The Power of Plankton: One small descent for phytoplankton, one giant win for Earth’s carbon storage!

Plankton, even if often barely visible to the naked eye, can be seen from space when they form blooms, highlighting their importance in spite of their tiny size and the little significance we've historically given them. Schools of fish, cetaceans jumping over the surface, coral reefs… This is what the world visualizes when thinking about our vast oceans. But none would be possible without plankton, since they are both the primary food source for marine ecosystems while also playing a key role in the ocean's carbon cycle, regulating the Earth’s climate. But how does this happen?  

Phytoplankton are microscopic plant-like organisms that live in the sunlit part of the ocean. They generate half of the global primary production and are the main drivers of the biological carbon pump (BCP), through which they remove carbon dioxide from the atmosphere via photosynthesis and transform it into organic matter to build their cellular tissues. Zooplankton, drifting grazers of the sea, consume them. Some of the fecal pellets (zooplankton "poop"), as well as dead bodies of phytoplankton and of any other pelagic organisms, sink as detritus as part of "marine snow" to the dark cold waters where light doesn’t reach. Some of this organic material gets degraded along the way, leading to the release of CO₂, but a small portion settles into the deep ocean, where it can become part of marine sediments. This way, carbon dioxide is sequestered for hundreds or thousands of years in the deep ocean. However, even if phytoplankton protects us from even higher carbon dioxide levels in the atmosphere, global warming has begun to slow down this phytoplankton-driven pump. Scientific research is needed to find practical solutions to this issue.

A) Foraminifera; B) Tripos colony; C) Cymbulioidea, Pteropoda; D) Collodaria, Radiozoa, Rhizaria; E) Scina, Amphipoda; F) Cyclopoida (left) and Calanoida (right); G) Balanus nauplius larva, cf. Lepas; H) Calocalanus pavo; I) Cyclopoida, Copepoda; J) Planktonic foraminifera, Globorotaliidae; K) Sapphirina cf. metallina; L) Polychaeta cf. Vanadis; M) Diatom cf. Coscinodiscus; N) Polychaeta juvenile; L) Pteropoda. Photos by Marja Koski and Jana Piñel Rodríguez.

Calocalanus pavo would probably win the copepod beauty contest, but Sapphirina, with its characteristic guanine hexagonal platelets that make it shimmer like a blue jewel, doesn’t drift too far behind.

Take a look at a droplet of seawater and you will see an entire tiny world of small organisms… while this might be true for the smallest microbes, to look for the largest plankton we use plankton nets. This allows us to collect the organisms present in many liters of water (up to hundreds!) and concentrate them into a sort of bucket. The plankton soup is ready to be observed and fixed!

We call those buckets/jars cod-ends. The nets descend to their intended depth (down to 1000 m for this campaign!) and, one at a time, open and shut such that each net represents a separate portion of the water column. Once all nets reach the surface, they're thoroughly rinsed in a super scientific process: spraying them down with a hose. The material from each cod-end is filtered into a small bottle and then comes the saddest part: saying goodbye to the creatures we catch in the name of science and a better understanding of the ocean's carbon pump. We thank them for their service.