Why should you care? Part I: Bioindication

You may be wondering why anyone would care about these often small and unnoticed creatures.  The most important contribution lichens have to offer is to the earth.  They are among the first organisms to colonize disturbed areas.  After a fire or some other type of destruction occurs in an area, lichens grow there.  On a geological time scale, some species physically break down rock, forming soil.  Most famously, lichens can be used as biological indicators of pollution and change.  Lichens have been used as surrogates to determine how polluted different areas are.  Different species have different levels of tolerance, so the presence of tolerant species and the lack of intolerant species to a certain pollutant indicates that the area under question is highly polluted.  "Lichen deserts" are found downwind of factories, indicating the pattern of atmospheric pollutants.  By studying changes in lichen morphology and physiology one can surmise how polluted a specific area is.  Lichens readily absorb everything from the atmosphere because, unlike plants, they have no stomata (holes in leafs that keep gases in, let gases out, or take gases in) or cuticle (protective waxy coating on leaves).  Thus, they can absorb lots of pollution, even to the point where it kills them. 

The presence of certain species can also be an indicator of ecosystem health.  Lichens such as Lobaria species have cyanobacteria, which are involved in nitrogen fixation.  Scientists have found that such "cyanolichens" can make a huge impact on the nitrogen cycle of an ecosystem.  And since nitrogen is an essential element for all of life and can only be used by animals in forms that autotrophs (organisms that produce their own food) make, cyanolichens are critical to ecosystem health and stability.

What is a Lichen?

Lichens are a unique life form. It's strange that scientists classify them when you consider that they are two different organisms living together in some kind of relationship. (There is debate about whether or not the relationship is a mutualism, i.e. a relationship that is beneficial for both parties, or a form of controlled parasitism.) In short, a lichen is an alga (pl. algae) or cyanobacterium (formerly known as a blue-green alga) and a fungus that live together. But in a lichen, the two partners form a completely unique organism that doesn't look like either partner does alone. The fungus forms the body of the lichen (aka the thallus) as well as the attachments for anchoring it to what it grows on (the substrate). The alga or cyanobacterium performs photosynthesis, providing the "food" for the relationship. Because the fungus doesn't really do much work and takes food from the alga or cyanobacterium, some consider this a controlled parasitism. There is a cute drawing of this scenario in William Purvis's book Lichens, where a blob of a fungus has put some green algal cells behind bars and is holding the key and smiling like a glutton.

I want this blog to help lay people, including children, understand lichens, their significance, and why I think they are the coolest organisms on the planet.