| Congresso Brasileiro de Microbiologia 2023 | Resumo: 401-2 | ||||
Resumo:Reef corals have been threatened by climate change, with more frequent and intense bleaching events leading to extensive coral mortality and loss of coral cover worldwide. In the face of this, the corals’ photosymbiont assemblages have received particular attention as a key to understanding the bleaching process and its recovery better. To assess the effects of thermal anomalies, the scleractinian coral Mussismilia harttii and the hydrocoral Millepora alcicornis were monitored through the El Niño 2015/2016 at a Southwestern Atlantic (SWA) coral reef. Tissue samples from these species were collected to identify changes in photosymbiotic assemblages over time through metabarcoding via next-generation sequencing of the ITS2 rDNA region. A severe bleaching event (57% of colonies bleached) was documented, triggered by a < 3 ºC-week heatwave, but no mortality was detected. The hydrocoral was more susceptible than the scleractinian, displaying bleaching symptoms earlier and experiencing a longer and more intense bleaching event. The composition of photosymbionts in the M. alcicornis population was affected only at the rare biosphere level (< 5% relative abundance), with the emergence of new symbionts after bleaching, especially Breviolum phylotype B43. Conversely, a temporary dysbiosis was observed in the M. harttii population, with one of the dominant symbiodiniaceans (Symbiodinium phylotype A4 and Cladocopium phylotype C3) decreasing in relative abundance at the peak of the bleaching, which negatively affected the total beta diversity. After colonies' complete recovery, symbiodiniaceans' dominances returned to normal levels in both hosts. These results highlight critical differences in how the two coral species cope with bleaching in the Southwestern Atlantic (SWA) with no mortality records. The factors contributing to holobionts’ survival are still poorly understood. However, they could be attributed to the host mechanisms of oxidative stress mitigation and feed mode balancing, but also to adjustments in photosymbiont assemblages composition during and after bleaching or all this together. Even subtle changes in photosymbiont composition, such as the documented dysbiosis, may contribute to the acclimatization of the holobiont. These findings contribute to the understanding of the role of photosymbionts throughout the bleaching–recovery process and follow the observed resilience of Brazilian coral reefs to bleaching. However, the recently documented vulnerability of those species, mainly M. alcicornis, to more severe heat anomalies, reinforces the urgent need for monitoring programs and research focused on SWA corals to determine priorities for coral reef conservation and management. Palavras-chave: coral bleaching, global climate change, Symbiodiniaceae, thermal anomalies, zooxanthellae Agência de fomento:Coral Vivo Project and its sponsors Petrobras, through the Petrobras Environmental Program, and Arraial d’Ajuda Eco Parque | |||||