A new model to help scientists understand the many influences on young corals finding a "forever home" on a reef has been developed by researchers from the Australian Institute of Marine Science (AIMS) and The University of Western Australia (UWA).
The model can help identify what type of local conditions might maximise restoration actions that use larvae seeding .
When corals reproduce, or spawn, tiny larvae drift around the reef. These coral larvae need to find a suitable reef surface to settle on and begin growing.
There are many factors influencing where they end up calling home: water movements or currents driven by waves and tides, the types of reef surface larvae prefer, and which types of reef habitats they encounter as they drift across the reef.
But deciphering how these processes interact and influence settlement remain largely unexplored because of the difficultly in observing and measuring the dispersal and settlement of tiny coral larvae in the wild.
Lead author on the study, AIMS@UWA PhD candidate Molly-Mae Baker said the model would help to address key gaps in scientific knowledge.
"There's still so much we don't know about how coral larvae settle and attach to a place where they will spend the rest of their lives," she said.
"So far, studies in controlled environments like aquariums have tended to focus on one factor at a time in relation to settlement and have not been able to fully consider how interactions between factors could be affecting where the larvae settle in the wild.
"Our model takes into account the interactions between three main factors - currents, the type of surface corals prefer like sand, rocks or coral rubble, and how these are all configured in the environment."
Unexpected patterns of settlement
The scientists tested the model with a variety of scenarios and found the interactions could lead to contrasting and unexpected patterns of coral larvae settlement, including conclusions regarding the surfaces larvae prefer for settlement.
"We would expect larvae to settle in the highest abundances on the surfaces they find most attractive on a reef," said Ms Baker.
"Instead, we found that different types of currents could sometimes influence coral larvae to settle on less attractive surfaces. The interactions between the factors also influenced the number of corals that were able to settle successfully. For example, settlement was generally lower in scenarios with no currents compared to the other hydrodynamic conditions we tested.
"What emerged was highly variable patterns of settlement."
The scientists also applied their model to a case study site on Ningaloo Reef off the Western Australian coast, finding that multiple factors could interact to produce unexpected patterns of settlement in these more complex natural environments.
The model will help scientists optimise their field-based sampling methods as well as identify what type of local conditions might maximise restoration success.
Co-author Dr Anna Cresswell, from AIMS, said understanding settlement processes across small scales is important for predicting population growth and ecosystem recovery from disturbance events.
"As pressure grows on coral reef systems from climate change and other natural and anthropogenic disturbances, there is a pressing need for models like this one to help us understand more precisely the many processes that underpin coral reef recovery," she said.
The paper was published in the journal Ecological Modelling: Modelling interactive effects of biological and environmental factors on fine-scale coral settlement patterns - ScienceDirect .
The research was supported by The University of Western Australia and the Australian Coral Reef Resilience Initiative (ACRRI), which is jointly funded by BHP and the Australian Institute of Marine Science.
