|Thesis Advisor||孙 松 研究员|
|Place of Conferral||北京|
|Keyword||西北冰洋 浮游动物群落 桡足类 年际变化 垂直分布|
根据浮游动物的种类组成和丰度，整个西北冰洋可以划分出3个地理分布上相隔离的群落：近岸浅水、陆坡过渡和深海群落。近岸浅水群落位于最南部，陆坡过渡群落位于最北部的楚科奇海陆坡区和波弗特海边缘，深海群落则包括楚科奇海台、楚科奇深海平原以及加拿大海盆的所有深水站位。桡足类和藤壶幼体是近岸浅水群落最主要的组成类群（>90%），深海群落则由桡足类占绝对优势（>90%），过渡群落兼具前两个群落的特征。近岸浅水群落的浮游动物种类组成和丰度在一定程度上受到白令海入流水的影响，但仍然以本地繁殖和发育的伪哲水蚤（Pseudocalanus spp.）、北极哲水蚤（Calanus glacialis）以及藤壶幼体（Barnacle larva）为最主要的种类。陆坡过渡和深海群落的物种组成主要为极北哲水蚤（Calanus hyperboreus）、细长长腹水蚤（Metridia longa）、拟真刺水蚤（Paraeuchaeta spp.）等北极种类和伪哲水蚤、北极哲水蚤等广布型种类。近岸浅水群落浮游动物总丰度自2003至2012年呈上升的趋势，这说明在楚科奇海浅水区，浮游动物群落总丰度受益于海冰的快速消退和生长季节的延长。然而，由于站位分布、覆盖范围以及调查时间上的差异，难以对比陆坡过渡群落和深海群落的年际间差异。同时由于调查范围广大，地理分布上的巨大差异掩盖了楚科奇海内部不同水团的影响。楚科奇海作为西北冰洋最受关注的海区，浮游动物的群落结构、影响因素和年际变化还需进一步细化。
根据现有的科学假设，楚科奇海是底栖食物链向浮游食物链主导转化最早发生的海域。为了研究楚科奇海夏季浮游动物群落的年际变化及其空间异质性，我们选取4个航次楚科奇海的站位，在划分不同地理群落的基础上比较了它们的年际变化格局。根据浮游动物种类组成和丰度，楚科奇海存在3个地理群落：南部近岸、中部陆架和北部陆坡群落。北部陆坡群落浮游动物总丰度较低且以桡足类为主（>90.0%），中部和南部群落丰度高，由桡足类和底栖动物浮游幼体共同主导（86.1—97.0％）。从2003到2008年，北部陆坡群落的平均丰度从112.4个/m3增加到182.9 个/m3，并且所有终生浮游类群的丰度都呈增高趋势，只有阶段性浮游幼体丰度减少。中部和南部群落浮游动物总丰度呈波动趋势，分别在2012和2010年出现最高值，但是两个群落的总平均丰度却呈现线性增加的趋势。从优势种组成上看，北部群落除了桡足类外只有圆胃住囊虫（Oikopleura vanhoffeni）优势度大于0.02，优势种完全一致且优势度变化较小。中部和南部群落的优势种在组成、数量和优势度上都有明显的年际差异。该结果表明，即使在楚科奇海内部浮游动物群落年际变化也存在显著的地理差异，以终生浮游类群为主的北部陆坡区群落结构稳定，主要表现为丰度增加；南部近岸和中部陆架群落组成和丰度都存在明显的年际差异，且终生浮游类群和阶段性浮游幼体趋势性并不一致，但总体上也是增加的趋势。
深水海盆区浮游动物的垂直分布模式和地理差异也是北冰洋浮游动物研究的热点之一。利用2012年9月01—06日采自马卡诺夫海盆和楚科奇深海平原共4个站位的分层浮游动物样品，我们研究了浮游动物在0—1000m水层的垂直分布以及地理差异。结果表明，浮游动物在0—200m分布密集而在200—1000m比较稀少。在数量上占优势的种类中，植食性为主的拟长腹剑水蚤（Oithona similis）、北极哲水蚤和极北哲水蚤集中在200m以浅的水层。虽然在200m以下杂食性种类矮小微哲水蚤（Microcalanus pygmaeus）、隆剑水蚤（Oncaea spp.）和细长长腹水蚤的丰度也明显降低，但是占浮游动物总丰度的比例却明显更高。两个调查海区浮游动物种类组成相似，但是楚科奇深海平原大型桡足类极北哲水蚤的丰度较高，而小型桡足类丰度较低。在垂直分布上差异主要在于500—1000m水层，马卡诺夫海盆站位丰度在22.7—92.6个/m³之间，而楚科奇深海平原只有1.6个/m³。深海区浮游动物丰度的地理差异说明生物泵的作用存在空间异质性。类似地理差异产生的原因在于楚科奇深海平原存在数量较多的极北哲水蚤，它们在春季融冰前就上升到表层摄食冰藻，显著降低了有机物的垂直通量。
|Other Abstract||The Arctic Ocean ecosystem is undergoing dramatic oceanographic change related to decreasing ice coverage and increasing temperature over the last decades. Zooplankton plays a key role in marine ecosystem. It is the linkage between primary producers and secondary consumers. Zooplankton is also a driving force of marine biological pump, playing an important role in the marine biogeochemical cycle. Considering the short life span and weak swimming ability, planktonic sepcies may be more sensitive to environmental changes than other marine organisms, and they have been used as indicators of global changes in many studies. Retreat of sea-ice showed an accelerated trend after 2003 and reached the record minimum of 3.41 million km2 in 2012. To detect the potential response of zooplankton communities to rapid ice decline in this period, its composition, geographical distribution and inter-annual change were investigated with samples collected in epipelagic waters (<200m) in summer of 2003, 2008, 2010 and 2012. Meanwhile, specific difference in vertical distribution pattern of copepods was investigated in Makarov Basin and Chukchi Abyssal Plain in 2012.|
