We’re coming to the end of our time here in Kenya and we’ve amassed some amazing memories of the wildlife with great views of large mammals such as giraffe, zebra, elephant, hippos, and a variety of antelopes including the ubiquitous dik-diks. In addition, between us we’ve put together a bird list of about 130 species for the site. But as always it’s the smaller things that have fascinated me the most and some of the student project groups have worked with pollinators, ants, and other invertebrates.

One of those fascinations has been the life that exists beneath some of the rocks that are embedded in the red soils of this part of the savanna. Turn them over and you often find the green growths of what are probably cyanobacteria – so-called “blue-green algae” – which are true bacteria and not at all related to algae, even though they also photosynthesise.

The question arises, of course, of how an organism that requires sunlight to survive is able to grow under a stone? Our investigations have shown that they only live under quartz rocks, mainly those that are lighter in colour. Quartz is of course a crystal and it allows a small amount of sunlight to pass through, typically only one or two percent of the sunshine hitting the rocks. There’s also greater humidity under the stones so it’s a relatively more benign place to grow than the savanna, especially in the dry season.

There’s a great review of these microbial communities, and their ecological importance, by Chan et al. called Hypolithic microbial communities: between a rock and a hard place.

Here’s some photographs that I took of these hypolithic photosynthesisers:

Oh, ok, if you insist: here’s some giraffe: