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

Abstract

Tropical shrimp aquaculture systems in New Caledonia regularly face major crises resulting from outbreaks of Vibrio infections. Ponds are highly dynamic and challenging environments and display a wide range of trophic conditions. In farms affected by vibriosis, phytoplankton biomass and composition are highly variable. These conditions may promote the development of harmful algae increasing shrimp susceptibility to bacterial infections. Phytoplankton compartment before and during mortality outbreaks was monitored at a shrimp farm that has been regularly and highly impacted by these diseases. Combining information from flow cytometry, microscopy, pigment and phylogenetic analysis, the presence of Picocyanobacteria, Prasinophyceae and Diatomophyceae were detected as dominant phytoplankton groups and Cryptophyceae, Prymnesiophyceae and Dinophyceae as minor components. At the onset of the first shrimp mortalities, Bacillariophyceae increased while Cyanobacteria, Prymnesiophyceae and Dinophyceae decreased in the water column, followed by proliferation of Prasinophyceae. Several taxa were identified as potential harmful algae (Cyanobacteria, dinoflagellates and Phaeocystis).

Response of phytoplankton to organic enrichment and shrimp activity in tropical aquaculture ponds: a mesocosm study

“…Samples were defrosted at ambient temperature and subsequently analysed using a FACSCan flow cytometer (BD-Biosciences, San Jose, CA) equipped with an air-cooled argon laser (488 nm, 15 mW). Methodology and data analysis used in this study are fully described in Lemonnier et al (2016). Based on cellular RALS and fluorescence properties, several populations were conventionally distinguished (e.g.…”

“…According to the ecological theory of r/K selection, an unstable environment in pond containing high nutrient levels is particularly favorable to select for fast-growing organisms as opportunistic pathogens (De Schryver and Vadstein, 2014). This lack of stability linked to an imbalance in the N:P ratio may promote the development of toxic algal species stressful for shrimp, playing directly or indirectly a role in disease outbreaks in shrimp aquaculture ponds in New Caledonia (Lemonnier et al, 2006;Lemonnier et al, 2010;Lucas et al;Lemonnier et al, 2016).…”

Dynamics and succession of plankton communities with changing nutrient levels in tropical culture ponds of whiteleg shrimp

“…Thalassiosira spp. is a nano planktonic diatom that grows rapidly when nutrients are increased; it has been reported as a major component of the spring diatom bloom in shallow euphotic zones of many coastal waters (Guillard & Kilham 1977, Waite et al 2005 and also a significant proportion of phytoplankton community in densely stocked shrimp ponds (Melo et al 2010, Lemonnier et al 2016. By virtue of their importance in substantially contributing to the growth performance of L. vannamei even at adult stages (Moss 1994) and provision of adequate levels of the dietary requirements of PUFAs, eico sapen taenoic acid and/ or docosahexa enoic acid and arachidonic acid (Volkman et al 2006), these centric diatom species are highly desirable in shrimp ponds.…”

“…A positive effect on water quality and productive shrimp performance during the co-culture of 3 species of microalgae and shrimp in a zero-water exchange system was recently demonstrated by Ge et al (2016). Species succession is often ob served in shrimp ponds, starting with some beneficial flagellate and diatom species, followed by unfavourable noxious dinoflagellates after a month of culture (Yusoff et al 2002, Lemonnier et al 2016, Lemonnier et al 2017.…”

“…In spite of key roles played by these plankton communities in regulating water quality and in shrimp diet, our knowledge on their composition, abundance, dy na mics and succession in shrimp aquaculture ponds is fragmentary (e.g. Burford et al 2003, Casé et al 2008, Lemonnier et al 2016. The majority of previous studies have solely characterized the phytoplankton or the environmental factors, while inter relationshipsparticularly with respect to water quality parameters influencing phytoplankton dynamics and succession -have re ceived limited attention.…”