Why sunburst lichen doesn’t need sunscreen: Nature News
I was lucky enough to participate in an eclipse event (organized by the Gulf of Maine Research Institute) that was held just north of Houlton, Maine, this past week.
I drove up to Eastport for the weekend before heading inland to experience totality. Upon arrival in Eastport, I encountered what I took to be a good omen — heralding lots of sunshine (not so common this time of year in northern Maine) on eclipse day — beautiful sunburst lichen growing on an abandoned building along the waterfront.
As I anxiously awaited Monday’s eclipse, I explored the rest of town and found sunburst lichen in abundance along the coast, anywhere there was lots of sun — on rocks, trees and rock walls.
The sun emits a wide range of radiation, for example, longer wavelength radiation like heat, shorter wavelength radiation like visible light, and even shorter wavelength radiation that falls in the ultraviolet range of the electromagnetic spectrum. The shorter the wavelength, the higher the energy and, therefore, the more damaging the radiation. Overexposure to ultraviolet radiation is a well-known cause of skin cancers and sunburn in humans because it has enough energy to penetrate our skin cells and damage the DNA; a good reason to wear protective clothing and sunscreen on sunny days. But what to do if you are a sunburst lichen, living on the exposed rocky coast or on the top of a mountain?
Sunburst lichen is common along the coast here in New England. A lichen is a symbiotic organism that is composed, at the bare minimum, of a fungal partner and a photosynthesizing partner (algae or bacteria, or both) called a photobiont.
The fungal partner houses the photobiont, forming an outer skin (called the cortex), which protects the underlying photobiont from environmental hazards like drying out, physical abrasion, and, when in exposed locations, the sun.
Different species of lichens have different pigments in their cortex that help protect the photobiont from damaging UV radiation. Pale yellow usnic acid is found in beard lichens, melanins in brown, floppy rock tripes, and anthraquinone pigments give the sunburst lichen its deep yellow to orange-red color and is also found in the red tops of British soldier lichens. These pigments can absorb or scatter ultraviolet wavelengths, shielding the photobiont like sunscreen (Rachel Sargent Mirus, Northern Woodlands 2021). Lichens appear to be able to regulate the expression of these pigments — the stronger the sunshine, the denser the pigments. If you find these lichens on some exposed rock along the coast, they’ll blast you with brilliant yellow. Those that grow in more shaded woodlands will be greener; they don’t need all that sunscreen.
While the eclipse gave us a chance to look at the sun for a few seconds with impunity, when totality ended, we donned our eclipse glasses and returned to our normal relationship with the sun — a delicate balance. Solar radiation is required for almost all life to exist on this planet, but at the same time is dangerous enough that we have all come up with adaptations to protect ourselves from its more damaging rays. We have sunglasses and sunscreen; lichens have their gorgeous pigments.
Susan Pike, a researcher and an environmental sciences and biology teacher at Dover High School, welcomes your ideas for future column topics. Send your photos and observations to spike3116@gmail.com. Read more of her Nature News columns at Seacoastonline.com and pikes-hikes.com, and follow her on Instagram @pikeshikes.
