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1.
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   

2.
2004-2016年夏季长江口网采浮游植物及其影响因素   总被引：1，自引：0，他引：1  
基于2004-2016年夏季长江口生态监控区13年的生态环境调查数据,开展网采浮游植物年际变化及其与环境因子关系研究。结果表明：（1）共鉴定出浮游植物7门263种,以硅藻占绝对优势,甲藻次之,物种数呈增加趋势,其中硅藻种类数占有比下降,而甲藻的种类数占有比呈上升趋势;（2）总细胞丰度、硅藻细胞丰度和甲藻细胞丰度都呈上升趋势,除2014年外,其余年份硅藻细胞丰度都占绝对优势并与总细胞丰度的分布曲线和变化趋势基本一致;（3）水平分布模式及其年际变化受环流变化和水团消长的影响,总体趋势是河口区细胞丰度较低,由河口到外海呈逐渐增大趋势,部分年份呈现先增大后减小的趋势;（4）生物多样性多年呈下降趋势,物种组成随空间和时间变化较大,只有较少的种类能够保持稳定,多数物种只是偶尔被检出;（5）中肋骨条藻有10年为区域第一优势种,41种常见种中有31种细胞丰度呈增加趋势,10种细胞丰度呈下降趋势。（6）浮游植物细胞丰度与活性磷酸盐和无机氮具有相关性,种类数、多样性指数除了与溶解氧、氨氮、叶绿素a无相关性外与其他10种环境因子都相关。本研究能够较好反映研究区域浮游植物的本底情况及演变趋势。  相似文献   

3.
《Oceanologica Acta》1999,22(1):67-84
Diatom and coccolithophorid abundance and diatom assemblage composition found in the water column along the Portuguese margin, during upwelling and non-upwelling conditions, are compared to the distribution patterns observed in the recent sediments from the same area. The water column results indicate a one order of magnitude increase in phytoplankton biomass during upwelling conditions (summer), with diatoms being the most important contributors. Coccolithophorids, on the contrary, dominate the phytoplankton in winter (non-upwelling). The comparison of the upwelling and non-upwelling spatial distribution of these phytoplankton groups to their sedimentary record reveals the sediment record as a reflection of the upwelling situation, preserving most of its original spatial variability. The comparison between living and fossil diatom assemblages indicates that from the two genera which dominate the summer biologic assemblage, Pseudo-nitzschia and Chaetoceros, Pseudo-nitzschia is not represented in the sediments, while Chaetoceros is the dominant form of the sediment. Thalassiosira which occurs in the same abundance in both seasons, responding to both river and upwelling nutrient input, can not be a reliable indicator of any single process. However, this genus distribution in the sediments can be used as an indicator of continuous nutrient availability.Such results are of great importance for paleoceanographic reconstructions since they constitute a good indication that the sediment record, even though somewhat altered with respect to assemblage composition, does reflect the water column characteristics.  相似文献   

4.
《Oceanologica Acta》1999,22(3):319-336
Diatom and coccolithophorid abundance and diatom assemblage composition found in the water column along the Portuguese margin, during upwelling and non-upwelling conditions, are compared to the distribution patterns observed in the recent sediments from the same area. The water column results indicate a one order of magnitude increase in phytoplankton biomass during upwelling conditions (summer), with diatoms being the most important contributors. Coccolithophorids, on the contrary, dominate the phytoplankton in winter (non-upwelling). The comparison of the upwelling and non-upwelling spatial distribution of these phytoplankton groups to their sedimentary record reveals the sediment record as a reflection of the upwelling situation, preserving most of its original spatial variability. The comparison between living and fossil diatom assemblages indicates that from the two genera which dominate the summer biological assemblage, Pseudo-nitzschia and Chaetoceros, Pseudo-nitzschia is not represented in the sediments, while Chaetoceros is the dominant form of the sediment. Thalassiosira, which occurs in the same abundance in both seasons, responding to both river and upwelling nutrient input, can not be a reliable indicator of any single process. However, this genus distribution in the sediments can be used as an indicator of continuous nutrient availability. Such results are of great importance for paleoceanographic reconstructions, since they constitute a good indication that the sediment record, even though somewhat altered with respect to assemblage composition, does reflect the water column characteristics.  相似文献   

