I'm Lichen These Lichens!

What could be a better way to study the interactions between Cape Breton species than a perfect example of symbiosis? Symbiosis is the mutualistic relationship between two different species where each species gains some benefit from the interaction. The species discussed here are lichens. I'm sure everyone reading this has seen lichens at some point during a walk through the woods and not known what exactly they're looking at.

Lichens are composed of a fungus and a photosynthetic symbiont (photobiont) such as algae or cyanobacteria living in a special biological relationship called symbiosis. The fungal component of lichens is responsible for absorbing nutrients and structural support of the lichen. The algal component uses photosynthesis to produce carbohydrates or energy. Lichens can be classified based on their structure into 3 groups: crustose - crusty and flat; foliose – leafy; and fruticose – shrubby. We most often see lichens on trees but they can also be classified based on the locations in which they are found. The 3 groups are: corticolous – tree bark; saxicolous – rocks; and terricolous – soil.

Commonly known as Old Man's beard, this is a fruiticose lichen, Usnea sp. This picture was taken on Coxheath Mountain Wilderness Trail, Coxheath, NS in May 2009.

The most important use of lichens has to be as monitors of air quality. It has been known for over 140 years that lichens are extremely sensitive to air pollution and therefore make excellent indicators for changes in atmospheric quality especially in highly urbanized and industrialized regions. In an area where the air quality is extremely poor you won’t find any lichens because a rise in pollutant levels in an area kills the lichens living in that area. To understand how this works you need to have an understanding of the delicate structure of lichens. The sensitivity of lichens can be attributed to their ability to absorb chemicals rapidly from air and water. It is also their composition as a symbiotic relationship between two components that determines their sensitivity to pollutants because if a pollutant affects the well-being on even one component, say the fungus, this throws off the balance of the symbiotic relationship and the partnership breaks down and the lichen dies.

More Usnea sp. found in Northside East Bay Trail. Photo taken February 2010.

Some pollutants are especially harmful to lichens such as sulphuric acid, nitric acid (both components of acid rain), fluorides, ozone, hydrocarbons, and metals. Some lichens are more sensitive than others making them more conspicuous indicators of a change in air quality because they will disappear first from an area. These more sensitive lichens include the fruticose species such as Usnea, Ramalina, Teloscistes, Lobaria, Panaria and Nephroma. Usnea, seen in the photograph above, was found by our natural history class several times in regions throughout Cape Breton along the Louisbourg lighthouse trail, Coxheath Mountain Wilderness Trail, Northside East Bay and along the trail at Gillis Lake Falls. I have personally found this lichen throughout Cape Breton and this is an indicator of our excellent air quality in most areas of the island. A difference in lichens can be found within Cape Breton Island between areas that are more industrialized such as Port Hawkesbury where there is a very high level of air pollutants to areas in the highlands where there is basically no industrialization at all to areas such as Whitney Pier which may have been affected in the past due to pollutants from the now closed Sydney Steel Plant which closed in 2000 and an increase in lichen diversity may be found.

Usnea sp. growing on a tree in Northside East Bay. Photo taken February 2010.