海洋生物分类与系统演化实验室知识库

小型底栖生物是海洋沉积环境中数量和种类最占优势的后生动物类群，对沉积环境的结构、物质循环和能量流动起着重要作用。在对海洋沉积环境进行监测的过程中，小型底栖生物是一项重要的指标。线虫是小型底栖生物中数量最占优势且多样性最高的类群，其群落结构和功能复杂多样，可反映环境的变化，因而在小型底栖生物研究中备受关注。但线虫物种的形态鉴定极为困难且费时费力，很大程度上制约了这一领域的发展。随着分子手段的发展，目前很多形态分类上争论不休的问题得以解决，但由于相关序列的代表性不足，许多类群的归属问题仍悬而未决。

本文首先对渤海莱州湾和黄海牟平近海、东海南麂列岛潮间带以及西北太平洋深海进行了小型底栖生物群落组成和环境状况分析。在此基础上，通过采集和分离线虫样品，结合形态学与分子测序手段，对海洋沉积物中最丰富且常见的嘴刺目、单宫目和色矛目线虫进行了系统发育分析。

对多种生境的小型底栖生物研究显示，莱州湾和牟平近海平均丰度分别为1979 ind/10 cm²和2741 ind/10 cm²，南麂岛潮间带年平均丰度为556 ind/10 cm²，西北太平洋深海平均丰度147 ind/10 cm²。在莱州湾和牟平近海，小型底栖生物群落的分布同叶绿素a和脱镁叶绿素的分布趋势相一致，同时，依据不同底质条件下细化的标准，线虫桡足类丰度比值（N/C）可以反映出这两个海域有机质的污染情况。在南麂岛潮间带，不同沙滩间的差异显著，火焜岙（HKA）叶绿素a含量高于大沙岙（DSA），小型底栖生物丰度与叶绿素a含量呈现极显著正相关；火焜岙小型底栖生物丰度的季节波动更剧烈；缓步动物在火焜岙中高潮带的丰度较高，低潮带少有检获，且季节变化与其他类群相反；大沙岙开放区（DSAK）和大沙岙保护区（DSAB）之间夏季小型底栖生物群落之间丰度和垂直分布的显著差异体现了人为踩踏扰动对浅层（0~8 cm）小型底栖生物群落的显著负面影响，但经过至多三个月的扰动消除，可基本恢复至扰动前水平。而深海部分，所分析的环境因子同小型底栖生物群落相关性较弱，相关研究尚无统一的结论产生。

通过对三种生境下小型底栖生物的分析，沉积物粒径对于小型底栖生物垂直分布影响显著，沉积物粒径越小，分布于表层的小型底栖生物比例越高。本研究中，潮间带和近海受到的人为活动干扰最为剧烈，在这两类生境中，小型底栖生物群落的丰度、垂直分布情况以及N/C值等可以作为监测人类活动干扰的有效指标。

本研究主要在青岛沿海和南麂列岛采集线虫样品，通过拍摄多焦面图像留存线虫形态特征，同时获取核糖体小亚基（SSU）和核糖体大亚基（LSU）基因序列，共获得45种63条SSU基因序列和44条LSU基因序列。在此基础上，结合数据库中已有的部分相关序列，进行系统发育分析。

最大似然法（ML）和贝叶斯系统发育推断法（BI）均支持矛线亚纲为线虫动物最早的分支类群。作为自由生海洋线虫中最丰富的类群之一，嘴刺目可分为五大支。其中，在现行的发育系统中属于Ironina的Leptosomatidae与Enoplina聚为一支，且支持率较高；Alaimina和Ironidae等分支的支持率较低；还有一些类群并未形成单系，如Oxystominidae、Oncholaimidae、Anoplostomatidae以及Ironidae。其它类群中，单宫目Monhysterida和薄咽目Araeolaimida均未形成单系类群；微咽线虫总科Microlaimoidea未与其它链环目Desmodorida类群聚在一起，支持该总科从链环目中分离出来；色矛目Chromadorida所包含的5个科各自支持率均较高，但整体的支持率较低。类似的系统发育问题仍有待进一步解决。

