黄海春季水华过程中微微型浮游生物的变化特点

于2007年3—4月在黄海中部海域采用流式细胞术研究了春季水华过程中聚球藻、微微型真核浮游生物和异养细菌的生物量变化。聚球藻和微微真核型浮游生物的生物量与叶绿素a浓度变化基本呈现相反的趋势,在水华前期较高,水华期迅速下降,直至水华后期又有所升高。异养细菌在整个水华过程中变化较小,生物量在水华期最高,与水柱叶绿素a浓度呈极显著正相关(r=0.319,p<0.01)。水华期这三类微微型浮游生物对浮游植物总碳生物量的贡献很低。纤毛虫和鞭毛虫捕食可能是导致聚球藻和微微型真核浮游生物在水华期生物量降低的主要原因。     

胶州湾海月水母(Aurelia sp.1)丰度周年变化及对浮游动物群落的影响

2009年2—12月间在胶州湾大沽河口邻近海域的逐月现场调查中,利用垂直拖网研究了海月水母碟状体和水母体的时空分布情况以及对其它浮游动物类群的影响,并探讨了海月水母的生态适应性。结果表明:海月水母的碟状体4月份开始在胶州湾出现,并且丰度逐渐增加,到6月份达到最高峰。海月水母的水母体集中在7月份大量出现。碟状体和水母体高峰期的月平均丰度分别为2.9和1.3ind/m3。碟状体开始出现时的水温平均为11.5℃,数量高峰期的水温为20.6℃,而水母体高峰期的水温为25.2℃。该海域的浮游动物总丰度(不含夜光虫)在5—7月份有个高峰期,其中5月份最高值为486.9ind/m3。7月份海月水母高峰期,浮游动物的丰度没有明显下降,两者丰度的地理变化之间也没有显著的相关性。但是通过对2006—2010年间的浮游动物各类群丰度对比,2009年海月水母暴发时夜光虫和桡足类春季丰度高值显著低于其它年份。     

Chlorophyll a increase induced by surface winds in the northern South China Sea

The response of chlorophyll a (Chl a) concentration to wind stress is analyzed in the South China Sea (SCS), using in-situ data of Chl a and remote sensing data (QuikScat-sea surface wind (SSW), AVHRR-sea surface temperature (SST), AVISO merged-sea level anomalies (SLA), SeaWiFSderived Chl a and MODIS Terra-derived Chl a) in August/September/October 2004, 2006 and 2009. The variability of SSW, SST and SLA 7 d before in-situ Chl a sampling (including the work day of in-situ Chl a sampling) with the same latitude and longitude of the study area are investigated, and the correlation coefficients are calculated between these hydrographic factors and in-situ Chl a concentration. The results show that the Chl a-SSW correlation coefficients at upper layers (such as 0 m and 25 m) are more significant than those at deeper layers (such as 50, 75 and 100 m) 1-3 d before, which indicates that there is a time lag of strong surface winds stimulating phytoplankton bloom. By analyzing the relationship among the daily remote sensing derived (RSderived) SSW, SST, SLA and 3 d averaged SeaWiFS/MODIS-derived Chl a concentration in the northern SCS in September 2004 and 2009 respectively, it shows that the intensity and speed of surface winds could have great influence on extend of Chl a increase. If surface winds reach 4-5 m/s over, Chl a concentration would increase 1-3 d after the process of strong surface winds in open sea area of the northern SCS mainly during September.     

