FTIR combined with chemometric tools — a potential approach for early screening of grazers in microalgal cultures

Microalgal predation is one of the imminent threats for mass algae cultivation in open ponds. Invasion of predators results in total clearance of algal biomass within 24–48 h. Detection of contamination in microalgal cultures using online spectroscopy has attracted considerable interest among researchers. Currently reported spectral markers such as hyperspectral and multispectral tools, using visible wavelengths of light, mainly detect changes in the pigment composition or degradation associated with contaminants, especially predators. Unlike monitoring of pigment composition, our work leverages the species-discriminatory potential of Fourier transform infrared (FTIR) spectroscopy in combination with chemometric tools for detection of predators. Here we report FTIR-based signature features, at 1346, 1363, and 1382 cm⁻¹, for detection of Oxyrrhis marina–mediated grazing in cultures of Dunaliella tertiolecta. Based on a partial least square regression (PLSR) model (R² = 0.894), the signature spectra can indicate the presence of O. marina at a concentration of 5 × 10² cells mL⁻¹ and at least 72 h prior to the culture crash. As opposed to offline grazer monitoring tools, the potential for FTIR-based flow-through design in combination with multivariate methods could enable real-time and non invasive means of early detection of algal grazers.