海洋生态与环境科学重点实验室知识库

蛇尾是海洋底栖生态系统的重要类群，近些年，蛇尾的数量在北黄海獐子岛海域持续增多，存在种群暴发风险。獐子岛海域是我国北方重要的海洋牧场，也是我国最大的虾夷扇贝养殖基地，在该海域出现蛇尾增多的现象是否与人工养殖活动相关？大量的蛇尾是否会影响养殖生物的生存？这些问题无论是从养殖产业还是生态系统健康和安全方面都亟待解决。但是目前为止，由于蛇尾类生物基本没有开发利用价值，它们在海洋生态系统中的作用与地位研究较少，我们缺少对蛇尾的基本了解。本论文从蛇尾基础生物学和生态学出发，通过海底图像方法调查獐子岛海域蛇尾的数量及分布特征，分析其食性、繁殖生物学以及与养殖海域的相互关系，在獐子岛海域开展蛇尾种群数量变动机理的研究，取得以下主要研究成果：

（1）设计了一套新的拖曳式水下拍摄系统（Towed Underwater Video-Camera System，TUV system）以及图像处理软件（Shewei 1.0），用于通过海底拍摄方法对獐子岛海域蛇尾的调查。测试结果显示，TUV系统是一套简单、价廉、易操作的适用于近海的着底型拖曳式水下拍摄系统，该系统可以高效地获取海底图像，用于大型底上生物组成、数量及种群分布特征等的调查和分析。从海底图像上，几乎所有大于1 mm的底上生物均可以被准确地识别出，主要包含棘皮类、双壳类、甲壳动物、刺胞动物和底栖鱼类。测试结果显示出现在该海域的蛇尾主要有三种，分别是紫蛇尾、浅水萨氏真蛇尾和司氏盖蛇尾。通过在测试站位对三种蛇尾的丰度和生物学特征进行测定和计算，建立了在该海域利用海底图像进行蛇尾调查和分析的统一方法。利用TUV系统，本文分别于2017年5月、8月、10月及2018年1月对獐子岛海域蛇尾进行了4次季度月海底图像调查，以分析三种主要蛇尾在獐子岛的数量现状、分布特征及其于养殖海域的相互关系。

（2） 三种蛇尾在獐子岛海域的数量关系是紫蛇尾>浅水萨氏真蛇尾>司氏盖蛇尾，分别占据獐子岛海域不同区域。紫蛇尾主要分布在该海域的北部，丰度为58.82–272.61 ind. m^-2，分布型为成群分布。紫蛇尾在该海域从39.1°N到39.3°N呈“J”形分布，与该海域沉积物波痕的分布区域十分吻合，该区域的强水动力作用引起海底碎屑再悬浮，增加了紫蛇尾获取食物的机会，是影响紫蛇尾在该海域分布的主要因素。聚集成团是紫蛇尾的主要分布特点。獐子岛海域紫蛇尾大多聚集成小团（< 0.02 m²）生活，但是随着紫蛇尾对海底的覆盖率的增加，更多大聚集团开始出现。因此，大聚集团的出现可能是紫蛇尾种群数量增加的一个信号。

（3） 浅水萨氏真蛇尾主要分布在该海域的南部，丰度为14.78–17.95 ind. m^-2，分布型为成群分布，季节差异不大。浅水萨氏真蛇尾的盘径大小分布范围为1.7–22.8 mm，集中分布在5–15 mm（88.21%–98.43%）。其中，十月份的总体盘径显著小于其他月份（p<0.05），主要是由于十月份的小个体（5–10 mm）所占比重较多，达57.85%。并且，十月份的小个体主要出现在该海域最南部的S10和S15站位，其丰度在这两个站位显著多于其他站位（p<0.05）和其他季节（p<0.05）。由于獐子岛海域南端靠近黄海冷水团，因此，我们推测十月份发现的大量小个体可能是浅水萨氏真蛇尾夏季在冷水团繁殖的结果，冷水团可能是獐子岛海域浅水萨氏真蛇尾的重要补充来源。

（4） 司氏盖蛇尾主要分布在该海域的北部，丰度为0.57–3.61 ind. m^-2，分布型为成群分布，是獐子岛海域三种蛇尾中数量最少的物种。司氏盖蛇尾的盘径主要集中在5–15 mm，占所有测量盘径的73.74%–87.33%。同时，我们也记录了其他大型底上生物的种类组成和丰度，结果显示，其他大型底上生物的平均丰度为60.08 ind. m^-2，其中虾夷扇贝的平均丰度为0.68 ind. m^-2，可以看出，蛇尾种群的数量（155.57 ind. m^-2）在獐子岛海域占绝对优势，缺少天敌是蛇尾在獐子岛海域增多的原因之一。

