Work find

About a week ago, I got new work – well, I have worked there every year since the first time, about six years ago – in the Department of Aquatic Sciences and Assessment at the Swedish University of Agricultural Sciences (SLU). In fancy terms, I could be said to be sorting benthic invertebrates, meaning that I pick out small, bottom-dwelling creatures from samples of lake or river bed, separating them from mud, debris and various types of plant material they come with. This is the rough work before experts take over to determine the species of the animals, and use that data to assess certain environmental parameters (e.g. acidity) of the water. Previously, I have also been doing some gross classification into major groups.

The benthic zone is a more technical term for the bottom of a body of water. Here, we are only concerned with Swedish freshwater bodies, so there are no marine creatures. We do not specifically look for invertebrates, but there are no bottom-dwelling vertebrate animals, at least not in Swedish lakes and rivers; thus, we only find invertebrates in the samples – with a few exceptions, such as occasional fish that accidentally are caught with the sample (which gives it a horrid smell, I might add), and another that I will describe soon.

A chironomid (a type of mosquito) larva. In the samples we work with, they are white or paler brown, in contrast to their bright red colour in life. Still, the very distinct shape – stiff along the trunk’s main section, and curved inward at the two ends – is an easy way of identifying them among a mesh of plant threads. Picture from http://www.glerl.noaa.gov/seagrant/GLWL/Benthos/Insecta/Diptera/Diptera.html

(Un?)fortunately, the sample has been stored in highly concentrated alcohol for some months, so everything is dead, colourless and sometimes downright soggy. For the sorter, this is both good and bad: the creeps are dead and therefore relatively easy to grab with a pair of tweezers, but the alcohol (I think) has destroyed their pigments, so everything is white, light yellow-brown-grey, making the animals more tricky to spot. Still, once you get used to it, that is not much of a problem – soon, you learn to screen the material for their distinct shapes or textures. 

An asellid, a freshwater-dwelling lice, related to woodlice. Compare (a) the live form with (b) the dead, decolourised ones. Sources: (a) http://www.insecte.org/forum/viewtopic.php?f=45&t=47011 (b) http://digilander.libero.it/enrlana/e_prfr.htm

This job has its pros and cons. The animals are so small that one must use a stereoloupe (similar to a microscope, but you have the material in bowls or Petri dishes instead of flat slides), and anyone who has worked for hours by one knows how bad it hurts your neck and back if you sit still for too long; also, it occasionally also hurts my eyes a lot, especially if I need to focus hard for a lengthy period of time. Also, this work requires considerable discipline, patience and, most importantly, self-control – when those freaky bastards get entangled or completely wrapped in sinewy plant threads, you are filled with desires to smash your fist right through the sample, or throw the stereoloupe out the window and laugh as it cracks into millions of pieces against the ground, three stories below. I’m usually not an aggressive guys, and neither is my good friend Tim, who worked with this too this winter (his company saved me from going completely mad, something I owe him much for), but we both recognise these scary, yet completely understandable impulses and lusts for spontaneous destruction.

On the plus side, it is a calm, quiet job, with little physical pressure, except on the neck region and the eyes. Also, it is a way of acquainting yourself with some aquatic animals, and, perhaps more usefully, it gives you practice to identify different types of animals, and tell animals apart from plants (and rocks). Now, distinguishing animals from plants might seem to be a ridiculously easy thing – “plants are green, and animals can move” (…ahem…) – but remember that these samples are essentially colourless, so, instead, you practice other ways of identifying animals, e.g. symmetry (some animals have no symmetry, but they are marine), specific texture, shapes, etc. For the part of identifying different forms of invertebrates, this job is quite good practice for a paleontology aspirant, since many of these have fossil relatives. I have found gastropods, plenty of bivalves, crustaceans (including ostracods, although they are planktonic, so we don’t pick them, and isopods), arachnids, and several forms of arthropod larvae and worms, which, however, lacking a skeleton, are not as common fossils.

Still, the main reason why I even wanted to write about this job here is because of the marvellous find I made on my first day this time: lots of bones! In one of the samples, there was a partial skeleton, almost completely disarticulated (i.e. the bones are not attached as they were in life). First, I casually spotted something I though looked funnily much like a vertebra. After disregarding that possibility, it was not many seconds before I found another one. I looked closer, and yes! Those were definitely vertebrae!

I hardly know anything about vertebrae, but it is never too late to begin to learn about them, so I picked out as many as I could during my coffee pause (I don’t drink coffee anyway) and brought them home for examination. I also found other bones – maybe ribs, fin spines, and perhaps even a scapular blade (homologous to our shoulder blade).

Of course, I immediately thought about what kind of animal this could be. A fish was a clear possibility, but I did not want to rule out amphibious vertebrates, such as frogs. However, when I looked at the sample description, I learned that it had been taken at a depth of 18 metres. I doubt that frogs would be at such depths. Of course, it could really have been anything that could have fallen into the water and sunk to the bottom, but I find it most likely to be a fish, until I can find out for sure.

I intend to ask permission at my old school to use their stereoloupes to study this, my first skeleton find, when their term begins (ate August, so I have a good month before I am off to England). Hopefully, this will help me learn a great deal about (fish) vertebrae.