Thursday, September 29, 2016

Diatom of the month – September 2016: Aulacoseira granulata

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                   ( 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” (

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?

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:

Tuesday, August 23, 2016

Diatom of the month – August 2016: Didymosphenia geminata

Many algae are able to form blooms, sometimes releasing dangerous toxins for aquatic organisms and people. Cyanobacteria are most infamous for producing blooms such as those ongoing in Florida's coastal waters, but other algae, including diatoms, can create such vast colonies too. The large (100,001-1,000,000 µm3) asymmetrical biraphid Didymosphenia geminata, or colloquially ‘didymo’ is one of them; it attaches to stones in rivers by stalks (made of mucopolysaccharides, long chains of sugar molecules) that can be 1 m long! Didymo is invasive in Argentina, Chile, and New Zealand, where this video was released in 2008 to inform the fishing community that they should clean and dry all their gear to avoid spreading this species to other water bodies.

Fig. 1. (top) Didymosphenia geminata (scalebar = 10 µm; photo by Mart Schmidt); (bottom) numerous cells and mucilage stalks from South Boulder Creek (November 2011) - credit/source: Sarah Spaulding (

This diatom is also widely present in the United States, Europe, Russia and parts of Asia (Fig. 2), and it surprisingly occurs mostly in rivers and streams that are oligotrophic (with scarce nutrients) and unshaded, rather than eutrophic (with abundant nutrients), as is the case for many cyanobacteria blooms. Interestingly, stalks and thus colonies are larger with lower nutrients, as D. geminata cells compete for scarce phosphorus (P), an often limiting nutrient2; blooms are due to a phenomenon called oligotrophication, or nutrient depletion in turn linked to acid rain, nitrogen enrichment, snowmelt and growing season timing shifts, and lower P in the oceans due to reduced salmon populations3. High light levels are also required by this species to produce the stalks that comprise most of its blooms biomass.


Fig. 2. Global distribution of Didymosphenia geminata (Source: Invasive Species Compendium).

The discovery that this diatom preferentially forms blooms with [P] < 1-2 µg/L (or ppb, parts per billion) stems from a sequence of experiments (see Fig. 3), and studies culminating in Bothwell and colleagues’ epiphany that blooms do not seem to persist despite, but because of, low P3.

Fig. 3. Experimental flume on the bank of the Waitaki River (New Zealand). Source: Bothwell & Kilroy (2011).

In the first place, the current spread of the “woolly-looking thick mats” of D. geminata started with fisher people accidentally transporting its cells on felt-soled waders, and fishing gear (Fig. 4)4. Thankfully, initiatives to stop the production of this type of boots are taking place, a simple and direct measure to avoid, or at least limit, the associated negative impacts on the quality of drinking and recreational waters in many rivers worldwide.

Fig. 4. Didymosphenia geminata bloom (Heber River, Vancouver Island, September 1989), in Bothwell et al. (2009).

  1. Source:
  2. Kilroy C. & Bothwell M. (2011). Environmental control of stalk length in the bloom-forming, freshwater        benthic diatom Didymosphenia geminata (Bacillariophyceae). Journal of Phycology 47: 981–989.
  3. Bothwell M.L.Taylor B.W. & Kilroy C. (2014) The Didymo story: The role of low dissolved phosphorus in the formation of Didymosphenia geminata blooms. Diatom Research 29, 229-236.
  4. Bothwell M.L., Lynch D.R., Wright H. & Deniseger J. (2009) On the boots of fishermen: the history of didymo blooms on Vancouver Island, British Columbia. Fisheries, 34, 382–388.

Monday, August 22, 2016


The Peril of Peat: Sea Level Rise in South Florida: Part 1

Post by: Ben Wilson


Ben Wilson having some fun in the mud
I love mud. Seems like I have for a long time now. It’s squishy and smelly, and once you get a little bit on you, you might as well go all out. I’m lucky in that the two most recent places I’ve lived, coastal Alabama and now in Miami, have had ample areas for me to get my mud fix. However, over the past century those areas have been dramatically decreasing, and given current and future climate change, they may disappear at an even greater rate. Over the next two blog posts, I will tell you how human development has altered water flow in the past, further exacerbating the problem of today: sea level rise. In order to save the mud, we must first look at what caused this problem in the first place.

Drain, baby, Drain

Whole books have been written on why and how the Everglades have been modified and managed, but I will just hit the highlights here. The Everglades as it is today began forming about 5,000 years ago when sea level began to stabilize following the last ice age. During the rainy season, water would spill over the banks of Lake Okeechobee and flow as a sheet down the Florida Peninsula. Beginning in the 1880s and continuing into the 1940s, attempts began to drain the Everglades in order to use its fertile land for agriculture. Canals and dikes were highly successful at shuttling water away from the Everglades. However, this soon caused extensive droughts and fires, leading people to realize that water flow needed to be managed to create the perfect balance of not too much water to flood the crops, but enough to prevent drought.

 As you can see below, all these efforts completely altered the water flowing through the Everglades and threw a stable ecosystem into imbalance. Much less water is getting to the coastal Everglades, and this is becoming a large problem because of the ever growing issue of climate change.

