Uncovering the obscure world of cold-water corals

Illustration of cold water coral mound
A cold water coral mound next to famous landmarks for size comparison, illustrated by Anna van der Kaaden

Most people have heard of tropical corals like Australia's Great Barrier Reef. But what about lesser-known cold water corals? We speak to Anna van der Kaaden, a PhD researcher at the Copernicus Institute of Sustainable Development and the Royal Netherlands Institute for Sea Research (NIOZ). She tells us about this essential ecosystem-supporting organism found in barren deep waters, how her research on the topic led to a side job making scientific animations, and why it's so important for science to reach a broader public.

Tropical coral reefs are home to a rich variety of fish and other organisms. Their iconic colouring is thanks to a close relationship with coloured algae, which through absorbing sunlight and carbon dioxide also provide energy to corals. But other kinds of corals exist as well. Anna van der Kaaden studies ‘cold-’ or ‘deep-water’ corals. “These are similar, but live in the deeper, cooler parts of the ocean where there is no sunlight,” she explains. “This means that cold-water corals do not live with algae—they must obtain their food in other ways and are not as brightly coloured as tropical corals”.

Oases in the desert

Just like their tropical counterparts, cold-water corals form extensive reefs that attract many different organisms. “But because the deep-sea is quite bare these reefs are very important, maybe even more important than reefs in shallow waters,” she says. The deep-sea has no sunlight, so most energy comes from the ocean surface in the form of sinking organic matter—dead algae and other organisms. The journey from ocean surface to the deep-sea is a very long one, typically several hundreds of meters or even kilometres. On the way, organic matter gets eaten by organisms in the water column or degraded by microbes. Little nutrition reaches the seafloor, which is why it is sometimes called the ‘deep-sea desert’. “Teeming with fish and other forms of life, cold-water coral reefs are oases in this desert,” explains van der Kaaden.

Teeming with fish and other forms of life, cold-water coral reefs are oases in this desert

So why do we study these cold-water coral reefs? Although found in the deepest parts of the ocean, cold-water corals are not immune to Anthropogenic pressures. Fishing equipment drags over the seafloor, breaking down the 3D structure of the reefs that is needed to maintain a healthy food web. Another issue is deep-sea mining of rare minerals and metals, which is only getting worse as demand increases.

Little known about cold water corals

 “We know we don’t want to lose them, but still don’t know much about them: their main food source, how they grow, how they react to changes in temperature or ocean acidification, when, why and how the corals spawn and where their larvae end up,” she explains.

The starting idea for van der Kaaden’s PhD was to build a model for cold-water coral growth, similar to models of the self-organisation of arid vegetation, mussels, and algae. “When I started to gather knowledge on the growth of cold-water corals, I realised it was all very case-specific and hard to generalize. But after a frustrating first year and with the help of many amazing colleagues, I published a few papers that, for the first time touch upon the general process of cold-water coral reef growth. It is a very nice example of how you can bring some new perspectives into a topic from a different background and of how working truly interdisciplinary can take research a step further”.

Photo of Anna van der Kaaden with her father's art
Anna van der Kaaden with a ‘pattern’-piece made by her father: Light on surface III (1998).

How local interactions between tiny things can bring about large-scale patterns has always interested Van der Kaaden. “And I don’t only mean organisms and their environment”. Her dad is an artist and uses this principle to make art. “When I was eight years old, he exhibited a piece in a school that arranged little pieces of painter’s tape with folded corners on a wall to create an amazing pattern. During the day, the kids would tug on the tape and I loved seeing how the patterns changed as the kids interacted with it. When I learned about self-organization in nature during my BSc, I was sold”.

Making knowledge broadly available

Van der Kaaden’s work on corals also got her into science communication. It started with a competition within NIOZ, where PhDs were asked to make a video about their research. “The examples they gave were mostly people recording themselves while doing fieldwork. My work is theoretical, so I didn’t think much of it,” she explains. This was until a bad allergic reaction led her to a YouTube channel explaining the different types of reaction with animations. “This gave me inspiration to make an animation about my PhD. It was only a week before the deadline and I drew everything by hand on an iPad, stitched it together in very basic video-software and won the competition”. Before long, colleagues began to hire her to make animations for their research.

Restoring trust in science

She also thinks better communication will make it easier for non-scientists to trust science. “As society, we’re moving towards an era where everyone has their own individual truth. Opinions are presented as facts or people boldly state ‘truths’ that have never been investigated. We can avoid this by being more transparent and by telling our personal stories: we are people gathering knowledge from research”. 

So what’s next? “I want to make a podcast where researchers talk about their research from a very personal perspective. I’ve tried it out with my supervisor Max Rietkerk (listen here), and when time allows might do more. But there are so many other ideas, so who knows!”

Further reading

van der Kaaden A-S, van Oevelen D, Rietkerk M, Soetaert K and van de Koppel J (2020). Spatial Self-Organization as a New Perspective on Cold-Water Coral Mound Development. Frontiers in Marine Science 7:631.

van der Kaaden A-S, Mohn C, Gerkema T, Maier S R, de Froe E, van de Koppel J, Rietkerk M, Soetaert K, van Oevelen D (2021). Feedbacks Between Hydrodynamics and Cold-Water Coral Mound Development. Deep-Sea Research Part I 178.