Harmless sea snail parasite causes mass mortalities in numerous commercial scallop populations in the northern hemisphere

Abstract

Apicomplexans comprise a group of unicellular, often highly pathogenic, obligate parasites exploiting either one or two hosts to complete a full reproductive cycle. For decades, various scallop populations have suffered cyclical mass mortality events, several of which shown to be caused by apicomplexan infections. We report the first dual mollusc life cycle for an apicomplexan: a species highly pathogenic in various pectinid bivalve species, but apathogenic when infecting the common whelk as Merocystis kathae. The sympatric distribution of the common whelk and scallops in the North Atlantic makes transmission extremely effective, occurring via the gastrointestinal tract, by scavenging and predation in whelks and unselective filter feeding in scallops. Infective sporozoites from whelks utilize scallops´ haemocytes to reach muscular tissue, where asexual reproduction occurs. Phylogenetically, this apicomplexan is robustly placed within the Aggregatidae and its inclusion in analyses supports a common ancestry with other basal invertebrate apicomplexans. Scallops seem able to regulate low-level infections of M. kathae as they exist in normal populations while epizootics occur during high levels of exposure from locally infected whelks. A targeted removal of whelks from valuable scallop grounds would be advantageous to minimize the occurrence of M. kathae epizootics and prevent damaging economic losses.

Polyphyletic origin, intracellular invasion, and meiotic genes in the putatively asexual agamococcidians (Apicomplexa incertae sedis)

“…cyamus and Rh. polygordiae were the sister group of the coccidians Margolisiella islandica and Pseudoklossia pectinis 15,22,23 , but their common clade was never strongly affiliated with gregarines, cryptosporidians, or coccidiomorphs. Reasons for the lack of resolution might be two-fold: Rh.…”

“…Margolisiella islandica infecting the Iceland scallop Chlamys islandica is the closest described relative of rhytidocystids with complete Leukart's triad in monoxenous life cycle ( Fig. 5) 15,22,23 . Pseudoklossia pectinis is a putatively heteroxenous parasite of Pecten maximus: gamogony and sporogony occur in the great scallop, and a merogonic phase is supposed to be in some other host 28 .…”

“…The term "Eococcidia" refers to Eos-the goddess of the dawn in Greek mythology, who rose in the morning from the Oceanus; the prefix "eo-" is used in geology and biology for the designation of something to be early (Eococcidia-early coccidians). Coccidian genera Merocystis and Aggregata are also candidate members to Eococcidia since they were recovered as close relatives of Rhytidocystis, Pseudoklossia, and Margolisiella 23,29 .…”

Convergence of a Disease and Litigation Leading to Increased Scallop Discard Mortality and Economic Loss in the Georges Bank Fishery

“…). Since then, the common whelk Buccinum undatum has been identified as the definitive host for this parasite, with sea scallops acting as an intermediate host (Kristmundsson and Freeman ). Whelks are predators and scavengers on sea scallops; if an infected population of sea scallops and whelks are left undisturbed, increases in the density and age of the scallops (older scallops having been exposed to the infection longer) may increase the pathogenicity of the parasite in the scallop population.…”

A qPCR-Based Survey of Haplosporidium nelsoni and Perkinsus spp. in the Eastern Oyster, Crassostrea virginica in Maine, USA

“…Marine mollusks are prone to epizootic episodes of a different nature (reviewed in [1]), with new reports of mortalities, as more countries move from fisheries to aquaculture practices and monitoring systems are in place [2][3][4][5]. The eastern oyster is an indigenous species to Maine [6], with oyster aquaculture leases in state waters first granted in 1975 (University of Maine Aquaculture Research Institute, 2014).…”