Oddities and curiosities in the algal world

The term algae refers to a polyphyletic, non-cohesive and artificial assemblage, of O2-evolving, photosynthetic organisms. The profound diversity of size, shape, habitat, metabolic traits and growth strategies makes this heterogeneous assemblage of both prokaryotic and eukaryotic species an almost unlimited source of curious and unusual features. Algae display an incredible adaptability to most environments, and provide an excellent system for testing hypotheses concerning the evolution of ecological tolerance. In fact, they are not limited to temperate waters, but can survive at very low depth and very low irradiance, and thrive beneath polar ice sheets. Upon adaptation to life on land, algae have colonized such surprising places, as catacombs, tree trunks, hot springs, and can also resist desiccation in the desert regions of the world. Moreover, relations between them and other organisms, which include competition within and between species for space, light, nutrient or any limiting source, are based on a variety of associations, which includes epiphytism, parasitism, and symbiosis. Algae can share their life with animals, growing on sloth hair, inside the jelly capsule of amphibian eggs, upon the carapaces of turtles or shells of mollusks, camouflaging the dorsal scute of harvestmen. They can also light up the sea at night, and cause infections in animals and humans.