Artificial selection of coral larval heat tolerance to support coral restoration (RRAP ECT 2.1)

Updated: 2026-05-22

Testing of coral thermal tolerance under simulations of stress events is essential for determining the efficacy of artificial selection as a viable tool for large-scale coral restoration. While aquariums provide controlled environments that can isolate specific variables, such as temperature, they cannot account for the complex ecological variables and interactions which naturally occur on reefs (e.g., competition, predation, environmental fluctuations, etc.). Field testing of artificially selected coral offspring is therefore essential to understanding various trait and environmental trade-offs that can influence coral performance post intervention. Here we phenotyped (rapid heat stress test; following Naugle et al. 2024 and Denis et al. 2024) and bred Acropora spathulata colonies then imposed a thermal stress test on their larvae to define whether artificial selection: (1) induced a genetic bottle neck in coral larval cultures and (2) impacted the performance of coral recruits in a field-based coral seeding experiment. Gravid colonies (N = 5) were collected (hammer and chisel) on October 2023 from Davies Reef in Bindal Sea Country (S18.81958°, E147.63129°; GBRMPA permit G21/38062.1) where they were brought onboard an AIMS research vessel for their heat stress test then transported to the AIMS National Sea Simulator facility for coral spawning. For days post gamete fertilisation, the developed coral larvae were artificially imposed to a thermal stress event with three treatment groups: Ambient (27 degrees C), Sub-lethal (33 degrees C), and lethal Selection (35 degrees C). The temperature treatments were held until > 50% mortality was reached in the Selection treatment. The surviving larvae from each treatment were settled for the field deployment. Coral larvae were settled onto preconditioned (i.e., early successional mixed crustose algal and bacteria biofilms) concrete settlement tiles (~ 200 mm X 200 mm). The tiles yield 400 individual tabs that are compatible with coral seeding devices being tested and developed by the Coral Aquaculture and Deployments team in the Reef Restoration and Adaption Program at AIMS (Whitman et al. 2025; Jurriaans et al. 2025; Page et al. 2025; Ramsby et al. 2026). During settlement, an inoculate of Symbiodiniaceae algae (~ 1 X 104 cells mL-1 of C1 radiation, SCF 049.01, cultured in the AIMS Symbiont Culture Facility) was added to the tank for coral uptake. 162 coral seeding devices with live corals were deployed to Davies Reef. A single device contained slots for three tabs, one tab from each of the treatment groups (Ambient, Sub-lethal, Selection). At the deployment, devices were linked in a chain of six devices then hand-delivered to three plots on the reef by divers. Each site (N=9) contained three device plots, three device chains, and 18 devices in total. Three sites from the back reef (5-9 m depth), lagoon (2-5 m), and reef flank (5-7 m) were selected.