Polychaetes are important benthic macrofauna that lives in sediments, usually in intertidal flats with high organic content and high sulfide. It has been suggested that polychaete bioturbation could perform environmental remediation. During the process, the microbial community plays important roles. Here, we used high-throughput sequencing technology to study the bioturbation effects on the bacterial community in the polychaete (Perinereis aibuhitensis) burrows at different tidal positions in intertidal flat. The results showed that the bacterial communities were dramatically influenced by the polychaete bioturbation. The ACE, Chao, and Shannon indices of the polychaete burrows increased in summer. Dominant phyla in the polychaete burrows were Proteobacteria, Campilobacterota, Desulfobacterota, Chloroflexi, and Bacteroidota, and the dominant bacterial families were Sulfurvaceae, Flavobacteriaceae, Rhodobacteraceae, Woeseiaceae, Desulfobulbaceae, and Sulfurimonadaceae. Results of linear discriminant analysis effect size (LEfSe) showed that groups that include organic matter degraders, such as Bacteroidota, Flavobacteriaceae, Rhodobacteraceae, Woeseiaceae, and groups that include sulfur oxidizers, such as Campilobacterota, Sulfurovaceae, Rhodobacteraceae, Desulfobulbaceae, and Sulfurimonadaceae, were significantly increased due to the polychaete bioturbation. The polychaete bioturbation reduced the complexity of the bacterial co-occurrence network while increased its modularity and homogeneity. The polychaete bioturbation also changed the functional groups, which significantly enhanced in functional groups of aerobic nitrite oxidation, nitration, dark thiosulfate oxidation, dark sulfur oxidation, and dark sulfite oxidation, while nitrogen respiration and nitrate respiration decreased. These results provide insight into the impact of bacterial communities under the intertidal polychaete bioturbation.

Bioirrigation is a process corresponding to animal-induced transport of porewater solute or exchange between interstitial and overlying waters. How and why the burrowing macrobenthos complete this process remain unclear. Here, we used two infaunal-behavior observation devices to investigate the ventilation behaviors of the benthic polychaete Perinereis aibuhitensis Grube, a species that is widespread along the Asian coast with a wide temperature range, at various temperatures (5°C, 10°C, 15°C, 20°C, and 25°C). The two typical movement behaviors of P. aibuhitensis, axial crawling and radial undulation, as well as associated parameters, were delimited and quantified. We found that the radial undulation frequency of P. aibuhitensis and the associated pumping rate (PR) increased significantly with temperature (T, 5-25°C); this relationship can be described by the regression equation PR = −0.0067T2 + 0.29T - 0.52 (R2 = 0.749, P < 0.05; n = 15). The relationship between axial crawling velocity (ACV) and temperature (T, 5-25°C) can be expressed by the regression equation ACV = -0.0001T3 + 0.0059T2 - 0.063T + 0.28 (R2 = 0.997, P<0.05; n = 15). In general, pumping efficiency increased as temperature decreased, implying that the polychaete increasingly conserved energy at lower temperatures. Peak pumping volume (4.36 L d-1) was observed at 25°C, as a result of radial undulations. Thus, we concluded that radial undulation was the primary movement that led to bioirrigation. The dissolved oxygen demand was the key factor driving the initiation of radial undulation, and the specific aim of radial undulation was to increase oxygen availability by pumping new seawater into the burrow. Thus, radial undulation is critical for polychaete survival. The dissolved oxygen threshold level at which pumping was initiated increased with temperature, suggesting more energy conserved at lower temperatures. This pumping strategy of P. aibuhitensis is consistent with optimality theory, and is here designated the “optimal dissolved oxygen obtainment strategy”.

The selectivity of Perinereis aibuhitensis larvae on different sediment types was studied using an experimental behavioral device in the lab. There were six types of sediment with different organic matter content: 2.19, 2.30, 2.86, 3.25, 3.51, and 5.52%. The results indicated significant differences in the six treatments’ organic matter content ( p < 0.05). When the P. aibuhitensis larvae initially attached to the sediment, the larvae’s density showed no significant difference among the six treatments. The density of larvae decreased gradually during the experimental period. It increased with the increasing organic matter content in sediment at every sampling time, but there was no significant difference ( p > 0.05). The larvae’s specific growth rate in the first month was significantly higher than those in the second and third months ( p < 0.05). The mortality showed no significance at different sediments in equal sampling times, but the mortality was lower in high organic matter content sediments. This study showed that the P. aibuhitensis larvae did not make an active selection; random selection happened when initially attached to the sediment with different organic matter contents. Higher organic matter content in the sediment was more conducive to larvae survival, and the organic matter content is the limitation factor on the mortality and the density. The different densities in the natural habitat of P. aibuhitensis might occur due to the passive selection by the environment.