5.
《Oceanologica Acta》1998,21(2):293-305
In the Urdaibai estuary, despite its small volume in relation to the tidal prism, phytoplankton grows massively in the upper and intermediate zones of the estuary during summer when rainfall is low to moderate. Data obtained in 23 sampling transects along the longitudinal axis of the estuary, undertaken in July 1993 and August 1994, showed three distinct zones in terms of the phytoplankton species composition: in the upper zone the phytoplankton assemblage was dominated by the diatoms Cyclotella spp., the dinoflagellate Glenodinium foliaceum, cryptophytes and euglenophytes; in the intermediate zone the diatom Chaetoceros ceratosporus, the dinoflagellates Peridinium quinquecorne and Prorocentrum minimum and cryptophytes were the most abundant; in the lower zone diatoms such as Leptocylindricus danicus and Skeletonema costatum together with the dinoflagellates Prorocentrum spp. were dominant. The distribution and abundance of these phytoplankton forms is discussed in relation to variations in salinity, water column stratification, nutrients and temperature, which in turn vary mainly as a function of meteorological conditions (i.e. rainfall, irradiance) and tidal amplitude. The longitudinal distribution of phytoplankton cells suggests that the diatoms Cyclotella spp. and Chaetoceros ceratosporus undergo a greater dispersion along the estuary during rain events than the flagellates, thus contributing to the transport of silica to the outer areas of the estuary.  相似文献   

6.
The dynamics of phytoplankton abundance with seasonal variation in physicochemical conditions were investigated monthly at 10 stations around the Chagwi-do off the west coast of Jeju Island, Korea, including inshore, middle shore, and offshore in the marine ranching area from September 2004 to November 2005. Water temperature varied from 12.1 to 28.9°C (average 18.8°C), and salinity from 28.9 to 34.9 psu (average 33.7 psu). The chlorophyll a concentration was 0.02-2.05 μg L1 (average 0.70 μg L1), and the maximum concentration occurred in the bottom layer in April. A total of 294 phytoplankton species belonging to 10 families was identified: 182 Bacillariophyceae, 52 Dinophyceae, 9 Chlorophyceae, 12 Cryptophyceae, 6 Chrysophyceae, 4 Dictyophyceae, 13 Euglenophyceae, 6 Prymnesiophyceae, 5 Prasinophyceae, and 5 Raphidophyceae. The standing crop was 2.21-48.69x104 cells L1 (average 9.23x 104 cells L1), and the maximum occurred in the bottom layer in April. Diatoms were most abundant throughout the year, followed by dinoflagellates and phytoflagellates. A phytoplankton bloom occurred twice: once in spring, peaking in April, and once in autumn, peaking in November. The spring bloom was represented by fourChaetoceros species andSkeletonema costatum; each contributed 10–20% of the total phytoplankton abundance. The autumn bloom comprised dinoflagellates, diatoms, and phytoflagellates, of which dinoflagellates were predominant.Gymnodinium conicum, Prorocentrum micans, andP. triestinum each contributed over 10% of the total phytoplankton abundance.  相似文献   

7.
大亚湾生态监控区的浮游植物年际变化   总被引：2，自引：0，他引：2  
依据国家海洋局、国家海洋局第三海洋研究所等权威机构2004~2007年所获的数据和资料,对大亚湾生态监控区近4a长时间尺度的浮游植物群落年际变化进行分析,通过物种组成、丰度变化、优势类群演替、群落结构及赤潮灾害事件来反映生境的退化,探讨其变化的主要原因及趋势。结果表明,浮游植物群落由暖水种占绝对优势转变为广温广布种占主导地位。种类与丰度呈逐年下降的态势,浮游植物丰度的分布保持西高东低,近岸高于远岸的特征,浮游植物的高丰度与营养盐丰富及温排水有关。终年以硅藻为优势种群,优势种演替具有明显的季节与年际变化,细长翼根管藻(Rhizosolenia alataf.gracillima)是春季稳定的优势种,柔弱拟菱形藻(Pseudo-nitzschia delicatissma)是夏季稳定的优势种,春末甲藻的优势度增加明显。浮游植物群落多样性指数呈逐年下降趋势,均匀度呈逐年上升态势。浮游植物的异常增殖及过度集中导致多样性较低,种间比例不均匀,群落结构单一。赤潮季节性发生频繁,发生频率及引发种类呈上升趋势,海洋环境脆弱。  相似文献   

