Effects of chemical cues on feeding and foraging behavior in the sea urchin Mesocentrotus nudus.

Overgrazing by sea urchins is a primary driver of kelp forest degradation, leading to "urchin barrens" characterized by diminished biodiversity and productivity. While behavior-based management using chemical cues shows promise, the development and systematic evaluation of novel repellents for Mesocentrotus nudus remain limited. We investigated the behavioral responses of sea urchins to chemical cues from coffee waste (CW) and starfish (SF) through a series of four stepwise experiments including attraction, feeding-suppression, repellence, and barrier tests. In the attraction test, sea urchins exhibited robust foraging activity toward sea mustard (SM), whereas CW and SF elicited no attractive response. In the feeding-suppression test, methanol extracts of both CW and SF significantly reduced the grazed area on Avicel plates when combined with SM extract, with CW demonstrating superior suppressive effects. In the repellence test, seawater extracts of both substances induced rapid escape responses in actively feeding sea urchins; notably, CW elicited more consistent and complete avoidance behavior. Finally, in the barrier test, both substances effectively deterred sea urchins from reaching SM, showing comparable efficacy. These results demonstrate that CW and SF function as potential chemical repellents across diverse behavioral contexts under laboratory conditions. In particular, CW, an abundant industrial byproduct, represents a promising candidate for further practical evaluation in marine forest restoration. These findings highlight the potential of behavioral control via chemical cues as a noninvasive, scalable strategy for the spatial regulation of sea urchins in marine ecosystems.