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Turns out coral kids like pink bubblegum too!

Alexandra Ordonez Alvarez at Lizard Island_2021


Sharlene King
5 June 2023

A pink bubblegum-like seaweed that acts as reef cement is proving remarkably enticing for baby corals searching for a home, says a Southern Cross University coral expert.

With its flat, hard and colourful (pink, purple or yellow) structure more closely resembling coral than a leafy fleshy seaweed, these crustose coralline algae (CCA) bely expectations.

If corals are the bricks of the reef, then CCA are the mortar.

The rock-hard calcareous algae grow as a crust over and between the fragments and gaps in coral reefs, producing calcium carbonate in their skeletons and essentially cementing coral skeletons on the reef together.

Yet what’s most intriguing for Southern Cross University’s Coral Larval Restoration Team, led by Distinguished Professor Peter Harrison, is that many CCA species are irresistible to swimming coral larvae ready to establish a permanent home by metamorphosing into a single coral polyp on a suitable surface.

“CCA release specific chemical cues that coral larvae use to find suitable surface to settle and metamorphose.”

“CCA play a major role in coral larval settlement and post-settlement survival because they release specific chemical cues that coral larvae use to find suitable substrate (surface) to settle and metamorphose,” said CCA expert and Post Doctoral Researcher, Dr Alexandra Ordonez Alvarez.

“A number of coral species depend on CCA to settle and metamorphose, and therefore the absence of CCA on the reef could directly affect the rate of coral settlement and survival.

“However, not all species of CCA induce settlement and the community of CCA is variable depending on the habitat. Thus it is essential to understand the influence of different species of CCA that will promote post settlement survival and growth to improve restoration success.”

CCA coloured pink and orange at Lizard Island credit Alexandra Ordonez Alvarez
Pink and orange-coloured CCA (foreground) growing underneath branching coral at Lizard Island (credit Alexandra Ordonez Alvarez).

A major grant from the Paul G Allen Family Foundation is helping Dr Ordonez Alvarez pursue this research alongside Distinguished Professor Peter Harrison. One of the goals of Professor Peter Harrison’s project is to optimise coral reef restoration methods in the field, in locations like the Great Barrier Reef.

“With my CCA experiments, we aim to execute reef-based research that will allow us to expand our knowledge on the role of different CCAs and unlock key information to help us enhance coral recruitment and survival,” said Dr Ordonez Alvarez.

The 2022 coral spawning season on the Great Barrier Reef has seen Dr Ordonez Alvarez conduct CCA experiments at both the Whitsundays and on Lizard Island.

“The aim is to determine the ideal conditioning time of settlement devices (typically limestone tiles) in situ on the ocean floor to allow suitable CCA community development to enhance coral larvae settlement and survival,” said Dr Ordonez Alvarez.

Preliminary results show clear settlement preference for some species of CCA more than others. This is one of the first experiments carried out in situ and supports laboratory experiments completed by other scientists.

“The next step is to monitor post settlement survival that will help us determine which CCA species are more beneficial for coral survival,” said Dr Ordonez Alvarez.

White coloured coral settler next to pink coloured CCA credit Alexandra Ordonez Alvarez
A coral settler (centre of image) has established itself next to CCA (credit Alexandra Ordonez Alvarez).

An underwater delight

The Colombian national initially pursued coral research but pivoted after she was introduced to the world of CCA.

“I found them fascinating,” Dr Ordonez Alvarez said.

“Their ability to produce calcium carbonate skeletons make them important coral reef builders and cementers. They are commonly referred as ‘the glue of the reef’.

“Knowing CCA’s importance for coral reefs and corals and how little we know about their biology and ecology inspired me to study them. During my PhD I learned more about their taxonomy, biology and ecology and I was hoping one day I would be able to use this knowledge to help coral reef restoration programs. I feel honoured to be part of Professor Peter Harrison’s lab, to learn from him and his team and have the opportunity to deeply explore this relationship between corals and CCA.”

“It’s great to have Alexandra’s unique skills and expertise with CCA. I’m certain she will become a leading researcher in this important field.”

Working together to support the world's coral reef ecosystems

Dr Ordonez Alvarez joined the Coral Larval Restoration Team about 18 months ago and has quickly established herself as a leading member.

“It’s great to have Alexandra’s unique skills and expertise with CCA ecology and biology available to the coral larval restoration projects, and I’m certain she will become a leading researcher in this important field of research,” said Professor Harrison.

“She brings a wealth of knowledge and practical reef-based experience to the research and has been actively training and mentoring team members in the art of identifying and understanding the essential roles CCA play on coral reef ecosystems.”

For Dr Ordonez Alvarez, citing a well-known scientist’s work is one thing; being invited to work alongside them as a peer is an entirely different matter.

“I knew about Professor Harrison’s work for a long time and I cited his work numerous times. I truly enjoy working with him, I admire his work and the way he inspires people. He is really passionate about his work and after all of these years working on coral reproduction, he still gets very excited with every step of the process,” said Dr Ordonez Alvarez.

“Working on the Great Barrier Reef with Professor Harrison is a true honour and an amazing opportunity. Not only I get to see and explore such a beautiful and complex ecosystem, but I get to work with one of the most prestigious scientists in the field. 

Dr Ordonez Alvarez thanked the US philanthropic organisation Paul G Allen Family Foundation backing Professor Harrison’s coral larval restoration project, particularly to understand the crucial role CCA play in the first week or so of a coral polyp’s life.

“The Paul G Allen Family Foundation supports my CCA work through Peter’s project. It is a privilege to be supported by this Foundation which is interested in preserving and protecting the ocean. I am grateful that the Foundation sees the value of my research and with their support we will be able to improve our knowledge to save the reefs,” Dr Ordonez Alvarez said.

“My hope is that every action that we are taking right now to save the reefs will be seen in the near future, and that more people will become aware of the challenges that coral reefs are facing and join the efforts to save them.”

Two coral species growing on CCA at Lizard Island credit Alexandra Ordonez Alvarez
Two different coral colonies (centre) growing on CCA at Lizard Island (credit Alexandra Ordonez Alvarez).

Media contact

Sharlene King, Media Office at Southern Cross University +61 429 661 349 or [email protected]