8.
Winter Distribution of Diatom Assemblages in the East China Sea   总被引：3，自引：0，他引：3  
We examined the spatial distributional relationships between diatom assemblages and water types during the winter in the East China Sea. Principal component analysis was used to identify two water types and two diatom assemblages in the study area. Coastal water types along the mainland China coastline had low temperature and salinity levels, but high nitrate levels. The shelf-mixing water type in the rest of the study area had higher temperatures and salinities and lower levels of nitrate. Diatom assemblage distribution was not spatially consistent with water type. The Kuroshio assemblage had a large standing stock, distributed along the surface of the shelf break. This assemblage is likely the result of Kuroshio surface water coming into contact with nutrient-rich water in the shelf area, triggering proliferation of certain diatom species. A background assemblage with low standing stock level persisted over the entire study area in both coastal water and the shelf-mixing water types. Our results support previous research: the background assemblage is due to poor growth conditions such as the convection of water during winter; there were no significant seasonal variations in the species composition.  相似文献   

9.
通过1999年和2010年夏季同期7月在白令海(169°E~166°W,50°N~67°N)获取的94份浮游植物样品分析,获得了近十年的始末两个时间节点的浮游植物群落结构与时空变化,探讨了浮游植物群落动态及其与环境因素的关联。研究结果显示,共鉴定浮游植物(>10μm)5门58属153种,分为3个生态类群。硅藻是浮游植物的主体,种类多丰度高,占总种类数目的66.7%,占总丰度的95.2%。鉴于样品属性和空间范围的不同,物种组成有细微差别,丰度有较大差异且空间分布明显不同,高丰度区受控于上层营养盐供给和表层环流系统。优势种从北方温带大洋性硅藻演变为广温广盐性与冷水性硅藻,1999年以西氏新细齿状藻为第一优势种,柔弱伪菱形藻次之;2010年以丹麦细柱藻为第一优势种,冷水性的诺登海链藻次之并在陆架和陆坡占优。浮游植物群落结构较为稳定,由深水群落和浅水群落组成。深水群落分布于太平洋西北部和白令海盆,种类组成以温带大洋性的西氏新细齿状藻、长海毛藻、大西洋角毛藻和广布性的菱形海线藻、扁面角毛藻、笔尖根管藻为主,丰度低,种间丰度分配均匀,优势种多元化,物种多样性高;浅水群落分布于白令海陆坡和陆架,主要由冷水性的诺登海链藻、叉尖角毛藻、聚生角毛藻和广布性的丹麦细柱藻、旋链角毛藻组成,丰度高,种间丰度分配不均匀,优势种突出,物种多样性低。白令海夏季浮游植物种类组成及丰度变化直接受控于表层环流、营养盐、春季冰缘线等环境因素。  相似文献   

10.
本文依托2008年夏季中国第三次北极科学考察航次,对西北冰洋海盆区和楚科奇海陆架营养盐及光合色素进行了测定和分析。根据海水理化性质将研究海区分为5个区,并使用CHEMTAX软件（Mackery et al.,1996）讨论了西北冰洋不同海区浮游植物群落组成结构及其与环境因子之间的关系。结果显示在楚科奇海陆架区,太平洋入流显著影响浮游植物生物量和群落结构。高营养盐Anadyr水团以及白令陆架水控制海域,表现出高Chl a且浮游植物以硅藻为主,相反,低营养盐如阿拉斯加沿岸流控制海域,Chl a生物量低且以微型,微微型浮游植物为主。在外陆架海区,海冰覆盖情况影响着水团的物理特征及营养盐浓度水平,相应地显著影响浮游植物群落结构。在海冰覆盖区域,硅藻生物量站到总Chl a生物量的75%以上;在靠近门捷列夫深海平原海区,受相对高盐的冰融水影响（MW-HS）,营养盐浓度和Chl a浓度相对海冰覆盖区略高,浮游植物结构中微型、微微型藻类比重增加,硅藻比例则降至33%;南加拿大海盆无冰海区（IfB）,表层水盐度最淡,营养盐浓度最低,相应地显示出低Chl a生物量,表明海冰消退,开阔大洋持续时间延长,将导致低生物量及激发更小型浮游植物的生长,并不有利于有机碳向深海的有效输出。  相似文献   

