Images of the phytoplankton Trichodesmium taken by chief scientist trainee Eric Orenstein using the Scripps Plankton Camera developed by the Jaffe lab at Scripps Institution of Oceanography.
When I was kid I couldn’t read Judi Barrett’s book, Cloudy with a Chance of Meatballs, often enough. In the book all sorts of wild and sometimes delicious food came down from the sky. I just loved to imagine living in a world where my favorite foods magically rained down from above. Sadly though, a world like that is just too good to be true. Or is it?
In the ocean an important group of organisms, called phytoplankton, use the energy from sunlight to convert carbon dioxide from the atmosphere into sugars. Although it’s not magic, some might argue that the complex physiology required to perform photosynthesis is even more impressive! Phytoplankton then use these sugars to divide and grow, providing food to marine organisms and forming the basis of many marine food webs. As small organisms, called zooplankton, feed on phytoplankton they produce waste rich in carbon as well as other elements like nitrogen and phosphorus. This waste then sinks down into the dark ocean, moving important nutrients out of surface waters and providing food for bacteria. Phytoplankton can also die and aggregate, these sinking aggregates also move important elements out of the surface waters. These processes are integral the cycling of nutrients and carbon in the marine environment.
Different phytoplankton are found in different parts of the ocean depending on a variety of factors including nutrient and light availability as well as temperature. Here at station ALOHA one group of important primary producers are cyanobacteria [1, 2]. Cyanobacteria can be microscopic, free floating cells, such as Prochlorococcus, or long filaments of cells easily seen by the eye, such as Trichodesmium. Trichodesmium and some other cyanobacteria genera can perform the relatively unique task of nitrogen fixation, the conversion of nitrogen from the air into biologically available nitrogen compounds. This is especially important at station ALOHA where nitrogen concentrations are low. Some cyanobacteria are even specialized to live inside of species from another group of phytoplankton, diatoms. Diatoms containing these nitrogen fixers benefit from having an intracellular nitrogen source. Each year these diatoms have a boom of growth in the summer, accounting for up to 20% of annual productivity at station ALOHA.
It may not be spaghetti and meatballs, but phytoplankton, zooplankton waste and dying cells suit many marine organisms just fine. Perhaps the world Judi Barrett inspired me to dream of wasn’t so unrealistic after all.
1. Karl DM, Bidigare RR, Letelier RM. Long-term changes in plankton community structure and productivity in the North Pacific Subtropical Gyre: The domain shift hypothesis. 2001. doi=10.1.1.500.283
2. Karl D, Letelier R, Tupas L, Dore J, Christian J, Hebel D. The role of nitrogen fixation in biogeochemical cycling in the subtropical North Pacific Ocean. Nature. 1997;388:533–8. doi:10.1038/41474.
3. Karl DM, Church MJ, Dore JE, Letelier RM, Mahaffey C. Predictable and efficient carbon sequestration in the North Pacific Ocean supported by symbiotic nitrogen fixation. Proc Natl Acad Sci. 2012;109:1842–9. doi:10.1073/pnas.1120312109.