Environmental factors contributing to the development of brown muscle disease and perkinsosis in Manila clams (Ruditapes philippinarum) and trematodiasis in cockles (Cerastoderma edule) of Arcachon Bay

Abstract

The aim of the present study was to identify environmental factors that could explain the distribution of different pathologies of commercially exploited intertidal bivalves in an Atlantic lagoon, Arcachon Bay. In particular, the role of the salinity gradient as a driver was explored. The Manila clam Ruditapes philippinarum experienced two severe pathologies, perkinsosis, which is due to a protozoan parasite, and brown muscle disease (BMD), the etiological agent of which remains unknown. Perkinsus olseni infection was very low in a small low-salinity area but, at the scale of the entire lagoon, was more influenced by organic matter content in the sediment and by emersion time. BMD prevalence was also 2.6 times higher in the higher organic content area but was also negatively correlated with salinity. The sympatric cockle (Cerastoderma edule) was affected by eight trematode species. These parasites have a complex life cycle that generally involves three free-living host species. The distribution of the different trematode communities was rather patchy within Arcachon Bay with no clear relationship with measured environmental factors. The dominance of particular trematode species could be due to the presence of other hosts involved in their life cycle, making it more difficult to detect a major environmental driver. This survey demonstrated that salinity is not a major factor explaining disease distribution in this temperate lagoon. This result has consequences for the research of 'refuge areas' (free of diseases) or 'hot spots' (heavy infection) for species of high economic value.

Co-infection of two eukaryotic pathogens within clam populations in Arcachon Bay

“…Perkinsosis disease is regularly detected in local Manila clam populations in Arcachon Bay, but no associated mortality events have been reported so far ( Dang et al, 2010a , b ; de Montaudouin et al, 2016b ). Sampling station localisation within the lagoon and some environmental parameters were determined for Andernos station exclusively by de Montaudouin et al (2010) and at a higher scale by Binias et al (2014) . Here, we sampled 50 Manila clams on the 7th to 8th of November 2018 in five contrasted stations for which some environmental data were available ( Dang et al, 2010a ; Binias et al, 2014 ; Figure 1 ).…”

“…Sampling station localisation within the lagoon and some environmental parameters were determined for Andernos station exclusively by de Montaudouin et al (2010) and at a higher scale by Binias et al (2014) . Here, we sampled 50 Manila clams on the 7th to 8th of November 2018 in five contrasted stations for which some environmental data were available ( Dang et al, 2010a ; Binias et al, 2014 ; Figure 1 ). Two stations (IAO and Piquey) are in “group 2” as defined by Binias et al (2014) , and qualified herein as “external.” This group gathered stations in oceanic position with high grain size median, high mean salinity, low organic matter and silt & clay contents ( Supplementary Table S1 ).…”

“…Here, we sampled 50 Manila clams on the 7th to 8th of November 2018 in five contrasted stations for which some environmental data were available ( Dang et al, 2010a ; Binias et al, 2014 ; Figure 1 ). Two stations (IAO and Piquey) are in “group 2” as defined by Binias et al (2014) , and qualified herein as “external.” This group gathered stations in oceanic position with high grain size median, high mean salinity, low organic matter and silt & clay contents ( Supplementary Table S1 ). Piquey exhibits higher sediment grain size median than IAO.…”

“…Piquey exhibits higher sediment grain size median than IAO. Andernos, Lanton and Gujan belong to “group 4” as defined by Binias et al (2014) , and qualified herein as “internal.” This group gathered stations undergoing lower mean salinity. In this group, Andernos differs from Gujan and Lanton by its coarser sediments ( Table 1 ).…”

Phytoplankton versus macrophyte contribution to primary production and biogeochemical cycles of a coastal mesotidal system. A modelling approach

“…Sea surface height (SSH) observations at the Eyrac tide gauge were provided by the REFMAR website (www.refmar.shom.fr/ ARCACHON_EYRAC) and remain the property of SHOM (Naval Hydrographic and Oceanographic Service) and the Gironde DDTM (Sea and Territory Departmental Directorate). The model validation results concerning physical variables (SSH, TEMP and SAL) were recently published byBinias et al (2014) and are summarized inTable 1.…”