Morphology and molecular phylogeny of Pleurosigmapacificum sp. nov. (Pleurosigmataceae), a new tropical pelagic species from the Western Pacific Ocean.

A new species of pelagic diatom, Pleurosigmapacificumsp. nov., is described from the tropical Western Pacific Ocean. It has the typical features of Pleurosigma, including a slightly sigmoid raphe, intersected transverse and oblique striae, and loculate areolae with external opening slits and internal poroids. Morphologically, P.pacificum belongs to a species group of Pleurosigma with lanceolate valves, including P.atlanticum Heiden & Kolbe, P.nubecula W. Smith, P.indicum Simonsen, and P.simonsenii Hasle. However, P.pacificum differs by its smaller lanceolate valve and smaller intersection angle as well as elliptical areolae without a silica bar. The SSU rDNA and rbcL sequence data place P.pacificum in a basal position relative to other species of Pleurosigma. Our molecular phylogenetic analyses did not support the monophyly of lanceolate and slightly sigmoid species. Thus, the sigmoidality of valve outline cannot be considered as a criterion to define the species group.

[Standing crop and spatial distribution of meiofauna in Yellow Sea at late stage of Enteromorpha prolifera bloom in 2008].

An investigation was made on the standing crop, spatial distribution, sediment environment of meiofauna at 33 stations (including 22 stations in cold water mass area and 9 stations in Enteromorpha prolifera bloom area) in the Yellow Sea at the late stage of E. prolifera bloom in summer 2008. In this southern Yellow Sea area which was seriously impacted by the green algal bloom, the silt and clay contents in the sediments in 2008 had an obvious increase, compared with those in 2007, and the sediment chlorophyll-a and phaeophytin a contents in 2008 did not show obvious changes in cold water mass area but distinctly decreased in southern Jiangsu inshore area and Yangtze River estuary. Within the total 16 meiofaunal groups sorted, no marked variation was observed in their vertical distribution and in the contribution of each group to the total meiofauna. In 2008, the average abundance of meiofauna was (1375 +/- 793) ind x 10 cm(-2), and the biomass was (1203 +/- 707) micro x 10 cm(-2), both of which were decreased by about 1/3, compared with those in 2007. The meiofaunal standing crop was decreased more obviously in the stations heavily affected by the E. prolifera bloom, while that in the Yellow Sea cold water mass area was slightly increased, resulting in an unusual trend of meiofaunal standing crop decreasing from the central area of cold water mass to the inshore area in the southern Yellow Sea. By contrast, and as usual, the meiofaunal standing crop was increased from the cold water mass area to the inshore area in the northern Yellow Sea. Statistical analyses suggested that only the meiofaunal abundance had positive correlation with the salinity in the stations heavily affected by the green algal bloom. Our study indicated that macroalgal bloom obviously inhibited the standing crop of meiofauna in the inshore area. The decrease was not due to the deficiency of food concentration, but likely caused by the deposition and degradation of the E. prolifera bloom.