Upside down grazers

possible alien world?Imagine a world where animals graze on a surface of green extending above our heads. To me this sounds like a scene from a science fiction movie set on an alien world that requires ‘unabtainium’ or a ‘flux-vortex’ to exist. Yet, habitats like this exist on earth. The underside of sea ice is one (caves are probably another).

In the Arctic, the sun returns long before the ice melts. Since first year ice is relatively clear, sunlight can pass through. Algae takes advantage of this light and sets up shop on the bottom surface of the ice. A two-dimensional world is created in the normally three-dimensional euphotic zone.

Ice algae plays an important role at the base of the ecosystem. These algae blooms represent the beginning of the Arctic grazing season as no photosynthesis can occur during the long winter polar night. Since other phytoplankton are scarce this time of year, creatures flock to the icy roof for a meal. Diners include diatoms, protozoa, nematodes, copepods and others. Copepods in particular are a food source for bigger creatures and fish such Arctic cod. These fish are eaten by bigger fish, birds and marine mammals.

Light is critical for ice algae to thrive, so any snow covering the ice can have a negative impact. Too much snow and there won’t be enough light for the algae to grow. Additionally, particulates in the ice can block sunlight. A large mining or smelting operation could coat the ice in particles, blocking the algae’s light.

This ecosystem, like all others on our planet, will be impacted by climate change - and we don’t know exactly what the end result will be. Ice algae need the clearer first-year ice to grow. If warmer conditions made this ice melt sooner, the algae would sink and die. The grazers that depend on the algae would starve. On the sea floor, algae would decompose potentially creating anoxic conditions, a potentially fatal environment for bottom dwellers such as turbot, Greenland sharks and Arctic skate. Or, if warmer conditions result in less multiyear ice, potentially more first year ice could form. Ice algae would have more space to grow and more food could be available for all (assuming there was enough nutrients). 

Image is from here