Physiology, niche characteristics and extreme events: Current and future habitat suitability of a rhodolith-forming species in the Southwestern Atlantic.

ABSTRACT

Given the ecological and biogeochemical importance of rhodolith beds, it is necessary to investigate how future environmental conditions will affect these organisms. We investigated the impacts of increased nutrient concentrations, acidification, and marine heatwaves on the performance of the rhodolith-forming species Lithothamnion crispatum in a short-term experiment, including the recovery of individuals after stressor removal. Furthermore, we developed an ecological niche model to establish which environmental conditions determine its current distribution along the Brazilian coast and to project responses to future climate scenarios. Although L. crispatum suffered a reduction in photosynthetic performance when exposed to stressors, they returned to pre-experiment values following the return of individuals to control conditions. The model showed that the most important variables in explaining the current distribution of L. crispatum on the Brazilian coast were maximum nitrate and temperature. In future ocean conditions, the model predicted a range expansion of habitat suitability for this species of approximately 58.5% under RCP 8.5. Physiological responses to experimental future environmental conditions corroborated model predictions of the expansion of this species' habitat suitability in the future. This study, therefore, demonstrates the benefits of applying combined approaches to examine potential species responses to climate-change drivers from multiple angles.