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1.
Massive blooms of Phaeocystis colonies usually occur in the Belgian coastal zone (BCZ) between spring and summer diatom blooms but their relative magnitude varies between years. In order to understand this interannual variability, we used the biogeochemical MIRO model to explore the link between diatom and Phaeocystis blooms and changing nutrient loads and meteorological conditions over the last decade. For this application, MIRO was implemented in a simplified 3-box representation of the domain between the Baie de Seine and the BCZ. MIRO was run over the 1989–2003 period using actual photosynthetic active radiation (PAR), seawater temperature and riverine nutrient loads as forcing. The water mass residence time was calculated for each box based on a monthly water budget estimated from 1993–2003 water flow simulations of the three-dimensional hydrodynamical model COHSNS-3D. Overall MIRO simulations compare fairly well with nutrient and phytoplankton data collected in the central BCZ but indicate the importance of the hydrodynamical resolution frame for correctly describing the extremely high nutrient concentrations and biomass observed in the BCZ. Analysis of model results suggests that while interannual variability in diatom biomass depends on both meteorological conditions (light and temperature) and nutrient loads, Phaeocystis blooms are mainly controlled by nutrients. Further sensitivity tests with varying N and P loads suggest that only N reduction will result in significantly decreased Phaeocystis blooms without negative affects on diatoms, while P reduction will negatively affect diatoms. Moreover, Atlantic nutrient loads play such a great role in BCZ enrichment that reduction of Scheldt nutrient loads only is not sufficient to significantly decrease phytoplankton blooms in the BCZ. It is concluded that future nutrient reduction policies aimed to decrease Phaeocystis blooms in the BCZ without impacting diatoms should target the decrease of N loads in both the Seine and the Scheldt rivers.  相似文献   

2.
The trophic efficiency of the planktonic food web in the Phaeocystis-dominated ecosystem of the Belgian coastal waters was inferred from the analysis of the carbon flow network of the planktonic system subdivided into its different trophodynamic groups. A carbon budget was constructed on the basis of process-level field experiments conducted during the spring bloom period of 1998. Biomass and major metabolic activities of auto- and heterotrophic planktonic communities (primary production, bacterial production, nanoproto-, micro- and mesozooplankton feeding activities) were determined in nine field assemblages collected during spring at reference station 330. In 1998, the phytoplankton spring flowering was characterised by a moderate diatom bloom followed by a massive Phaeocystis colony bloom. Phaeocystis colonies, contributing 70% to the net primary production, escaped the linear food chain while the early spring diatom production supplied 74% of the mesozooplankton carbon uptake. The rest of mesozooplankton food requirement was, at the time of the Phaeocystis colony bloom, partially fulfilled by microzooplankton. Only one-third of the microzooplankton production, however, was controlled by mesozooplankton grazing pressure. Ungrazed Phaeocystis colonies were stimulating the establishment of a very active microbial network. On the one hand, the release of free-living cells from ungrazed colonies has been shown to stimulate the growth of microzooplankton, which was controlling 97% of the nanophytoplankton production. On the other hand, the disruption of ungrazed Phaeocystis colonies supplied the water column with large amounts of dissolved organic matter available for planktonic bacteria. The budget calculation suggests that ungrazed colonies contributed up to 60% to the bacterial carbon demand, while alternative sources (exudation, zooplankton egestion and lysis of other organisms) provided some 30% of bacterial carbon requirements. This suggests that the spring carbon demand of planktonic bacteria was satisfied largely by autogenic production. The trophic efficiency was defined as the ratio between mesozooplankton grazing on a given source and food production. In spite of its major contribution to mesozooplankton feeding, the trophic efficiency of the linear food chain, restricted to the grazing on diatoms, represented only 5.6% of the available net primary production. The trophic efficiency of the microbial food chain, the ratio between mesozooplankton grazing on microzooplankton and the resource inflow (the bacterial carbon demand plus the nanophytoplankton production) amounted to only 1.6%. These low trophic efficiencies together with the potential contribution of ungrazed Phaeocystis-derived production to the bacterial carbon demand suggest that during spring 1998 most of the Phaeocystis-derived production in the Belgian coastal area was remineralised in the water column.  相似文献   

