Division of labour on a microscopic scale

First author Dr Vera Nikitashina and Dr Georg Pohnert, Professor of Analytical Chemistry at Friedrich Schiller University Jena, collected fresh colonies directly from the open ocean and used stable-isotope tracing to reveal the exact exchange of substances between host and algae. This method allows to track the incorporation of supplied labelled compounds into the metabolism of the holobiont, revealing which pathways are active. The labelling experiments were conducted on-site at the Mediterranean Sea, while the detailed chemical analyses were performed later in the laboratory in Jena.

»It is fascinating to see how precisely this biological partnership is organized,« says Georg Pohnert. »In these regions of the ocean, the nutrients are very scarce, and for organisms that cannot photosynthesize, survival is very challenging. Yet Collodaria that are dependent on nutrients from their environment are highly abundant. Now we can understand how they overcome limited nutrition—they rely on their microscopic photosynthetic partners to do the work.«

»For the first time, we were able to identify the nature of the chemical compounds exchanged between the partners,« he adds. »The algae provide sugars produced through photosynthesis, and the host acquires protective compounds from the surrounding water. This highly efficient division of labour on a microscopic scale is the key to why these organisms can thrive even in the most nutrient-poor regions of the ocean.«

Important building block for modern climate research

The discovery provides an important building block for modern climate research and has significant implications for global environmental protection management. Because these tiny organisms are so widespread and play a crucial role in global biogeochemical cycles, the new data will enable scientists to predict much more accurately how marine plankton responds to climate change.

»Our results fundamentally refine our understanding of marine food webs,« emphasizes Vera Nikitashina. »With this knowledge, we can significantly improve ecological models of marine productivity and carbon storage. This will help us better understand and predict the direct impacts of anthropogenic activities on marine ecosystems.«