Taxonomic guides: below are the main guides I refer to, those with images e.g. Australian book/ manual of aquatic cyanobacteria and those with drawings and more detailed descriptions - The Freshwater of the British Isles, Manual of aquatic cyanobacteria and the papers by Jiri Komárek on straight and coiled types of Anabaena. I also use the Czech Cyano database.
1. Suggestions for other useful taxonomic guides?
2. Good formus for discussing taxonomic issues?
In one of my mesocosms I keep on coming across two different cyanobacteria species which are causing some identification problems (I'm not 100% confident):
- Pseudanabaena vs. Limnothrix
- Anabaena vs. Aphanizomenon
The samples are from heated (+4°C) mesocosms (3000L capacity) in Lancaster (North West England) and are fixed with Lugol's. Images taken in phase contrast at x40 (some at x63)
Pseudanabaena vs. Limnothrix:
Trichomes solitary and straight, sometimes slightly bent.
Trichome average width: 1.5 µm (sample 1 - December), 1.4 µm (sample 2 - June)
Cell length (where distinguishable) ~4.4µm
In sample 1 the cells were distinguishable with cross walls narrowed and with cells abutting and so were recorded as Pseudanabanea limnetica:
Brian Whitton in - 'The Freshwater Algal Flora of the British Isles' - highlights the taxonomic and nomenclatural problems of Oscillatoria limnetica (Pseudanabaena limnetica) and Oscillatoria redekei (Limnothrix redekei). Specifically he notes that populations of P.limnetica can merely be a growth form of L.redekei whereas it is unlikely that P.limnetica can be a growth form of L.redekei.
The advice needed:
What should I call this? I would have said Pseudanabaena based on the first sample but the second sample makes me question whether I am just seeing a different growth form of Limnothrix. Or am I actually seeing two different things? I'm suspecting that without genotypic information I won't be able to know with certainty and should note them down as Oscillatoriales however any comments about how other people deal with problematic species like this would be useful.
Solitary and straight but some bent at heterocyst, cell junction. Ends slightly tapering. Mean diameter at widest point - 3 µm, mean diameter at narrowest point - 2.5 µm.
See trichome diameter for cell diameters at narrowest and widest points.
Length: variable, sometimes hard to distinguish cell boundaries with certainty. From 30 cell measurements:
Min: 2.4 µm
Mean: 3.7 µm
Max: 5.9 µm
Generally longer than wide (4.6 µm x 4 µm ), distant and intercalary. Up to 7 heterocysts per trichome dispersed fairly evenly along the trichome. Some variability in size ± 0.9 µm.
Rarer than heterocysts distant and beside heterocysts and singular and seen in a pair. The two seen in a pair were next to a heterocyst. Sizes very variable
Length µm: 18, 15.6, 19.7, 12 (mean: 16.3 µm)
Width µm: 6.7, 7, 4.4, 4.6 (mean: 5.8 µm)
The image below shows two akinetes within the same trichome but of differing size. I wonder as akinetes are rare that a potentially nutrient limitation or another environmental pressure has initiated the start of differentiating vegetative cells to resting cells and that I have caught trichomes in the process of doing this? I'm not sure about the natural variability of akinetes within individual trichomes.
Concerns - instinctvely I thought it was Aphanizomenon however I was unsure about the degree of tapering at the end. Looking through all the keys cell size appears to be to big for most Anabaena species but I want to double check.
Advice: correct identification - please!