What chemical compound released by zooplankton feeding on phytoplankton signals a rich food source via smell?

Dimethyl sulphide (DMS)

The sense of smell, or olfaction, is suggested to be a far more crucial tool than sight for whale sharks locating productive feeding grounds across the open ocean. This capability is supported by their highly developed olfactory lobes in the brain. A key theory regarding prey detection centers on the release of dimethyl sulphide (DMS). This compound is a strong odor cue generated when zooplankton consume phytoplankton. The presence of DMS effectively signals to the shark that a dense, rich food source is located directly below them in the water column. Furthermore, surface feeding movements involving side-to-side scanning are hypothesized to be the shark using cues from both nostrils to maintain orientation within the densest part of the scent plume before the smell dissipates unevenly.