Dynamics of the parasite Marteilia refringens (Paramyxea) in Mytilus galloprovincialis and zooplankton populations in Alfacs Bay (Catalonia, Spain)

Abstract

Since the first description of Marteilia refringens (Paramyxea) in flat oysters Ostrea edulis in 1968 in the Aber Wrach, Brittany (France), the life-cycle of this parasite has remained unknown. However, recent studies, conducted in the 'claire' system, have proposed the planktonic copepod Acartia grani as a potential intermediate host for the parasite. Nevertheless, experimental transmission of the parasite through the copepod has failed. Recent studies in this field have reported the presence of the parasite in zooplankton from the bays of the Delta de l'Ebre, a more complex and natural estuarine environment than that of the claire. As a result, 2 new Marteilia host species were proposed: the copepods Oithona sp. (Cyclopoida) and an indeterminate Harpaticoida. Consequently, the objective of the present work was to study the dynamics of Marteilia in the zooplankton community from one of the bays, Alfacs Bay, as well as the dynamics of the parasite in cultivated mussels during 1 complete year. Six different zooplankton taxa appeared to be parasitized by M. refringens, including copepods (3 Calanoida, Acartia discaudata, A. clausi and A. italica; 1 Cyclopoida, Oithona sp.; and 1 Harpacticoida, Euterpina acutifrons), and larval stages of decapod crustaceans (zoea larvae of Brachyura, probably Portumnus sp.). These taxa are thus proposed as new subjects for study, since they could be intermediate hosts in the infection process of mussels by Marteilia.

Misuse of PCR assay for diagnosis of mollusc protistan infections

“…Finally, the authors conclude that there needs to be '…a more detailed study on the role of the newly identified hosts in the life cycle of the Marteilia parasite.' (p. 69, emphasis mine).In a subsequent paper, Carrasco et al (2007b) use the same unvalidated PCR assay to detect the presence of Marteilia refringens DNA in zooplankton samples. In their Table 1, they report the results of the PCR assay as positive or negative, which is appropriate.…”

Elucidating the life cycle of Marteilia sydneyi, the aetiological agent of QX disease in the Sydney rock oyster (Saccostrea glomerata)

“…refringens have focused on the identification of previously unknown morphological stages developing within Paracartia grani and more recently Paracartia latisetosa (Audemard et al, 2002;Carrasco et al, 2007Carrasco et al, , 2008Arzul et al, 2013;Boyer et al, 2013). To date, M. refringens has been identified in CI -CV copepodid stages of P. grani, adult females of P. grani and P. latisetosa (CIII is the earliest stage of P. grani in which M. refringens has been detected by ISH; parasitic stages have been detected in the alimentary canal, digestive epithelium and germinal site; ), CV males of P.…”

“…In addition, M. refringens has also been successfully transmitted from infected oysters (O. edulis) to P. grani where parasite development was detected , but conversely, these experiments have so far failed to infect oysters from infected copepods (Carrasco et al, 2007). Audemard et al (2001) hypothesised that either a period of maturation in the environment is required or that a second intermediate host is necessary.…”

“…Audemard et al (2001) hypothesised that either a period of maturation in the environment is required or that a second intermediate host is necessary. However, Carrasco et al (2007) emphasised that difficulties, either in collecting sufficient infected hosts or producing them through laboratory infections, severely limits the experimental capacity to establish the true nature of infection.…”

“…Consequently, it is perhaps more surprising that we detected 'true' positives in polychaetes at all, rather than the small number that we actually identified. (Audemard et al, 2002;Carrasco et al, 2007Carrasco et al, , 2008 and has led them to hypothesise that a third host, or period of maturation, is required in the life cycle of M. refringens.…”