Difficulty identifying algae in pond water samples

Hi Andrew,

The difficulties you’re having with identification are quite normal. It will certainly become easier as you acquire experience, but there will always find some things in your microscope that resist explanation! Increasing magnification and image resolution will help. Some of your images are in darkfield, or partial darkfield, which is not very good for identification (except for a few very specialized applications, like spotting spirochetes in human blood!). For instance, I wouldn’t even attempt to identify the filaments in the second image (experience suggests unhealthy remnants of a filamentous green alga, but without a glimpse of the chloroplasts even that is in doubt).

In the brightfield images, I see a few empty diatom frustules in the brightfield images. The ones that look like bent canoes are cymbelloid diatoms (possessing asymmetrical frustules, like those of Cymbella). there are lots of sites that offer help with diatom identification (this one, for instance: http://westerndiatoms.colorado.edu/ ).  I don’t pay much attention to them, as a group, but the procedures for identifying organisms are the same for all groups. You need to learn the basic anatomical features that set one taxon apart from the other. Does your diatom have a “raphe” (central line down the middle)? What kind of “striae” (perpendicular or oblique striations) does it have? And so on.

As for the green ball, it appears to be a small colonial volvocid in a gelatinous envelope, such as Pandorina morum. However, we don’t see a lot of detail, so I wouldn’t necessarily try to give it a genus, let alone species. A general, high-level identification should be satisfactory. I’d simply call it a “volvocid alga, possibly Pandorina.”

I hope this helps, a bit!

cheers,

Bruce

Hi Bruce,

Another thing that I find somewhat confusing is that the books should two views of each organism looking down (valvular view) and what looks like looking across the structure. One of the organisms in my photos on link below shows square structure and I am guessing this is crossways view as it does not appear to be the same as anything in books you kindly sent me. But I can’t tell which one!
Also my reading suggests these organisms have different looks when as spores or mature organisms but I don’t know what difference in view between two is…..

Andy

From: Thornett Andrew
Sent: Monday, May 29, 2017 03:16
To: Bruce Taylor
Subject: Re: Identifying pond organismsIt does indeed – thank you very much.
“empty diatom frustules” – that explains why I could not work those out – I thought it was weird that they were only simple square objects without anything obvious inside them! Why would they be empty? Are they the remnants of dead organisms or is this part of the division process?
Andy

From: Bruce Taylor
Sent: 29 May 2017 16:12
To: Thornett Andrew
Subject: Re: Identifying pond organismsYes, these are just the shells of dead organisms. Diatom shells are made of silica (like glass), and are very durable. When the organism dies, the living part of the diatom is consumed by bacteria or other protists, and the shell sinks down into the muck at the bottom of the water. They can pile up down there and form large deposits of “diatomaceous earth,” which can endure for millions of years.If most of the diatoms are dead, it is usually a sign that your sample is old, or that it was taken at a time of year when algae are mostly dormant.best,
Bruce