Diatom of the month – October 2016: Brachysira brebissonii

by Charlotte Briddon* 

Brachysira brebissonii (formerly known as Anomoeoneis brachysira) is a freshwater, benthic diatom. It is widespread in lakes and rivers from the Arctic to tropical and temperate regions. In 1981 the Anomoeoneis and Brachysira genera were separated, as two sets of longitudinal ribs were observed in Brachysira specimens, one surrounding the valve (marginally at the junction of valve face and mantle), and another composed of two straight ribs, discontinuous in the central area that border the raphe, which the genus Anomoeoneis lacks.






              Brachysira brebissonii (photo taken by Paul Hamilton at Egg Harbour Lakes, New Jersey, United States; see Hamilton, 2010).

Case study of Tasik Chini
I have chosen this diatom because it has played a meaningful role in aiding our understanding of past and current environmental conditions/water quality at Tasik Chini, (a flood pulse wetland in Malaysia). Tasik Chini, a natural freshwater flood pulse wetland, consists of a series of 12 interconnected basins in central Pahang and is hugely important from a conservation viewpoint in that it is has been awarded protected status by UNESCO's Man and Biosphere Programme. This program’s goals are to establish a scientific basis for the improvement of relations between people and their environments. It uses a combination of sciences to improve human livelihoods and to safeguard natural and managed ecosystems. Understanding how this lake has been impacted by an array of anthropogenic activities such as deforestation, mining and agriculture over the last 100 years or so is crucial in formulating conservation efforts to retain ecological integrity at this site.
 Oil Palm Plantation from the Tasik Chini lake catchment (photo: C. Briddon).
Brachysira brebissonii is acidophilous, it has an affinity for environments with pH < 7, with an optima of ~ 5.9 (Stevenson et al. 1991). Changes in abundance of this diatom in a sediment core can, therefore indicate pH variations in the lake over time. An abundance increase of this diatom over time may be due the onset of lake acidification from either natural (e.g. catchment geology or vegetation) and/or anthropogenic influences (such as atmospheric deposition of sulphates) (Wolfe and Kling, 2000).
 
   Nucifera Nelumbo, the famous water louts from Tasik Chini (photo: C. Briddon).

Analyzing a 90 cm sediment core taken from Basin 12 at Tasik Chini, we found this diatom to be most abundant in younger sediments deposited when anthropogenic impacts were largest at this site. The increasing relative abundance of Brachysira brebissonii provides important evidence of acidification and eutrophication of Tasik Chini over the latter half of the 20th century, most likely caused by increases in human activities such as mining, agriculture (palm oil and rubber plantations), hydrological manipulation and deforestation.
In addition, Brachysira brebissonii was found to be the most abundant diatom (~36 % maximum) in contemporary diatom habitats sampled in April 2016. It was observed in high numbers on leaves and stem of the iconic water lotus (Nelumbo nucifera), a key species for eco-tourism at Tasik Chini). Thus, this diatom may also be an indicator species for the presence of this floating-leaved plant.

*Charlotte is a first year Ph.D. student at the University of Nottingham, under Suzanne McGowan's supervision. She conducted her work on Brachysira brebissonii during her MRes studies at Keele University during a placement at the University of Nottingham Malaysia Campus.


References

Hamilton, P. (2010). Brachysira brebissonii. In Diatoms of the United States. Retrieved October 18, 2016, from http://westerndiatoms.colorado.edu/taxa/species/brachysira_brebissonii
Stevenson, R. J., Peterson, C.G., Kirschtel, D.B., King, C.C.,  Tuchman, N.C. (1991) Density-dependent growth, ecological strategies, and effects of nutrients and shading on benthic diatom succession in streams. Journal of Phycology 27, 59–69
Wolfe, A.P., Kling, H.J. (2001). A consideration of some North American soft-water Brachysira Taxa and description of Barctoborealis sp. nov. Lange-Bertalot –Festschrift

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