A quick and reliable menthol-induced bleaching protocol for the Caribbean staghorn coral, <i>Acropora cervicornis</i>

Corals and dinoflagellate algae form a unique mutualistic symbiosis that provides the energetic and structural foundation for shallow coral reef ecosystems. Despite the long success of this partnership in oligotrophic seas, coral reefs are in decline due to increasing threats from rising seawater temperatures and disease, both of which can lead to bleaching and mortality. In order to better understand the mechanisms that underpin this mutualism, it may be necessary to dismantle the coral-algal symbiosis. Previous studies have experimentally bleached corals using thermal stress, photosynthetic inhibitors (DCMU), and menthol. We compared lab-induced bleaching of staghorn coral <i>Acropora cervicornis</i> by menthol treatment to traditional thermal stress. The larger aim was to adapt existing bleaching protocols for this important coral species, providing a guide for future studies. Bleaching in corals treated with menthol or exposed to elevated temperature stress (31°C) was monitored by measuring photosynthetic activity determined by Fv/Fm using pulse-amplitude modulated (PAM) fluorescence and compared to untreated conspecifics. Corals were also monitored for symbiont density and overall health using the CoralWatch Coral Health Chart card throughout the experiment. We found that <i>A. cervicornis</i> bleached in response to both menthol treatment and thermal stress, but menthol treatment was more effective at reducing algal symbiont photosynthetic capacity (Fv/Fm) without negatively affecting the health of the coral. Our results indicate that menthol treatment at 0.38 mM rendered staghorn coral aposymbiotic within fourteen days without any visual or physiological damage to the coral. This study provides a simple and effective menthol-bleaching treatment protocol for future studies on staghorn coral.