Testate amoebae from the end of the earth!

Contributed by Matt Amesbury

The moss banks on Green Island on the Antarctic Peninsula provide a vivid green splash amidst the surrounding ice caps, glaciers and icebergs (Photo: Matt Amesbury)

The moss banks on Green Island on the Antarctic Peninsula provide a vivid green splash amidst the surrounding ice caps, glaciers and icebergs (Photo: Matt Amesbury)

The use of testate amoebae as a proxy for past changes in the hydrological status of peatlands has become ever more popular over the past two decades. Studies have been carried out over an increasing geographical range covering most major areas of northern hemisphere peatlands as well as in Patagonia and New Zealand amongst other places south of the equator. Despite this pushing of “amoebal” boundaries, there is one place you might certainly expect to be able to rule out moss-based testate studies: Antarctica.

Close up of Polytrichum strictum moss growing on Green Island (Photo: Matt Amesbury)

Close up of Polytrichum strictum moss growing on Green Island (Photo: Matt Amesbury)

Only a tiny 0.3% of the Antarctic continent is ice free, yet in parts of this seemingly minute slither, the climate is just about amenable enough to have permitted the formation of deep moss banks; accumulations of moss that grow a few millimetres each year and are then frozen stiff over the winter months only to thaw out in the short Austral summer and accumulate a little further. The most extensive moss banks are to be found on Elephant Island, located just off the northern tip of the Antarctic Peninsula. Here, the banks are almost three metres deep and around four to five thousand years old. At the other end of the scale, almost ten degrees of latitude further south at Lazarev Bay on Alexander Island as the Antarctic Peninsula begins to merge into the continental mass, comparatively tiny moss banks of only 40 cm depth still cling on to a dubious existence.

The rugged surface topography of a moss bank on Green Island (Photo: Matt Amesbury)

The rugged surface topography of a moss bank on Green Island (Photo: Matt Amesbury)

Work is currently underway to exploit these moss banks as a palaeoclimatic archive. The Antarctic Peninsula has warmed by 3°C since the 1950s making it one of the most rapidly warming parts of the globe, but there is comparatively little terrestrial palaeoclimate data to put this temperature rise into a longer-term perspective. Could this be where testate amoebae step into the fray once more?

The pioneering work of the British Antarctic Survey’s Humphrey Smith laid the foundations of knowledge on Antarctic testate amoeba throughout the 1970s and 80s. His work painstakingly analysed and recorded the distribution and ecology of moss bank Protozoan communities from the sub-Antarctic Islands (mainly on Signy and Elephant Islands) as well as the Antarctic Peninsula itself and latterly in sites spanning the entire circumference of the Antarctic continent. Taxonomic diversity was relatively low with the same few familiar faces cropping up over and again, perhaps most frequently the taxa Corythion dubium.

Campsite on Green Island with blue-eyed cormorants and the creaking icebergs just offshore as our only companions (Photo: Matt Amesbury)

Campsite on Green Island with blue-eyed cormorants and the creaking icebergs just offshore as our only companions (Photo: Matt Amesbury)

So when we began working in the region in 2012 we were faced with a lot of testate unknowns, especially in terms of their abundance, diversity and distribution in core samples; all of Smith’s work had been on surface samples. To date, we’ve counted assemblages from a range of locations ranging from the southerly extent of moss banks at Lazarev Bay to Elephant Island in the north. In some locations the concentration of tests is low enough to make counting rather unfeasible but in other places we have been able to produce records with relatively high diversity (for Antarctica!) and evidence of switching between taxa, suggesting that the method can be applied in the traditional sense that it is in more temperate regions. Corythion dubium remains the best friend of the Antarctic testate counter, being abundant and dominant in most profiles. But it is joined by Assulina, Difflugia, Euglypha, Pseudodifflugia, Trinema and Valkanovia taxa, as well as some as yet unidentified tests (pictures included – please get in touch if you recognise any!)

The ubiquitous Corythion dubium, found in abundance in most Antarctic Peninsula sites.

The ubiquitous Corythion dubium, found in abundance in most Antarctic Peninsula sites.

In our work at Lazarev Bay, recently published in Current Biology, we used the testate concentration profile as part of a multi-proxy record alongside carbon stable isotope discrimination and measures of moss growth rates and accumulation. The testate profile here, at the limits of moss bank growth, was swamped with C. dubium to the almost complete exclusion of other taxa but concentration values showed a rapid increase coherent with changes in the other proxies and with the recorded temperature changes in the region since the 1950s. C. dubium is a taxa that shows a wide range of recorded sizes in the literature, but morphometric work we have embarked on suggests it may be possible to consistently split these size fractions, perhaps offering more information on past changes than we currently realise.

Three examples of an a yet to be confirmed test from Ardley Island, Antarctic Peninsula.

Three examples of a yet to be confirmed test from Ardley Island, Antarctic Peninsula.

With such a relatively blank canvas of testate research in the Antarctic Peninsula and so much still to learn, there is a lot left to do and there are certainly more questions than answers at present. But even so, it is a remarkable testament to these fascinating organisms that they survive and flourish at the end of world (well, give or take a few degrees of latitude!).

Reference

Royles, J., Amesbury, M. J., Convey, P., Griffiths, H., Hodgson, D. A., Leng, M. J. and Charman, D. J. 2013. Plants and soil microbes respond to recent warming on the Antarctic Peninsula. Current Biology 23, 1702-1706.

About the author

Matt Amesbury is a Research Fellow at the University of Exeter.  He is a testate amoebae analyst with broad interests in Holocene climate change and peatland palaeoecology.  He is currently working on peat from New Zealand as well as moss banks in Antarctica. He is co-founder of the website Bogology which aims to share the science of peatlands and past climate change in a light-hearted and accessible way. He’d love you to visit him there.