As a consequence, we often collect a few litres of sea water and manipulate them in the lab. ‘Lab experiments’ are informative and give you an idea about individual model organisms or single aspects of the ocean biogeochemical cycles. But these micro-scale experiments have one big problem. They are like watching a monkey in a zoo: It gives you an idea about e single monkey, but it will never quite tell you what a jungle is all about.
What is needed is something of intermediate scale: a ‘mesocosm’ (from Greek mesos: 'middle' + kosmos: ‘world').
Our mesocosms
The mesocosms that we are using are large plastic bags (about 1 m across and 10 m deep) that hold around 6000 L of water. Out at sea, these plastic bags are submerged to a depth of around 20 m and then carefully pulled up to the surface. The filled bags now contain natural sea water with its unaltered plankton community. The bags are left floating in the sea for several days and thus experience the same environmental conditions as the surrounding open waters. The large volume of these mesocosms mimics the properties of the ocean to the extent that even stratification occurs. Yet, the artificial walls make it possible to manipulate the individual mesocosms and compile detailed budgets, which would not be possible in an open ocean environment.Where
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