Mud shrimp are considered as among the most influential ecosystem engineers in marine soft bottom environments because of their significant bioturbation activity and their high density. These organisms play a key role on the physical structure of sediments through intense sediment reworking activity and also deeply influence geochemical properties of sediments via frequent bioirrigation events. The influence that mud shrimp have on the environment is related to the magnitude of bioturbation processes and subsequently depends on their physiological condition. In natural environments, several factors act together and influence the well-being of organisms. Among them, the deleterious role of parasites on the physiology and the behavior of their host is well established. Aquatic organisms are also subject to pollutants released by anthropogenic activities. However, the effect of both stressors on the fitness and bioturbation activity of mud shrimp has never been investigated yet.

We conducted a 14-day ex-situ experiment to evaluate the influence of trace metal contamination (cadmium Cd) and parasitism infestation on the gene expression (molecular endpoint) and sediment reworking activity (behavioral endpoint) of the mud shrimp Upogebia cf. pusilla. At completion, mud shrimp exhibited substantial Cd bioaccumulation, with parasitized organisms showing a significantly lower contaminant burden than unparasitized specimens. Cadmium contamination induces modifications of gene expression in both unparasitized and parasitized organisms. We report an antagonistic effect of both stressors on gene expression, which cannot be fully explained by a lower Cd bioaccumulation. At the behaviour level, parasitism seems to reduce the sediment reworking activity of mud shrimp, while Cd contamination appears to stimulate this activity. This study highlights that the effects of multiple stressors may be quite different from the effects of each stressor considered individually. It should also motivate for more studies evaluating the influence of multiple stressors on different endpoints encompassing various levels of organization.

泥虾因其明显的生物扰动活动和高密度而被认为是海洋软底环境中最具影响力的生态系统工程师之一。这些生物通过强烈的泥沙返修活动对泥沙的物理结构起关键作用，并通过以下方式对泥沙的地球化学性质产生深远影响：频繁的生物灌溉事件。泥虾对环境的影响与生物扰动过程的大小有关，并随后取决于它们的生理状况。在自然环境中，几个因素共同作用并影响生物的福祉。其中，寄生虫在其宿主的生理和行为上的有害作用是众所周知的。水生生物还受到人为活动释放的污染物的影响。然而，尚未研究两种应激源对泥虾的适应性和生物扰动活性的影响。

我们进行了一个为期14天的异地实验，以评估痕量金属污染（镉Cd）和寄生虫侵染对虾虾Upogebia cf.的基因表达（分子终点）和沉积物返工活性（行为终点）的影响。普西拉。完成后，泥虾表现出大量的Cd生物富集，被寄生虫的生物显示出比未寄生虫标本低得多的污染物负担。镉污染会在未寄生虫和被寄生虫的生物中诱导基因表达的修饰。我们报告了两种应激源对基因表达的拮抗作用，这不能由较低的Cd生物积累来完全解释。在行为水平上，寄生寄生似乎会减少泥虾的底泥再加工活动，而Cd污染似乎会刺激这种活动。这项研究强调，多个压力源的影响可能与单独考虑的每个压力源的影响完全不同。