3.
The results of a phytoplankton survey conducted in coastal waters off western Ireland in 1980/1981 are reported. Surface values of temperature, salinity, NO3N, PO4P, Si, total N, total P and chlorophyll a (Chla) collected at 6 stations during 14 cruises are presented along with the species composition of the net phytoplankton.The spring bloom occurred in late April and was dominated by diatoms. Between April and July further diatom blooms occurred. In July and August dinoflagellates were dominant. This change was associated with the stratification of offshore water and low concentrations of Chla and nutrients. In Autumn large blooms of Ceratium tripos were found; it is suggested that the cause was heavy freshwater runoff. In autumn and winter some warm water oceanic species (e.g. Oxytoxum scolopax) occurred.  相似文献   

4.
We report results from two surveys of pCO2, biological O2 saturation (??O2/Ar) and dimethylsulfide (DMS) in surface waters of the Ross Sea polynya. Measurements were made during early spring (November 2006-December 2006) and mid-summer (December 2005-January 2006) using ship-board membrane inlet mass spectrometry (MIMS) for high spatial resolution (i.e. sub-km) analysis. During the early spring survey, the polynya was in the initial stages of development and exhibited a rapid increase in open water area and phytoplankton biomass over the course of our ∼3 week occupation. We observed a rapid transition from a net heterotrophic ice-covered system (supersaturated pCO2 and undersaturated O2) to a high productivity regime associated with a Phaeocystis-dominated phytoplankton bloom. The timing of the early spring phytoplankton bloom was closely tied to increasing sea surface temperature across the polynya, as well as reduced wind speeds and ice cover, leading to enhanced vertical stratification. There was a strong correlation between pCO2, ??O2/Ar, DMS and chlorophyll a (Chl a) during the spring phytoplankton bloom, indicating a strong biological imprint on gas distributions. Box model calculations suggest that pCO2 drawdown was largely attributable to net community production, while gas exchange and shoaling mixed layers also exerted a strong control on the re-equilibration of mixed layer ??2 with the overlying atmosphere. DMS concentrations were closely coupled to Phaeocystis biomass across the early spring polynya, with maximum concentrations exceeding 100 nM.During the summer cruise, we sampled a large net autotrophic polynya, shortly after the seasonal peak in phytoplankton productivity. Both diatoms and Phaeocystis were abundant in the phytoplankton assemblages during this time. Minimum pCO2 was less than 100 ppm, while ??O2/Ar exceeded 30% in some regions. Mean DMS concentrations were ∼2-fold lower than during the spring, although the range of concentrations was similar between the two surveys. There was a significant correlation between pCO2, ??O2/Ar and Chl a across the summer polynya, but the strength of these correlations and the slope of O2 vs. CO2 relationship were significantly lower than during the early spring. Summertime DMS concentrations were not significantly correlated to phytoplankton biomass (Chl a), pCO2 or ??O2/Ar. In contrast to the early spring time, there were no clear temporal trends in summertime gas concentrations. Rather, small-scale spatial variability, likely resulting from mixing and localized sea-ice melt, was clearly evident in surface gas distributions across the polynya. Analysis of length-scale dependent variability demonstrated that much of the spatial variance in surface water gases occurred at scales of <20 km, suggesting that high resolution analysis is needed to fully capture biogeochemical heterogeneity in this system.  相似文献   

