Prevalence and insights on the parasitic dinoflagellate Hematodinium sp. infection in the Norway lobster, Nephrops norvegicus

Abstract

Hematodinium sp. poses a significant threat to shellfish fisheries and aquaculture worldwide, causing morbidity and mortality events in various decapod species. The study focuses on the Clyde Sea Area (CSA) population of Nephrops and aims to elucidate key aspects of the Hematodinium-Nephrops pathosystem. This research confirms that Hematodinium sp. infection levels in the CSA align with previous data using body colouration and pleopod examination methods (Beevers et al., 2012; Stentiford et al., 2001a). This confirms that Hematodinium sp. is endemic to the region, with infection rates peaking in spring and summer and declining in autumn. The study highlights a correlation between infection severity and Nephrops size, with smaller individuals being more susceptible to disease progression. Female Nephrops, exhibiting behaviours such as burrow emergence and synchronized moulting in spring, are particularly prone to acquiring infection. the Building upon this knowledge, previously unexamined aspects of Nephrops microbiome dynamics were explored in both Hematodinium-negative individuals and those infected by Hematodinium sp. The analysis revealed that even at subpatent levels, infected lobsters exhibit significant changes in haemolymph microbiome richness and composition, indicating a rapid and persistent microbial response to Hematodinium sp. infection. The infection decreased haemolymph bacterial richness and increased opportunistic bacteria, while the gut microbiome shifted towards polysaccharide-degrading genera. This study also established a baseline for “healthy” microbiomes in Nephrops, with Proteobacteria dominating both haemolymph (46.1%) and gut (26.7%) microbiomes, a pattern consistent with other crustaceans. The haemolymph contained beneficial genera like Bifidobacterium and Lactobacillus, alongside opportunistic pathogens such as Pseudomonas. The gut featured diverse genera, including sulphate-reducing bacteria and the key member Candidatus Bacilloplasma, capable of influencing immune responses. Furthermore, the lipid dynamics between Hematodinium sp. and Nephrops were analysed, revealing clear similarities in lipid profiles between the parasite spores and the host hepatopancreas. This may indicate that the parasite relies on scavenging host-derived lipids for survival and possibly pathogenesis. Hematodinium sp. macrospores accumulate energy-rich lipids such as triacylglycerols, DHA, and EPA, which likely enhance membrane fluidity, motility, and stress resistance, thereby aiding in their survival and transmission of Hematodinium sp.. Future investigations should build upon these insights by incorporating comprehensive monitoring of Hematodinium sp. progression in captivity and exploring the environmental and biological cues that trigger sporulation. Additionally, further research into the specific mechanisms of lipid utilization and the roles of different spore types will advance the understanding of host-parasite interactions.