Since its rapid expansion in the Northern Adriatic Sea in 2023, the invasive blue crab (Callinectes sapidus) has emerged as a possible reservoir and vector of marine pathogens. The present research aimed to describe the diversity of culturable bacteria in crab haemolymph and seawater, emphasizing the detection of potentially pathogenic species and their potential ecological roles.
From June 2024 to February 2025, 420 blue crabs of different size categories were sampled in the Sacca di Goro Lagoon (Italy), along with seawater samples from the surrounding environment. The bacteriological assessment revealed significant seasonal fluctuations and correlations with crab size, showing increased colony-forming unit (CFU) values in larger specimens.
The predominant bacterial taxa belonged to the genus Vibrio, with Vibrio parahaemolyticus being most abundant during summer and autumn, and Vibrio splendidus prevailing in winter. Certain species, such as Vibrio crassostreae and Vibrio harveyi, were detected exclusively in larger crabs, whereas others, including Vibrio alginolyticus, were present across all size groups. Antimicrobial susceptibility testing revealed heterogeneous resistance patterns, suggesting that haemolymph-associated bacteria may act both as opportunistic pathogens and as reservoirs of resistance determinants.
This study provides the first evidence of seasonal variation in culturable haemolymph-associated bacteria of invasive C. sapidus populations from the Adriatic Sea, underscoring their potential influence on crab physiology, ecological interactions, and biosecurity risks for aquaculture systems.