（5） 紫蛇尾的繁殖活动在北黄海獐子岛海域具有明显的周期性，即在夏末和秋季开始发育，冬季性腺达到完全成熟，春季进行产卵，随后进入闲置期，且一年产卵一次。紫蛇尾的性腺发育在个体间和雌雄间均展现了强的同步性，有助于受精成功和幼体存活，这一特点可能是紫蛇尾在该海域保持高丰度的原因之一。底层海水温度和食物供给对紫蛇尾的繁殖起着重要作用。紫蛇尾性腺中含有大量的营养型吞噬细胞，与生殖细胞一起影响紫蛇尾性腺重量。因此，对于紫蛇尾来说，性腺指数不是研究其繁殖活动的合适的指标。另外，紫蛇尾的成熟卵细胞相对较小（75–150 μm），表明其幼体阶段为浮游态。浮游态幼体数量多、易扩散，为紫蛇尾在獐子岛海域的快速大量补充提供了基础。

（6） 浅水萨氏真蛇尾和紫蛇尾的食性均为杂食性，以食碎屑为主。两种蛇尾胃含物的真核生物组成存在相似性，但是由于摄食方式的不同，其主要食物来源不同。浅水萨氏真蛇尾主要摄食海底沉积物碎屑，其中贝类碎屑是其食物的重要来源之一，浅水萨氏真蛇尾与獐子岛贝类存在一定的捕食关系。紫蛇尾主要摄食水体中的悬浮物，在摄食方式上，与该海域的虾夷扇贝存在竞争关系。

本论文在獐子岛养殖海域开展蛇尾的调查和研究，有助于了解这一棘皮动物优势类群在海洋生态系统，尤其是底栖生态系统的作用和地位，通过分析其种群数量变动与养殖活动的相关性，进一步了解了人类活动对海洋底栖生态系统的影响，同时，为防控蛇尾类群在养殖海域暴发式增长对养殖生态系统的破坏提供生物学和生态学基础。

Ophiuroidea (brittle stars) is an important group in marine benthic communities. Recently, the number of brittle stars has been increasing in the Zhangzi Island area, northern Yellow Sea, which is the largest aquaculture zone for the Japanese scallops Patinopecten yessoensis in China. The population of brittle stars in this area has the risk of outbreaks. Considering the safety and health of mariculture and ecosystem, the questions that whether the increase of brittle stars is related to the aquaculture activities and whether the mass brittle stars will affect the survival of scallops are needed to be solved. However, there is litter research on the role or functions of brittle stars in the marine ecosystem in China so far due to the lack of value for utilization of this group. So we lack the basic knowledge of these brittle stars, let alone the reasons for their outbreaks in the aquaculture zone. Therefore, starting from the basic biology and ecology of brittle stars, this dissertation aims to explore the mechanisms of quantity variations of these brittle stars and its ecological effect in the Zhangzi Island area by investigating their abundance and distribution and analyzing their feeding biology and reproductive biology as well as the relationship between brittle stars and mariculture activities in this area. The main results are as follows:

(1) we designed a new underwater camera apparatus that named the towed underwater video-camera system (the TUV system) with the image processing software (shewei 1.0) to investigate brittle stars by using the method of seabed photography. The test results showed that the TUV system is a simple underwater apparatus that could be easy to operate and efficiently obtain seabed photographs on the hard sandy sea bottoms. This system could be used for investigations and analysis of the composition, quantity and distribution characteristics of megabenthic epifauna in coastal waters. From the seabed photographs, almost all epifauna larger than 1 mm could be identified, including echinoderms, bivalves, crustaceans, cnidarians and benthic fish. In addition, three dominant brittle stars, Ophiopholis mirabilis, Ophiura sarsii vadicola and Stegophiura sladeni, were identified. Through the calculation and measurement of the abundance and biological characteristics of these three brittle stars at the test stations, we have established the unified method for the investigations and analysis of brittle stars in the Zhangzi Island area by using seabed photographs. Then, we used the TUV system and conducted four investigations of brittle stars in this area in May 2017, August 2017, October 2017 and January 2018, respectively, to analyze the quantity status, distribution of brittle stars and their relationship with mariculture in the Zhangzi Island area.

