Bacterial characterization of a disease event in larval rearing system of tropical rock lobster (Panulirus ornatus)

Abstract Disease outbreaks in commercial larval rearing systems of the tropical rock lobster ( Panulirus ornatus ) pose significant challenges to the culture of this species. This study investigates bacterial succession during outbreaks of white leg disease (WLD), the latter associated with infections by Aquimarina spp. in early-stage P. ornatus phyllosoma. Bacteriome profiling was conducted to assess changes in bacterial composition and identify potential sources of pathogenic taxa. Transmission electron microscopy was used to depict ultrastructural changes in the pereiopods of diseased specimens. Oxford Nanopore 16S rRNA gene sequencing was used to profile bacterial diversity and community structure across larval development (0–16 days post-hatch, dph), revealing temporal shifts coinciding with the onset of disease. A marked decline in alpha diversity between 8 and 16 dph was observed concomitant with an increase in diseased animals. During this period, the pathogenic genus Aquimarina became dominant, replacing early taxa such as Vibrio , Ruegeria , Shimia , and Phaeobacter , and concurring with massive coagulative necrosis and the subsequent formation of ellipsoid, electron-dense, proteinaceous bodies in pereiopod tissues. Beta diversity analysis further revealed significant shifts in community structure, implying that bacterial dysbiosis may be an early indicator of WLD development. The findings suggest that disease results from a combination of bacterial maternal or environmental transmission, environmental acquisition, and bacteria-bacteria interactions. The study highlights the importance of maintaining bacterial balance to support a healthy aquaculture system for larval lobsters, suggesting that early bacterial disruption can facilitate disease emergence.