Feeding effect on reducing reactive oxygen species in the scleractinian coral <i>Galaxea fascicularis</i>

Reactive oxygen species (ROS) are thought to be involved in the mechanism of coral bleaching caused by high water temperature. Corals able to acquire nutriments through heterotrophy are more resilient to bleaching. However, the detailed mechanism for the alleviation of coral bleaching is not known. Here, we investigated the effects of feeding on ROS production in the coral Galaxea fascicularis to evaluate its potential as a mitigation technique of coral bleaching. The culture experiment was conducted with G. fascicularis in a 2×2 factorial design with and without food, ambient water temperature (27°C), and high water temperature (32°C). Artemia salina was used as a food source. The results showed that SOD enzyme activity in coral and zooxanthellae increased significantly at higher water temperatures and feeding led to a decrease of this activity. This indicates that feeding can reduce ROS production, especially in the host tissue, and potentially lessen cellular damage during heat stress. However, bleaching was not completely alleviated by feeding with reduced zooxanthellae density, chlorophyll-a and zooxanthellae protein contents observed under high water temperatures. Moreover the addition of food also led to lower calcification rates, regardless of temperature. These findings highlight the potential of using food addition as a mitigation technique of coral bleaching but this will require further investigation on the long term effects of feeding to better understand the limitations of the technique.