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1.
《Journal of Sea Research》2009,61(4):246-254
The aim of this study was to investigate controls on the phytoplankton community composition and biogeochemistry of the estuarine plume zone of the River Thames, U.K. using an instrumented moored buoy for in situ measurements and preserved sample collection, and laboratory-based measurements from samples collected at the same site. Instrumentation on the moored buoy enabled high frequency measurements of a suite of environmental variables including in situ chlorophyll, water-column integrated irradiance, macronutrients throughout an annual cycle for 2001 e.g. nitrate and silicate, and phytoplankton biomass and species composition. The Thames plume region acts as a conduit for fluvial nutrients into the wider southern North Sea with typical winter concentrations of 45 μM nitrate, 17 μM silicate and 2 μM phosphate measured. The spring bloom resulted from water-column integrated irradiance increasing above 60 W h m− 2 d− 1 and was initially dominated by a diatom bloom mainly composed of Nitzschia sp. and Odontella sinesis. The spring bloom then switched after ∼ 30 days to become dominated by the flagellate Phaeocystis reaching a maximum chlorophyll concentration of 37.8 μg L− 1. During the spring bloom there were high numbers of the heterotrophic dinoflagellates Gyrodinium spirale and Katodinium glaucum that potentially grazed the phytoplankton bloom. This diatom–flagellate switch was predicted to be due to a combination of further increasing water-column integrated irradiance > 100 W h m− 2 d− 1 and/or silicate reaching potentially limiting concentrations (< 1 μM). Post spring bloom, diatom dominance of the lower continuous summer phytoplankton biomass occurred despite the low silicate concentrations (Av. 0.7 μM from June–August). Summer diatom dominance, generally due to Guinardia delicatula, was expected to be as a result of microzooplankton grazing, dominated by the heterotrophic dinoflagellate Noctiluca scintillans, controlling 0.7–5.0 μm ‘flagellate’ fraction of the phytoplankton community with grazing rates up to 178% of ‘flagellate’ growth rate. The Thames plume region was therefore shown to be an active region of nutrient and phytoplankton processing and transport to the southern North Sea. The use of a combination of moorings and ship-based sampling was essential in understanding the factors influencing nutrient transport, phytoplankton biomass and species composition in this shelf sea plume region.  相似文献   

2.
The relationships between the spatiotemporal variation in phytoplankton community structure and environmental variables were investigated in the Kuroshio Extension (KE) region from winter to spring by analysing biomarker pigments. In winter, when the mixed layer was deep, phytoplankton communities were characterised by low biomass and a relatively high dominance of cryptophytes, followed by chlorophytes and pelagophytes. In spring, phytoplankton biomass generally increased with shoaling of the mixed layer. In April, when nitrate was not exhausted, chlorophytes became the most dominant group throughout the KE region, followed by cryptophytes. In May, in the south of the KE, phytoplankton biomass decreased with the depletion of nitrate and cyanobacteria dominated, whereas at the northern edge of the KE, phytoplankton biomass remained high. A predominance of diatoms occurred sporadically at the northern edge of the first ridge with a shallow mixed layer and an elevated nutricline. In contrast, the contribution of diatoms was low at the northern edge of the second ridge, despite high levels of nitrate and silicic acid, suggesting that factors other than macronutrient depletion limited diatom production. In general, the contribution of diatoms to the total phytoplankton biomass in the KE region was small in both winter (2.9%) and spring (16%). This study showed that the phytoplankton communities in the KE region during the spring bloom were generally composed of non-diatom phytoplankton groups, chlorophytes, cryptophytes, and prasinophytes. It is necessary to identify the roles of non-diatoms in grazing food chains to more accurately evaluate the KE as a nursery area for pelagic fish.  相似文献   

