Symbiodiniaceae probiotics for use in bleaching recovery

Abstract

Coral reefs are currently under threat as a consequence of local and global stressors, in particular, mass coral bleaching induced by climate warming. In conjunction with global cuts to carbon emissions, active restoration interventions are being investigated as an additional option to buy time while these stressors are mitigated. One intervention with the potential to improve recovery during or postbleaching involves the addition of probiotic treatments, that is the addition of microorganisms that provide benefits to the host. Fragments of the branching coral, Acropora millepora, were experimentally exposed to a bleaching event coupled with the inoculation of Symbiodiniaceae probiotics (Durusdinium trenchii and Cladocopium goreaui) to determine if these probiotic treatments could ameliorate bleaching related stress and mortality. Fragments inoculated with C. goreaui and exposed to 32°C for 6 days exhibited significantly less mortality (9.1 ± 5%) compared to corals exposed to 32°C without probiotics (66.7 ± 8%) or with D. trenchii (41.7 ± 9%). Fragments in the C. goreaui probiotic treatment also bleached less and exhibited the highest photosynthetic efficiency compared to fragments inoculated with the D. trenchii at 32°C. Internal transcribed spacer‐2 amplicon sequencing did not detect the inoculated D. trenchii and C. goreaui cells within A. millepora tissues at the end of the experiment, suggesting the corals did not reestablish symbiosis but instead used inoculated cells as a nutritional supplement, although other factors such as shuffling conditions may have had an effect. This study highlights that nutritional supplementation can possibly aid coral resilience to temperature stress, though a far more detailed understanding of the factors that influence host regulation during symbiosis establishment is required.