Himasthla spp. (Trematoda) In The Edible Cockle Cerastoderma edule: Review, Long-Term Monitoring And New Molecular Insights

Abstract

Trematodes are the main macroparasites in coastal waters. The most abundant and widespread form of these parasites is metacercaria. Their impact on their host fitness is considered relatively low but metacercarial larvae of some species can have deleterious effects on individuals and/or populations. This review focused on the cockle Cerastoderma edule and four species of the genus Himasthla; a common host–parasite system in marine coastal environments. Our aims were (1) to review literature concerning Himasthla continua, Himasthla elongata, Himasthla interrupta and Himasthla quissetensis in cockles; (2) to provide molecular signatures of these parasites and (3) to analyse infection patterns using a 20-year monthly database of cockle monitoring from Banc d'Arguin (France). Due to identification uncertainties, the analysis of the database was restricted to H. interrupta and H. quissetensis, and it was revealed that these parasites infect cockles of the same size range. The intensity of parasites increased with cockle size/age. During the colder months, the mean parasite intensity of a cockle cohort decreased, while infection occurred in the warmest season. No inter-specific competition between trematode parasites was detected. Furthermore, even if the intensity of H. interrupta or H. quissetensis infection fluctuated in different years, this did not modify the trematode community structure in the cockles. The intensity of infection of both species was also positively correlated with trematode species richness and metacercarial abundance. This study highlighted the possible detrimental role of Himasthla spp. in cockle population dynamics. It also revealed the risks of misidentification, which should be resolved by further molecular approaches.

Graphical abstract

Fig. 1.

Prevalence of Himasthla interrupta (black line) and Himasthla quissetensis (grey line) by shell length class and number of dissected cockles (bars).

Fig. 2.

Boxplot of H. interrupta (A) and H. quissetensis (B) intensity per cockle shell length and corresponding age and seasons. Absolute age was deduced from a recruitment date in May. The box (25–75% of the data) contains a black line (median) and a red line (mean). Whiskers represent the lower and upper values in the range of ±1.5 interquartile range, with outliers as black circles. Grey arrows indicate significant variation between successive months (Wilcoxon test, P < 0.01). For example, in the case of H. interrupta, the first value that is significantly different from May 0+ intensity is in December 0+.

Fig. 3.

Percentage of metacercariae per species (Curtuteria arguinae, Gymnophallus minutus, Psilostomum brevicolle, Renicola roscovitus, Diphterostomum brusinae and H. quissetensis) in Cerastoderma edule without (A) and with (B) H. interrupta.

Fig. 4.

Percentage of metacercariae per species (C. arguinae, G. minutus, P. brevicolle, R. roscovitus, D. brusinae and H. interrupta) in C. edule without (A) and with (B) H. quissetensis.