Microbial community dynamics in a larval aquaculture system of the tropical rock lobster, Panulirus ornatus

Abstract

Commercial scale rearing of the tropical rock lobster ( Panulirus ornatus) has been unsuccessful to date, with attempts characterised by periodic mass mortalities of early stage hatchery-reared larvae. Here, we investigate the microbiological and histopathological factors affecting early stage phyllosomas. Histopathology identified microbial infestation of phyllosomas, including proliferation of bacteria in the hepatopancreas and heavy external fouling of appendages and cuticle with filamentous bacteria and sessile protozoa. Scanning electron microscopy confirmed fouling by filamentous bacteria of at least two morphological types and also fouling by rod-shaped bacteria, indicative of a diverse epibiont community. Culture- and molecular-based microbial community analysis was performed on the water column, tank biofilm and whole phyllosomas of standard larval-rearing environments. No correlation between bacterial numbers (measured as colony-forming units [CFU] mL −1) and phyllosoma mortalities was established. Culture-based studies using selective media indicated that Vibrionaceae-related organisms were a dominant part of the microbial community and Vibrio parahaemolyticus was the most commonly isolated organism from each environment investigated. Limited microbial phylogenetic diversity was observed for culture-based studies when compared against molecular-based denaturing gradient gel electrophoresis (DGGE) results. DGGE profiles of water, biofilm and phyllosoma environments differed, indicative of unique microbial niches sustaining different microbial populations. These microbial populations appeared dynamic since DGGE profiles changed within each environment over the course of the experiment. Few Vibrio-affiliated sequences were retrieved from DGGE profiles highlighting differences between the two methods for assessing microbial diversity within the larval-rearing system.