3.
We characterized the community composition of phytoplankton in the western subarctic Pacific from the pre-bloom to the decline phase of the spring bloom with special reference to decreases in the silicic acid concentration in surface waters as an index for diatom bloom development. Furthermore, responses of heterotrophic bacteria and viruses to the spring bloom were also concomitantly investigated. Under pre-bloom conditions when nutrients were abundant but the surface mixed layer depth was relatively deep, chlorophyll (Chl) a concentrations were consistently low and green algae (chlorophytes and prasinophytes), cryptophytes, and diatoms were predominant in the phytoplankton assemblages as estimated by algal pigment signatures. Together with the shallowing of the mixed layer depth and the decrease in silicic acid concentration, diatoms bloomed remarkably in the Oyashio region, though the magnitude of the bloom in the Kuroshio-Oyashio transition (hereafter Transition) region was relatively small. A total of 77 diatom species were identified, with the bloom-forming diatoms mainly consisting of Thalassiosira, Chaetoceros, and Fragilariopsis species. It has become evident that the carotenoid fucoxanthin can serve as a strong indicator of the diatom carbon biomass during the spring diatom bloom. Differences in the species richness of diatoms among stations generally enabled us to separate the Oyashio bloom stations from the Transition and the Oyashio pre-bloom stations. Relatively high values of the Shannon-Wiener index for the diatom species were also maintained during the Oyashio bloom, indicating that a wide variety of species then shared dominance. In the decline phase of the Oyashio bloom when surface nutrient concentrations decreased, senescent diatom cells increased, as inferred from the levels of chlorophyllide a. Although the cell density of heterotrophic bacteria changed little with the development of the diatom bloom, viral abundance increased toward the end of the bloom, suggesting an increased likelihood of mortality among organisms including diatoms resulting from viral infection. This is the first report on the microbial trophodynamics, including viruses, during the spring diatom bloom in the western subarctic Pacific.  相似文献   

4.
The aim of this study was to investigate controls on the phytoplankton community composition and biogeochemistry of the estuarine plume zone of the River Thames, U.K. using an instrumented moored buoy for in situ measurements and preserved sample collection, and laboratory-based measurements from samples collected at the same site. Instrumentation on the moored buoy enabled high frequency measurements of a suite of environmental variables including in situ chlorophyll, water-column integrated irradiance, macronutrients throughout an annual cycle for 2001 e.g. nitrate and silicate, and phytoplankton biomass and species composition. The Thames plume region acts as a conduit for fluvial nutrients into the wider southern North Sea with typical winter concentrations of 45 μM nitrate, 17 μM silicate and 2 μM phosphate measured. The spring bloom resulted from water-column integrated irradiance increasing above 60 W h m− 2 d− 1 and was initially dominated by a diatom bloom mainly composed of Nitzschia sp. and Odontella sinesis. The spring bloom then switched after  30 days to become dominated by the flagellate Phaeocystis reaching a maximum chlorophyll concentration of 37.8 μg L− 1. During the spring bloom there were high numbers of the heterotrophic dinoflagellates Gyrodinium spirale and Katodinium glaucum that potentially grazed the phytoplankton bloom. This diatom–flagellate switch was predicted to be due to a combination of further increasing water-column integrated irradiance > 100 W h m− 2 d− 1 and/or silicate reaching potentially limiting concentrations (< 1 μM). Post spring bloom, diatom dominance of the lower continuous summer phytoplankton biomass occurred despite the low silicate concentrations (Av. 0.7 μM from June–August). Summer diatom dominance, generally due to Guinardia delicatula, was expected to be as a result of microzooplankton grazing, dominated by the heterotrophic dinoflagellate Noctiluca scintillans, controlling 0.7–5.0 μm ‘flagellate’ fraction of the phytoplankton community with grazing rates up to 178% of ‘flagellate’ growth rate. The Thames plume region was therefore shown to be an active region of nutrient and phytoplankton processing and transport to the southern North Sea. The use of a combination of moorings and ship-based sampling was essential in understanding the factors influencing nutrient transport, phytoplankton biomass and species composition in this shelf sea plume region.  相似文献   

5.
Two processes are generally explained as causes of temporal changes in the stoichiometric silicon/nitrogen (Si/N) ratios of sinking particles and of nutrient consumption in the surface water during the spring diatom bloom: (1) physiological changes of diatom under the stress of photosynthesis of diatom and (2) differences of regeneration between silicon and nitrogen. We investigated which process plays an important role in these changes using a one-dimensional ecosystem model that explicitly represents diatom and the other non-silicious phytoplankton. The model was applied to station A7 (41°30′ N, 145°30′ E) in the western North Pacific, where diatom regularly blooms in spring. Model simulations show that the Si/N ratios of the flux exported by the sinking particles at 100 m depth and of nutrient consumptions in the upper 100 m surface water have their maxima at the end of the spring diatom bloom, the values and timings of which are significantly different from each other. Analyses of the model results show that the differences of regeneration between silicon and nitrogen mainly cause the temporal changes of the Si/N ratios. On the other hand, the physiological changes of diatoms under stress can hardly cause these temporal changes, because the effect of the change in the diatom's uptake ratio of silicon to nitrogen is cancelled by that in its sinking rate.  相似文献   

