Seasonal Shifts in the Microbiota of Wild-Caught Danish Carcinus maenas

Underutilized and abundant in the Danish coastal area, Carcinus maenas has become a threat to the environment and to the local fisheries. In this study we investigated the microbiota and presence of microbial hazards of interest for human health in crabs caught over the period of one year, to investigate its potential for human consumption. Between 2023 and 2024, four seasonal samples of live specimens (n = 5) were caught off the Lillebælt (DK) coastal area. To characterize the microbiota of the crabs, a culture-dependent approach was used to determine total aerobic mesophilic count, total aerobic psychrotrophic count, Bacillus spp., Enterobacteriaceae, lactic acid bacteria, fungi, Salmonella spp., Listeria monocytogenes and Bacillus cereus. MALDI-TOF was used to corroborate results and further identify isolated microorganisms. The results were then compared with data obtained from amplicon sequencing of community 16S rRNA genes to compare family-level compositions of the microbiota. Of the pathogens of interest, B. cereus was detected during summer/autumn, reaching a maximum of 2.5 log cfu/g. Salmonella spp., and L. monocytogenes were below the limit of detection (<1 cfu/0.1 g). Spoilage bacteria were detected (e.g., Brochothrix spp., Carnobacterium spp., Photobacterium spp., Pseudomonas spp., Psychrobacter spp. and Shewanella spp.). The study highlighted significant seasonal changes (PERMANOVA, FDR-adjusted p = 0.00003) in the microbial composition. The gathered evidence suggests that with proper handling, the crabs could represent a safe resource.