Haemocyte responses of blue mussels (Mytilus edulis L.) transferred from a contaminated site to a reference site: can the immune system recuperate?

Abstract

We measured the haemocyte responses of the blue mussels, Mytilus edulis (L.), transferred from a contaminated site (Pictou, NS, Canada) to a relatively clean site (Richibucto, NB, Canada) to assess the capacity of recovery of haemocytes. Mussels from each site were caged in Richibucto. Haemocyte count, phagocytic capacity, mortality and mitotic activity were measured 1, 4 and 9 days after caging. At the end of the 9-day exposure, 15 mussels from each site were evaluated for their capacity to clear bacteria, 36 h after having been injected with Listonella anguillarum. Before caging, mussels native to Pictou had higher haemocyte counts and mitotic capacity and lower phagocytic capacity than mussels native to Richibucto. However, after the mussels had been caged and transferred from Pictou to Richibucto and as the exposure progressed, phagocytic capacity slowly rose to the level measured at Richibucto, the haemocyte count lowered and haemocyte mortality and mitotic activity rose. At the end of the experiment, bacteria clearing was more efficient in mussels originating from Richibucto than in those transferred from Pictou. This study shows a partial recovery of the haemocyte responses in mussels originating from an industrialized site and transferred to an unindustrialized environment, and illustrates the importance of linking descriptors of haemocyte activity with immunocompetency.