6.
Seasonal changes in nano/micro-zooplankton grazing on pico-, nano- and micro-size phytoplankton and heterotrophic nano-flagellates (HNF) feeding on heterotrophic bacteria were quantified by the dilution technique in the surface layer off Cape Esan, southwestern Hokkaido, Japan. Pico- and nano-size phytoplankton were major components throughout the year except in spring when a diatom bloom was observed. Although there was little seasonal variation in bacteria and HNF biomass throughout the year, the micro-zooplankton biomass varied appreciably with a peak in spring. Nano/micro-zooplankton grazing or feeding on pico-size chl-a and bacteria were well balanced throughout the year. However, nano-size and micro-size chl-a growth were much greater than grazing in summer. Nano/micro-zooplankton ingestion of phytoplankton was greater than their ingestion of bacteria almost throughout the year, which suggests phytoplankton are more important as food sources of nano/micro-zooplankton in microbial food webs off Cape Esan than bacteria off Cape Esan. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

7.
The decoupling of trophic interactions could be one of the severe consequences of climate warming in aquatic systems. The timing of phytoplankton blooms, in particular, can affect competition within the plankton community as well as food-web interactions with zooplankton and fish. Using long-term data from Helgoland Roads in the southern North Sea, we examine diatom seasonality, using three representative diatom species combined with environmental and copepod time series over the last four decades. The long-term annual abundances of Guinardia delicatula, Thalassionema nitzschioides and Odontella aurita exhibited interannual variations and dissimilar cyclic patterns during the time period under study (1962-2008). Of the three diatoms, G. delicatula showed a significant trend towards earlier bloom timings for 1962-2008 and a later decline of its abundance over time was found. Grazing and water transparency explained most of the bloom timing fluctuations of the diatoms considered. The annual timing of occurrences of each diatom species was correlated with their preceding concentrations. Earlier bloom timings occurred when autumn/winter concentrations were higher than average and later bloom timings occurred when autumn/winter concentrations were lower than average. Different environmental and predation variables related to the diatom bloom timings were found suggesting that climate warming might not affect the onset of the blooms of the three diatom species in the same manner. The results of the multiple linear regression analyses showed that the timings of decline of the three diatoms were mainly correlated with decreasing nutrient concentrations. Sunshine duration could prolong the duration of the blooms of T. nitzschioides and O. aurita provided that enough nutrients were available. In the case of G. delicatula, however, sunshine duration was negatively correlated with its end of the growth period. G. delicatula and T. nitzschioides showed later decreases in abundances under warmer spring and summer temperatures. Such species specific differences in the sensitivity to the forcing variables could lead to shifts in community structure and could ultimately have wider implications to the overall ecosystem health of the North Sea.  相似文献   

8.
黄海冷水团水域浮游植物群落粒级结构的季节变化   总被引：4，自引：0，他引：4       下载免费PDF全文
根据2006—2007年度4个季节航次的实测资料,分析了黄海冷水团水域浮游植物叶绿素及其粒级结构的时空分布特征及季节变化规律,结果表明,在研究海域30 m以浅叶绿素总量的平均含量从高到低的顺序为:春季的(1.01 mg/m3)、夏季的(0.81 mg/m3)、秋季(0.72 mg/m3)、冬季(0.68 mg/m3);在叶绿素浓度大于1 mg/m3和小于1 mg/m3的区域浮游植物粒级结构差异较大,在整个研究海域,粒径较小的微型和微微型浮游植物对总生物量的贡献始终占主导(65%),粒径较大的小型浮游植物在冬季和春季贡献率相对较高;从季节尺度看,浮游植物的平均粒级指数从大到小的顺序为:春季的(15.47μm),冬季的(11.08μm),秋季的(8.61μm),夏季的(6.52μm);尽管不同季节水文和化学环境差异显著,但是不同粒径浮游植物的贡献率随总生物量的变化表现出一致性的规律。对环境因子与叶绿素分布的相关分析表明,浮游植物的生长在夏季主要受到营养盐来源的限制,冬季主要受到水体混合引起的光照限制,秋季可能受到磷酸盐和水体混合的共同限制。浮游植物粒级结构的分布格局主要是由各组分在不同环境中的资源竞争优势决定的。  相似文献   

