Highly conserved thermal performance strategies may limit adaptive potential in corals

Abstract

Increasing seawater temperatures are expected to have profound consequences for reef-building corals' physiology. Understanding how demography changes in response to chronic exposure to warming will help forecast how coral communities will respond to climate change. Here, we measure growth rates of coral fragments of four common species, while exposing them to temperatures ranging from 19°C to 31°C for one month to calibrate their thermal-performance curves (TPCs). Our results show that, while there are contrasting differences between species, the shape of the TPCs was remarkably consistent among individuals of the same species. The low variation in thermal sensitivity within species may imply a reduced capacity for rapid adaptive responses to future changes in thermal regimes. Additionally, interspecific differences in thermal responses show a negative relationship between maximum growth and thermal optima, contradicting expectations derived from the classic ‘warmer-is-better’ hypothesis. Among species, there was a trade-off between current and future growth, whereby most species perform well under current thermal regimes but are susceptible to future increases in temperature. Increases in water temperature with climate change are likely to reduce growth rates, further hampering future coral reef recovery rates and potentially altering community composition.

Trade-offs in a reef-building coral after six years of thermal acclimation

“…The observed response of skeletal growth was in agreement with the thermal optimum ranging between 27.5 -29.5 °C that is known for a range of coral taxa from the Great Barrier Reef (GBR) or the Caribbean (Álvarez-Noriega et al, 2023;Silbiger et al, 2019). For P. verrucosa from the GBR, for instance, optimal calcification temperature was 29.5 °C and severe declines in calcification capacity have been noted beyond this optimum, with up to ~30 % declines already under 31 °C (Álvarez-Noriega et al, 2023). A similar situation can be assumed for the corals in the present study, where calcification rates at 31 °C were 40 % lower compared to the ambient temperature conditions.…”

Pushing the limits: expanding the temperature tolerance of a coral photosymbiont through differing selection regimes

“…Five nonlinear regression models ( thomas_2012, thomas_2017 , joehnk_2008, lactin2_1995, kamykowski_1985 ) were selected based on their ability to account for negative growth rates and have been successfully applied in constructing TPCs with marine phytoplankton (Barton et al ., 2023). Other models (e.g., Gaussian, Beta) previously used to construct TPCs for Symbiodiniaceae (Dilernia et al ., 2023) and corals (Álvarez-Noriega et al ., 2023; Jurriaans & Hoogenboom, 2019) were considered but not used since they did not allow for the fitting of negative growth rates. Models were fitted to each lineage and incorporated a model weight corresponding to the standard deviation in µ max observed for each experimental evolution treatment at each growth temperature.…”

Thermal tolerance traits of individual corals are widely distributed across the Great Barrier Reef

“…Intraspecific variation in coral heat tolerance exists at local scales [23][24][25][26][27][28][29] and is an indicator of adaptive capacity and metapopulation persistence probability 30,31 . Populations with low intraspecific variation may suffer near extirpation at local scales 18,32,33 . On the contrary, high intraspecific variation in physiological traits can buffer populations against the loss of genetic and functional diversity 25 .…”

“…Intraspecific variation in coral heat tolerance exists at local scales (e.g., Cunning et al, 2016; Drury, Bean, et al, 2022; Drury, Marhoefer et al, 2021; Martin, et al, 2022; Jin et al, 2016; McWilliam et al, 2022; Sampayo et al, 2008) and is an indicator of adaptive capacity and metapopulation persistence probability (Holstein et al, 2022; Howells et al, 2022; Parkinson et al, 2015). Populations with low intraspecific variation may suffer near extirpation at local scales (Álvarez-Noriega et al, 2023; Hughes et al, 2018; Riegl et al, 2018). On the contrary, high intraspecific variation in physiological traits can buffer populations against the loss of genetic and functional diversity (McWilliam et al, 2022).…”