We know you don’t know, ...what rhodoliths are

In this episode of the Spotlight series by the EURO MARINE, Dr. Prof. J?ao Silva, lead researcher of the RHODOCAR project and Scientific Advisor at Blusink, discusses the unknown potential of rhodoliths as carbon sink builders.

Likely less than 1% of the people reading this article will have heard about rhodolith beds, and even fewer could explain what they are or why they matter. In fact, despite their undeniable role in building ocean carbon sinks, less than 2% of all marine research focuses on them, leaving their immense potential largely untapped.

This article is here to help. Picture this: small, round stones, no bigger than your fist, scattered across the seafloor. But these aren’t just ordinary stones—they’re rhodoliths, living rocks made from solidified CO? turned into hard, colorful shells of pink, purple, and red. As they cluster together, these rhodoliths form vast seabeds that act like enormous carbon sinks, locking away carbon and helping to keep the ocean’s balance in check.

One of the most significant efforts in studying and quantifying the carbon capture impact of rhodolith beds is the EU-funded RHODOCAR project. With a budget of €147,815.04, this project monitored these ecosystems over three years and was designed to operate on a wide geographical scale, including rhodolith beds from different latitudes. It combined laboratory work, multi-factorial mesocosm experiments, and in situ studies, thereby covering a wide range of complexity—from the cellular level to entire communities.

Some of the key points to highlight from this podcast interview,

Uniqueness of rhodoliths when compared to other marine algae

Rhodoliths are unattached calcareous nodules that form hard, mineralized seabeds. The term "calcareous" is what differentiates them from other marine algae and plants. "They form calcareous structures by depositing calcium carbonate in the space between the cells and in some cases within the cells." This means that they create a hard structure, similar to a rock. What is even more impressive is that if you take one of these living pink rocks and weigh them, 95% of their weight is calcium carbonate and hence, last for more than a hundred years on the seabed, pilling up upon each other.

These calcareous nodules have minimal living requirements and are cryptic in abundance. They are widespread in marine ecosystems but can be difficult to detect, often appearing as mere pink rocks to the untrained eye. Because of this, experts, including Dr. Prof. Silva, have concluded that the actual abundance of these carbonate nodules is much greater than previously documented—by an order of magnitude.

The science of identifying carbon sinks focuses on the carbon budget, not just a one-way reaction

Accurate carbon capture quantification goes beyond a simple one-way reaction; it relies on the carbon budget, which is the combined effect of three key processes—photosynthesis, respiration, and calcification. This balance determines whether the seabed acts as a carbon sink or source. While photosynthesis absorbs CO?, both respiration and calcification release it—but not at the same rate. Given the expected vast biomass of rhodoliths and their rapid growth, they have the potential to remove significant volumes of carbon from the atmosphere. Research shows that most rhodolith beds act as long-term carbon sinks, with clear processes tipping the balance toward carbon removal on the seafloor.

A little hint from us: technological innovation can give the ocean floor that final push!

Cascading effect of Rhodoliths

Experts conclude that regardless of the latitude at which rhodoliths are found, they have a consistent positive impact on biodiversity. This means that, in addition to removing CO?, rhodoliths enhance biodiversity by supporting the development and growth of other organisms. As Dr. Prof. Silva explains, "When a rhodolith bed is present, biodiversity significantly increases because many organisms take advantage of the three-dimensional structure and complex morphology of rhodoliths for nesting, shelter, and as a food source."

Here are our key takeaways about rhodolith and Blusink beds:

• They aren't composed of a single species of algae. Instead, rhodoliths are formed by bundles of mineral nodules, multiple species of calcareous red algae, and other organisms that collectively create their structure.
• They aren’t made of fleshy algae; their structure primarily consists of calcium carbonate (CaCO?), which gives them a rigid, stone-like form that contributes to the permanence of the carbon sink.

What we hope you’ll remember: these seafloor systems are humanity's biggest, most scalable way to leverage the ocean's carbon cycle and have a measurable impact on biodiversity. Is there anything they can’t do?

We envision turning seafloors around the globe into carbon capture and storage powerhouses.

Dive deeper into ocean carbon capture at blusink.com

The Blusink team