What can be learned from the microbes on a turtle's shell?

Researchers have found that a unique type of algae, usually only
seen on the shells of turtles, affects the surrounding microbial
communities. It is hoped that these findings can be applied to
support the conservation of turtles. Previous research has shown
that a diverse microbiome can protect animals against infections.
Source: FS – All – Ecology – News 2
What can be learned from the microbes on a turtle's shell?