Historic water flow (left) versus current water flow as a result of intensive management (right) has led to dramatically less freshwater flowing south. Source

How could it get worse?

Do you know where your drinking water comes from? In south Florida, it comes from the Biscayne Bay aquifer, which is fed by rainwater that flows through the Everglades and seeps below the ground. The head pressure of freshwater aquifer is so great that it can push back saltwater from the ocean and keep it from coming inland. This vast aquifer is one of the reasons why this region has been able to cope with the population boom, now at over 6 million people living in south Florida. Now as you can guess by reading above, altering the flow of freshwater has diminished the aquifer, reducing its size and head pressure. But reduced flow from the north is not the only threat to this aquifer…
Past and predicted future sea level rise.  Source: IPCC (2013).
Climate change and the warming associated with it has accelerated sea level rise as oceans expand and arctic glaciers melt. Because there is less freshwater to push the oceans back, saltwater has begun to intrude at greater rates into the aquifer. This is threatening the drinking water supply as the pumping wells in coastal cities are starting to pull up undrinkable brackish water. Recently, some wells in Broward County on the eastern coast had to be abandoned due to saltwater intrusion. As the population continues to grow and seas continue to rise, this problem will only become exacerbated unless action is taken.


The zone where saltwater from the ocean and freshwater from the aquifer mix has been moving inland at a rapid pace, causing saltwater intrusion into pumping wells. Source: St. John’s River Water Management District.
So now that you know the causes of saltwater intrusion and one of the problems it is producing, I’m sure you are wondering “What about the mud?” and “What can we do to solve this?” Stay tuned for my next post to find out!

Wednesday, July 20, 2016

Diatom of the month – July 2016: Nitzschia amphibia

Nitzschia amphibia belongs to the nitzschioid group: its valves are symmetrical to both apical and transapical axes, and taper to bluntly rounded apices; the raphe is well developed near the valve margin, and enclosed within a canal1. The original description was made by Albert Grunow in 1852, when the US President was Millard Fillmore, the last one not to be affiliated with either the Democratic or Republican party. This is how ‘old’ are some of the species names of algae and other organisms that persist to this day, while new species are continuously described at an increasing rate. Grunow was one of the eight most ‘profilic’ algal taxonomists who described more than 1,000 species during their career, the others being Kützing, Gottfried, Hustedt, Agardh, Harvey, who worked in the 1800s, and Lange-Bertalot (the only one still alive and active) and Skvortsov in the 1900s2.

Fig. 1. a) Nitzschia amphibia in valve view and girdle view (scalebar = 10 µm(photos by Pat Kociolek); b) Florida Coastal Everglades LTER program diatom image database.

While the number of algal taxa discovered per taxonomist is increasing, the number of taxonomists is going down (Fig. 2), not a good sign on the already difficult road to a deeper understanding of thousands of species of algae and their ecology. New molecular and genetic techniques imply that doubtful / uncertain species (from a traditional taxonomy viewpoint) are increasingly called ‘clade’ (a grouping that includes a common ancestor and all the descendants, living and extinct, of that ancestor), ‘specimens’ (a single example of a collected alga) or ‘strains’ (a genetic variant or subtype). This creates the further challenge of integrating historical collections into such modern laboratory research2 to provide continuity, whilst improving the accuracy of such discoveries.


Fig. 2. The number of algal species described by each taxonomist keeps increasing while the number of specialized taxonomists is decreasing (source: Clerk et al., 2013).

So the algal taxonomy road, and this blog post, do lead somewhere2…here let’s zoom back on this month’s diatom. Nitzschia amphibia is a glass-encased moderately motile alga that likes muddy aquatic habitats, and is an indicator of phosphorus enrichment (>800 µg g-1 in Everglades periphyton), alongside other diatoms such as Gomphonema parvulum, Eunotia incisa, Rhopalodia gibba, and the green alga Mougeotia (which has a carbohydrate cell wall, not a silica one like diatoms)3. In general, Nitzschia species not only glide horizontally in epipelic habitats (mud), but also vertically through the substrates, and, together with stalk-forming diatoms like G. parvulum support the formation of complex three dimensional biofilms. Such 3D communities abound in the Everglades (Fig. 2), and other freshwater ecosystems, for example in Lake Sakadaš, in the Croatian part of the Danubian floodplain4, and along the River Team in Northern England, where Martyn Kelly studies, but also draws (and tells stories about) how various species attach to plants and other algae (Fig. 3). His work is another example of the successful and important marriage between science and art that we are experiencing!

 Fig. 3. A periphyton sampling site in Shark River Slough (SRS-1d) where Nitzschia amphibia can be found (photo: Franco Tobias, April 2008).