Meiofauna is well-recognised as an abundant and ubiquitous component of metazoa and plays a pivotal role in sediment stability, nutrient cycling and energy flow. So it is an important indicator to monitor marine sedimentary environment. Purported to be the most abundant metazoan group, nematodes play an important role in meiofauna ecology. While nematodes are inherently small animals, identification of them often requires high-resolution light microscopy. This factor makes nematode identification with morphological characteristics is often difficult and laborious, and no doubt contributes to the limited taxonomy in this group. With the developing of molecular tools, some phylogenetic confusion of nematodes has been resolved. Yet the representation of nematodes’ sequences is insufficient, so many phylogenetic relationships are still ambiguous.

On the one hand, this study focused on investigating and analyzing meiofaunal community and environment in Laizhou Bay of Bohai sea, Muping offshore area of Yellow sea, Nanji Islands’ intertidal zone of the East China sea and the Northwestern Pacific ocean. On the other hand, combining taxonomic characters and molecular sequences, we analysed phylogenic relationships of free-living marine nematodes, such as Enoplida, Monhysterida and Chromadorida, which were abundant in the ocean.

The result about meiofaunal abundance in various marine habitats revealed, meiofauna in Laizhou Bay, Muping offshore area, Nanji Island and the Northwestern Pacific ocean is 1979 ind/10 cm², 2741 ind/10 cm², 556 ind/10 cm² and 147 ind/10 cm², respectively. In Laizhou Bay and Muping offshore area, the content of chlorophyll-a had a significant positive correlation with meiofaunal abundance. According to reference values in different types of sediments, the nematode/copepod ratio (N/C) could be used to evaluate the condition of sediment organic pollution in the two sea areas. In Nanji Island, seasonal sampling revealed temperature and the content of chlorophyll-a had significant positive correlations with meiofauna abundance. There was higher abundance in HKA because of higher primary productivity, and seasonal fluctuation of meiofaunal abundance was much heavier than in DSA. Tardigrades were rich in high tide of HKA where had higher content of chlorophyll-a than in low tide, and the fluctuation of their abundance was opposite to other groups’ during one year. Tourists visiting decreased meiofaunal abundance and diversity in sallow layer (0~8 cm) and the community would recover within three monthes during off season. Meiofaunal community in the Northwestern Pacific ocean was weakly related with environmental parameters in our study, and a solid conclusion was still absent in similar researches.

Analyzing the meiofaunal structure and environmental parameters among these habitats, grain size negatively influenced the vertical distribution of meiofauna. Intertidal zones and sallow seas were easier to be disturbed by anthropogenic disturbance. The meiofaunal bundance, N/C, and vertical distribution of meiofauna were useful to monitor the influence of anthropogenic disturbance.

In the chapter of nematoda phylogeny, we mainly sampled nematodes from Qingdao and Nanji Island, and captured their morphological characters using multifocal images before getting their sequences. Finally we got 63 SSU and 44 LSU gene sequences of 45 nematode species and analyzed them combining with some sequences from database.

Both Maximum Likelihood and the Bayesian Inference method supported Dorylaimia as the earlist branch of Nematoda. As one of the richest nematode groups, Enoplida consisted of five clades in our research. Leptosomatidae belonged to Ironina in current phylogeny of Nematoda was placed in Enoplina with high support; Alaimina was poorly supported monophyletic clades; some families were paraphyletic, such as Oxystominidae, Oncholaimidae, Anoplostomatidae and Ironidae. In other groups, Monhysterida and Araeolaimida were recovered as paraphyletic clades in our analysis. And Microlaimoidea was placed outside the main group of Desmodorida and closer to Chromadorida, so we supported Microlaimoidea was separated from Desmodorida. Five families within Chromadorida recovered monophyletic with high support, but Chromadorida was paraphyletic with low support value. Similar ambiguities are still remaining and to be resolved.