11.
Upwelling occurs on the coast of Java between June and October, forced by local alongshore winds associated with the southeasterly monsoon. This causes variations in phytoplankton community composition in the upwelling zone compared with the surrounding offshore area. Based on pigments analysis with subsequent calculations of group contributions to total chlorophyll a(Chl a) using CHEMTAX, we studied the distribution and composition of phytoplankton assemblages in the subsurface chlorophyll maximum along the south coast of Java and the influence of upwelling. Nineteen phytoplankton pigments were identified using high-performance liquid chromatography, and CHEMTAX analysis associated these to ten major phytoplankton groups. The phytoplankton community in the coastal area influenced by upwelling was characterized by high Chl a and fucoxanthin concentrations, indicating the dominance of diatoms. In contrast, in the offshore area, the Chl a and fucoxanthin concentrations declined to very low levels and the community was dominated by haptophytes represented by 19′-Hexanoyloxyfucoxanthin. Accordingly, microphytoplankton was found to be the major size class in the coastal area influenced by upwelling, while nanophytoplankton was most abundant in the offshore area. Low concentrations of other accessory pigments indicated less contribution from dinoflagellates,prasinophytes, chlorophytes and cryptophytes. Photo-pigment indices revealed that photosynthetic carotenoids(PSCs) were the largest component of the pigment pool, exceeding the proportion of Chl a, with the average PSCTP up to 0.62. These distribution trends can mainly be explained by phytoplankton adaption strategies to upwelling and subsurface conditions by changing species composition and adjusting the pigment pool.  相似文献   

12.
长江口海域春季浮游植物的年际变化   总被引：2，自引：0，他引：2  
林梅  李扬 《海洋与湖沼》2017,48(2):303-311
于2014年5月在长江口海域采集海水样品,分析了浮游植物种类组成、细胞丰度、优势种等群落结构特征。共鉴定浮游植物105种,其中硅藻30属56种,甲藻19属41种,以及隶属于金藻、蓝藻等的8个种。浮游硅藻以近岸半咸水种为主,优势种类是中肋骨条藻(Skeletonema costatum);浮游甲藻以沿岸广布种为主,典型代表是东海原甲藻(Prorocentrum donghaiense)。为了更好地了解长江口海域浮游植物的年际变化趋势,本文收集整理了该海域1986—2014年间的春季数据,分析了浮游硅藻、浮游甲藻主要群落特征的年际变化,以及浮游硅藻优势种类细胞粒径的变化趋势。结果表明:(1)浮游硅藻、浮游甲藻的种类数均呈现不同程度的上升趋势,浮游甲藻的上升幅度更为明显;(2)浮游甲藻种类数在浮游植物种类数中的占有比例呈上升趋势,而浮游硅藻所占比例呈下降趋势;(3)浮游硅藻优势种类的细胞粒径呈现小型化趋势。  相似文献   

