Eutrophication in a tropical pond: Understanding the bacterioplankton and phytoplankton dynamics during a vibriosis outbreak using flow cytometric analyses

Abstract

In tropical shrimp ponds, the increasing of feed input, concomitantly with the stocking shrimp biomass, induces an eutrophication of the ecosystem. Although difficult to maintain, its stability is required to guarantee the success of the culture. A 110-day period of phytoplankton and bacterioplankton stock and dynamics in an earthen pond (1.2 ha area, 1 m depth) was monitored using flow cytometry to provide baseline information on community characteristics and ecosystem instability. Seven autotrophic cell types were identified over the whole sampling period. Prokaryotic cells included Synechococcus sp., a group named UNK which presented an atypical new flow cytometric signature and picoeukaryotes (PEUK). Nanophytoplankton cells were represented by 4 groups: NAN1, NAN2, NAN3 and Cryptophytes. During the first part of the survey, picophytoplankton dominated the phytoplanktonic assemblage. The mean abundance of total cells (up to 8 × 10 6 cells mL −1) was among the highest recorded in marine and brackish waters. Bacterial abundance and production ranged from 0.8 to 5.1 × 10 7 cells mL −1 and from 30 to 110 μg C L −1 h −1. A shift from pico to nanophytoplankton abundance was observed for a few days from d 96. During this period, heterotrophic bacteria production and abundance suddenly dropped, implying a change in the functioning of the microbial loop. This shift was concomitant with a significant shrimp mortality outbreak due to Vibrio penaeicida, the etiological agent of a disease known as Syndrome 93, which affects the shrimp industry in New Caledonia. This survey suggests that flow cytometric analysis could be used for the monitoring of aquaculture systems to improve our understanding of the complex phytoplankton and bacterial dynamics of these systems and its potential influence on disease development.

Dynamics of phytoplankton communities in eutrophying tropical shrimp ponds affected by vibriosis

“…The phytoplankton taxa selected to be included in this program were determined on the basis of previous reports on the equatorial Pacific Higgins and Mackey, 2000;DiTullio et al, 2003, Higgins et al, 2006 and tropical Indian ocean and all the information obtained via flow cytometric counting, microscopic observation, molecular analysis and previous studies on the same environment (Lucas et al, 2010). Photoacclimation processes were taken account on the basis of pigment ratios published by Laviale and Neveux (2011).…”

“…Whatever the disease, mortality appears in specific environmental conditions characterized by strong phytoplankton and bacterioplankton oscillations and abiotic parameters (pH, ammonia, etc.) close to stressful values (Lemonnier et al, 2006Lucas et al, 2010). Such conditions, which may occur in combination with another unknown triggering factor, weaken the host physiological status, parameters, increasing shrimp susceptibility to bacterial infections (Mugnier et al, 2013).…”

“…This technique, known as chemotaxonomy, has been widely and successfully used in marine, estuarine and freshwater environments Descy et al, 2009), but has been applied less frequently to tropical aquaculture ponds (Burford, 1997;Gárate-Lizárraga et al, 2009). Metagenomic analysis of flow-sorted selected cells was conducted on one fresh sample to estimate the diversity of two dominant cytometric groups: picoeukaryotes, which are highly abundant, and an unknown prokaryotic group regularly observed in shrimp ponds in New Caledonia (Courties and Boeuf, 2004;Lucas et al, 2010). The combination of cell sorting by FCM with molecular tools allows the molecular taxonomic identification of specific planktonic cells (Guillebault et al, 2010).…”

Advances, challenges, and directions in shrimp disease control: the guidelines from an ecological perspective

“…There is a strong indication that bacterioplankton abundance and composition play direct roles in numerous shrimp diseases (Lucas et al 2010;Xiong et al 2014b). A dramatic drop in heterotrophic bacteria production and abundance was shown to be concurrent with high shrimp mortality (Lucas et al 2010). Similarly, a sudden shift in the bacterial community caused severe mass mortality, which was primarily triggered by a significant increase in chemical oxygen demand (COD) and total phosphate (Xiong et al 2014b;Zhang et al 2014).…”

“…There is a strong indication that bacterioplankton abundance and composition play direct roles in numerous shrimp diseases (Lucas et al 2010;Xiong et al 2014b). A dramatic drop in heterotrophic bacteria production and abundance was shown to be concurrent with high shrimp mortality (Lucas et al 2010).…”