Non-photochemical quenching, a non-invasive probe for monitoring microalgal grazing: an early indicator of predation by Oxyrrhis marina and Euplotes sp.

Pranali Deore,Anbarasu Karthikaichamy,John Beardall,Santosh Noronha

doi:10.1080/26388081.2019.1651218

Pranali Deore, Anbarasu Karthikaichamy + Show 2 more

Open Access

https://doi.org/10.1080/26388081.2019.1651218

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Abstract

ABSTRACT Microalgae are major primary producers in aquatic environments, and many synthesize an array of industrially important biomolecules such as pigments, lipids and proteins. As a result, there is considerable interest in and effort into growing algae for industrial purposes. An economical method to produce a large amount of biomass is the use of the open-raceway pond cultivation platform. However, the nature of the cultivation and the nutrient-rich profile of such cultures attract contaminants such as zooplankton predators, which can result in a sudden culture crash. For effective pond management, an early indicator of grazer presence is needed to implement timely interventions. Currently available tools are offline, time-consuming and dependent on predator concentration. This study explores grazing-mediated changes in photosynthetic parameters during infestation of Dunaliella tertiolecta cultures by the heterotrophic dinoflagellate Oxyrrhis marina and the ciliate Euplotes sp. A significant reduction in non-photochemical quenching levels 24–48 h prior to the crash was observed in both bulk and single-cell prey samples. An increasing rate of grazer ingestion correlated with decreasing non-photochemical quenching levels as the culture progressed towards the crash. The reductions in the non-photochemical quenching levels were consistent in grazing cultures at different prey cell concentrations. Although the maximum photosynthetic yield remained unaltered, maximum relative electron transport rates were enhanced and the light-harvesting efficiency, alpha, reduced in comparison to controls. We suggest that, along with traditional methods, non-photochemical quenching monitoring could be used as a part of integrative pest management to minimize predator outbreaks.

Highlights

Microalgae are major primary producers in marine and freshwater environments. These organisms synthesize an array of biomolecules such as proteins, lipids and carbohydrates, which in turn provide the nutrients in the pelagic food web ecosystem used by the primary consumers, namely zooplankton and mesoplankton (Falkowski & Knoll, 2007)
Some of the metabolites produced by microalgae have biotechnological importance and, in recent years, microalgae have been exploited as potential sources for mass-scale production of feed, cosmetics and biofuel
This study aimed to explore the possibility of developing photophysiology-based measurements, Non-photochemical quenching (NPQ), as an early indicator of grazer infection of algal cultures and subsequent culture crash

Summary

Introduction

Microalgae are major primary producers in marine and freshwater environments. These organisms synthesize an array of biomolecules such as proteins, lipids and carbohydrates, which in turn provide the nutrients in the pelagic food web ecosystem used by the primary consumers, namely zooplankton and mesoplankton (Falkowski & Knoll, 2007). The nature of open-pond cultivation and the nutrient-rich properties of algal cells make the occurrence of invading microbes such as primary consumers an almost inevitable event (Carney et al, 2014). In high-rate algal ponds, seasonal variation in the density of grazer species, which resulted in a reduction of ~35–90% in algal productivity across a period of fourteen months, has been reported (Montemezzani, Duggan, Hogg, & Craggs, 2016). Often, invading grazers are a seasonal infestation and algal-grazer interactions are poorly characterized; the timely detection of invasion is important

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