Copepodamides: Widespread N-Acyl Taurine Alarm Cues in Marine Plankton

Copepodamides are N-acyl taurines isolated from copepods─the most abundant zooplankton on Earth and the main link between phytoplankton primary production and higher trophic levels. They act as interspecific alarm cues in marine plankton, as prey cells sensing copepodamides respond by launching defensive traits including toxin production, bioluminescence, and morphological changes to reduce predation risk, contributing to large-scale processes such as harmful algal bloom (HAB) formation. Here, we summarize research on copepodamides since their discovery in 2015 and outline current challenges and future opportunities. To date, 41 copepodamides have been identified from marine and freshwater copepods, and 21 marine protist taxa─including several abundant HAB-forming species─have been shown to respond to these cues. In situ measurements of copepodamides have been proposed to improve precision and lead time in HAB forecasting models, and their potential to increase yields of natural products in bioreactors warrants further investigation. Copepodamides provide a powerful framework for quantifying the costs and benefits of inducible defenses in phytoplankton. The widespread occurrence of copepodamides across aquatic habitats highlights the relevance of copepodamide signaling in HAB dynamics and marine food web interactions.