Influence of nitrate and dissolved organic carbon loading on the interaction of Microcystis aeruginosa and heterotrophic bacteria from hyper-eutrophic lake (Taihu Lake,China)

To investigate the interaction between cyanobacteria and heterotrophic bacteria under gradients of glucose and nitrate, a cyanobacterial strain of Microcystis aeruginosa was grown in microcosms with and without a freshwater bacterial mixture, which was collected from Lake Taihu. Concentrations of glucose (1350, 975, 600, 300, 150, and 37.5 μmol C L⁻¹) and nitrate (150, 300, and 9000 μmol N L⁻¹) were used in a range of combinations giving 9 different treatments of glucose:nitrate. In the microcosm without the bacterial mixture, M. aeruginosa abundance gradually increased with days in all treatments. However, M. aeruginosa had much lower density in some treatments with the bacterial mixture. The difference in M. aeruginosa growth could be explained by competition with bacteria in the cultures in which these were added. The abundance of M. aeruginosa and bacteria when grown together was nearly equal and the number of the bacterial species was highest in the treatment with 300 μmol C L⁻¹ and 150 μmol N L⁻¹. Our results suggest that at this glucose:nitrate ratio M. aeruginosa and the bacterial mixture maintain a balance, and bacteria maintain diversity. In conclusion, we propose that dissolved organic carbon and nitrate availability fundamentally affects the structure as well as stoichiometry of pelagic associations.     

The influence of extreme floods from the River Danube in 2006 on phytoplankton communities in a floodplain lake: Shift to a clear state

The influence of extreme floods from the River Danube in 2006 on the species composition and vertical distributions of phytoplankton was studied in a shallow floodplain lake, Lake Sakadaš (Kopa?ki Rit Nature Park, Croatia) which in the last few decades was in a turbid state characterised by high phytoplankton concentrations. As a consequence of extremely high floods, the whole floodplain area (approximately 16 km²) became one lentic habitat with well developed macrophyte vegetation. Seasonal dynamics of chlorophyll a (Chl a) concentration in the lake had a characteristic pattern for the shallow lakes with dense macrophyte vegetation. Extremely low mean phytoplankton abundance and biomass were found in the conditions of very high nutrient concentrations. Dominant phytoplankton species were diatoms and chlorococcal green algae from the functional groups characteristic for a mixed environment. The canonical correspondence analysis (CCA) demonstrated that nutrients and temperature were significant environmental variables for their development. The sequence of phytoplankton seasonality, vertical distribution of phytoplankton, as well as the domination of rapidly acclimating phytoplankton forms (R-strategists) indicated clear, well-mixed conditions and a highly disturbed environment. Our results suggest that the occurrence of extreme flooding can be a stressor high enough for the transition from a turbid to a clear state of the floodplain lake. Possibly, cyclic shifts between alternative stable states in floodplain ecosystems can be expected as a consequence of the impact of extreme hydrological events induced by a climate change.     

Changes of the plankton community composition during chemical neutralisation of the Bockwitz pit lake

Lake Bockwitz, a pit lake in a former lignite open-cast mine south of Leipzig (Germany), was neutralised (from pH 2.65 to pH 7.1) by addition of soda ash (14,620 t) from 2004 to 2007. The additions had to be continued due to ongoing inflows of acid ground and surface water. This paper reports on the changes in the plankton community accompanying the neutralisation.At the beginning, the community composition and biomass was comparable to other acidic pit lakes, i.e. the pigmented flagellates Chlamydomonas and Ochromonas dominated the autotrophs, and ciliates and rotifers were the top predators. The biomass was small (maximum 2 mg fresh weight per litre) and decreased until the end of 2008. With increasing pH, the autotrophic community became more diverse, whereby diatoms, chrysophyceans and blue greens contributed significantly to biomass. Although neutral pH conditions were achieved in autumn 2007, picocyanobacteria were not present until the end of 2008. In addition, crustaceans were under-represented in terms of biomass and diversity. Daphnids were not found. We attributed this to short-term changes of the ionic composition of the water and to the limited time available for non-acido-tolerant organisms to colonise the system.     

