediment at the Nakdong River Estuary in Korea was employed. Results show that the uptake of ammonium by MPB under darkened conditions was lower than during light periods. Based on the findings, it proposes that the affinity of MPB for DIN may be associated to the environmental conditions to which they are exposed.