13.
白令海特征区域的表层沉积硅藻分布及其古海洋学意义   总被引：1，自引：1，他引：0  
对白令海表层沉积物样品进行硅藻分析,共鉴定硅藻30属56种(含变种),并确定17种硅藻新记录,其中包括Kisseieviella carina等3种化石种。白令海表层沉积物中的硅藻优势种为Neodenticula seminae,Fragilariopsis cylindrus和Fragilariopsis oceanica,在白令海北部陆坡深水区附近以Neodenticula seminae为主,而在白令海北部陆架以Fragilariopsis cylindrus和Fragilariopsis oceanica为主。对硅藻结果进行聚类分析,可以划分出3个硅藻组合,硅藻组合Ⅰ代表海冰种硅藻组合,组合Ⅱ代表受阿拉斯加流影响的大洋浮游硅藻组合,组合Ⅲ代表上述两个硅藻组合之间的过渡组合。Fossula arctica是17种硅藻新记录之一,首次记录于白令海表层沉积物中,其百分含量分布趋势与Fragilariopsis cylindrus和Fragilariopsis oceanica的相近,在白令海北部陆架为11.7%~17.1%,而在陆坡深水区附近明显减少,是继Fragilariopsis cylindrus和Fragilariopsis oceanica之后白令海又一海冰指示种,并有望成为一种有效的海冰变化替代物运用于晚第四纪以来白令海海冰进退历史研究。  相似文献   

14.
The abundance of diatoms in the water column and the downward vertical flux of diatom cells from the euphotic zone were investigated during a time series of 11 monthly cruises (June 1994–July 1995) to Station ALOHA (22°45′N, 158°00′W) as one component of the Hawaii Ocean Time-series (HOT) Program. The diatom community was studied using light microscopy and by high-performance liquid chromatographic (HPLC) pigment analyses. Distinct diatom assemblages were found in the mixed-layer and in the Deep Chlorophyll Maximum Layer (DCML). Diatom cell abundances in the water column were generally low during the year, except in July 1994, when they increased in the upper euphotic layer. Two lightly silicified species (Hemiaulus hauckii [Grunow] and Mastogloia woodiana [Taylor]) were mainly responsible for this increase. Other less abundant diatom species present in the mixed-layer assemblage showed a similar temporal pattern. H. hauckii contained Richelia-type endosymbionts with heterocysts and was presumably able to fix dinitrogen. Both species of diatoms also were an important component of the vertical diatom flux out of the euphotic zone, which, likewise, was highest in July 1994. During this maximum export period, aggregates of these two species were collected in the drifting sediment traps. In the DCML, diatom abundances and export were low throughout the year, with the exception of one genus (Pseudonitzschia) for which a slight concentration increase was observed in spring. Reflecting the observed diatom cell abundance and vertical flux, fucoxanthin concentrations (a pigment marker for diatoms) did not indicate any significant increase of diatom pigment biomass in the DCML during the year. Ratios of diadinoxanthin to chromophyte pigments suggested that the phytoplankton cells sinking out of the euphotic zone in midsummer originated from the mixed-layer. The attenuation of the pigment vertical fluxes with depth was significantly lower for fucoxanthin, indicating a generally slower decay of diatom flux with depth compared with other phytoplankton groups. Our findings suggest that, in the subtropical North Pacific Ocean, summer conditions seem to favor the development of selected species of diatoms in the mixed-layer and that these assemblages appear to be more important with regard to export production than those in the DCML.  相似文献   

15.
李照  宋书群  李才文  俞志明 《海洋学报》2017,39(10):124-144
通过2013年3月和8月在长江口及其邻近海域进行的多学科综合调查,研究了枯水期和丰水期浮游植物的群落结构和空间分布特征,并探讨了影响其分布的环境因子效应。枯水期共发现浮游植物3门41属80种（不包括变种和变型）,以硅藻为主,主要优势种为具槽帕拉藻（Paralia sulcata）;浮游植物细胞丰度介于0.15×103~16.35×103 cells/L,平均值为（3.24±3.14）×103 cells/L;浮游植物细胞丰度在长江口外东北部海域形成高值,垂直变化较小,硅藻刻画了浮游植物的空间分布。丰水期共发现浮游植物4门67属135种（不包括变种和变型）,甲藻物种数量和细胞丰度均升高,主要优势种为东海原甲藻（Prorocentrum donghaiense）和骨条藻（Skeletonema sp.）;浮游植物细胞丰度介于0.2×103~1 925.45×103 cells/L,平均值为（41.67±186.00）×103 cells/L;浮游植物细胞丰度在长江口外形成南北两个高值区,随水深增加,细胞丰度逐渐降低。浮游植物的空间分布受长江口冲淡水影响,与盐度和浊度有显著的相关性;N/P比影响浮游植物群落结构,随着N/P比升高,甲藻的相对丰度升高,硅藻的相对丰度逐渐降低。浮游植物在层化水体的上层大量繁殖是底层低氧形成的必要条件,硅藻具有较高的沉降速率,因而以硅藻为主的群落更利于低氧的形成。  相似文献   

