Lingfeng Huang

Weak coupling between heterotrophic nanoflagellates and bacteria in the Yellow Sea Cold Water Mass area

A study was carried out to investigate the grazing pressure of heterotrophic nanoflagellates (HNF) on bacteria assemblages in the Yellow Sea Cold Water Mass (YSCWM) area in October, 2006. The results show that the HNF abundance ranges from 303 to 1 388 mL−1, with a mean of 884 mL−1. The HNF biomass is equivalent to 10.6%–115.6% of that of the bacteria. The maximum abundance of the HNF generally occurred in the upper 30 m water layer, with a vertical distribution pattern of surface layer abundance greater than middle layer abundance, then bottom layer abundance. The hydrological data show that the YSCWM is located in the northeastern part of the study area, typically 40 m beneath the surface. A weak correlation is found between the abundances of HNF and bacteria in both the YSCWM and its above water layer. One-way ANOVA analysis reveals that the abundance of HNF and bacteria differs between inside the YSCWM and in the above water mass. The ingestion rates of the HNF on bacteria was 8.02±3.43 h−1 in average. The grazing rate only represented 22.75%±6.91% of bacterial biomass or 6.55%+4.24% of bacterial production, implying that the HNF grazing was not the major factor contributing to the bacterial loss in the YSCWM areas.

Spatial and temporal distribution of nanoflagellates in the northern South China Sea

Seasonal variation, horizontal and vertical distribution, and cell size of nanoflagellates, together with physico-chemical and biological factors, were studied in the northern South China Sea (SCS). It was found that nanoflagellate abundance ranged from 0.157xa0×xa0103 to 9.193xa0×xa0103xa0cells/ml (with a mean of 0.891xa0×xa0103) in winter (February, 2004), while it ranged from 0.107xa0×xa0103 to 5.417xa0×xa0103 xa0cells/ml (with a mean of 0.599xa0×xa0103) in summer (July, 2004). Nanoflagellates were more abundant in winter than summer in offshore regions, showing an unique seasonal pattern in this subtropical marginal sea. The abundance of nanoflagellates decreased from the estuary to the offshore region. Vertical distribution of nanoflagellates coupled well with that of bacteria and Chl a. The small size fraction of less than 5xa0μm dominated the nanoflagellate populations. Wind-driven mixing, eddies, availability of nutrients as well as Chl a and abundance of picoplankton seemed to be the major controlling factors for the spatial distribution and seasonal variation of nanoflagellates in the study area.

Tracing organic matter removal in polluted coastal waters via floating bed phytoremediation

Organic matter removal by cultured Sesuvium portulacastrum in constructed floating beds was studied during a 20 day greenhouse experiment and an 8 month field campaign in the polluted Yundang Lagoon (southeastern China). Experiments were traced via dissolved organic carbon (DOC) concentration, fluorescence excitation-emission matrix and absorption spectroscopy. Two terrestrial humic-like, one marine humic-like and one protein-like components were identified by parallel factor analysis. The terrestrial humic-like and protein-like components, DOC and absorption coefficient (a280) decreased during the greenhouse experiment. The intensities of four fluorescence components were all reduced during the field experiment. These results demonstrate the clear potential of floating bed phytoremediation techniques for reducing organic pollution degree in brackish environments. The rhizosphere may play an important role during phytoremediation. Our results show that spectrophotometric measurements such as fluorescence provide a useful tool for examining the removal of different organic moieties during various bioremediation processes.

Inhibitory effect of Salicornia europaea on the marine alga Skeletonema costatum

Exploiting the negative biochemical interference between plants and algal species has been suggested as a method to control harmful algal blooms. In this work, we investigated the inhibitory effect of the salt marsh halophyte Salicornia europaea against the marine alga Skeletonema costatum. S. europaea suppressed the growth of S. costatum in a nutrient-sufficient co-culture system, indicating that the inhibition of algal growth was because of the phytotoxic effect of S. europaea, rather than nutrient competition. We tested aqueous and organic extracts from S. europaea roots against S. costatum. The organic extracts inhibited growth and affected the cell size and chlorophyll a content of S. costatum in a dose-dependent manner. Among the three tested organic extracts, the methanol extract had the greatest effects on S. costatum, followed by butanol extract, and then the chloroform extract. Two flavonoids, rutin and quercetin-3-β-D-glucoside, were identified in the methanol extract by high performance liquid chromatography. The concentration of rutin was much higher than that of quercetin-3-β-D-glucoside. In an algal bioassay, rutin inhibited the growth of S. costatum and the inhibitory effect increased with increasing rutin concentration and with decreasing initial algal density. Therefore, we concluded that S. europaea negatively affects the growth of S. costatum, and that rutin, a metabolite of S. europaea, may play a role in this inhibitory effect.

