Coralline in climate change: understanding an overlooked but essential seaweed

Emma Jourdain (she/her) is a PhD Botany student. In 2023, Emma conducted a five-week experiment on Quadra Island with Hakai Marine Institute looking at the physiological and molecular responses of coralline algae to temperature and pH, thinking in terms of ocean warming and ocean acidification caused by climate change.

Emma describes coralline algae as an overlooked group of seaweeds that are essential across the world, but especially in BC where corallines are the hidden foundation behind kelp forests. Corallines are quite small, grow slowly, and calcify, meaning they deposit calcium carbonate creating hard structures. Ocean acidification wears away at calcium carbonate similar to how acidic drinks wear away at our teeth.

With her molecular background, Emma approached her study of these essential algae through a unique combination of physiological and molecular considerations. She thought beyond the physiological level to assess climate stress, also examining what happens at the molecular, or transcriptomic, level. Emma considered how genes respond to temperature and pH changes. There can be similarities between the physiological and the molecular data, but sometimes they can differ. By only relying on one, results can be misleading. By measuring both, Emma is able to reach a more comprehensive understanding of how corallines respond to climate stress.

She explains, “If there are certain genes involved with metabolism that get down-regulated in response to temperature, that’s another way of measuring stress which is very different than what you’re capturing if you’re only looking at growth or calcification data. There is also a whole cohort of genes that are stress response genes that may be upregulated in response to temperature and help the organism adapt to the change."

Emma encourages the importance of assessing the effects of climate change on multiple biological levels, saying, “Just looking at physiology isn’t enough. Doing this combined approach is the best way to get an integrative understanding of how a given organism is responding to a stressor.”

Beyond her work, Emma’s time on Quadra Island was meaningful through the chance to create genuine connections. She reflects, “I really appreciated and valued having a team not only to support me with the work, but also to always be there to discuss. In the end, we all became really good friends and Quadra Island is such an amazing spot.”

Another highlight was the chance to expand her data analysis experience by working with transcriptomics for the first time. It was challenging at first, and she had to go back to revise her data set a few times, but it resulted in gaining a new skill that enriches Emma’s research.

More recently, returning to Hakai Marine Institute, Emma expanded on her original work and added the consideration of coralline algae as habitats for other organisms. She describes, “They have been shown to induce settlement of different invertebrate larval stages.”

Certain invertebrates will settle on corallines more than other substrates, such as bare rock. How corallines induce settlement is unknown, but one key organism that depends on corallines is the sunflower sea star, an essential organism that is endangered in the Pacific Northwest and down the West Coast.

Emma shares, “In 2013, there was a disease that basically wiped out their population. There has been a lot of work to figure out what that disease was and to try to start bringing back their populations. I was thinking about how corallines are an important place for these larval sea stars to live, but what happens when they are stressed because of the climate stressors we were looking at?”

So, Emma’s corallines were stressed again, followed by an attempt to settle the sea star larvae onto them to see if their settlement was impacted by the corallines being stressed. This data is currently being analyzed.

“It’s really important to think of organisms in the greater ecosystem that they live in,” Emma says. “We care about our individual study species, but thinking about them in a bigger picture is important.”

Emma is also a Teaching Assistant and educator. In 2025, she co-designed and co-led a seaweed workshop on Quadra Island called “Wonders of Seaweed” for kayak guides and naturalists to help inform their guides. At UBC’s Martone Lab, she supports training undergraduate students, graduate students, and technicians in molecular and physiological methods.

Outside of her research and academics, Emma enjoys spending time outdoors. She has completed many of the big hikes in British Columbia and wishes to complete more.