9.
Phytoplankton growth and microzooplankton grazing were studied during the 2007 spring bloom in Central Yellow Sea. The surveyed stations were divided to pre-bloom phase (Chl a concentration less than 2 μg L−1), and bloom phase (Chl a concentration greater than 2 μg L−1). Shipboard dilution incubation experiments were carried out at 19 stations to determine the phytoplankton specific growth rates and the specific grazing rates of microzooplankton on phytoplankton. Diatoms dominated in the phytoplankton community in surface waters at most stations. For microzooplankton, Myrionecta rubra and tintinnids were dominant, and heterotrophic dinoflagellate was also important in the community. Phytoplankton-specific growth rates, with an average of 0.60±0.19 d−1, were higher at pre-bloom stations (average 0.62±0.17 d−1), and lower at the bloom stations (average 0.59±0.21 d−1), but the difference of growth rates between bloom and pre-bloom stations was not statistically significant (t test, p=0.77). The phytoplankton mortality rate by microzooplankton grazing averaged 0.41±0.23 d−1 at pre-bloom stations, and 0.58±0.31 d−1 during the blooms. In contrast to the growth rates, the statistic difference of grazing rates between bloom and pre-bloom stations was significant (after removal of outliers, t test, p=0.04), indicating the importance of the top-down control in the phytoplankton bloom processes. Average potential grazing efficiency on primary productivity was 66% at pre-bloom stations and 98% at bloom stations, respectively. Based on our results, the biomass maximum phase (bloom phase) was not the maximum growth rate phase. Both phytoplankton specific growth rate and net growth rate were higher in the pre-bloom phase than during the bloom phase. Microzooplankton grazing mortality rate was positively correlated with phytoplankton growth rate during both phases, but growth and grazing were highly coupled during the booming phase. There was no correlation between phytoplankton growth rate and cell size during the blooms, but they were positive correlated during the pre-bloom phase. Our results indicate that microzooplankton grazing is an important process controlling the growth of phytoplankton in spring bloom period in the Central Yellow Sea, particularly in the “blooming” phase.  相似文献   

10.
In the northwestern Mediterranean Sea, Coastal Zone Color Scanner images suggest that the eddies that participate in the restratification following deep convection interact with the spring phytoplankton bloom. The mechanisms for this interaction are studied using a biogeochemical model embedded in an eddy-resolving primitive equation ocean model. The model is initialized with a patch of dense water surrounded by a stratified ocean, which is characteristic of the winter situation. The atmospheric forcing is artificially held constant, in order to focus solely on the mesoscale variability. After a few days, meanders develop at the periphery of the patch, inducing its sinking and spreading. Mesoscale upward motions are responsible for the shoaling of the mixing layer in the trough of the meanders. As sunlight is the main factor regulating primary production at this time of year, this shoaling increases the mean exposure time of the phytoplankton cells and thus enhances productivity. Consequently, the majority of phytoplankton production is obtained at the edge of the patch, in agreement with in situ data. Through advection, phytoplankton is then subducted from these sources towards the crest of the meanders. Our results suggest that this mesoscale transport is responsible for a decorrelation between phytoplankton biomass and primary production.  相似文献   

11.
Phytoplankton dynamics in the upper reach of the northern San Francisco Bay estuary are usually characterized by low biomass dominated by microflagellates or freshwater diatoms in winter, and high biomass dominated by neritic diatoms in summer. During two successive years of very low river discharge (the drought of 1976-77), the summer diatom bloom was absent. This is consistent with the hypothesis that formation of the diatom population maximum is a consequence of the same physical mechanisms that create local maxima of suspended sediments in partially-mixed estuaries: density-selective retention of particles within an estuarine circulation cell. Because the estuary is turbid, calculated phytoplankton growth rates are small in the central deep channel but are relatively large in lateral shallow embayments where light limination is less severe. When river discharge falls within a critical range (100–350 m3 s?1) that positions the suspended particulate maximum adjacent to the productive shallow bays, the population of neritic diatoms increases. However, during periods of high discharge (winter) or during periods of very low discharge (drought), the suspended particulate maximum is less well-defined and is uncoupled (positioned downstream or upstream) from the shallow bays of the upper estuary, and the population of neritic diatoms declines. Hence, the biomass and community composition of phytoplankton in this estuary are controlled by river discharge.  相似文献   

