Pockmarks are circular-shaped depressions that increase seabed heterogeneity and are characterized by discontinuous fluid emissions. To understand how environmental conditions of pockmarks affect the structure of macro- and meiofauna, we investigated two sites in a pockmark field in the northwestern Madagascar margin. In a comparative approach, we explored the community structure of the dominant taxa (Polychaeta, Nematoda and hyaline foraminifera) in each component (macro-, metazoan meiofauna and foraminifera, respectively). The investigated active pockmark showed approximately two times higher meiofauna abundance compared to in a site away from another pockmark field, but macrofauna showed the opposite trend, with almost half density at the pockmark site. However, at both sites, macro- and meiofauna showed higher richness and abundance values in the top well-oxygenated layers of the sediment than in the underlaying ones. Polychaeta and Nematoda showed lower richness in the pockmark, opposed to hyaline foraminiferans, but lower evenness in the pockmark was found for the three groups. The detection of gas flares in the water column attests of the recent activity within the pockmark. High amount of sulfur-bearing minerals (mainly pyrite) evidences a production of dissolved free sulfides (not detected at the time of sampling) by sulfate reduction process driven by organic matter degradation and anaerobic oxidation of methane. Furthermore, recent increase in sedimentation rates in the past 70 years and organic matter inputs could have led to higher organic matter degradation rates resulting in reduced conditions and a high oxygen consumption. All this together seem to act as key factors in the determination of variation in richness, abundance and community composition of macrofauna and meiofauna. Additionally, some taxa seem to be more tolerant to these extreme conditions, such as species belonging to the Nematoda genus Desmodora and the phylum Kinorhyncha, which are highly abundant in the pockmark, and hence, may be considered as potential bioindicators of pockmark activity in this area. Further studies are required for a better assessment.

麻点是增加海床异质性的圆形凹陷，其特征是不连续的流体排放。为了了解麻状环境条件如何影响大型动物和小型动物的结构，我们调查了马达加斯加西北缘麻状野中的两个地点。在比较方法中，我们探讨了每个组成部分（分别为宏，后生meiofauna和有孔虫）中的优势类群（Polychaeta，线虫和透明有孔虫）的群落结构。与远离另一个麻点场的地点相比，所研究的活动麻点显示的meiofauna丰度大约高出两倍，而大型动物则显示出相反的趋势，麻点处的密度几乎为一半。但是，在两个站点上 大型和中层动物在沉积物的顶部充氧层中的富集度和丰度值高于底层。与透明质有孔虫相反，Polychaeta和Nematoda在麻油中显示出较低的浓淡度，但在三组麻油中，麻油和线虫中麻油含量较低。在水柱中检测到的气体火炬证明了麻子内部最近的活动。大量的含硫矿物（主要是黄铁矿）证明了由有机物降解和甲烷的厌氧氧化驱动的硫酸盐还原过程产生了溶解的游离硫化物（在采样时未检测到）。此外，最近70年来沉积速率的增加以及有机物的投入可能导致更高的有机物降解率，从而导致条件减少和高耗氧量。所有这些似乎共同成为确定大型动物和小型动物的丰富度，丰度和群落组成变化的关键因素。此外，一些分类单元似乎更能耐受这些极端条件，例如属于线虫属的物种。Desmodora和门Kinorhyncha门在痘痕中高度丰富，因此可以被认为是该地区痘痕活动的潜在生物指标。需要进行进一步研究以进行更好的评估。