Mysterious Marimo


I was recently approached by a lady who was quite curious as to what mystical energies could have created the increasingly popular marimo balls that are often seen for sale in aquarium shops. Surely no natural force could create such spherical wonders in nature, right? She seemed quite disappointed by my answer and left feeling cheated of the super natural mechanism she was looking for. However, before we discuss the source of these fury green balls, let's start at the beginning. 

Marimo balls or lake balls are a specific growth form of a macroalga known scientifically as Aegagropila linnaei. It belongs to the Cladophoraceae family and can be found in lakes throughout the northern hemisphere. They are most popularly known from lakes in Japan where they hold serious cultural significance. The word "marimo" is Japanese for "ball seaweed."

So, how does this species of alga form itself into a ball? The answer is not mystical, though it is quite specific. To start with, the ball form of this alga is not the only way it grows. Populations will also form as mats on the lake bed, carpeting rocks and other debris. When pieces break off and become free floating, tidal action gently rolls them around. As they grow and move, they become tangled up and gradually form themselves into this spherical shape. The overall shape and survival of the alga in this form is reliant on this tidal motion. All parts of the ball actively photosynthesize and if it is not exposed to light all over, the shaded parts die and the ball will be no longer. Luckily, the alga reproduces vegetatively so the broken parts can still go on living.

Sadly, marimo balls are not doing too well in the wild. As we have seen with so many other species, human impacts are taking their toll on Aegagropila linnaei. Eutrophication, logging, and development within the watersheds that feed these lakes are causing the once clear waters to become quite murky. As this issue increases, the alga can no longer photosynthesize on a level that can sustain its populations. Acid rain is another big issue. Marimo balls tend to grow in calcareous lakes. As the water acidifies, they are unable to cope. Finally, one of the other issues facing the marimo balls is their popularity. In some areas, they are being harvested for the aquarium trade at unsustainable levels. One source claims that a majority of marimo balls for sale in aquarium shops are sourced from the Ukraine, which means that those populations are under serious pressure. 

Luckily, their popularity may also lead to more protective measures. For instance, they are so important to Japanese culture that they are now a protected species there. The Netherlands is also waking up to the decline of this species. Until more can be done, it is best to only buy from nursery grown sources. Formation of the balls has been done in an artificial setting. Truly, no species is safe from the irresponsible nature of modern man.

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