海洋生物分类与系统演化实验室知识库

       海洋大型底栖动物（Marine Macrozoobenthos）是海洋生态系统的重要组成部分，长江口邻近海域受到复杂的自然环境和剧烈的人类活动的共同影响，属于生态敏感区域，研究该海域大型底栖动物群落的变化对保护海洋生物多样性和维护海洋生态系统稳定均有重要意义。另外，长江口邻近海域时常发生季节性的氧亏损事件，但目前少有针对该海域轻度氧亏损对大型底栖动物群落影响的系统性研究。本论文以大型底栖动物群落为主要研究对象，研究了长江口（Yangtze River Estuary）邻近海域大型底栖动物群落的时空变化及环境因子的影响；基于该海域的底层溶解氧（DO，dissolved oxygen）数据，研究了轻度氧亏损对大型底栖动物群落季节变化的影响；并利用大型底栖动物评价指数对该海域近来的底栖生态环境进行了评估。本论文主要包含以下四部分工作。
       利用1959年、2000-2001年、2011-2012年、2014-2015年四个时期的大型底栖动物和底层海水环境因子的调查数据，研究了长江口邻近海域大型底栖动物群落的长期变化及其与环境因子的关系。四个时期共采集到624种大型底栖动物，多毛类在各主要类群中占优且随时间推移有增加的趋势。聚类分析（cluster analysis）、主坐标分析（PCO analysis，principal coordinates analysis）和多元方差分析（PERMANOVA，permutational multivariate analysis of variance）的结果表明，这四个时期的大型底栖动物群落存在着明显的差异。从典范对应分析（CCA，canonical correspondence analysis）和冗余分析（RDA，redundancy analysis）的结果可看出，底层海水的温度、盐度、水深显著影响了大型底栖动物群落的长期变化（CCA的前两轴解释了89.6%的物种-环境关系变化，RDA的前两轴解释了94.3%的物种-环境关系变化）。K优势度曲线的结果（曲线的相对高度逐时期升高）、ABC（abundance/biomass comparison）曲线的结果（W值在1959年为0.311，2000-2001年为0.305，2011-2012年为0.222，2014-2015年为0.167，逐时期减小）和Shannon-Wiener指数（H'，log 2）的结果（H’的范围在1959年为2.29-5.03，2000-2001年为2.86-4.55，2011-2012年为2.28-4.56，2014-2015年为1.79-4.43，呈逐时期减小的趋势）均表明，研究海域的底栖生态状况随时间推移有恶化趋势。
       利用2015年2月-2016年1月期间连续10个月（除2015年8月、12月外）的大型底栖动物和底层海水环境因子的调查数据，研究了长江口邻近海域大型底栖动物群落的南北差异及驱动该差异形成的主要环境因子。主成分分析（PCA，principal component analysis）的结果和多元方差分析的结果均显示，该海域的底层海水环境因子有显著的季节差异和南北差异。主坐标分析和聚类分析的结果揭示了该海域大型底栖动物群落显著的南北分布差异，并表明大型底栖动物在该海域存在斑块状分布的现象。用BIOENV分析和CCA揭示了大型底栖动物群落差异与环境因子之间的关系，结果表明底层海水的水深、盐度、浊度是与大型底栖动物群落南北差异相关的主要环境因子，其中水深对该差异的贡献最大。长江冲淡水（CDW，Changjiang Diluted Water）是造成底层海水环境因子和大型底栖动物群落的南北差异的一个重要驱动因素。ABC曲线的结果表明，长江口邻近海域北部的大型底栖动物比南部的受到更大程度的干扰，这可能是因为北部地区受到长江（Yangtze River）的干扰更严重。
       利用2015年8月和12月的大型底栖动物和底层海水环境因子数据，研究了长江口邻近海域大型底栖动物群落的夏、冬季节变化及轻度氧亏损对该变化的影响。PCA和PERMANOVA的结果表明，该海域的底层海水环境因子在夏季和冬季之间存在着显著差异。底层海水的溶解氧在夏季处于轻度氧亏损状态，而在冬季则处于常氧状态。PERMANOVA的结果表明，大型底栖动物群落在夏季和冬季之间发生了明显的季节变化。多元回归和CCA揭示了底层海水环境因子（特别是溶解氧）与大型底栖动物群落季节变化的关系，并尝试用线性回归模型描绘了大型底栖动物多样性指数与轻度氧亏损的关系。结果表明，长江口邻近海域的季节性轻度氧亏损与大型底栖动物群落的季节变化显著相关，但它并不会对群落造成明显的破坏，相反，我们推测轻度氧亏损可能会使大型底栖动物的天敌数量减少，在一定程度上减小大型底栖动物的生存压力，从而造成大型底栖动物群落结构的季节性波动。溶解氧只能解释大型底栖动物群落季节变化的一部分，其他环境因子，特别是水深、磷酸盐和浊度，也对群落变化有很大影响。
       利用2015年2月-2016年1月期间连续10个月（除2015年8月、12月外）的大型底栖动物和底层海水环境因子的调查数据，对长江口邻近海域的底栖生态环境进行了评估。评估使用了AMBI（AZTI Marine Biotic Index）、M-AMBI（multivariate-AZTI Marine Biotic Index）和BOPA（benthic opportunistic polychaetes amphipods）三个生物评价指数。结合三个指数的评估结果以及对这三个指数和四个与富营养化相关的底层海水环境因子（叶绿素a、溶解无机氮、磷酸盐、硅酸盐）进行的Pearson相关分析的结果，认为M-AMBI最适用于该海域的底栖生态环境评估。四个与富营养化相关的环境因子以及底栖生态状况均呈现出相似的与离河口和海岸远近相关的空间分布模式，表明该海域可能处于富营养化的环境压力下。根据M-AMBI的结果，该海域有两个主要的受干扰区域：一个位于长江口以东，另一个位于浙江省以东。研究发现，这两个受干扰区域的形成可能主要与长江冲淡水有关。M-AMBI的结果表明，该海域的底栖生态状况在这一年里没有发生明显的季节变化。
       本论文的主要研究发现和创新点包括：长江口邻近海域的大型底栖动物群落在过去的半个多世纪里发生了显著的变化，大型底栖动物的多样性随时间推移呈下降的趋势，底栖生态环境也呈现出恶化的趋势；该海域的大型底栖动物群落存在显著的南北差异，长江冲淡水是造成该差异的一个主要因素；季节性轻度氧亏损与该海域大型底栖动物群落的季节变化显著相关，它会使大型底栖动物的天敌数量减少，一定程度上有利于部分大型底栖动物的生存，从而造成底栖生物群落结构的季节性波动；大型底栖动物群落动态变化可以很好地反映生态环境的长期变化，M-AMBI可以较好地适用于该海域的底栖生态环境评估。

