I started identifying and calculating phytoplankton and cyanobacteria biovolumes from the mesocosm experiment. This is great because I love plankton but also not so great because it gives me lots of taxonomic nightmares. I have some great in-house expertise at the Centre for Ecology and Hydrology for phytoplankton and cyanobacteria (Laurence Carvalho and Helen Woods) but sometimes for some trickier ones its good to cast the net a bit wider to get as much advice as possible. As cyanobacteria is now what I'm all about, I need to make sure I get this spot on so I'm hoping the wider cyanobacteria specialist community will give me a helping hand every now and again!
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?
Specific identification advice:
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):
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:
Sample 2 - most cells were indistinguishable apart from a few trichomes where some cell walls could be seen so I then questioned whether I was actually seeing Limnothrix redekei rather than Pseudanabaena.
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.
Anabaena vs. Aphanizomenon:
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.
Tapering ends and akinete
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
Akinetes are quite variable in size and shape. Some have slightly dented middles and clearly defined cell walls whilst others are straighter and longer. Unfortunately when I saved the images with the measurements on them in jpeg format the measurements were lost. Size noted down in my note book are:
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.
What I think this is: Aphanizomenon gracile.
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!
I have managed to turn my rather unhealthy obsession with plankton in to my day job. Things don't get much better than this! This blog documents my PhD research and the plankton delights I encounter along the way.