5.
Living benthic foraminiferal faunas of six stations from the continental shelf of the Bay of Biscay have been investigated during three successive seasons (spring, summer and autumn 2002). For the three investigated stations, bottom water oxygen concentration, oxygen penetration into the sediment and sediment organic carbon contents are all relatively similar. Therefore, we think that the density and the composition of the foraminiferal faunas is mainly controlled by the quantity and quality of organic input resulting from a succession of phytoplankton bloom events, occurring from late February to early September. The earliest blooms are positioned at the shelf break, late spring and early summer blooms occur off Brittany, whereas in late summer and early autumn, only coastal blooms appear, often in the vicinity of river outlets. In spring, the benthic foraminiferal faunas of central (B, C and D) and outer (E) continental shelf stations are characterised by strong dominance in the first area and strong presence in the second area of Nonionella iridea. In fact, station E does not serve as a major depocenter for the remains of phytoplankton blooms. If station E is not considered, the densities of this taxon show a clear gradient from the shelf-break, where the species dominates the assemblages, to the coast, where it attains very low densities. We explain this gradient as a response to the presence, in early spring, of an important phytoplankton bloom, mainly composed of coccolithophorids, over the shelf break. This observation is supported by the maximum particles flux values at stations close to the shelf break (18.5 g m− 2 h− 1) and lower values in a station closer to the coast (6.8 g m− 2 h− 1). In summer, the faunal density is maximum at station A, relatively close to more varied phytoplancton blooms that occur off Brittany until early June. We suggest that the dominant species, Nonion fabum, Cassidulina carinata and Bolivina ex. gr. dilatata respond to phytodetritus input from these blooms. In autumn, the rich faunas of inner shelf station G are dominated by N. fabum, B. ex. gr. dilatata, Hyalinea balthica and Nonionella turgida. These taxa seem to be correlated with the presence of coastal blooms phenomena, in front of river outlets. They may be favoured by an organic input with a significant contribution of terrestrial, rather low quality organic matter.  相似文献   

6.
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7.
The colony-forming Phaeocystis species are causative agents of dense bloom occurrences in coastal waters worldwide. It is difficult to separate them because of the different morphologies associated with their colonial stages. In this study we applied molecular approaches to analyze the genetic variation of Phaeocystis globosa and Phaeocystis pouchetii from several geographic regions, and to assist in tracing the dispersal of bloom-forming Phaeocystis species in coastal waters of China. The sequences of the internal transcribed spacers (ITS1 and ITS2) of rDNA and the 5.8S ribosomal RNA gene of Phaeocystis strains were determined. Sequence comparison shows that P.globosa was the most divergent to P. pouchetii, exhibiting sequence divergence higher than 0.08. However, lower genetic divergences existed between strains of P.globosa. The sequence comparison of the Phaeocystis rDNA ITS clearly shows that the species isolated from the southeast coast of China is identified as P.globosa rather than P. cf. pouchetii or other species. Furthermore, the significance of rDNA variation in distinct global populations of P.globosa suggested it might have had sufficient time to accumulate detectable mutations at the rDNA locus, supporting the hypothesis of ancient dispersal of P.globosa to many areas, meaning that P.globosa blooms in the coastal waters of China are endemic rather than a newly introduced species or a foreign source. Finally, based on the high divergent region of rDNA ITS, a pair of species-specific primers for P.globosa were designed, they could be useful to detect the presence of this species in mixed plankton assemblages or flagellate stages that are recognized with diffculties by means of conventional microscopy.  相似文献   

8.
In the spring of 1995, short-term variations in the concentration of particulate and dissolved dimethylsulfoniopropionate (DMSP) and dimethylsulfide (DMS) were monitored in the western Wadden Sea, a shallow coastal region in open connection with the North Sea. Significant correlations were found between abundance of Phaeocystis globosa and particulate DMSP; concentrations increased rapidly from 100 to 1650 nM in the middle of April. Highest DMS concentrations were found during the initial phase of the exponential growth of the bloom. DMS production and loss rates of DMSP and DMS were estimated experimentally during various phases of the bloom. DMS production and consumption were roughly in balance, with production only slightly exceeding consumption at the start of the bloom. Rates of production and consumption were highest during the exponential growth phase of Phaeocystis and declined in the course of the bloom (from 300–375 to less than 5 nmol dm−3 d−1). Demethylation of DMSP increased during the bloom (from 11 to 1300 nmol dm−3 d−1); it accounted for up to 100% of the DMSP loss at the end of the bloom. The shift from DMSP cleavage to demethylation in the course of a Phaeocystis bloom implies that DMS concentrations are not necessarily highest at the peak or towards the end of blooms.  相似文献   

