Lichens live above the high tide line along most rocky shores. Lichens are actually two organisms living together, each benefiting the other. The fungal component has a relatively thick outer surface which protects the lichen from environmental extremes. In addition the fungus can absorb from 3 to 35 times its weight in water allowing precious water to be stored and used at a later time. Why would this be an advantage? Numerous projections anchor the fungus to the rock surface. Algal cells live within the fungus. The algal cells produce food photosynthetically feeding both components of the lichen. It is no wonder that lichens are common in many other harsh environments. You may be more familiar with lichens growing on tree trunks or gravestones. The illustration below shows the relationship between the algal and fungal components.
The act of living together, each benefiting the other, is called symbiosis. Can you call to mind any examples of symbiosis? Plant and animal cells are thought to contain organisms that have become integral parts of the cell. Mitochondria, for example, are responsible for producing energy in cells. Where did they come from? How do we know that they were once living organisms? Are they still living organisms? Could cells do without them? Why is this a symbiotic relationship?
Note the orange lichen Xanthoria spp. on a vertical rock face in West Quoddy Head, Lubec Maine.
Note the orange lichen Xanthoria spp. the high tide line on a vertical rock face in Acadia National Park in Maine.
Xanthoria spp. Two Lights State Park Cape Elizabeth, Maine
Note the lichen Xanthoria spp. in Lubec Maine .
Note the black lichen Verrucaria spp. on upper rock surfaces at Reid State Park
The lichen Verrucaria spp., shown above, is a common lichen attached to rock surfaces above the high tide line. It is generally thin and resembles patches of tar.
The green alga Enteromorpha spp. attached to the lichen Verucarria spp.
Two photographs of two unidentified lichens, photographed at Bailey Island Maine.
In addition the tiny green alga Prasiola spp. can often be found attached to rock surfaces here It is about 10-25 mm in height and resembles Ulva, a green alga illustrated in the description of the Red Algal Zone.