Corals depend on microbes for their survival and are well known for their relationship with photosynthetic single-celled algae. These microalgae provide food for the corals in return for shelter and essential nutrients, making a symbiotic, or mutually beneficial, relationship.
Studies have shown that the types of micro-algal symbionts (Symbiodiniaceae) in the partnership affect the corals’ physiology; some help corals to grow quickly while others improve corals’ tolerance to warmer and extreme temperatures. This relationship is very delicate and in prolonged periods of high temperature and strong light, the micro-algae can be lost, and coral bleaching occurs. This can lead to mass colony mortalities.
Recent pioneering research at AIMS has demonstrated that micro-algal symbionts selectively cultured at elevated temperatures can transfer some heat tolerance to one coral species. Expanding the range of species that may benefit from this, as well as optimising methods to get these symbionts into corals needs more research.
In 2021, we tested different inoculation densities of four different types of cultured symbionts and identified the minimum density required for effective uptake in the larvae and early settled stages of four coral species across 2 coral families. The juveniles of two of these species were grown for up to 6 months to assess the fitness of the different coral x symbiont combinations.
In 2022, we used the optimal symbiont densities found in 2021, and using the same four symbiont types, we upscaled the uptake of symbionts from the scale of millilitres (10 to hundreds of larvae – experimental scale) to litres (10s of thousands of larvae – applied scale). These juveniles were also monitored for growth and survival for two months and then subjected to a heat stress experiment to examine the performance of different coral x symbiont pairings.
In 2023, we will further optimise the inoculation procedure by assessing the effects of inoculation frequency (i.e. number of inoculation events) on uptake.
This work will collectively provide valuable data on the impacts of selectively cultured symbionts on the fitness of multiple coral species during early life stages and inform methods for optimising the uptake of these symbionts by young corals. This knowledge is important to maximise success of planned upscaled coral aquaculture and restoration endeavours to re-seed degraded coral reefs.
Feature image credit: Katarina Damjanovic