(2) The quantity relationship of three brittle stars was O. mirabilis>O. sarsii vadicola>S. sladeni, and they distributed in different areas of the Zhangzi Island area. O. mirabilis was mainly distributed in the north of this area, with an abundance of 58.82–272.61 ind. m^-2. The distribution area of O. mirabilis was J-shaped from 39.1°N to 39.3°N, which was consistent with the distribution of ripples in this area. The strong bottom current caused the resuspension of bottom debris, and increased the chance for O. mirabilis to obtain food, which was the main factor affecting the distribution of O. mirabilis in the Zhangzi Island area. Furthermore, O. mirabilis aggregated in clusters on the sea bottom. In the Zhangzi Island area, most of them gathered in small clusters (< 0.02 m²), but with the increase of the coverage rate, more large clusters began to occur. Therefore, the emergence of large clusters may be a signal of increasing population in O. mirabilis.

(3) O. sarsii vadicola was mainly distributed in the south of this area, with an abundance of 14.78–17.95 ind. m^-2. The distribution pattern of O. sarsii vadicola was clumped with little seasonal difference. The disc diameter of O. sarsii vadicola was 1.7–22.8 mm and concentrated in 5–15 mm (88.21%–98.43%). The mean disc diameter in October was significantly smaller than that in other months (p<0.05), due to the large proportion of small individuals (5–10 mm) in October, accounting for 57.85%. These small individuals in October mainly distributed at S10 and S15, and the abundance of small individuals in this month was significantly higher than that in other stations (p<0.05) and other months (p<0.05). These two stations are the southernmost stations in this area that are affected by the Yellow Sea Cold Water Mass (YSCWM). Therefore, we speculate that a large number of small individuals found in October may be the result of reproduction of O. sarsii vadicola in summer in the YSCWM, and the YSCWM might be an important supplement source of this species in the Zhangzi Island area.

(4) S. sladeni was mainly distributed in the north of this area, with a least abundance of 0.57–3.61 ind. m^-2. The disc diameter distribution showed a peak between 5 mm to 15 mm with a proportion of 73.74%–87.33%. Additionally, we also recorded the composition and abundance of other macrobenthos. The mean abundance of other macrobenthos was 60.08 ind. m^-2, among which the mean abundance of P. yessoensis was 0.68 ind. m^-2. Therefore, lack of enemies may be one of the reasons for the outbreaks of brittle stars in this area, as the quantity of brittle star was dominant in the Zhangzi Island area.

(5) O. mirabilis had a clear annual reproductive cycle in the Zhangzi Island area, with gametogenesis occurring during late summer and autumn, fully mature gonads being found in all winter, and a main spawning occurring in spring followed by a spent period. The gonadal development of O. mirabilis exhibited a strong synchrony among individuals and between sexes. Such synchronous reproduction contributes to both fertilization success and offspring survival, which may be the reason for the high density of O. mirabilis in the aquaculture area. Sea temperature and food availability played an important role in O. mirabilis reproduction. Abundant nutritive phagocytes were found in the gonads of O. mirabilis, which, together with the germ cells, affected the weight of the gonads. Therefore, gonad index (GI) was not an appropriate indicator of reproductive activity in O. mirabilis. In addition, the mature oocytes of O. mirabilis were relatively small (75–150 μm), indicating that the larval development was planktotrophic. The planktotrophic larvae usually indicate the high quantity and widespread, which provides a basis for quick and abundant recruitment of O. mirabilis in this area.

(6) O. sarsii vadicola and O. mirabilis were both omnivorous and detritus feeders in the Zhangzi Island area. The eukaryote composition in the stomach contents of these two species was similar, but their food sources were different due to the different feeding strategies. O. sarsii vadicola mainly fed on the sediment detritus, among which the shellfish detritus was an important source. Thus, there was a certain predation relationship between O. sarsii vadicola and shellfish in the Zhangzi Island area. O. mirabilis mainly fed on suspended particles in the water, and based on the feeding strategies, it competed with the Japanese scallops in this area.

In conclusion, based on the investigations and research of brittle stars in the Zhangzi Island area, this dissertation makes contributions to the understanding of the role and status of this dominant echinoderm group in marine ecosystem, especially in the benthic ecosystem. By analyzing the relationship between quantity variation of brittle stars and aquaculture activities, we can further figure out the impact of human activities on the marine benthic ecosystem. Meanwhile, this dissertation provides biological and ecological basis for the prevention and control of the damage to the aquaculture ecosystem caused by the explosive increase of brittle stars.