9.
The dynamics of ice formation and phytoplankton bloom development in the coastal region of the Okhotsk Sea, Hokkaido, where the Japanese scallop, Mizuhopecten yessoensis, are cultured were investigated using seven years (1998–2004) satellite data from the Special Sensor Microwave/Imager (SSM/I) and Sea-viewing Wide Field-of-view Sensor (SeaWiFS). The interannual variability of sea ice cover and timing of spring bloom occurrences were analyzed. Longer ice cover in 1999, 2001 and 2003 with the presence of ice until early April and shortened ice cover in 1998, 2000, 2002 and 2004 with the occurrence of ice until early March were recognized at this area. Variability in the timing of sea ice retreat and development of spring blooms at the scallop areas were observed. Progression of a single ice edge bloom showed higher Chl-a concentration compared to development of an initial ice edge bloom followed by a later open water bloom. Higher concentration of phytoplankton biomass was observed in the initial bloom when sea ice melting is delayed compared to when the sea ice leaves earlier. Wind events were also observed to affect the occurrences of spring bloom.  相似文献   

10.
High concentrations of the phytoplankton metabolite dimethylsulfoniopropionate (DMSP) and its degradation product dimethylsulfide (DMS) are associated with blooms of Phaeocystis antarctica in the Ross Sea, Antarctica. Episodic and rapid vertical export of Phaeocystis biomass to deep water has been reported for the Ross Sea, therefore we examined the distribution and microbial consumption rates of DMSP and DMS throughout the sub-euphotic water column. Total DMSP (dissolved+particulate; DMSPt) was present at 0.5–22 nM at depths between 70 and 690 m during both the early bloom (November) and the late bloom (January). Sub-euphotic peaks of DMSP were sometimes associated with mid-water temperature maxima, and elevated DMSP below 70 m was found mainly in water masses characterized as Modified Circumpolar Deep Water or Antarctic Shelf Water. Overall, 50–94% of the integrated water-column DMSPt was found below the euphotic zone. At one station during the early bloom, local maxima of DMSPt (14 nM) and DMS (20 nM) were observed between 113 and 240 m and these maxima corresponded with high chlorophyll a concentrations, P. antarctica cell numbers, and Fv/Fm (the quantum yield of photosystem II). During the late bloom, a sub-euphotic maximum of DMSPt (15.8 nM) at 250 m cooccurred with peaks of chlorophyll a concentration, DMSP lyase activity, bacterial production and dissolved DMSP consumption rates. DMSP turnover contributed ～12% of the bacterial carbon demand between 200 and 400 m. DMS concentrations peaked at 286 m but the maximum concentration (0.42 nM) was far lower than observed during the early bloom, probably because of relatively rapid biological consumption of DMS (1–3 turnovers per day) which, in turn, contributed to elevated dissolved dimethylsulfoxide (DMSO) concentrations. Relatively stable DMSPt distributions at some sites suggest that rapid sinking of Phaeocystis biomass is probably not the major mechanism responsible for mesopelagic DMSP accumulations. Rather, subduction of near-surface water masses, lateral advective transport or trapping of slowly sinking P. antarctica biomass in intermediate water masses are more likely mechanisms. We found that a culture of P. antarctica maintained cellular integrity during 34 days of darkness, therefore the presence of intact cells (and DMSP) at depth can be explained even under a slow sinking/advection scenario. Whatever the mechanism, the large pools of DMSP and DMS below the euphotic zone suggest that export exerts a control on potential DMS emission from the surface waters of the Ross Sea.  相似文献   

11.
春、秋季南黄海浮游纤毛虫丰度及生物量的分布差异   总被引：1，自引：0，他引：1  
Seasonal variation of marine plankton spatial distribution is important in understanding the biological processes in the ocean.In this study,we studied spatial distribution of planktonic ciliate abundance and biomass in the central deep area(station depth greater than 60 m) and the coastal shallow area(station depth less than 60 m) of the southern Yellow Sea(32°–36.5°N,121°–125°E) in spring(April) and autumn(October–November) of 2006.Our results showed that both ciliate abundance and biomass in the surface waters were higher in spring((1 490±2 336)ind./L;(4.11±7.81) μg/L) than in autumn((972±823) ind./L;(1.11±1.18) μg/L,calculated by carbon).Ciliate abundance and biomass in the surface waters of the coastal shallow area were similar in spring and autumn.However,in the central deep area,those values were much higher in spring((1 878±2 893) ind./L;(5.99±10.10)μg/L) than in autumn((738±373) ind./L;(0.74±0.76) μg/L).High values of ciliate abundance and biomass occurred in the central deep area in spring and in the coastal shallow area in autumn.Mixotrophic ciliate Laboea strobila was abundant in the central deep area in spring,when a phytoplankton bloom occurred.However,in autumn,L.strobila was abundant in the coastal shallow area.Boreal tintinnid Ptychocyli obtusa was found in spring.Both L.strobila and P.obtusa were concentrated in the surface waters when their abundance was more than 1 000 ind./L.Peaks of these species were in the subsurface waters when their abundance was less than 400 ind./L.This study showed that both high abundance and biomass of ciliates occurred in different areas in southern Yellow Sea seasonally.  相似文献   