       Marine Macrozoobenthos is an important part of the marine ecosystem. Adjacent areas of the Yangtze River Estuary are under combined influence of the complex natural environment and intense human activities, which are ecologically sensitive areas. Studying variations of the macrozoobenthic community in this region has important implications for both protecting marine biodiversity and maintaining the stability of the marine ecosystem. In addition, the seasonal oxygen deficiency often occurs in adjacent areas of the Yangtze River Estuary, but few systematic studies were done on the influence of mild oxygen deficiency on the macrozoobenthic community in these areas. Taking macrozoobenthic community as the main research object, the present paper studied the temporal and spatial variations of the macrozoobenthic community and the influence of environmental variables in adjacent areas of the Yangtze River Estuary. Based on the bottom dissolved oxygen (DO) data in the study area, the influence of mild oxygen deficiency on seasonal variation of the macrozoobenthic community was studied. The benthic ecological environment of the study area was evaluated by macrozoobenthic evaluation indices. The present paper mainly includes the following four parts of work.

       Based on the research data of macrozoobenthos and bottom seawater environmental variables in four periods including 1959, 2000-2001, 2011-2012 and 2014-2015, the long-term variation of the macrozoobenthic community and its relationship with environmental variables were studied in adjacent areas of the Yangtze River Estuary. A total of 624 macrozoobenthic species were collected in the four periods, and Polychaeta dominated in the main taxonomic groups and tended to increase over time. The results of cluster analysis, PCO (principal coordinates analysis) and PERMANOVA (permutational multivariate analysis of variance) showed that significant differences existed in the macrozoobenthic community among the four periods. The results of CCA (canonical correspondence analysis) and RDA (redundancy analysis) showed that water temperature, salinity and depth of the bottom seawater significantly influenced the long-term variation of the macrozoobenthic community (the first two axes of CCA and RDA separately explained 89.6% and 94.3% of the species-environment relationship variance). The result of K-dominance curves (the relative elevation of the curves increased with period), the result of ABC (abundance/biomass comparison) curves (the W value decreased with period, which was 0.311 in 1959, 0.305 in 2000-2001, 0.222 in 2011-2012, and 0.167 in 2014-2015) and the result of Shannon-Wiener index (H’, log 2) (the range of H’ was 2.29-5.03 in 1959, 2.86-4.55 in 2000-2001, 2.28-4.56 in 2011-2012, and 1.79-4.43 in 2014-2015, which showed a decreasing trend with period) all showed that the benthic ecological status of the study area tended to deteriorate with time.

