Nature the artist.

This is part of the small sea-wall that prevents erosion around the bridge over the river Ythan. 
The horizontal bands are an example of zonation, the way in which plant and animal communities organise themselves in distinct bands, dependent upon their relative abilities to withstand such environmental pressures as salinity, temperature and desiccation etc. The zones here are brown fucoid seaweeds on the shore, green algae, a black lichen, and finally a yellow lichen. Nature just loves a bit of order!