12.
An intense diatom bloom developed within a strong meridional silicic acid gradient across the Antarctic Polar Front at 61°S, 170°W following stratification of the water column in late October/early November 1997. The region of high diatom biomass and the silicic acid gradient propogated southward across the Seasonal Ice Zone through time, with the maximum diatom biomass tracking the center of the silicic acid gradient. High diatom biomass and high rates of silica production persisted within the silicic acid gradient until the end of January 1998 (ca. 70 d) driving the gradient over 500 km to the south of its original position at the Polar Front. The bloom consumed 30 to >40 μM Si(OH)4 in the euphotic zone between about 60 and 66°S leaving near surface concentrations <2.5 μM and occasionally <1.0 μM in its wake. Integrated biogenic silica concentrations within the bloom averaged 410 mmol Si m−2 (range 162–793 mmol Si m−2). Average integrated silica production on two consecutive cruises in December 1997 and January 1998 that sampled the bloom while it was well developed were 27.5±6.9 and 22.6±20 mmol Si m−2 d−1, respectively. Those levels of siliceous biomass and silica production are similar in magnitude to those reported for ice-edge diatom blooms in the Ross Sea, Antarctica, which is considered to be among the most productive regions in the Southern Ocean. Net silica production (production minus dissolution) in surface waters during the bloom was 16–21 mmol Si m−2 d−1, which is sufficient for diatom growth to be the cause of the southward displacement of the silicic acid gradient. A strong seasonal change in silica dissolution : silica production rate ratios was observed. Integrated silica dissolution rates in the upper 100–150 m during the low biomass period before stratification averaged 64% of integrated production. During the bloom integrated dissolution rates averaged only 23% of integrated silica production, making 77% of the opal produced available for export to depth. The bloom ended in late January apparently due to a mixing event. Dissolution : production rate ratios increased to an average of 0.67 during that period indicating a return to a predominantly regenerative system.Our observations indicate that high diatom biomass and high silica production rates previously observed in the marginal seas around Antarctica also occur in the deep ocean near the Polar Front. The bloom we observed propagated across the latitudinal band overlying the sedimentary opal belt which encircles most of Antarctica implying a role for such blooms in the formation of those sediments. Comparison of our surface silica production rates with new estimates of opal accumulation rates in the abyssal sediments of the Southern Ocean, which have been corrected for sediment focusing, indicate a burial efficiency of 4.6% for biogenic silica. That efficiency is considerably lower than previous estimates for the Southern Ocean.  相似文献   

13.
The aim of this study was to investigate the cycling of dissolved inorganic and organic nutrients using moored instrumented buoys (SmartBuoys) during the spring bloom in the North Sea. The instrumentation on the buoys enabled high frequency measurements of water-column integrated irradiance and in situ chlorophyll to be made, and also preserved water sample collection which were used for dissolved inorganic and organic nutrient analyses. The SmartBuoys were located in the year-round well-mixed plume zone associated with the River Thames and in the summer stratified central North Sea. These site locations allowed comparison of nutrient concentrations and cycling, and spring bloom development at two contrasting sites. The spring bloom was expected to be initiated at both stations due to increasing insolation and decreasing suspended load leading to higher water-column integrated irradiance. Due to differences in suspended load between the sites, the spring bloom started ∼2 months earlier in the central North Sea. The spring bloom in the Thames plume also resulted in higher maximum phytoplankton biomass due to the higher pre-bloom nutrient concentrations associated with riverine input. The use of SmartBuoys is also shown to allow the cycling of dissolved organic nutrients to be examined over the critical, and often undersampled, spring bloom period. Dissolved Organic Nitrogen (DON) clearly increased during the spring bloom in the central North Sea compared to winter concentrations. DON also increased in the Thames plume although showing greater winter variability related to higher riverine and sedimentary dissolved organic matter input at this shallow (∼18 m) coastal site. DON increase during the spring bloom was therefore related to primary production at both sites probably due to active release by phytoplankton. At both stations DON decreased to pre-bloom concentrations as the bloom declined suggesting the released DON was bioavailable and removed due to heterotrophic uptake and production. The preserved nutrient samples from the central North Sea site were also suitable for Dissolved Organic Phosphorus (DOP) analysis due to their low suspended load with similar trends and cycling to DON, albeit at lower concentrations. This suggested similar processes controlling both DON and DOP. The variable timing of short term events such as the spring bloom makes sampling away from coastal regions difficult without the use of autonomous technology. This study demonstrates for the first time the applicability of using preserved samples from automated buoys for the measurement of dissolved organic nutrients.  相似文献   