16.
2001年冬季渤海的浮游植物群落结构特征   总被引：17，自引：0，他引：17  
研究了2001年冬季覆盖渤海56个测站的浮游植物物种及其群落特征。共发现浮游植物3门37属72种(不包括未定名物种)。物种主要以温带近岸型硅藻为主，优势种主要尖刺伪菱形藻、浮动弯角藻、偏心圆筛藻、具槽帕拉藻(Parnlia sulcata)和环纹劳德藻。其中的尖刺伪菱形藻、偏心圆筛藻和具槽帕拉藻是冬季渤海浮游植物的关键种。分析认为：细胞丰度的平面分布由浮游硅藻的分布所决定。同1983年同期资料相比发现，优势种没有较大变化，但其优势程度顺序和细胞丰度发生了一定的改变，整个浮游植物群落的细胞丰度有大幅度增加。冬季渤海浮游植物群落的多样性程度是低的。  相似文献   

17.
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   

18.
Time-series of remotely sensed distributions of phytoplankton, sea ice, surface temperature, albedo, and clouds were examined to evaluate the variability of environmental conditions and physical forcing affecting phytoplankton in the Beaufort and Chukchi Seas. Large-scale distributions of these parameters were studied for the first time using weekly and monthly composites from April 1998 to September 2002. The basic data set used in this study are phytoplankton pigment concentrations derived from the Sea-viewing Wide Field-of-view Sensor (SeaWiFS), ice concentrations obtained from the Special Sensor Microwave Imager (SSM/I) and surface temperature, cloud cover, and albedo derived from the Advanced Very High Resolution Radiometer (AVHRR). Seasonal variation of ice cover was observed to be the dominant environmental factor as the ice-edge blooms followed the retreating marginal ice zones northward. Blooms were most prominent in the southwestern Chukchi Sea, and were especially persistent immediately north of the Bering Strait in nutrient-rich Anadyr Water and in some fronts. Chlorophyll concentrations are shown to increase from a nominal value during the onset of melt in April to a maximum value in mid-spring or summer depending on location. Large interannual variability of ice cover and phytoplankton distributions was observed with the year 1998 being uniquely associated with an early season occurrence of a massive bloom. This is postulated to be caused in part by a rapid response of phytoplankton to an early retreat of the sea-ice cover in the Beaufort Sea region. Correlation analyses showed relatively high negative correlation between chlorophyll and ice concentration with the correlation being highest in May, the correlation coefficient being −0.45. 1998 was also the warmest in the 5 years globally and the sea-ice cover was least extensive in the Beaufort/Chukchi Sea region, partly because of the 1997–1998 El Niño. Strong correlations were noted between ice extent and surface temperature, the correlation coefficient being highest at −0.79 in April, during the onset of the bloom period.  相似文献   

19.
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   

20.
通过现场围隔实验,模拟赤潮发生过程,研究了种群不同生长阶段中不同粒级浮游植物种群的变化情况。结果表明,添加营养盐能有效促进浮游植物的生长,东海原甲藻围隔（M1）和自然水体围隔（M2）中浮游植物分别于第7天和第4天出现生长高峰,叶绿素a最大值分别为112．79mg／m和235．60mg/m。微型浮游植物与微微型浮游植物存在竞争,微型对微微型生长的抑制作用：M2〉M1。在营养盐丰富时,硅藻的增殖速率比东海原甲藻快,达到高峰期时间短,消亡也快。硅的减少促进硅藻水华的消亡。  相似文献   

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