Do trace metal contamination and parasitism influence the activities of the bioturbating mud shrimp Upogebia cf. pusilla?

Does parasitism influence sediment stability? Evaluation of trait-mediated effects of the trematode Bucephalus minimus on the key role of cockles Cerastoderma edule in sediment erosion dynamics

In coastal environments, bioturbators greatly influence the physical and biogeochemical properties of sediments with consequences for central ecological processes such as erosion dynamics. In addition to their direct impact on sediment stability, bioturbators can have an impact on sediment erosion processes by modulating the growth of microphytobenthic organisms that stabilise the surface layer of sediments. The direct and indirect influences of bioturbators on sediment dynamics depend on the magnitude of their activity and inherently on their physiological state. Bioturbators are infected by various parasites, which have a substantial impact on their physiology and behaviour. However, the knock-on effects of parasites on key ecosystem functions like sediment dynamics remain poorly studied. We conducted flume experiments to investigate the indirect influence of the trematode Bucephalus minimus parasitising the common cockle Cerastoderma edule on the dynamics of sandy sediments enriched or not with microphytobenthos (MPB). Cockles modified bed roughness, sediment surface erodibility and hence destabilised sandy sediments. In sediments not enriched with MPB, both unparasitised and parasitised organisms had a similar impact on the stability of sandy sediments. In contrast, parasitism slightly reduced the destabilisation effect of cockles in MPB-enriched sediments. In the latter, parasitised cockles did not interfere with MPB growth whereas unparasitised organisms constrained the microalgae development. However, the enrichment of the surface layers of sandy sediments with MPB did not modulate the erosion dynamics of these environments. Thus, the lower destabilisation effect of parasitised cockles was not here linked to a stabilisation effect of MPB. When standardised for length, parasitised cockles were lighter than unparasitised organisms. Weakened cockles may have had a lower bioturbation potential than unparasitised conspecifics. If so, the influence parasitised cockles had on sediment erodibility and sediment roughness may have been reduced. The absence of a parasitism effect on the dynamics of MPB-unenriched sediments remains nonetheless unclear.

Seasonal influence of parasitism on contamination patterns of the mud shrimp Upogebia cf. pusilla in an area of low pollution

Very few studies have characterized the concentrations of pollutants in bioturbating species. These species are considered as ecosystem engineers and characterizing stressors, such as contaminants, that impact them could lead to a better understanding of the functioning of ecosystems. In addition to contaminants, bioturbators are affected by a wide range of stressors, which can influence their physiological status and their ability to accumulate pollutants. Among these stressors, parasitism is of particular concern due to the ubiquity of parasites in natural environments and their influence on the fitness of their host. This study aims to assess the relationship between parasitism and metal accumulation in the bioturbating mud shrimp Upogebia cf. pusilla. A one-year seasonal survey was conducted in Arcachon Bay, France, with the aims of (1) characterizing the levels of metals in the mud shrimp and (2) evaluating the influence of two macroparasites (a bopyrid isopod and a trematode) on the variation of the metal content in mud shrimp. The bopyrid parasite castrates its female host and a particular attention has therefore been paid to the reproductive cycle of female mud shrimp by quantifying the expression of the vitellogenin gene that encodes the major yolk protein in female crustaceans. The levels of contaminants in mud shrimp appeared low compared to those reported in other crustaceans in areas of higher pollution. Even at these low contamination levels, we observed a significant impact by the bopyrid parasite that depends on season: bopyrid-infested organisms are generally more contaminated than their uninfested conspecifics except in summer when the opposite trend was observed. We suggest that the bopyrid indirectly interferes with the metal accumulation process by altering the reproductive capabilities of the mud shrimp. On the opposite, very low influence of the trematode parasite on the metal content of the host was found.

Ecosystem Engineering by Thalassinidean Crustaceans: Response Variability, Contextual Dependencies and Perspectives on Future Research

Ecological functions in marine sedimentary habitats are greatly influenced by bio-engineering organisms. Thalassinidean crustaceans are particularly important in this regard, given their density, spatial occupancy and burrowing depths. These features coupled with high per capita engineering rates (bioturbation mainly) and the ability to modulate multiple resources simultaneously, place thalassinids amongst the most influential of ecosystem engineers in marine ecosystems. Research on these organisms has focused on mechanisms by which engineering effects are propagated, whilst drawing attention to the impact of ecosystem modification on ecological processes. However, disparities in the outcomes of global research suggest that complex dependencies underpin ecological responses to thalassinideans that we do not yet fully understand. It is in this context that this review draws attention to some of the dependencies in question, specifically by using existing models and hypotheses to (i) demonstrate how these dependencies can alter ecological responses to ecosystem engineering by thalassinids, and (ii) explain variability observed in outcomes of existing research. This review also shows the potential for explicit inclusion of such dependencies in future research to generate new knowledge on thalassinidean ecosystem engineering, from both fundamental and global change perspectives. More broadly, this review is a contribution towards advancing a predictive and mechanistic understanding of thalassinidean ecosystem engineering, in which biotic and abiotic dependencies are integrated.

How does the bopyrid isopod Gyge branchialis interfere with trace metal bioaccumulation in the mud shrimp Upogebia cf. pusilla?

Parasites are widespread in natural environments, and their impacts on the fitness of their host and, at a broader scale, on ecosystem functioning are well recognized. Over the last two decades, there has been an increasing interest in the effects of parasites in conjunction with other stressors, especially pollutants, on the health of organisms. For instance, parasites can interfere with the bioaccumulation process of contaminants in their host leading to parasitized organisms exhibiting lower pollutants burdens than unparasitized individuals for example. However, the mechanisms underlying these patterns are not well understood. This study examined how the bopyrid parasite Gyge branchialis could lower the cadmium (Cd) uptake of its mud shrimp host Upogebia cf. pusilla. When exposed to water-borne Cd, parasites were able to bioaccumulate this trace metal. However, the uptake of Cd by the parasite was low and cannot entirely explain the deficit of Cd contamination of the host. The weight of gills of parasitized organisms was significantly reduced compared with unparasitized organisms. We suggest that by reducing the surface for metal uptake, parasites could lower the contaminant burden of their host.