14.
东亚边缘海区浮游植物春华的纬向与年际变化   总被引：1，自引：1，他引：0  
Combined studies of latitudinal and interannual variations of annual phytoplankton bloom peak in East Asian marginal seas(17°–58°N, including the northern South China Sea(SCS), Kuroshio waters, the Sea of Japan and the Okhotsk Sea) are rarely. Based on satellite-retrieved ten-year(2003–2012) median timing of the annual Chlorophyll a concentration(Chl a) climax, here we report that this annual spring bloom peak generally delays from the SCS in January to the Okhotsk Sea in June at a rate of(21.20±2.86) km/d(decadal median±SD). Spring bloom is dominant feature of the phytoplankton annual cycle over these regions, except for the SCS which features winter bloom. The fluctuation of the annual peak timing is mainly within ±48 d departured from the decadal median peak date, therefore this period(the decadal median peak date ±48 d) is defined as annual spring bloom period. As sea surface temperature rises, earlier spring bloom peak timing but decreasing averaged Chl a biomass in the spring bloom period due to insufficient light is evident in the Okhotsk Sea from 2003 to 2012. For the rest of three study domains, there are no significant interannual variance trend of the peak timing and the averaged Chl a biomass. Furthermore this change of spring phytoplankton bloom timing and magnitude in the Okhotsk Sea challenges previous prediction that ocean warming would enhance algal productivity at high latitudes.  相似文献   

15.
The distribution of phytoplankton composition, cell abundance and biomass from an area along the Western Antarctic Peninsula was studied during three summers, with the aim of understanding its dynamics over spatial and interannual scales. The studied area is characterized by seasonal sea-ice retreat and advance. Algae composition and concentration were found to be highly variable through the area as well as from year to year. Small unidentified phytoflagellates, diatoms and cryptophytes were the main phytoplankton groups, contributing the major proportion of total phytoplankton cell abundance and biomass concentration. Three annually recurrent phytoplankton assemblages were recognized in the area according to the algae composition and abundance: a diatom bloom associated with the sea-ice edge, an assemblage dominated by small unidentified phytoflagellates and cryptophytes, and a diatom-enriched assemblage in open waters. The distribution of these assemblages varied from year-to-year. During the summers preceded by early sea-ice retreat, the diatom bloom was spatially restricted and the other two assemblages occupied extended regions, whereas during the late sea-ice retreat year, the diatom bloom extended over a larger region and the other assemblages occupied smaller regions or were just absent. It was detected that these assemblages resemble different stages of the phytoplankton seasonal cycle, and that their distribution through the area can be related to a latitudinal and longitudinal gradient in the phytoplankton growth onset timing, associated with the progressive sea-ice retreat during spring. The local environmental conditions associated with each assemblage were also analyzed, but further study is needed for understanding the causes of the replacement of one assemblage by another through the area. On the other hand, the interannual variability in the distribution of the assemblages can be related to year-to-year differences in the timing of phytoplankton growth onset, associated with variations in the timing of the sea-ice retreat.  相似文献   

16.
CHEMTAX analysis of high-performance liquid chromatography(HPLC) pigment was conducted to study phytoplankton community structure in the northern Bering Sea shelf, where a seasonal subsurface cold pool emerges. The results showed that fucoxanthin(Fuco) and chlorophyll a(Chl a) were the most abundant diagnostic pigments, with the integrated water column values ranging from 141 to 2 160 μg/m2 and 477 to 5 535 μg/m2, respectively. Moreover, a diatom bloom was identified at Sta. BB06 with the standing stock of Fuco up to 9 214 μg/m3. The results of CHEMTAX suggested that the phytoplankton community in the northern Bering Sea shelf was dominated by diatoms and chrysophytes with an average relative contribution to Chl a of 80% and 12%, respectively, followed by chlorophytes, dinoflagellates, and cryptophytes. Diatoms were the absolutely dominant algae in the subsurface cold pool with a relative contribution exceeding 90%, while the contribution of chrysophytes was generally higher in oligotrophic upper water. Additionally, the presence of a cold pool would tend to favor accumulation of diatom biomass and a bloom that occurred beneath the halocline would be beneficial to organic matter sinks, which suggests that a large part of the phytoplankton biomass would settle to the seabed and support a rich benthic biomass.  相似文献   

