New research sheds light on phytoplankton blooms
Aug 2, 2013 – Plankton. We remember learning about these tiny things floating around the ocean in science class, and have maybe even seen them depicted in the popular cartoon program “Spongebob Squarepants.” Yet their role in Earth’s oceans may not be as commonly known. Phytoplankton, a specific type of plankton, serves as the foundation of many productive fisheries and also absorbs CO2 from the Earth’s atmosphere. With many fisheries declining and concern about global climate change on the rise, research on phytoplankton dynamics continues to be imperative. A new study reveals when and why phytoplankton in the subarctic Atlantic reaches annual population climax (plankton bloom) as well as how future shifts in climate can affect our microscopic friends.
Studies dating back to 1935 have tried to understand phytoplankton dynamics given their critical role in sustaining marine food chains and helping regulate global climate. However, recent technological advances in satellite imagery now allow for much more complex and comprehensive studies.
A new study by researchers, including the Center for Marine Assessment and Planning’s (CMAP) David A. Siegel, builds on former phytoplankton bloom studies but takes a closer look at the effect of the “disturbance-recovery process.” The process states that the deepening of the mixed layer (a homogenized range of depth on the ocean surface), which occurs in early winter, provides a disturbance in plankton interaction. This disturbance initially reduces phytoplankton population but subsequently allows the population to skyrocket into its springtime climax.
Sounds counterintuitive? Let’s explain. When the mixed layer depth increases due to cooler early-winter temperatures, the difficulty of light penetration, which phytoplankton relies on for cell division, increases, as does the dilution of the phytoplankton population. Since light limitation creates less phytoplankton to eat and dilution makes grazing more difficult, their predators (zooplankton) suffer population decreases. This momentary reduction of predation allows phytoplankton populations to recover and increase rapidly as spring temperatures decrease the mixed layer depth.
That brings us to the overarching question: what does it mean and why should we care? Well, forward projections have indicated that winter mixed layer depths will become shallower over the next 100 years. That decrease in depth may negatively affect plankton cycles, with possible negative effects on fisheries and atmospheric carbon levels as well. Although this bustling plankton activity may be geographically distant from our everyday life, the products of their activity are close to home.