Abstract
BackgroundThe parasitic dinoflagellates of the genus Hematodinium represent the causative agent of so-called bitter or pink crab disease in a broad range of shellfish taxa. Outbreaks of Hematodinium-associated disease can devastate local fishing and aquaculture efforts. The goal of our study was to examine the potential role of the common shore (green) crab Carcinus maenas as a reservoir for Hematodinium. Carcinus maenas is native to all shores of the UK and Ireland and the North East Atlantic but has been introduced to, and subsequently invaded waters of, the USA, South Africa and Australia. This species is notable for its capacity to harbour a range of micro- and macro-parasites, and therefore may act as a vector for disease transfer.MethodsOver a 12-month period, we interrogated 1191 crabs across two distinct locations (intertidal pier, semi-closed dock) in Swansea Bay (Wales, UK) for the presence and severity of Hematodinium in the haemolymph, gills, hepatopancreas and surrounding waters (eDNA) using PCR-based methods, haemolymph preparations and histopathology.ResultsOverall, 13.6% were Hematodinium-positive via PCR and confirmed via tissue examination. Only a small difference was observed between locations with 14.4% and 12.8% infected crabs in the Dock and Pier, respectively. Binomial logistic regression models revealed seasonality (P < 0.002) and sex (P < 0.001) to be significant factors in Hematodinium detection with peak infection recorded in spring (March to May). Male crabs overall were more likely to be infected. Phylogenetic analyses of the partial ITS and 18S rRNA gene regions of Hematodinium amplified from crabs determined the causative agent to be the host generalist Hematodinium sp., which blights several valuable crustaceans in the UK alone, including edible crabs (Cancer pagurus) and langoustines (Nephrops norvegicus).ConclusionsShore crabs were infected with the host generalist parasite Hematodinium sp. in each location tested, thereby enabling the parasite to persist in an environment shared with commercially important shellfish.
Highlights
The parasitic dinoflagellates of the genus Hematodinium represent the causative agent of so-called bitter or pink crab disease in a broad range of shellfish taxa
When referring to the presence of Hematodinium, we refer to the occurrence via polymerase chain reaction (PCR) alone unless otherwise stated
Model 1 combined the data from both locations, and using the presence of Hematodinium as the response variable, revealed that season, sex and haemolymph opacity were significant factors associated with the presence of the parasite (Table 2, Model 1)
Summary
The parasitic dinoflagellates of the genus Hematodinium represent the causative agent of so-called bitter or pink crab disease in a broad range of shellfish taxa. Carcinus maenas is native to all shores of the UK and Ireland and the North East Atlantic but has been introduced to, and subsequently invaded waters of, the USA, South Africa and Australia This species is notable for its capacity to harbour a range of micro- and macro-parasites, and may act as a vector for disease transfer. Davies et al Parasites Vectors (2019) 12:472 lobster (Nephrops norvegicus) fishery based on the west coast of Scotland (UK) have been estimated to be of the order GBP 2–4 million [3,4,5] In another key economic crustacean, the edible crab (Cancer pagurus), infection levels of up to 30% have been reported in juveniles (prerecruit) in the Bristol Channel (UK), indicating that this infection alone can cause significant reduction in stocks [6]. In North America, outbreaks have infected up to a third of the Tanner crab (Chionoecetes bairdi) and snow crab (C. opilio) stocks in southeast Alaska and Newfoundland, respectively [8, 9]
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