Abstract
There is a paucity of knowledge regarding the diversity and impact(s) of disease-causing fungi in marine animals, especially shellfish. In efforts to address this knowledge gap for the shore crab Carcinus maenas, a year-long disease screen was carried out across two sites in Swansea Bay (Wales, UK) with a view to characterising putative fungal infections. Crabs were sampled between November 2017 and October 2018, and screened systematically for disease signatures using haemolymph (blood) preparations, targeted PCR and tissue histopathology. Strikingly, mycosis was confirmed in ~0.4% of total crabs tested (n = 1191) and restricted to one location only (Mumbles Pier). Clinical infections were observed in four out of four infected crabs. In these animals, the gills and hepatopancreas were congested with fungal morphotypes. In addition, some evidence indicates haemocyte (immune cell) reactivity toward the fungi. Phylogenetic placement of the partial internal transcribed spacer (ITS1) gene regions amplified from three mycotic crabs revealed the causative agent to be related to hypocrealean fungi, thereby representing a novel species.
Highlights
Crustaceans are known to be infected by a number of disease-causing agents, including bacteria and viruses, infections caused by fungi and oomcyetes are reported rarely [1]
A well-documented pathogen of Crustacea is the causative agent of crayfish plague, Aphanomyces astaci [5], a pathogenic oomycete [6]
Some oomycetes have been incorrectly described as fungi; fungi and oomycetes both grow as filamentous hyphae, their lineages diverged before the split of fungi from plants and animals [7]
Summary
Crustaceans are known to be infected by a number of disease-causing agents, including bacteria and viruses, infections caused by fungi and oomcyetes are reported rarely [1]. Fungal infections have been observed in a range of marine environments and hosts from macroalgae, seagrass, mangrove, coral, and crustaceans to marine mammals [2]. A recent review estimated that the 1100 species of marine fungi identified may only represent ~10%. The first recorded occurrence of Halioticida noduliformans, a Haliphthoros-like parasitic oomycete thought to lead to reduced fecundity in H. gammarus was reported [12]. In the case of fungal infections of crustaceans, there are very few examples that have been extensively studied in terms of their virulence, pathobiology and host response
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