Abstract
Detritivorous sea cucumbers are important processors of reef sediments and have been hypothesized to enhance coral growth by altering local nutrient availability and seawater chemistry, but whether these effects translate into improved coral performance remains untested. We conducted two analogous field experiments in Mo’orea, French Polynesia, to test whether the sea cucumber Holothuria atra enhances coral growth or photosynthetic efficiency. In the first experiment, we enclosed Acropora pulchra with zero versus two sea cucumbers per 0.25 m 2 , approximating natural densities at our site, and found no detectable effect of sea cucumber presence on growth. In 2025, using densities of four per 0.25 m 2 and enclosing three coral species, A. pulchra growth was 41% greater and Pocillopora verrucosa growth was 17% greater in cages with versus without sea cucumbers. The photosynthetic efficiency of Pocillopora verrucosa was also increased, but that of A. pulchra was not. Porites rus showed no significant response for either metric. Thus, sea cucumbers can enhance coral growth and photophysiological performance under field conditions, but these benefits vary across species, response variables, and apparently sea cucumber density. As sea cucumbers have been widely depleted from tropical reefs, identifying the mechanisms and density thresholds governing these effects will be important for understanding the ecological consequences of their loss and their potential role in supporting coral reef stability or recovery.