Phytoplankton production and physiological adaptation on the southeastern shelf of the Agulhas ecosystem

An investigation of phytoplankton production and physiology was undertaken during two research cruises on the southeastern shelf of southern Africa. The data set included photosynthesis-irradiance and active fluorescence parameters, phytoplankton absorption coefficients and HPLC pigment concentrations. Primary production was estimated to vary over a similar range for both cruises within 0.27–3.69 g C m⁻² d⁻¹. Pigment indices indicated that diatoms were dominant on the first cruise and the communities were subject to conditions where the mixed layer was deeper than the euphotic zone and they optimized their photosynthesis to very low light intensities at the bottom and below the euphotic zone. Mixed diatom-flagellate populations were observed during the second cruise where the euphotic zone was deeper than the mixed layer and the populations adapted to irradiances higher in the euphotic zone. In response to a mean lower water column PAR, it was found that these mixed communities increased the proportion of chlorophyll a in the pigment pool and had a higher quantum yield of photochemistry and higher light-limited photosynthetic efficiency.     

The COPAS’08 expedition to the Patagonian Shelf: Physical and environmental conditions during the 2008 coccolithophore bloom

Here we present observations of the hydrography of the Patagonian Shelf, shelf break and offshore waters, with reference to the environmental conditions present during the period of peak coccolithophore abundance. Analysis of a hydrographic dataset collected in December 2008 (austral spring/summer), as part of the Coccolithophores of the Patagonian Shelf (COPAS) research cruise, identified 5 distinct surface water masses in the region between 37°S and 55°S. These water masses, identified through salinity gradients, displayed varying mixed layer depths, macronutrient inventories and chlorophyll-a fluorescence. Subantarctic Shelf Water (SSW), located to the north of the Falkland Islands and extending north along the shelf break, was also host to a large coccolithophore bloom. The similarities between the distribution of calcite, as seen in remote sensing data, and SSW indicate that the coccolithophore bloom encountered conditions conducive to bloom development within this water mass. Analysis of chemical and environmental data also collected during the COPAS cruise revealed that many of the commonly cited conditions for coccolithophore bloom development were present within SSW (e.g. low N:P ratio, high N:Si ratio, shallow mixed layer depth). In the other water masses present on the Patagonian Shelf greater variability in these same parameters may explain the more diffuse concentration of calcite, and the smaller size of possible coccolithophore blooms. The distribution of SSW is strongly influenced by the latitudinal variation in shelf break frontal width, which varies from 20 to 200 km, and consequently strong hydrographic controls underlie the position of the coccolithophore bloom during austral summer.     

Modeling the timing of spring phytoplankton bloom and biological production of the Gulf of St. Lawrence (Canada): Effects of colored dissolved organic matter and temperature

The effects of colored dissolved organic matter (CDOM) from freshwater runoff and seasonal cycle of temperature on the dynamic of phytoplankton and zooplankton biomass and production in the Gulf of St. Lawrence (GSL) are studied using a 3-D coupled physical-plankton ecosystem model. Three simulations are conducted: (1) the reference simulation based on Le Fouest et al. (2005), in which light attenuation by CDOM is not considered and maximum growth rate (_μmax${\mu }_{\max }$) of phytoplankton and zooplankton are not temperature-dependent (REF simulation); (2) light attenuation by CDOM is added to REF simulation (CDOM simulation); and (3) in addition to CDOM, the _μmax${\mu }_{\max }$ of phytoplankton and zooplankton are regulated by temperature (CDOM+TEMP simulation). CDOM simulation shows that CDOM substantially reduces phytoplankton biomass and production in the Lower St. Lawrence Estuary (LSLE), but slightly reduces overall primary production in the GSL. In the LSLE, the spring phytoplankton bloom is delayed from mid-March to mid-April, resulted from light attenuation by CDOM. The CDOM+TEMP simulation shows that the spring phytoplankton bloom in the LSLE is further delayed to July, which is more consistent with observations. Annual primary production is reduced by 33% in CDOM+TEMP simulation from REF and CDOM simulations. Zooplankton production is the same in all three simulations, and export of organic matter to depth is reduced in CDOM+TEMP simulation, suggesting that temperature controlled growth of phytoplankton and zooplankton enhances the coupling between primary production and zooplankton production under the seasonal temperature cycle of the GSL.