Facultative autotrophy as a resilience trait in Brazilian corals

• Grant number: 25/06423-8
• Support Opportunities: Scholarships in Brazil - Master
• Start date: June 01, 2025
• End date: January 31, 2027
• Field of knowledge: Biological Sciences - Ecology - Ecosystems Ecology
• Principal Investigator: Miguel Mies
• Grantee: Mariana Ferreira Acipreste
• Host Institution: Instituto Oceanográfico (IO). Universidade de São Paulo (USP). São Paulo , SP, Brazil
• Associated research grant: 23/09180-3 - The historical global impacts of climate change on coral reefs: the role of refugia and key oceanographical and functional traits, AP.JP

Abstract

The resilience of a reef environment is largely linked to the biological traits of its coral community. Several functional traits such as bathymetric plasticity, turbidity adaptation and robust morphology can contribute to resilience by making corals less susceptible to stress. Another trait that plays a critical role in sustaining stressed coral communities is their heterotrophic capacity. Corals are mixotrophic organisms because they function as both autotrophs (due to their symbiotic association with Symbiodiniaceae dinoflagellates) and heterotrophs. The latter is performed via the capture of suspended plankton and organic matter. Heterotrophy has been widely demonstrated as a compensatory mechanism to bleaching because the carbon deficit produced by the symbiont loss may be replenished by heterotrophic feeding.The heterotrophic capacity of Brazilian corals has only recently been investigated. However, it has been shown that coral species within the Mussismilia genus, endemic to Brazil, are intense zooplanktivores. When subjected to thermal stress, metal contamination, and reduced light availability, these corals widely demonstrated their trophic plasticity by actively feeding and thus compensating for the reduced photosynthetic contribution of their symbionts. Furthermore, Mussismilia spp. are currently the only known corals capable of spawning while completely bleached, and this ability is believed to be linked to their increased heterotrophic input.During the 2019 bleaching event, which was the most severe on record for Brazil, multiple colonies of Mussismilia braziliensis, M. harttii, and M. hispida at Recife de Fora (Bahia State) remained fully bleached (i.e., pale white, with minimal presence of dinoflagellate symbionts) for an exceptionally long period of 10-13 months. Despite this, the colonies not only managed to survive but appeared to be healthy. This has led to the insight that some Brazilian coral species may be facultative autotrophs and occasionally function as strict heterotrophs. Such possibility, however, remains untested. Conducting this investigation is significant for many reasons. If Mussismilia spp. are indeed facultative autotrophs, capable of surviving without the nutritional input from their symbionts as long as they have access to food, it would be an unprecedented discovery. Second, this finding could change our understanding of their response to climate change, as well as that of Brazilian reefs, given their role as primary reef-builders. Lastly, such a discovery could have far-reaching implications for various other initiatives, including coral reef restoration practices as methods for enhancing heterotrophic behavior could be applied.