Golden Algae
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A Note on the Taxonomy of Golden Algae
The class Chrysophyceae ("golden algae" or "golden-brown algae") previously included many taxa that are now known to belong to distinctly different lineages; taxonomists have erected new classes to accommodate these taxa, and Synurophyceae is one such class (Nicholls & Wujek, 2015). The Synurophyceae were distinguished from the Chrysophyceae based on traits such as pigmentation, the form of siliceous scales covering the cells, and the presence or absence of certain organelles (Siver, 2015). Phylogenetic evidence, however, has yet to resolve the relationship between these groups: whether they truly represent two separate classes, or whether the Synurophytes constitute a distinct sub-group within the Chrysophytes, remains to be seen (Siver et al., 2015). Still, Siver et al. (2015) noted that phylogenetic studies have been consistent in finding that Synurphytes do indeed constitute a monophyletic group, despite the uncertainty regarding their taxonomic rank relative to the Chryosphyceae.
Setting aside matters of molecular taxonomy, our key did not further separate these groups primarily because they are alike in many of the defining traits that can be seen using light microscopy. In terms of coloration, motility, colonial or unicellular nature, and external cell covering, there is at least some overlap between the two. The information given below will first focus on the similarities between Chrysophyceae and Synurophyceae, and will then explore the differences between them.
Morphological Features of Golden Algae
Chloroplasts of both chrysophytes and synurophytes exhibit golden or golden-brown coloration (Chrysophyceans are sometimes referred to as “golden algae” or “golden-brown algae”), and both groups contain unicellular and colonial genera. All synurophytes are flagellated and are motile (Siver, 2015). Chrysophytes, on the other hand, are represented by both motile and non-motile (i.e., flagellated and non-flagellated) forms (Nicholls & Wujek, 2015). Flagellates of both groups are heterokonts, meaning they possess two flagella which differ in length (this can also be helpful for separating these taxa from flagellate green algae).
The presence of a covering composed of siliceous scales is integral to the definition of Synurophyceae (Siver, 2015). Siliceous bristles may also be present; these bristles are often long and prominent on cells of Mallomonas. You’ll likely be able to make out the presence of Synurophytes’ scales using a light microscope, and in many cases they’ll be hard to miss. However, we have seen Synura colonies whose scales are only subtly visible—always look closely! Some Chrysophyte genera also possess scales, but they are different from those found on Synurophyte cells (Nicholls & Wujek, 2015). These differences, however, may require advanced microscopy techniques (scanning or transmission electron microscopy, SEM and TEM, respectively) to detect. The only scaly, spiny member of Chrysophyceae that we have encountered is Chrysosphaerella, a genus of colonial flagellates. Another key difference between the two is Synurophytes’ lack of an eyespot (Siver et al., 2015).
In some Chrysophyte genera, cells are surrounded by a lorica. Dinobryon is fairly common in our samples; cells in this genus are housed within vase-shaped loricas. Cells of Bitrichia, another loricate Chrysophyte genus we have observed, possess loricas that taper into long, pointed spines.
Dinbryon (Chrysophyceae), with eyespots labelled.
Ecology of Golden Algae
Most genera of Chrysophytes are typically planktonic, and Synurophytes are exclusively planktonic (Wehr & Sheath, 2015). Both groups are often abundant in the plankton of lakes when temperatures are low during spring turnover (Siver, 2015). In planktonic water samples analyzed by NJCWST, Mallomonas and Dinobryon have thus far been the most commonly observed representatives. Over the course of a year-long phytoplankton sampling project, chrysophytes & synurophytes were most abundant in the winter and early spring, according to NJCWST’s microscopic examinations.
Chrysophytes are more common in lakes with lower levels of nutrients, where they can out-compete other algae; in more eutrophic waters, they may reach greater abundances when water temperatures are cooler (Nicholls & Wujek, 2015). Synurophytes are also more common in low- to moderate-productivity (oligotrophic to mesotrophic) waters—though not in ultra-oligotrophic waters—and often account for only a small fraction of the total phytoplankton biomass in eutrophic waters (Siver, 2015).
Genera Observed by NJCWST
Commonly observed
Dinobryon
Synura
Mallomonas
Occasionally or rarely observed
Uroglena
Chrysosphaerella
Bitrichia
Chrysodidymus
Chrysolykos
Ochromonas
Pseudokephyrion
Image Gallery
Click the arrows next to each genus listed below to view photos.
Bitrichia
Chrysolykos
Chrysosphaerella
Dinobryon
Mallomonas
Ochromonas
Pseudokephyrion
Synura
Uroglena
References
Nicholls, K.H., & Wujek, D.E. (2015). Chrysophyceae and Phaeothamniophyceae. In J. D. Wehr, R. G. Sheath, & J. P. Kociolek (Eds.), Freshwater Algae of North America: Ecology and Classification (2nd ed). Waltham, MA: Elsevier.
Siver, P.A. (2015). Synurophyte Algae. In J. D. Wehr, R. G. Sheath, & J. P. Kociolek (Eds.), Freshwater Algae of North America: Ecology and Classification (2nd ed). Waltham, MA: Elsevier.
Siver, P.A., Jo, B.Y., Kim, J.I., Shin, W., Lott, A.M. and Wolfe, A.P. (2015), Assessing the evolutionary history of the class Synurophyceae (Heterokonta) using molecular, morphometric, and paleobiological approaches. American Journal of Botany, 102: 921-941. https://doi.org/10.3732/ajb.1500004
Wehr, J. D., & Sheath, R. G. (2015). Introduction to the Freshwater Algae. In J. D. Wehr, R. G. Sheath, & J. P. Kociolek (Eds.), Freshwater Algae of North America: Ecology and Classification (2nd ed). Waltham, MA: Elsevier.