Have you ever noticed small, fuzzy, snowflake-like spheres floating in Squam Lake? These are colonies of the cyanobacteria Gloeotrichia echinulata, commonly called Gloeo. But how do these tiny organisms get from the bottom of the lake to the surface where we can see them? The process is fascinating and tied closely to the lake’s seasonal chemistry.
Gloeo begins its life cycle as specialized cells called akinetes, which survive in the lake sediment through the fall and winter. As spring and summer arrive, the water warms and stratification develops. By June, the bottom layer of the lake often becomes anoxic, or depleted of oxygen. This lack of oxygen changes the water chemistry, releasing phosphorus that had been bound in the sediment.
The overwintering Gloeo cells in the bottom layer absorb and store this phosphorus, which fuels their growth. As they germinate and form colonies, the cells develop a gas vacuole, an organelle that increases buoyancy. Once buoyant enough, these colonies slowly rise to the lake’s surface.
When Gloeo reaches the surface, it enters a low-phosphorus environment. Squam Lake’s upper waters do not contain enough phosphorus to support high growth of other phytoplankton, which is why the lake maintains its clarity and low chlorophyll levels. But Gloeo has a unique advantage: it can fix atmospheric nitrogen, converting it into ammonia that it can use as food. This ability allows it to thrive at the surface without competing with other species.
Gloeo will continue to thrive at the surface until environmental conditions change, such as cooling water temperatures in the fall. As it dies off, cells slowly sink back to the bottom, leaving akinetes in the sediment to survive the winter and restart the cycle the following year.
In short, Gloeo’s journey is powered first by phosphorus released from the lake’s sediments and later by its ability to make its own food from nitrogen at the surface. Sunlight, warm temperatures, and calm conditions all help it maintain its place in the upper water column, creating the blooms that are so visible to lake-goers. Cell counts are consistently coming in around 500-2500 cells/mL from samples collected by members of the public and us. The state issues a recreational advisory at 70,000 cells/ml. So even though it is visible with the naked eye, we are seeing cell abundances well below the advisory level.
