# Microbiome dynamics associated with Hematodinium sp. infection in Norway lobster (Nephrops norvegicus)

## TL;DR

This study explores how the microbiome of Norway lobster changes during infection by the Hematodinium parasite, revealing significant shifts in bacterial communities linked to disease progression.

## Contribution

The study provides the first insights into the pathobiome of Norway lobster infected with Hematodinium sp., highlighting microbiome changes associated with infection.

## Key findings

- Infected lobsters showed marked shifts in bacterial richness and community composition in haemolymph and gut tissues.
- Subpatent infections were associated with persistent microbiome changes, suggesting early microbial responses to the parasite.
- Smaller, more susceptible lobsters had reduced haemolymph microbiome richness, potentially linking microbiome health to disease severity.

## Abstract

The parasite Hematodinium sp. causes morbidity and seasonal mortality events in more than 40 decapod species globally and therefore, it is now recognised as a significant threat to the future sustainability of shellfish fisheries and aquaculture worldwide. Among these, Norway lobster (Nephrops norvegicus), an important representative of the marine benthos and supporting the most valuable shellfish fishery in the UK, experience yearly seasonal Hematodinium sp. patent infections. Currently, little is known about the N. norvegicus microbiome and potential role during Hematodinium sp. infection. Therefore, in this study we investigated the microbiome dynamics of N. norvegicus associated with Hematodinium sp. infection and disease progression in the haemolymph and gut. N. norvegicus were sampled from the Clyde Sea Area, Scotland during the peak of the Hematodinium sp. patent infection. The presence and intensity of Hematodinium sp. infection were determined using the body colour method (BCM), pleopod method (PM), histology (heart, gonads, hepatopancreas, gills and muscle) and molecular tools (PCR).

Marked shifts in the bacterial richness of the haemolymph and significant alterations in the overall bacterial community composition of both tissues were observed in infected lobsters. These changes, observed even at subpatent levels of infection (only positive by PCR), indicate a prompt and persistent microbiome shift associated with Hematodinium sp. infection. Furthermore, smaller healthy animals (25.2 ± 1.20 mm CL) known to be particularly susceptible to high severity infection displayed a decreased microbiome richness in the haemolymph suggesting a potential link between the host microbiome and susceptibility to disease progression, a possibility that merits further research.

This study offers the first insights into the pathobiome of N. norvegicus due to Hematodinium sp. infection and disease that in turn provides a foundation for further studies on the pathogenesis of this important parasitic disease.

The online version contains supplementary material available at 10.1186/s42523-025-00416-w.