Diatom of the month - November 2015: Encyonema evergladianum

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by Luca Marazzi*

‘Who’ is it?
Encyonema evergladianum is a diatom living attached to various substrates, but is also able to move, if it needs to. It was originally described in 1997 by Krammer from samples collected in the Florida Everglades, USA.

                 Scalebar = 10 µm    Scalebar = 5 µm 

 Encyonema evergladianum (Length range: 16-33 µm; Width Range: 4-6 µm; Striae in 10 µm: 20-22)

Where does it live?
This beautiful diatom lives in the Everglades periphyton mats, characteristic multi-color ‘biological carpets’ inhabited by bacteria, fungi and, importantly, by algae attached to soil and plants that feed all sorts of critters. These are in turn eaten by fish that, as we know, become food for birds and for humans too.

Nine mile pond.

                   
                       Calcareous periphyton mat.    



In the interior Everglades, these mats have a top calcium carbonate (CaCO3) layer produced by cyanobacteria (Gaiser et al. 2011, Hagerthey et al. 2011). These photosynthetic organisms are a lower-quality food for invertebrates and fish than diatoms and green algae (Geddes and Trexler, 2003). Encyonema evergladianum has been observed in rivers throughout South Florida and in Central Texas, but these records have not been confirmed. Our young scientist Viviana Mazzei found this species in karstic, freshwater wetlands up to the spectacular coastal mangroves in Everglades National Park.

Why are we studying it?
To understand how sea level rise affects the abundance of Encyonema evergladianum and the concentrations of solutes (for example, calcium, sodium, chlorine) and nutrients (nitrogen and phosphorus) in the periphyton mats, one of the things we do is to control small parts of the environment in mesocosm (‘middle-sized world’) experiments. By increasing salinity and phosphorus levels in the periphyton mats, we are generating new ecological knowledge to help conserve the Everglades, an ecosystem at high risk, as you can see in this recent TV documentary: “Everglades Under Attack”.





    
Scheme of freshwater (FW), marine water (MW) and groundwater (GW) flows and varying ratios nitrogen : phosphorus concentrations (N:P).   

Mesocosm experiment in Key Largo to assess effects of salinity and phosphorus on diatom abundance and periphyton mat mineral content.

What can you do?
Let us not forget where some of our food and a lot of the oxygen we breathe come from, invisible aquatic plants like our diatom of the month! Many fish eat snails and other little animals that feed on hundreds of species of algae like Encyonema evergladianum. Share this information with your friends, family and colleagues, follow us on Facebook and go visit the Everglades, a unique wetland that we need to study and protect as our natural heritage!
* Postdoctoral Associate in Dr. Evelyn Gaiser's lab at Florida International University. 

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