Highly conserved thermal performance strategies may limit adaptive potential in corals

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 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..., We collected nine colonies of four common reef-building coral species (Acropora hyacinthus, Acropora tenuis, Pocillopora verrucosa, and Stylophora pistillata) to investigate temperature-growth relationships. The colonies were collected at Kelso Reef (-18.445˚, 146.993˚) in the Great Barrier Reef in March 2021 at depths between 2 and 8 m and subsequently transported to the National Sea Simulator (SeaSim) in the Australian Institute of Marine Science. From each colony, we obtained 10 fragments and pasted those fragments on aragonite plugs. One fragment per colony was allocated to each of 10 temperature treatments (19, 21, 23, 25, 26, 27, 28, 29, 30, and 31˚C) and allocated to a 50L experimental tank. Each temperature treatment had three replicate tanks, and all tanks had identical flow rates (0.8 L min-1), light intensities (cumulative daily light integrals were 6.48 mol photons m-2 d-1), and feeding regimes (2x106 cells L-1d-1of microalgae and 0.06 Artemia nauplii L-1d-1).
The fragments ...,