12.
During 24, three-day cruises to Dabob Bay, Washington State, USA, from February 4 to April 26, 2002, and February 4 to May 1 2003, we examined the relative growth and grazing rates of phytoplankton and microzooplankton using dilution experiments. Experiments were conducted over two time intervals: 8–10 h during the nighttime only, or 24 h from noon to noon. We used water from two depths during each cruise: from the surface mixed layer, and from a deep layer below the seasonal thermocline. During 2002, there was one mid-sized bloom consisting mainly of Thalassiosira spp. in early February, and a larger bloom in April comprised of two Chaetoceros spp. and Phaeocystis sp. During 2003, there were also two blooms, one in early February, which was again dominated by Thalassiosira spp., and a second larger bloom in mid-April, comprised mainly of Thalassiosira spp. and Chaetoceros spp. During all four of these blooms, and for both water source depths, specific grazing rates of microzooplankton were most often as high or higher than the calculated phytoplankton specific growth rates. The major microzooplankton categories that could have accounted for this were (1) a large Gyrodinium spp., (2) a group of fusiform-shaped mid-sized Protoperidinium species, and (3) three loosely defined taxonomic groups consisting of naked ciliates, tintinnids, and unidentified heterotrophic dinoflagellates. Based on our measurements, it appears that the microzooplankton community grazing pressure can often exert significant control on phytoplankton biomass, even during the extremely productive spring bloom periods and under several different diatom-dominated bloom types. These results suggest that even in highly productive estuarine ecosystems, which are often nurseries to economically important fisheries species, microzooplankton play a critical role and may significantly alter the availability and efficiency of transfer of energy to higher trophic levels.  相似文献   

13.
An extremely dense bloom of the potentially toxic dinoflagellate Alexandrium tamarense was observed in the lagoons of Cà Pisani (Veneto, Italy) in summer 1993. The lagoons were experiencing a significant eutrophication impact, receiving waste waters from intensive fish culture plants. During their bloom dinoflagellates in the lagoons reached densities of 2 to 4 × 106 cells·dm−3 and a biomass of over 100 g·m−3. The bloom produced drastic ecological changes in the lagoons. It caused nocturnal anoxia, mortality of macrophytes and the build-up of labile organic matter in the water column. Grazing by the tintinnid Favella sp. contributed to the termination of the bloom of the flagellates. The results show that coastal aqua culture probably stimulates dinoflagellate blooms in shallow brackish lagoons.  相似文献   

14.
Using the data obtained in 1999–2000 during the spring bloom of phytoplankton (late May–early June), the variability of the pigment concentrations, the phytoplankton biomass and species compositions, and the hydrological conditions on the eastern shelf of Sakhalin Island was studied. The study resulted in revealing 135 microalgae species belonging to eight divisions. The most diversely presented were the Dinophyta dinoflagellates and Bacillariophyta diatoms (70 and 53 species, respectively). The concentration of chlorophyll a in the euphotic zone amounted, on average, to 3.8 mg/m3 in 1999 and 2.4 mg/m3 in 2000. It was shown that, in the northern and southern parts of the coastal zone, the concentration of chlorophyll a and the phytoplankton density in the spring were considerably different and depended on the hydrological conditions. In the north, their maximum values were found in the area of the depth break and were determined by the tidal mixing. The increased algae concentrations and temperature inversions at depths of 400–600 m confirm the downslope sliding of the near-bottom shelf waters. In the southern part, the high phytoplankton concentrations in the surface layer in 1999 confirmed by the monthly averaged estimates from the SeaWiFS satellite color scanner were caused by the abnormal northward propagation of the Soya Current waters and by intense tidal mixing.  相似文献   

