It takes more than just salt sensitivity to make a lichen a good indicator of whether a site has experienced the first effects of sea level rise. The lichen’s own life history also comes into play.
Species like the powdery medallion lichen (left photo) can be killed if subjected to too much salt water by a storm or flood. But this lichen’s quick reproduction lets it swiftly recolonize after the sea recedes. Larger species with slower growth and reproduction, and also low salt tolerance, like the ruffled blue jellyskin (right photo), can better tell the saltwater history of a site. These salt-intolerant lichens could not have survived and grown if a saltwater event like storm spray or flooding had occurred at any point during their life. Since some lichen species can live for decades or longer, the record they provide can be both hyperlocal in space and extensive in time.
Of the 48 different lichen species Rosentreter and DeBolt found at their two Florida survey sites, 11 are reliable indicators of salt water’s presence. Seven of the species only like to grow in places with very low saltwater impact, while four are salt tolerant, so finding them growing suggests the site has a moderate history of salt and a higher risk of being affected by rising seas.
In general, they found that the species that best indicate if a site will be relatively safe from sea level rise and saltwater inundation are lichens that are larger and leafier and often light green or blue in color. But lichens can be tricky to identify, and some promising indicator species look quite similar to less useful ones. “You’ve got to be at least an intermediate plant person to figure it out,” says Rosentreter.
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I have been learning more and more about Lichens this year!
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