底内动物不仅具有较强的适应沉积环境的生理耐受能力,还具有适应沉积环境的行为策略,而且其行为策略与周围微环境关系密切,研究两者的关系可以从行为学角度阐释生物扰动的生态学意义.本研究利用底内动物行为学观察装置研究温度(15℃、20℃和25℃)对不同规格[大规格(2.2±0.2)g、中规格(1.5±0.2)g、小规格(0.7±0.2)g]双齿围沙蚕(Perinereis aibuhitensis Grube)行为特征的影响,探究了不同行为过程对洞穴水交换、营养盐和溶解氧变化规律的影响.结果 表明,双齿围沙蚕的径向起伏频率随温度的升高而升高(P＜0.05).不同规格双齿围沙蚕的轴向爬行速度差异显著(P＜0.05),大规格沙蚕的轴向爬行速度随着温度的升高而减慢,而中规格和小规格沙蚕的轴向爬行速度随着温度的升高而加快.温度和规格对双齿围沙蚕的径向起伏和轴向爬行时间影响不显著(P＞0.05).规格对双齿围沙蚕的泵水量、泵水速率、轴向爬行速度及营养盐溶出效率影响显著(P＜0.05).泵水量和营养盐溶出效率均随着规格的增加而增大,大规格沙蚕的泵水量最高可达10.01 L/d;径向起伏是双齿围沙蚕在洞穴中的主要运动方式和泵水方式,其洞穴中磷酸盐、亚硝酸盐、氨氮和硫化物的溶出效率分别可达109.80 μg/(cm2·d)、6.02 μg/(cm2·d)、60.56 μg/(cm2·d)和15.40 μg/(cm2·d).双齿围沙蚕泵水溶解氧阈值随着温度的升高和规格的增大呈上升趋势.结果 表明,小规格双齿围沙蚕对高温和低氧环境的适应能力强于大规格沙蚕;双齿围沙蚕的泵水运动(生物灌溉)随温度的升高和规格的增大而增强,其主要驱动因子是洞穴微环境的溶解氧含量;双齿围沙蚕的泵水溶解氧阈值可使其消耗最少的能量获得最高的溶氧收益,符合"最佳性理论",可称之为"最佳溶氧收益策略".通过生物灌溉作用加速沉积物营养盐释放的现象是双齿围沙蚕为获得充足溶氧而产生的连带效应.

为了解北方典型养殖海湾——桑沟湾水域浮游植物群落结构的时空变化特征及其影响因素,于2017年4月(春季)、7月(夏季)、11月(秋季)和2018年1月(冬季)对桑沟湾水域21个站点进行4个航次的大面调查.结果显示,调查期间,该湾共采集到浮游植物31属51种,其中,硅藻(Diatom)24属43种,甲藻(Dinoflagellate)3属4种,绿藻(Chlorophyta)2属2种,金藻(Chrysophyta)2种,蓝藻(Cyanophyta)1种.按照季节划分,春季22种,夏季20种,秋季23种,冬季20种.优势度指数分析结果表明,硅藻是绝对优势种,其中,具槽帕拉藻(Paraliasulcate)为全年优势种,数量百分比在18.6％～84.9％之间.浮游植物细胞丰度在0.16×103～12.20×103个/L之间,表现为冬季＞春季＞秋季＞夏季.物种多样性指数(Shannon)范围为0.69～1.35,物种均匀度指数J(Pielou)范围为0.42～0.70.磷酸盐是桑沟湾浮游植物生长的主要限制营养盐.研究结果揭示了桑沟湾养殖水域浮游植物的时空变化特征,为深入认识养殖生态系统的结构和功能提供了基础数据.

利用行为学实验装置研究了双齿围沙蚕(Perinereis aibuhitensis)对低潮区、中潮区和高潮区沉积物表层为10、60 cm深以下的沉积物的选择行为.3个潮区表层为10 cm的沉积物编号分别为1#、2#、3#,3个潮区60 cm以下的沉积物编号分别为4#、5#、6#.结果 显示,在实验装置一中,不同沉积物的有机物含量无显著差异(P＞0.05),1#和4#沉积物中,C含量显著高于2#沉积物(P＜0.05),4#沉积物中,N含量显著高于2#和6#沉积物,不同沉积物的H2S含量均差异显著(P＜0.05);1#沉积物间隙水中,H2S含量显著高于其他各组(P＜0.05).规格和底质类型对双齿围沙蚕的选择行为无显著影响(P＞0.05);规格对双齿围沙蚕搜寻时间影响显著(P＜0.05),而底质类型则对搜寻时间无显著影响(P＞0.05).在实验装置二中,6#沉积物中有机物含量显著高于1#和2#沉积物(P＜0.05),C、N含量均显著高于其他沉积物(P＜0.05),2#沉积物中,H2S含量显著高于其他沉积物(P＜0.05);各个沉积物间隙水中H2S含量均差异显著(P＜0.05).底质类型和规格对双齿围沙蚕的移动距离均有显著影响(P＜0.05).研究表明,小规格双齿围沙蚕比较活跃和敏感,倾向于选择H2S含量较低的底质;在底质内部钻蚀时,双齿围沙蚕倾向于选择物质含量较低的底质.总体来看,双齿围沙蚕对自然栖息地底质类型选择性不强.

针对桑沟湾养殖海区海带(Laminaria japonica)的超容量养殖现象,研究了该海区中标准化养殖模式和传统养殖模式的海带生长差异.结果 显示,在标准化养殖模式下,海带长、宽、平均厚度、湿重、投影面积和特定生长率均高于传统养殖模式,单棵海带重量显著提高,且海带的碳、氮和蛋白质含量明显高于传统养殖模式,海带品质大大提升.养殖后期,标准化养殖海区养殖海带垂直投影面积之和与对应养殖海区面积之比为6.33,而传统养殖模式的比值为9.15;标准化养殖海区海带所处水层下方的光照强度显著高于传统养殖区,海带所处水层的海流流速也高于传统养殖区.研究表明,桑沟湾海带标准化养殖模式使海带养殖密度降低,海带生长速度和品质均得以提高;在标准化养殖模式下,海带重叠较小,接受的光照比传统养殖模式充足;较快的海流使标准化养殖海区营养盐更新速度更快,这两方面可能是导致2种养殖模式下海带生长和品质产生差异的原因.