Factors regulating population dynamics of the amphipod Ampithoe valida in a eutrophic subtropical coastal lagoon

Year-round investigations were carried out to address the population dynamics of amphipod Ampithoe valida and its potential regulating factors in the Yundang Lagoon (a eutrophic subtropical coastal lagoon in Xiamen City, China) from October 2007 to October 2008. The results show that A. valida population was largely composed of juveniles and reached a peak abundance (12.02×103 ind./m2) in March, but sharply shrunk in July. The monthly variation pattern of A. valida seemed to follow that of Ulva lactuca which is the main food resource for A. valida, indicating a strong influence of food availability on A. valida population dynamics. Life cycle studies in laboratory indicate that A. valida adopted an r -selected life strategy, e.g., rapid growth rate (0.216–0.302 mm/d), consecutive breeding (4–10 times), short reproductive rhythm (9–17 d) and huge fecundity (24–192 eggs or 6–94 juveniles per brood), which contributed to the fast population growth of A. valida from January to March. Although temperature may also be a significant cause, A. valida could grow quickly and show normal reproductive traits (i.e., the timing of sexual differentiation or maturity, the reproductive rhythm, the number of broods all through its lifespan and offspring production) in temperature between 15–30°C. Therefore, the temperature variation in the lagoon water should not account for the sharp variation of A. valida population by affecting the survival, growth and reproduction of the amphipod. However, negative correlation between water temperature and U. lactuca biomass in the lagoon suggested that temperature could have indirectly affected the population dynamics of A. valida by affecting its food availability. The authors conclude that, in the Yundang Lagoon, the population dynamics of A. valida was mainly controlled by the food availability rather than water temperature.

Flexible optical waveguide beam splitters based on directional coupling

A fundamental 1×2 beam splitter based on directional coupling of flexible optical waveguides is presented. The coupling and transmission characteristics of the beam splitter are investigated by using the plane wave expansion method and finite-difference time-domain method, respectively. Calculated results indicate that, for this beam splitter, without any structural optimization, near-complete transmission is observed within a wide frequency band. Combining the fundamental 1×2 beam splitter with flexible optical waveguides, we construct a simple and compact 1×4 beam splitter. Those beam splitters are expected to be applied to highly dense photonic integrated circuits.

Amphipods fail to suppress the accumulation of Ulva lactuca biomass in eutrophic Yundang Lagoon

The Gross growth efficiency (GGE) is defined as the amount of consumer carbon produced relative to the amount of prey ingested in a given time interval. In population ecology, it can be considered as an index for the ability of a consumer to convert the biomass of food into its population production. In this study, it was firstly applied to estimate the role of amphipods grazing in the biomass dynamics of macroalgae (Ulva lactuca) in Yundang Lagoon (a subtropical eutrophic coastal lagoon, Xiamen City, China). It was found that amphipods were the dominant group (82.2%–98.7%) in the benthic assemblage, in which five amphipod species (Corophium uenoi, Ampithoe valida, Grandidierella japonica, Grammaropsis laevipalmata and Caprella panantis) were observed in the lagoon. However, only A. valida significantly consumed U. lactuca among these amphipod species. A series of experiments were conducted to estimate the consumption of U. lactuca by A. valida. It was suggested that the monthly secondary production (P) of A. valida using size frequency method ranged from 2.39 to 13.68 g/m2. GGE of A. valida exponentially reduced with body size and was closely associated with water temperature. Therefore, GGE equation for different months using the temperature recorded during the field investigation was fitted. The monthly consumption of U. lactuca was figured out to be 86.7–1 549.0 g/m2 by the sum of consumption (P/GGE) by A. valida at different size, accounting for 2.0%–37.5% of U. lactuca production. It indicates that the grazing effect of A. valida did play a role in reducing the accumulation of U. lactuca biomass when A. valida was abundant, but it finally fails to limit the U. lactuca growth in Yundang Lagoon. Low abundance of A. valida and high nutrient loading may be two major reasons for the outbreak of U. lactuca bloom in the lagoon.