A perspective on the current status of approaches for early detection of microalgal grazing

Consumption of microalgae, as prey, by predatory zooplankton is a major ecological process in aquatic environments. The presence of predators in large-scale cultivation, such as in open ponds, results in a devastating loss of microalgal biomass, often referred to as a “pond crash.” Reported biomass losses of 20–30% due to predator invasion in open cultivation systems is one of the bottlenecks in achieving a desired economically viable system. Many commercial scale algal cultivation setups have reported clearance of prey within 2–5 days after detection of predators. Knowledge of how to monitor and manage algal pests is limited. Research to date is largely driven towards the development of predator mitigation strategies, whereas monitoring is mainly limited to traditional (direct) methods such as microscopy- and oligonucleotide-based screening. Use of online and real-time measures for in situ estimation of microalgal grazing is sparsely reported. We suggest that more knowledge about microalgal grazing at the pond level is required for the development of indirect screening measures, based on unique features of microalgal prey and predator interactions, to enable online monitoring. This article systematically reviews the current status of available methods, both at laboratory and field level, for early detection of microalgal grazing.