       Based on the research data of macrozoobenthos and bottom seawater environmental variables in ten months from February 2015 to January 2016 (except August and December of 2015), the north-south difference of the macrozoobenthic community and its major environmental driving factors were studied in adjacent areas of the Yangtze River Estuary. The results of PCA (principal component analysis) and PERMANOVA showed that significant seasonal and north-south differences existed in the bottom seawater environmental variables in the study area. The results of PCO and cluster analysis revealed the significant north-south difference in the macrozoobenthic community in the study area, and a phenomenon of patchy distribution was indicated for the macrozoobenthos in this area. BIOENV analysis and CCA were used to reveal the relationship between the difference of macrozoobenthic community and the environmental variables, which indicated that depth, salinity and turbidity of the bottom seawater were major environmental variables related to the north-south difference of the macrozoobenthic community, and depth contributed most to the difference. The CDW (Changjiang Diluted Water) was an important driving factor for the north-south differences of the bottom seawater environmental variables and the macrozoobenthic community. The result of ABC curves showed that the macrozoobenthos in the northern part of adjacent areas of the Yangtze River Estuary suffered more disturbance than those in the southern part, which could be because the northern part suffered more disturbance from the Yangtze River.

       Based on the research data of macrozoobenthos and bottom seawater environmental variables in August 2015 and December 2015, the seasonal difference of the macrozoobenthic community between summer and winter and the influence of mild oxygen deficiency on the difference were studied in adjacent areas of the Yangtze River Estuary. The results of PCA and PERMANOVA showed that significant difference existed in the bottom seawater environmental variables between summer and winter in the study area. The dissolved oxygen in the bottom seawater was in mild deficiency in summer but normoxic in winter. The result of PERMANOVA showed that significant seasonal difference existed in the macrozoobenthic community between summer and winter. The relationship between the bottom seawater environmental variables (especially dissolved oxygen) and the seasonal variation of the macrozoobenthic community was revealed by multiple regression and CCA, and the relationship between macrozoobenthic diversity indices and mild oxygen deficiency was tried to portray with linear regression models. The results showed that the mild seasonal oxygen deficiency in adjacent areas of the Yangtze River Estuary was significantly correlated with the seasonal variation of the macrozoobenthic community, but it would not cause great damage to the community, and in contrast, we speculated that it could reduce the number of natural predators of the macrozoobenthos, reducing the survival pressure of the macrozoobenthos to some extent, in this way causing the seasonal fluctuation of the macrozoobenthic community structure. Dissolved oxygen accounted for only part of the seasonal variation in the macrozoobenthic community, which was also strongly influenced by other environmental variables, particularly depth, phosphate and turbidity.

       Based on the research data of macrozoobenthos and bottom seawater environmental variables in ten months from February 2015 to January 2016 (except August and December of 2015), the benthic ecological status of adjacent areas of the Yangtze River Estuary was assessed. Three biotic indices including AMBI (AZTI Marine Biotic Index), M-AMBI (multivariate-AZTI Marine Biotic Index) and BOPA (benthic opportunistic polychaetes amphipods) were used in the assessment. Combined with the assessment results of the three indices and the results of Pearson correlate analysis between the indices and four bottom seawater environmental variables (chlorophyll a, dissolved inorganic nitrogen, phosphate and silicate) related to eutrophication, M-AMBI was considered to be most suitable for the benthic ecological environment assessment in the study area. The four environmental variables related to eutrophication and the benthic ecological status showed similar spatial distribution patterns related to the distance to the estuary and the coasts, indicating that the study area could be under the environmental pressure of eutrophication. According to the result of M-AMBI, two major disturbed regions existed in the study area: one was located to the east of the Yangtze River Estuary, and the other was located to the east of Zhejiang Province. It was found that the formation of these two disturbed regions could be mainly related to the CDW. The result of M-AMBI showed that no significant seasonal variation occurred in the benthic ecological status of the study area during the year.

       The main findings and innovation points of this paper includes that: significant variation happened in the macrozoobenthic community in adjacent areas of the Yangtze River Estuary over the past more than half a century, and the biodiversity tended to decrease and the benthic ecological environment tended to deteriorate; significant north-south difference existed in the macrozoobenthic community in the study area, and the CDW was a key factor that caused the difference; the mild seasonal oxygen deficiency was significantly related to the seasonal variation of the macrozoobenthic community in the study area, which would reduce the number of natural predators of the macrozoobenthos, benefitting the survival of some macrozoobenthos to some extent, in this way causing the seasonal fluctuation of the macrozoobenthic community structure; The dynamic changes of the macrozoobenthic community could well reflect the long-term changes of the ecological environment, and M-AMBI was suitable for the benthic ecological environment assessment in the study area.