15.
The partial pressure of CO2 (pCO2) and dissolved inorganic carbon (DIC) were monitored in shallow coastal waters located inside and outside giant kelp beds (Macrocystis pyrifera) located in the Kerguelen Archipelago (Southern Ocean). Photosynthesis and respiration by microplankton and kelp lead to marked pCO2 and DIC diel cycles. Daily variations of pCO2 and DIC are significant in the spring and summer, but absent in the winter, reflecting the seasonal cycle of biological activity in the kelp beds. If the kelp beds seem to favour the onset of phytoplankton blooms, most of the primary production inside the kelp beds is due to the kelp itself. The primary production of Macrocystis kelp beds in the Sub-Antarctic high-nutrient, low-chlorophyll (HNLC) waters off the Kerguelen Archipelago is elevated and closely linked to light availability. This production is significant from October to March and reaches its climax in December at the solar radiation maximum.  相似文献   

16.
Our objective was to track microbial processes associated with serial degradation of organic matter derived from algal blooms. To do this, we analyzed population fluctuations and growth responses of major phylogenetic groups of free-living marine bacteria. We used bromodeoxyuridine immunocytochemistry–fluorescence in situ hybridization methodology to examine marine bacterial community development during and after a diatom bloom in a mesocosm. We revealed that the Roseobacter/Rhodobacter, SAR11, Alteromonas, and Bacteroidetes groups were clearly major phylotypes responsible for most free-living bacterial biomass and production throughout the experiment. The clearest bacterial response was a proliferation of the Alteromonas group (cells with large volumes) during development of the bloom (up to 30?% of actively growing cells). Populations of these bacteria declined sharply thereafter, likely due to grazing. Alteromonas group responses suggest that these bacteria strongly influenced the flux of organic matter at an early bloom stage. The growth potential of Bacteroidetes was relatively large as the bloom peaked; this early development probably contributed to the initial stage of bloom decomposition. In contrast, the contribution of Roseobacter/Rhodobacter to total bacterial production increased at a late stage of decomposing of the bloom. The contributions of Betaproteobacteria, SAR11, and SAR86 groups to total bacterial abundance and production were relatively minor throughout the experiment. These results imply that the ability to utilize organic matter derived from diatoms varies among bacterial phylotypes, and, frequently, less abundant but ecological specialist taxa such as Alteromonas may play major roles in the flux of organic matter during diatom blooms.  相似文献   

17.
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   

18.
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   

19.
Dissolved organic matter (DOM) composition and dynamics in temperate shallow coastal bays are not well described although these bays may be important as local sources of organic carbon to ocean waters and are often sites of economically-important fisheries and aquaculture. In this study surface water samples were collected on a monthly to bi-monthly basis over two years from a mid-Atlantic coastal bay (Chincoteague Bay, Virginia and Maryland, USA). Dissolved organic carbon (DOC) concentrations and light absorbance characteristics were measured on sterile-filtered water, and high-molecular weight (> 1 kDa) dissolved OM (DOM) was isolated to determine stable isotope composition and molecular-level characteristics. Our time series encompassed both a drought year (2002) and a year of above-average rainfall (2003). During the dry year, one of our sites developed a very intense bloom of the brown tide organism Aureococcus anophagefferens while during the wet year there were brown tide bloom events at both of our sampling sites. During early spring of the wet year, there were higher concentrations of > 1 kDa DOC; this fraction represented a larger proportion of overall DOC and appeared considerably more allochthonous. Based upon colored dissolved organic matter (CDOM) and high-molecular weight DOM analyses, the development of extensive phytoplankton blooms during our sampling period significantly altered the quality of the DOM. Throughout both years Chincoteague Bay had high DOC concentrations relative to values reported for the coastal ocean. This observation, in conjunction with the observed effects of phytoplankton blooms on DOM composition, indicates that Chincoteague Bay may be a significant local source of “recently-fixed” organic carbon to shelf waters. Estimating inputs of DOC from Chincoteague Bay to the Mid-Atlantic Bight suggests that shallow productive bays should be considered in studies of organic carbon on continental shelves.  相似文献   

20.
赵苑  赵丽  张武昌  刘诚刚  魏皓  肖天 《海洋与湖沼》2012,43(6):1030-1038
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。  相似文献   

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