Fig. 4. Three dimensional biofilms from the River Team (Northern England) as depicted by British diatom scholar and artist Martyn Kelly; river bed with the filamentous green alga Cladophora and numerous attached diatoms such as Craticula, Navicula, and Nitzschia (circled in red). Source: Kelly (2011) “Of microscopes and monsters - Journeys through the hidden world of Britain’s freshwaters” -

      2. De Clerck O.D., Guiry M.D., Leliaert F., Samyn Y., Verbruggen H. (2013) Algal taxonomy: a road to nowhere?
          Journal of Phycology, 49: 215–225.
      3. Gaiser E.E., McCormick P.V., Hagerthey S.E. & Gottlieb A.D. (2011) Landscape Patterns of Periphyton in the
          Florida Everglades, Critical Reviews in Environmental Science and Technology, 41(S1), 92–120.
      4.   Žuna Pfeiffer T., Mihaljević M., Špoljarić D., Stević F. & Plenković-Moraj A. (2013) The disturbance-driven
          changes of periphytic algal communities in a Danubian floodplain lake. Knowledge and Management of
          Aquatic Ecosystems (2015) 416, 02.

Wednesday, June 15, 2016

Diatom of the month – June 2016: Eunotia cisalpina

This month’s diatom comes from quite far, some 5,000 miles or 8,100 km North-East of Florida: Northern Italy. Its name is Eunotia cisalpina (on this side of the Alps, the southern side), and it was described a few years ago1 by Marco Cantonati, the Science Museum of Trento’s (MUSE) Head Limnologist and Phycologist whom I am visiting this week. We are at the foot of the famous and wonderful Dolomites mountains, one of over 50 UNESCO World Heritage sites in Italy, comprising some of the highest limestone walls in the world. North-west from here, small mountain lakes, springs, and mire pools dot the landscape of the Adamello and Cevedale mountain ranges; their waters have lower mineral content than the calcareous Dolomites due to the prevalence of siliceous rocks, such as granites. These oligotrophic, acidic, low conductivity habitats are perfect for E. cisalpina (and for E. fallacoides and E. insubrica, other new taxa to science described in the same 2011 paper1). The authors of the discovery can now say that, some 10 years earlier, they had ‘confused’ Eunotia cisalpina with E. islandica1. This is common in taxonomy, as observing more specimens and features or using new methods, allows investigators to identify and thus name new taxa in a time consuming yet exciting scientific process.

Left) Mountain lake in the Adamello, where rocks are mostly siliceous, and waters have very low alkalinity. This lake, as several others on the eastern slopes of the Presanella subgroup of the Adamello mountain range, beautifully faces the Brenta Mountain group (Western Dolomites); in this image, the contrast between different lithological substrata is shown, a characteristic of the Adamello-Brenta Nature Park. Right) further east, the Dolomites are made of dolomite (CaMg(CO3)2 or calcium magnesium carbonate) and extend over 1,000 km2 in the Lombardia, Veneto, Trentino Alto Adige, and Friuli Venezia-Giulia regions. Source:

Diatoms of the genus Eunotia are symmetrical to the transapical axis, but asymmetrical to the apical axis, and have a short raphe allowing them a limited movement ( An estimated 600 Eunotia species exist globally, many of which are / can be used to monitor freshwater acidification caused by industrialization, due to their preference for low pH waters3. A number of diatoms living in these pristine mountain habitats are included in the Red List2, as these environments are sensitive to airborne acid deposition, and other pollution by metals. In particular Al, Ba, and Mn react with acid compounds, and seem to cause teratological mutations in diatom cells (congenital abnormalities)4, thus threatening important primary producers in remote lakes and wetlands.

 Some of the shapes and sizes of Eunotia cisalpina. Source: Cantonati et al. (2011)1. Scale bar: 10 µm.

Another very interesting ecological characteristic of some Eunotia species is their apparent ability to resist desiccation by forming vegetative cells that survive heating1. This brings us back to the global warming challenge and its associated risks of more frequent and/or more intense droughts in a variety of freshwater ecosystems, from the 3,000 m alpine lakes in Europe to the Florida Everglades and other large wetlands in every continent. Diatoms and other algae, are indeed helping us to figure out how anthropogenic, including climatic changes, are profoundly modifying natural habitats. However, the scientific community needs much increased and sustained funding provision from public and private institutions to better and faster improve our ecological knowledge of such dangerous environmental changes. This is especially true for the detailed taxonomic and molecular work required to discover new species, know their biology and ecology, and use them as indicators of environmental conditions to advise decision makers on what to do, and not to do, to preserve and sustainably ‘manage’ ecosystems.

1. Cantonati M. & Lange-Bertalot, H. (2011). Diatom monitors of close-to-pristine, very low alkalinity habitats: three new Eunotia species from springs in Nature Parks of the south-eastern Alps. Journal of Limnology, 70, 209-221.
2. Lange-Bertalot H. & D. Metzeltin (1996). Indicators of Oligotrophy. In: H. Lange-Bertalot (Ed.), Iconographia Diatomologica. Koeltz, Koenigstein, 1-390.
3. Lange-Bertalot H., Witkowski A. & Bąk M. (2011). Eunotia and some related genera. In: H. Lange-Bertalot (Ed.), Diatoms of Europe. A.R.G. Gantner Verlag, K.G., Ruggell, 6: 1-747.
4. Furey P.C., Lowe R.L. & Johansen J.R. (2009). Teratology in Eunotia taxa in the Great Smoky Mountains National Park and description of Eunotia macroglossa sp. nov. Diatom Research, 24, 273-290.