Estuarine nutrient loading affects phytoplankton growth and microzooplankton grazing at two contrasting sites in Hong Kong coastal waters

To investigate the effects of enhanced nutrient loading in estuarine waters on phytoplankton growth and microzooplankton grazing, we conducted monthly dilution experiments at 2 stations in Hong Kong coastal waters with contrasting trophic conditions. The western estuarine station (WE) near the Pearl River estuary is strongly influenced by freshwater discharge, while the eastern oceanic station (EO) is mostly affected by the South China Sea. Growth rates of phytoplankton were often limited by nutrients at EO, while nutrient limitation of phytoplankton growth seldom Occurred at WE due to the high level of nutrients delivered by the Pearl River, especially in the summer rainy season. Higher chlorophyll a, microzooplankton biomass, phytoplankton growth and microzooplankton grazing rates were found at WE than at EO. However, the increase in chlorophyll greatly exceeded the increase in phytoplankton growth rate, reflecting different response relationships to nutrient availability. Strong seasonality was observed at both stations, with temperature being an important factor affecting both phytoplankton growth and microzooplankton grazing rates. Picophytoplankton, especially Synechococcus, also exhibited great seasonality at EO, with summer abundances being 2 or 3 orders of magnitude higher than those during winter, Our results confirm that in eutrophic coastal environments, microzooplankton grazing is a dominant loss pathway for phytoplankton, accounting for the utilization of >50%, of primary production on average.

Impact of tidal front on the distribution of bacterioplankton in the southern Yellow Sea, China

Three surveys were carried out in anchovy spawning periods in southern Yellow Sea in May and June 2001, and June 2002. Chlorophyll a (Chl-a) concentration, bacterioplankton abundance, biomass and their variations along the zone of tidal fronts were investigated. The results showed that (1) high Synechococcus abundance distributed more often in frontal area and middle-surface layer of a stratified zone; and (2) the maximal abundance of bacteria occurred in stratified and mixed zone. 2006 Elsevier B.V. All rights reserved.

The Bopyridae (Crustacea: Isopoda) parasitic on thalassinideans (Crustacea: Decapoda) from China

Eight species among six genera of bopyrid isopods (representing the subfamilies Pseudionmae and loninae) infesting thalassinideans from China are reported. Of these, four species are new to science: Gyge.fujianensis n. sp., Progebiophilits elongatus n. sp., Upogebione bidigitatus n. sp., and Procepon liuruiyui n. sp., infesting Upogebia major (de Haan), Nihonotrypaea japonica Ortmann, Upogebia carinicauda (Stimpson), and Austinogebia wuhsienweni (Yu). One species, lone cornuta Bate, 1864, is recorded for the first time from Chinese waters and from a new host. Pseudione longicauda Shiino, 1937, Gyge ovalis (Shiino, 1939), and Progebiophilus sinicus Markham, 1982, previously known from Hong Kong or Taiwan, are recorded for the first time from mainland China, extending their range north.

Spatial variations of size-fractionated chlorophyll, cyanobacteria and heterotrophic bacteria in the Central and Western Pacific

Geographic and vertical variations of size-fractionated (0.2-1 mu m, 1-10 mu m, and >10 mu m) Chlorophyll a (Chl.a) concentration, cyanobacteria abundance and heterotrophic bacteria abundance were investigated at 13 stations from 4 degrees S, 160 degrees W to 30 degrees N, 140 degrees E in November 1993. The results indicated a geographic distribution pattern of these parameters with instances of high values occurring in the equatorial region and offshore areas, and with instance of low values occurring in the oligotrophic regions where nutrients were almost undetectable. Cyanobacteria showed the highest geographic variation (ranging from 27x10(3) to 16,582x10(3) cell l(-1)), followed by Chl.a (ranging from 0.048 to 0.178 mu g l(-1)), and heterotrophic bacteria (ranging from 2.84x10(3) to 6.50 x 10(5) cell l(-1)). Positive correlations were observed between nutrients and Chl.a abundance. Correspondences of cyanobacteria and heterotrophic bacteria abundances to nutrients were less significant than that of Chl.a. The total Chl.a was accounted for 1.0-30.9%, 35.9-53.7%, and 28.1-57.3% by the >10 mu m, 1-10 mu m and 0.2-1 mu m fractions respectively. Correlation between size-fractionated Chl.a and nutrients suggest that the larger the cell size, the more nutrient-dependent growth and production of the organism. The ratio of pheophytin to chlorophyll implys that more than half of the > 10 mu m and about one third of the 1-10 mu m pigment-containing particles in the oligotrophic region were non-living fragments, while most of the 1-10 mu m fraction was living cells. In the depth profiles, cyanobacteria were distributed mainly in the surface layer, whereas heterotrophic bacteria were abundant from surface to below the euphotic zone. Chl.a peaked at the surface layer (0-20 m) in the equatorial area and at the nitracline (75-100 m) in the oligotrophic regions. Cyanobacteria were not the principle component of the picoplankton. The carbon biomass ratio of heterotroph to phytoplankton was greater than 1 in the eutrophic area and lower than 1 in oligotrophic waters.