It has been waaaaay too long since I posted anything on my blog. I apologise for that. Funny how life can speed-up and suck all your time—especially over Christmas holidays when you have kids! Anyhow, I’m back and will try and get back into the habit of posting more regularly…
I collected a few of these critters last summer from the same stream that I collected specimens of the freshwater wild flatworm (Polycelis coronata). As far as I can tell they are all specimens of the freshwater gammarid amphipod Gammarus lacustris. Given that this is the only species of freshwater amphipod from the family Gammaridae found in British Columbia, the identification is a safe bet. However, I was pretty excited about finding the flatworms and really didn’t put much effort into photographing the amphipods. Too be honest, they were really active and a challenge to shoot. So I just took a few quick photos and then move on the worms. I figured I’d get back to photographing amphipods later in the summer, but it just didn’t happen. At the time I wasn’t satisfied with the photos I did get and just filed and forgot them.
A week or so ago I was going through some files and came across these pictures, which I had honestly forgotten about. As often happens, when I looked at them I decided they weren’t all that bad after all—funny how often that happens. To be fair, they aren’t my best work: the water wasn’t clean enough, their poses aren’t exactly inspiring, and the dead leaf they are crawling on makes for a distracting backdrop. The leaf was from their native stream, but they would have looked much better against some green aquatic plants.
The critters themselves are pretty cool though. These amphipods are common throughout North America and feed on bits of organic debris: dead plant and animal material. I read that they need well-oxygenated water which means they are typically found in cold water. However, around where I live I seen to run into them in most non-stagnant bodies of freshwater. I live in an area with a lot of agricultural run-off, so perhaps that means that there is bounty of detritus for them to feed on.
Whenever (and wherever) I have collected freshwater Gammarus in the past, they have been coloured drab shades of brown and olive green like the animal in the photo directly below. But as you can see, the Gammarus I collected from this particular stream showed some real diversity in colouration, including some really pretty specimens (like the one at the top of the page) which had bright red spots on a translucent yellowish body. Others had a single very obvious bright red spot on their side. I still don’t know if the spot was on the critter’s exoskeleton or was something inside the body…and I still can’t tell from these photos.
Clearly I need to get back to this stream again this summer to collect more Gammarus and do a better job of photographing them. I’d especially like to capture some more interesting behaviour than just sitting on a dead leaf.
All of these photos were taken with the animals in a small aquarium, using the same set-up that I have described previously (see: Photography of a diving beetle part 1).
The technical stuff:
Camera: Olympus E-620 digital SLR
Lens: Zuiko 35mm macro
Settings: manual exposure (F11 @ 1/125 sec)
Lighting: on-camera flash (full power)