Review: Bucephalus minimus, a deleterious trematode parasite of cockles Cerastoderma spp.

Abstract

Trematodes are the most prevalent and abundant macroparasites in coastal waters. They display a complex life cycle with alternation of free-living and parasitic stages generally involving three host species. The most deleterious stage is in the first intermediate host (a mollusc) where the parasite penetrates as miracidium larvae and asexually multiplicates in sporocysts/rediae to provide cercariae larvae. However, due to basic low prevalence in ecosystems, this system remains difficult to study. Taking the example of the cockle (Cerastoderma edule), an exploited bivalve along North-Eastern Atlantic coasts, and Bucephalus minimus, its most prevalent parasite as first intermediate host, we summarised the 51 most relevant papers (1887-2015). Besides, a 16-year monthly monitoring was performed at Banc d'Arguin (Atlantic coast of France), and allowed to obtain a sufficient number of infected cockles (276 out of 5,420 individuals) in order to provide new information concerning this parasite/host system. Sporocysts (diameter 80-500 μm) and developing cercariae (length 300-500 μm) are not visible before cockle reaches 16-mm shell length and then prevalence increases with host size. Seasonality of infection was not observed but variation of prevalence was significant among years and negatively correlated to the temperature of the former year, which could correspond to the period of infection by miracidium. Seven other species of trematode were identified in cockles as second intermediate host. For six of them, metacercariae abundance per individual was 2 to 12 folds higher in B. minimus-infected cockles, exacerbating the potential negative impact on host. From the parasite point of view, metacercariae can be considered as hitchhikers, taking advantage of the abnormal migration of B. minimus-infected cockles to the sediment surface where they become more vulnerable to predators that are also the final hosts of many of these parasites.

Seasonal variation of transcriptomic and biochemical parameters of Donax trunculus related to its infection by Bacciger bacciger (trematode parasite)

“…Total prevalence of infection showed a seasonal pattern being highest in July (33%) and lowest in May (0%) as opposite to what was observed in Spain (Ramón et al 1999, Delgado andSilva 2018). Knowing that generally the prevalence of trematodes infecting bivalves as first intermediate host is positively correlated to host size (Magalhães et al 2015), the observed seasonal pattern could be related to the shell length confounding factor. Despite the clams sampled in May (B.…”

“…Studies of first host -parasite systems and consequent predictions of disease events are very difficult to accomplish mostly due to generally low prevalence of these parasites and/or sudden high prevalence outbreaks that are followed by mass mortalities (Thieltges et al 2008, Magalhães et al 2015. The effects of the sporocyst, the parasitic stage occurring in the first intermediate host, are often severe and negative impacts are described at the reproduction (Carballal et al 2001), growth (Bowers 1969) and behaviour (Babirat et al 2004) As previously demonstrated by other authors studying other 1 st host-parasite systems (Curtis andHubbard 1990, Magalhães et al 2017), our findings demonstrated that prevalence calculated after host dissection was higher than prevalence calculated by cercariae emergence.…”

“…A similar trend was described by Ramadan and Ahmad (2010) studying the same host-parasite system in the north-east coast of Egypt. Seasonality in trematodes infecting their first intermediate host is not frequently observed, mainly due to the natural low prevalence of these parasites and consequent difficulty to find infected hosts (Magalhães et al 2015). Nevertheless, most of the authors tend to converge by identifying summer and the positively correlated high temperatures as the season presenting the highest prevalence (demonstrated by Bowers (1969) in South Wales and by Desclaux et al (2002) (Soudant et al 2013).…”

Large scale patterns of trematode parasite communities infecting Cerastoderma edule along the Atlantic coast from Portugal to Morocco

“…This study is among the few reports on large-scale trematode communities infecting cockles (e.g. de Montaudouin et al, 2009;Magalhães et al, 2015) and represents the first large-scale assessment of latitudinal gradient (and abiotic related factors) as a driver of trematode communities composition in Cerastoderma edule as a host model. In addition, this is the first exhaustive study on trematode species composition in Moroccan cockles.…”

The ecology, evolution, impacts and management of host–parasite interactions of marine molluscs

“…Parasites have been shown to interfere significantly with host populations (reviewed in Magalhães et al, 2015) by initiating diseases that affect reproduction in complex manners, as well as affecting absolute host population numbers (see Fig. 3).…”