Diatom of the month – September 2016: Aulacoseira granulata

by Luca Marazzi*

Last week about 800 ecologists from 72 countries, including myself, attended and presented their research at the 10th INTECOL Wetlands conference in the beautiful city of Changshu (2 hrs west of Shanghai). Before this event that takes place every four years (in 2012 we were in Orlando for INTECOL 9), I was honored to give a long seminar on my work on the algal communities of the Okavango Delta and Everglades at the Nanjing Institute of Geography and Limnology (NIGLAS) of the Chinese Academy of Sciences. I was invited to do that by my friend Xuhui Dong (we studied together for our PhD at the UCL Environmental Change Research Center in the UK). Xuhui and his colleagues recently conducted a paleolimnology study of several floodplain lakes along the mighty Yangtze River (Dong et al., 2016), where they found large numbers of Aulacoseira granulata [(Ehrenberg) Simonsen 1979], which is therefore our September diatom (a belated post).



           Fig. 1. Diatoms of the genus Aulacoseira are characterized by point symmetry around their center                   (http://westerndiatoms.colorado.edu/): above: filament with live cells; below (left): frustule with spine
                                                below (right): cell with spines. LM scalebar = 10 µm.

This is a centric, planktonic, non-motile, filament-forming species that needs medium nutrient levels (mesotrophic), and prefers turbulent conditions. In Liangzi Lake Taibai Lake, and Shitang Lake (Fig. 2), A. granulata reached relative abundances of 78% in reference communities from sediment cores dating 1800-1950. This is due to the fact that, before the 1950s, the lake was subject to strong mixing2 and free exchanges of mass and energy with the Yangtze River through its connection with the lakes, which seem to have created good conditions for large populations of this diatom3.

Fig. 2. Geographical distribution of 10 diatom-based palaeolimnological sites along the Yangtze River in Eastern China (Source: Dong et al., 2016).

Given the impressive number and extent of lakes and wetlands near the conference venue (369 wetlands, totaling 32,037 hectares, paddy fields excluded, or ~ 25% of Changshu city's total area5), many types of diatoms and other algae must very happy around here! And no wonder that Changshu may well become the first Wetland City under the Ramsar Convention on Wetlands of International Importance. Among these wetlands, I and another ~50 attendees or so visited the Shanghu Lake, Nanhu Urban Wetland Park, and Shajiabang National Wetland Park (see Fig. 3); these are human-made aquatic ecosystems, and very peaceful and nature-and-culture-rich oases in an extremely densely populated region of China. Definitely worth a visit, if you happen to be around.

Fig. 3. Boating in a beautiful spot of the Shanghu Lake site during the conference excursion.


“The 10th INTECOL Wetlands conference logo includes water, bird, fish and plant four wetland elements which combine into an integrity. The shapes of flying crane, green aquatic plant, and swimming fish link into a colorful ribbon, expressing the 10th INTECOL International Wetlands Conference would be a linkage of international communication, exchange and cooperation for wetlands professionals and workers over the world” (http://www.intecol-10iwc.com).

Analyzing the abundance patterns of Aulacoseira granulata and other planktonic and benthic diatoms, paleolimnologists are able to reconstruct past environmental conditions, such as nutrients, pH, salinity, plant cover, and land use so that gradual and abrupt environmental changes can be better understood and predicted. Wetlands are under severe threats (the Wetland Extent Index has declined 30% in the 1970-2008 period4), understudied, and not too clearly defined yet, therefore, if we want to deeply inform their conservation and sustainable management, international collaborations stemming from high-profile conferences such as INTECOL Wetlands are crucial. I am happy to report from Changshu that this community is very motivated and vibrant. And diatoms, beyond being stunning living organisms, are essential to better understand aquatic ecosystems, so let’s conserve them and their habitats, shall we?

* Postdoctoral Associate in Dr. Evelyn Gaiser's lab at Florida International University.

1. Dong X., Yang X., Chen X., Liu Q., Yao M., Wang R. and Xu M. Using sedimentary diatoms to identify reference conditions and historical variability in shallow lake ecosystems in the Yangtze floodplain. Marine and Freshwater Research 67, 803–815.
2. Owen R., and Crossley R. (1992). Spatial and temporal distribution of diatoms in sediments of Lake Malawi, central Africa, and ecological implications. Journal of Paleolimnology, 7, 55–71.
3. Yang G.S., Ma R.H., Zhang L., Jiang J.H., Yao S.C., Zhang M., and Zeng H. (2010). Lake status, major problems and protection strategy in China. Journal of Lake Sciences, 22, 799–810.
4. Dixon MJR, Loh J, Davidson NC, Beltrame C, Freeman R, Walpole MJ. (2016). Tracking global change in ecosystem area: The Wetland Extent Trends Index. Biological Conservation, 193, 2735.
5. Source: http://www.intecol-10iwc.com


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