One of the surprises of our short visit to Malta was encountering signs directing us to “Clapham Junction”, which turned out to be the informal name for an area known in Maltese as Misraħ Għar il-Kbir. The term arises from the deep “cart tracks” gouged into the limestone pavements which criss-cross in the manner of railway lines outside a busy station. Similar ruts are found at several locations in Malta and pose one of the island’s great archaeological mysteries. The best guess is that they originated at around 2000 BC, possibly as a result of primitive carts or sleds being pulled across the naturally weak limestone.
Clapham Junction, Malta. The right hand picture shows the deeply-rutted limestone pavement that gives the area it’s name.
On the day we visited, the site was almost deserted. The downside of this was that we stumbled through the scrubby vegetation for some time before we actually found the tracks for ourselves (eventually sighting another couple of tourists on a nearby ridge). But there is something quite special about straying away from the tourist honeypots, away from interpretation boards and signage, and exploring these locations alone.
The cave complex at Għar il-Kbir, April 2015.
A little further away, behind a dry stone wall, the land fell away into a natural hollow, which was, until the roof collapsed a natural “karst cavern”. Caves around the edge of this hollow show signs of habitation: walls at the entrance and dividing the living space within the caves. Life as a troglodyte makes perfect sense in the harsh Mediterranean climate of Malta and there is evidence that these caves were inhabited until the early 19th century.
Inside, my eyes were caught by the blue-greenish films on many of the rocks. Algae, like humans, do not thrive in the hot, dry climate here so, again like humans, they seek out cooler, more shaded situations. I scratched a few flakes of the film off the stones to take home so that I could have a closer look. When I got back, I put them on a slide with a drop of water and put this under my microscope for a closer look. What I saw was a mass of tiny cells. My best guess at a name for these colonies is Gloeocapsa alpina (the species name was suggested by Allan Pentecost) . We have met this genus at least once before, co-incidentally also associated with an archaeological site (see “More reflections from the dawn of time”). If you look closely at the final picture, taken by Chris Carter, you’ll see the typical prokaryotic cell lacking distinct chloroplasts.
Inside the largest cave at Għar il-Kbir with (right) the blue-green crust under the microscope (scale bar: 10 micrometres (= 1/100th of a millimetre).
The higher humidity in the caves makes it slightly easier for the algae to survive than outside and there is also evidence that cave-dwelling species have specially-adapted photosynthetic apparatus to allow them to make the most of the limited light that is available here. Understanding the growth off microorganisms in environments like this also needs a major re-adjustment in thinking. Outside the caves we had been wandering through masses of wild flowers that thrive in the spring in the makkja (the Maltese term for the Mediterranean scrub vegetation). When we pass through the entrance to the cave, however, we have to slow our mental time clocks down, and stop thinking in terms of annual, biennial or perennial plants. These algae, along with those that thrive as crusts in deserts, hot and cold, are opportunistic, capable of “shutting down” their metabolism for long periods (years, if necessary) then “rebooting” to make the most of brief periods when there is enough water to function.
The cyanobacterium Gloeocapsa alpina from Għar il-Kbir, Malta, April 2015. Photograph by Chris Carter.
So much for the algae. The sun was now high in the sky and if you really want to understand the ecological realities of the Mediterranean climate, I recommend a three kilometre walk to the nearest village in search of shade, a drink and some lunch.
Albertano, P. (2012). Cyanobacterial biofilms in monuments and caves. pp. 317-344 In: The Ecology of Cyanobacteria II: Their Diversity in Space and Time (edited by B.A. Whitton). Springer, Dordrecht.
Vestal, J.R. (1993). Cryptoendolithic communities from hot and cold deserts: speculation on microbial colonization and succession. Pp. 5-16. In: Primary Succession on Land (edited by J. Miles & D.W.H. Walton). Blackwell Scientific Publications, Oxford.