Based on species composition and abundance of each station, three geographical communities were identified in the western Arctic Ocean: Coastal Neritic Community (CNC), Slope Transitional Community (STC) and Deep-sea Community (DC). CNC located in shelf waters of the Chukchi Sea and Alaskan costal waters; STC located in the north of Chukchi Slope and the edge of Beaufort Sea; DC include all deep-sea stations of Chukchi Plateau, Chukchi Abyssal Plain and Canadian Basin. Copepods and barnacle larva were two main taxa of CNC (>90%) and DC was dominated only by copepods (>90%), while STC showed both characteristics of CNC and STC. Species composition and abundance of CNC were affected partially by influx of Bering Water, while native species (Calanus glacialis, Pseudocalanus spp., Barnacle larva) were still the main components of zooplankton. Arctic species (Calanus hyperboreus, Metridia longa, Paraeuchaeta spp.) and widespread species (C. glacialis and Pseudocalanus spp.) were main contributors to total abundance of STC and DC. Total zooplankton abundance of CNC increased from 2003 to 2012 (1092.4-1648.7 ind/m3), it indicated that zooplankton community of CNC benefited from prolonged growing season. While it was difficult to compare the inter-annual changes of STC and DC due to the variable station setting and investigate time. Moreover, geographical distribution of different zooplankton communities which result in large-scale investigate areas would cover the inner differences of CNC.
Along with shrinking in sea-ice coverage, trophic structure is hypothesized to shift towards planktonic-dominating, which may most likely be tested in the Pacific-influenced Arctic shelf region. In order to evaluate the response of the Chukchi Sea communities to climate changes, we combined zooplankton samples and investigated the inter-annual changes in regions with various physical and biological characters. Three geographically separated communities were identified by hierarchical cluster analysis, including the north Chukchi Sea community (NCS) governed by Arctic cold water, the Bering Sea water influenced central (CCS) and south (SCS) Chukchi Sea community. Zooplankton abundance was low in NCS and dominated by copepods (>90%). It was about ten times higher in CCS and SCS, co-dominated by copepods and barnacle larvae (86-98％). In the NCS community, similar dominant species were recorded in 2003 and 2008, but total abundance increased from 118.9 to 182.5ind/m3. Average zooplankton abundance of all Pacific-influenced stations increased from 2003 to 2012, but lowest average abundance was observed in 2012 and 2010 in the CCS and SCS community, respectively. Barnacle larvae, C. glacialis, Pseudocalanus spp. and Oikopleura vanhoffeni were identified as dominant species of the CCS community, and those for the SCS community included also Eucalanus bungii with Pacific origin, as well as Acartia spp., O. longissina and other merozooplankton commonly observed in neritic waters. Numerical increase was observed only in C. glacialis. We propose spatial heterogeneity for the Chukchi zooplankton community changes in response to global warming. Numerical increase is expected in Arctic waters with constant structure, and inter-annual variability in composition is also significant in shallow waters receiving Pacific inflows. Despite the fluctuation of average abundance separately in SCS and CCS, average of these two communities increased linearly from 2003 to 2012.
Copepods were the most important herbivorous zooplankton group in marine ecosystem. In the Arctic Ocean, copepods have evolved complex life cycle strategies to survive harsh environment, and such adaptation ability can further determine their response to climate changes. Species sensitivity is essential to understanding of climate-induced ecological consequences. To determine the species and regional specific responses of planktonic copepods in the western Arctic Ocean, we compiled field observations during a period of rapid ice retreat, and compared variability in abundance of different ecological groups. Three types of habitats were identified, namely the Chukchi Shelf (CS) characterized by warm water in upper 30 m layer, Canadian Basin (CB) containing stations deeper than 1000 m, and Chukchi Slope/Plateau (CSP) sharing similar temperature with CB. Pacific-origin species presented overwhelmingly in CS and can hardly reach basal area. Coastal Arctic species were sampled from all stations but comparatively high abundance was recorded in CS. Oceanic Arctic species distributed evenly in all habitats in 2003, but was absent from CS in the other years. Opportunistic Arctic species were low in abundance with evident year-to-year difference in distribution patterns and species assemblages. In CB, much lower total abundance was observed in 2010 and 2012 (17.6 and 12.5 ind/m3) comparing to 2003 and 2008 (56.5 and 82.3 ind/m3). Both coastal and oceanic Arctic species decreased during this period. Highest abundance in CS and CSP present in 2012 as 745.8 and 1049.9 ind/m3, followed by 2003 (326.0 and 373.6 ind/m3). Numerical increase in 2012 was contributed mostly by large-sized Calanus glacilis, in which extremely high abundances of 568.8 and 844.4 ind/m3 were recorded. Based on dominance of young copepodites, we propose C. glacialis as the beneficiary of summer sea-ice minimum in 2012, induced by successful local recruitment rather than direct physical transportation. The decrease of copepod abundance in basal area shows consistence with previous opinion that phytoplankton production in Canadian basin does not increase but shift towards smallest algae dominating.
In addition, vertical distribution patterns and geographical differences of zooplankton community was also one hotspot of Arctic zooplankton research. Using samples collected in epi- and meso-pelagic layers of the Makarov Basin (MB) and Chukchi Abyssal Plain (CAP) in September 2012, vertical distribution and geographic difference of zooplankton were analyzed. According to species composition and abundance, both diversity and abundance of zooplankton changed with depth. Zooplankton was mainly gathered in 0-200m and relatively rare in 200-1000m. Herbivorous species, such as O. similis, C. glacialis and C. hyperboreus, gathered in 0-200m and dominated in number. Although abundance of omnivorous species such as M. pygmaeus, Oncaea spp. and M. longa aslo decreased with depth, their percentages in total abundance increased to the contrary. Despite similar species assemblages recorded in each layer, epipelagic abundance of large copepod C. hyperboreus was higher and that of small copepods was lower at CAP station than the MB stations, whereas in 200-1000m layer total abundance was much lower in CAP. Abundance of zooplankton in 500-1000m layer varied between 22.7 and 92.6 ind/m³ in MB, but was only 1.6 ind/m³ in CAP. Geographical differences of zooplankton abundance in mesopelagic layer were in accord with the heterogeneity in the function of biological pump. It is suggested that low zooplankton abundance in mesopelagic layer of CAP was induced by high density of C. hyperboreus in epipelagic layer, which starts feeding before ice melting in the spring and consequently reduced the downward flux of organic matter formed mainly by ice algae.
|Subject Area||海洋调查与监测 ; 海洋科学其他学科|
|徐志强. 西北冰洋夏季浮游动物群落结构和年际变化[D]. 北京. 中国科学院大学,2016.|
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