Investigating heat resistance in corals
Since 2013, the National Sea Simulator (SeaSim) has been a pivotal resource in advancing our understanding of coral heat resistance and the potential for human-assisted evolution to bolster coral resilience.
Assisted evolution involves accelerating naturally occurring evolutionary processes to help corals adapt to predicted future climate ocean scenarios, such as rising temperatures and ocean acidification.
SeaSim’s state-of-the-art facilities have enabled researchers to explore various assisted evolution strategies, including:
- heat stress preconditioning
- managed breeding
- hybridisation, and
- manipulation of the coral-microalgal symbiosis.
The research conducted at SeaSim highlights the potential of these innovative approaches. It also underscores the critical role that controlled, large-scale experimental systems play in developing strategies to protect and preserve coral reefs in the face of climate change.
Environmental stress preconditioning
Environmental stress preconditioning is a process where corals are exposed to sublethal stress to induce physiological changes that increase their tolerance to future stress events. SeaSim’s advanced capabilities allow for multi-generational, large-scale mesocosm studies on a variety of reef organisms, assessing their responses to current and future environmental conditions. These projects have examined the nature and extent of environmental preconditioning in corals, and whether this process can increase resilience of coral offspring to future ocean conditions.
Managed breeding
Managed breeding includes selective breeding within and between populations of the same species, as well as hybridisation between species. Within-population breeding aims to enhance thermal tolerance of the offspring and to increase the frequency of heat-adapted genotypes on the reef. Breeding between populations (a.k.a intraspecific hybridisation) looks to enhance the spread of naturally warm-adapted genes across the Great Barrier Reef to buffer populations on cooler reefs against warming and bleaching. The success of these approaches relies on pre-existing gene variants for local temperature adaptation and the parental transmission of temperature tolerance. SeaSim’s sophisticated, large-scale coral reproduction systems have been crucial in testing the feasibility, benefits, and risks of these approaches. In SeaSim researchers are interbreeding the most tolerant individuals from a reef, as well as corals from warmer far northern and cooler central Great Barrier Reef corals, creating multiple families of crosses from the different bioregions. The resultant families are exposed to temperature stresses in experimental systems to test whether offspring with at least one tolerant parent regions are more resilient to temperature under warmer conditions with no fitness disadvantage under cooler conditions. Growth, survival, and temperature tolerance of these offspring are tested across multiple life stages.
Interspecific hybridisation
Interspecific hybridisation, where eggs and sperm of two different species fertilise and produce viable offspring, is another process being investigated in SeaSim to enhance coral population resilience. This process, which occurs naturally, but is rare in nature, can increase genetic diversity and potentially create novel genetic combinations that are beneficial for adaptation. SeaSim has facilitated the spawning and hybridisation of multiple coral species, allowing researchers to grow these hybrids under predicted future ocean conditions and test for temperature resilience in hybrid offspring. To date, some hybrids have shown greater resilience to temperature stress compared to purebred corals, and ongoing research on second-generation hybrids will investigate if they retain these advantageous traits.
Modifications of algal symbiont communities
Corals rely on a symbiotic relationship with a diverse community of photosynthetic microalgae (Symbiodiniaceae), which can influence their susceptibility to bleaching. Researchers have successfully enhanced the heat tolerance of Symbiodiniaceae species by growing them ex-hospite over multiple generations at elevated temperatures in the AIMS Symbiont Culture Facility (SCF). When reintroduced into chemically bleached adult corals or early coral life stages that still lack symbionts, these modified symbionts have demonstrated an ability to maintain symbiosis long-term, promoting faster recovery from bleaching and enhancing heat tolerance without compromising coral growth.
Through its advanced facilities and capabilities, the SeaSim has enabled researchers to conduct extensive multi-generational studies on stress conditioning, managed breeding, and the modification of algal symbiont communities. These efforts have yielded significant insights into how corals can be adapted or conditioned to withstand future ocean conditions, how genetic diversity can be enhanced through hybridisation, and how symbionts can be modified to enhance coral heat tolerance.