17.
Sendai Bay is located on the Pacific coast of northern Japan and suffered serious damage following the 2011 off the Pacific coast of Tohoku earthquake and tsunami in March 2011. To assess the impact on the marine ecosystem, information was needed on the phytoplankton communities and their seasonal variation. However, such information was limited. Therefore, an intensive monitoring of the phytoplankton was carried out from March 2012 to April 2014. Seasonal variation of the phytoplankton community was similar at coastal and offshore stations. Total phytoplankton biomass, based on Chl a concentration, peaked in spring and then decreased to a minimum in summer, before gradually increasing during early winter and peaking again in the following spring. This seasonal pattern was consistent with previous studies conducted before the earthquake and tsunami. Also, size structure of the phytoplankton community and its four main groups was estimated from the size-fractioned samples of Chl a. Our results also showed that the spring bloom consisted of large diatoms, with their growth ceasing due to nitrogen depletion. The bloom was followed by a summer period where cyanobacteria and picoeukaryote became dominant, with high cell densities in spite of low nutrient concentrations. In addition, sporadic environmental changes, such as those following typhoons, were observed. These resulted in large increases/decreases in individual phytoplankton groups.  相似文献   

18.
The concentration of nutrients was measured during the spring phytoplankton bloom in Funka Bay over a 5-year period (1988–92). During the winter mixing period, nutrient concentrations were similar in every year except in 1990 when a high concentration of silicate was observed. There was interannual variation in the onset of the bloom, presumably depending on the stability of the water column. The bloom developed in early March when the Oyashio water (OW), which has a lower density than the existing winter water, flowed into the bay and the pycnocline formed near the bottom of the euphotic zone. In this case, high chl a was found only in the euphotic zone and nutrient utilization was limited to this zone. In the year when the inflow of OW was not observed by April, the bloom took place at the end of March without strong stratification and high chl a was found in the whole water column, accompanied by a decrease in nutrients. Interannual differences were found not only at the beginning of the decrease, but also in the thickness of the layer which showed a decrease in nutrients. Primary production from the beginning to the end of the spring bloom was estimated from the nutrient budget before and after the spring bloom. The integrated production over the spring bloom period ranged from 25 to 73 g C m-2, which accounts for 19–56% of the annual production in this bay. We found that the timing of the bloom was strongly dependent on the inflow of OW, but the amount of production was not clearly related to this timing.  相似文献   

19.
The new diatom species Mediopyxis helysia was described to science from clones found in 2003 in the North Sea, northern Wadden Sea, and the Gulf of Maine. Seven years after its first occurrence, we observed Mediopyxis to contribute up to almost 50% of the biovolume of the diatoms during a diatom spring bloom in the western Wadden Sea. Grazing experiments based on the dilution technique could not detect any microzooplankton grazing impact on the bloom community. Mediopyxis is now also well established in the western Wadden Sea and does have the potential to become a dominant species. The reasons for its success remain largely unresolved but avoidance of being grazed might be one factor. Future research on this new species is needed to understand the success and forecast the ecological footprint of this large diatom species arriving in the western European Seas.  相似文献   

20.
A vertical one-dimensional ecosystem model with vertical migration of zooplankton was constructed and applied to Station A-7 off Sanriku district of Japan in the northwest Pacific Ocean. The model consists of an eight-compartment ecosystem model coupled with a physical model of the oceanic mixed layer. The transition of phytoplankton species responsible for the spring bloom is well reproduced by this model with vertical migration of zooplankton but is not simulated by the model without vertical migration. This new model also simulates an observed inter-annual variability of the spring bloom, with the timing and intensity of the simulated bloom in a given year depending upon the strength of mixing during the preceding winter. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

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