Green crab Carcinus maenas symbiont profiles along a North Atlantic invasion route

ABSTRACT: The green crab Carcinus maenas is an invader on the Atlantic coast of Canada and
the USA. In these locations, crab populations have facilitated the development of a legal fishery in
which C. maenas is caught and sold, mainly for use as bait to capture economically important
crustaceans such as American lobster Homarus americanus. The paucity of knowledge on the
symbionts of invasive C. maenas in Canada and their potential for transfer to lobsters poses a
potential risk of unintended transmission. We carried out a histological survey for symbionts of C.
maenas from their native range in Northern Europe (in the UK and Faroe Islands), and invasive
range in Atlantic Canada. In total, 19 separate symbiotic associations were identified from C. maenas collected from 27 sites. These included metazoan parasites (nematodes, Profilicollis botulus,
Sacculina carcini, Microphallidae, ectoparasitic crustaceans), microbial eukaryotes (ciliates,
Hematodinium sp., Haplosporidium littoralis, Ameson pulvis, Parahepatospora carcini, gregar -
ines, amoebae), bacteria (Rickettsia-like organism, milky disease), and viral pathogens (parvolike virus, herpes-like virus, iridovirus, Carcinus maenas bacilliform virus and a haemocyteinfecting rod-shaped virus). Hematodinium sp. were not observed in the Canadian population;
however, parasites such as Trematoda and Acanthocephala were present in all countries despite
their complex, multi-species lifecycles. Some pathogens may pose a risk of transmission to other
decapods and native fauna via the use of this host in the bait industry, such as the discovery of a
virus resembling the previously described white spot syndrome virus (WSSV), B-virus and ‘rodshaped virus’ (RV-CM) and amoebae, which have previously been found to cause disease in aquaculture (e.g. Salmo salar) and fisheries species (e.g. H. americanus).