The limestone from which the Burren is built is a famously permeable rock, so any rain quickly seeps through the surface layers and standing or flowing water at the surface is relatively rare in limestone country, except where the water table is relatively close to the surface. Even so, the water table rises and falls throughout the year, meaning that lakes in these regions tend to be fluctuate in size and, in many cases, dry up altogether. In the Burren, these transient lakes are referred to as “turloughs” and are one of the characteristic landscape features of the area.
You get a better sense of the nature of Lough Gealáin, one of these turloughs, standing near the summit of Mullaghmore. The light blue zone is shallow water overlying marl with a darker blue zone indicating deeper water. Surrounding the shallow water there is an area that grades into the true terrestrial vegetation, characterised by crisp white mats of dried-out filamentous algae that crunched underfoot as we walked around. These represent a zone that would have been submerged during the winter, but which is now exposed as the water table falls back. All turloughs are fed by groundwater springs and, in this case, the deep zone is thought to overly a collapsed cavern which itself may be a channel through which groundwater flows, ebbing up to the surface when the flow is too great for the channel to accommodate.
Approaching the shore of Lough Gealáin, I noticed several spherical or hemispherical white jelly-like blobs sitting on the exposed marl. These are colonies of a protozoan, Ophyridium versatile, an organism which contains many tiny algal cells (called “zoochlorellae”). It was of particular interest to me because I had been explaining to my students in Galway how the earliest algal cells were the result of a protozoa-type organism engulfing a primitive alga and then, rather than digesting it and using its energy straight away, preferring to enslave it, reaping its energy over a longer time period. “Enslave” might be a harsh term as these relationships are often viewed as “win-win”, with the alga gaining protection in exchange for the renewable energy it provides to the protozoan.
By coincidence, we also saw Ophyridium versatile at a very different habitat during our fieldtrips to Connemara (to the west, rather than the south, of Galway). The water here is much softer (conductivity: 108 µS cm-1rather than 330 µS cm-1) and the colonies much greener in appearance but the organisms inside looked remarkably similar. Unfortunately, in both cases the cells did not enjoy their journey from the west of Ireland to my microscope and were well past their best by the time that I photographed them. Apologies: I basically broke several of the rules I set out in “What’s in a sample (2)”. You can, nonetheless, make out the zoochlorellae inside the protozoan mothership. There are better images of Ophyridium versatile in “On fieldwork”.
Also visible in the gel matrix (but difficult to photograph) were many small diatoms. Others have noted the presence not just of diatoms, but of other algae, bacteria and protozoa also hitching a ride in the Ophyridium colonies. Whilst the zoochlorellae are within the cells within the gel, these are outside the cells but within the gel. For the diatoms, the relationship is not obligatory but still likely to be a “win-win” symbiosis. They gain protection whilst the oxygen they produce contributes to the overall buoyancy of the colonies. The most abundant diatom seemed to be a species of Encyonopsis but this is a difficult genus to identify in the live state, so I’ll need to get it digested and mounted before I can write more. There does seem to be some evidence that the Ophyridium colonies develop a characteristic assemblage of diatoms, different to that in the surrounding habitat, so it will be interesting to see just what is in my sample.
Unless you know what you are looking for, Ophyridium colonies are easily overlooked or dismissed. But they pose some interesting questions about how organisms interact. It should not be a surprise that one of the papers I found in my scan of the literature was co-authored by Lynn Margulis, who first recognised the importance of symbiosis to evolution (see “Origin story …”). Although the Ophyridium cells are still nominally functional heterotrophic protozoans, studies have shown that all their carbon is supplied by their resident algal cells and the main contribution from their “feeding” is other nutrients such as nitrogen and phosphorus. There is sufficient interdependence that the next steps of Margulis’ endosymbiosis theory – loss of unneeded genetic material from the zoochlorellae– seems entirely plausible. But, then, alongside this very tight partnership, the Ophyridium colonies also have these looser associations with diatoms and other microorganisms. Maybe these are more like our own gut microbiomes, playing a role in the overall “health” of the colony in ways we are yet to discover? Understanding the role of the human gut microbiome is now a big research question. It is quite intriguing to think that the same type of questions occur right across the living world, even for apparently primitive protozoans.
References
Dute, R. R., Sullivan, M. J., & Shunnarah, L. E. (2000). The diatom assemblages of Ophrydium colonies from South Alabama. Diatom Research 15: 31-42.
Duval, B. & Margulis, L. (1995). The microbial community of Ophyridium versatile colonies: endosymbionts, residents, and tenants. Symbiosis 18: 181-210.
Eaton, J.W. & Carr, N.G. (1980). Observations on the biology and mass occurrence of Ophyridium versatile(Müller) (Ciliphora: Peritrichida) and associated algae in Lough Ree, Ireland. Irish Naturalists Journal 20: 55-60.
Mark, A., McKim, S., Lowe, R., & Kociolek, J. P. (2019). Diatom community composition within Ophrydiumcolonies in Northern Michigan and the description of a new species of Encyonopsis Krammer. The Great Lakes Botanist 58: 221-232.
Sand‐Jensen, K., Pedersen, O., & Geertz‐Hansen, O. (1997). Regulation and role of photosynthesis in the colonial symbiotic ciliate Ophrydium versatile. Limnology and Oceanography 42: 866-873.
Some other highlights from this week:
Wrote this whilst listening to: The Corrs Unplugged. Sharon Corr was the support act for Jeff Beck (see below), leading me back to their music.
Currently reading: Very readable translation of Delphine de Vigan’s short but moving novel Gratitude, then Cyprian Ekwensi’s 1962 novel Burning Grass, about the nomadic Fulani of northern Nigeria.
Cultural highlight: I bought tickets to see sixties guitar legend Jeff Beck before the first lockdown. The concert was cancelled twice before finally going ahead last week. The concert would have attracted little attention beyond men of a certain age with a penchant for jazz-inflected rock were it not for the announcement earlier in the week that Johnny Depp was making guest appearances on the tour. Depp won his high-profile libel case on the day we saw them, which pushed the concert onto the front pages of all the newspapers the following day.
Culinary highlight: recreated a recipe we had encountered at the Seafood Bar in Galway: “rhubarb and custard”, with the custard replaced by a sabayon made with white port.
microscopesandmonsters 