Macro attack
November 15, 2006, 5:06 pm by Jess. Filed under: love those goofy b*st*rds.

Benthic macroinvertebrates. They’re not actually that big. Not big enough to star in a horror movie (Attack of the Bottom-Dwelling Gargantuan Spineless Things?). But they’re visible to the naked eye, which is convenient for us. These aquatic creatures can tell us a lot about water quality. Some, when faced with pollution, gurgle, “Bring it on!” while others expire at the slightest dip in dissolved oxygen.

Recently I got to go out and scrounge up some of these critters. I and some other stream enthusiasts set up a complex mouse-trap-like mechanism, involving tubes, baubles, pulleys, bait, and suction, in the stream, then retreated while our prey ensnared themselves.

Really, we just plopped a net in the current and violently raked and scrubbed the creekbed to free the clinging critters into our net. The we emptied the net into a bucket and proceeded to sort the bugs in ice cube trays, examine them with nifty Transformer-like field microscopes, and identify them.

In a good stream, you’ll find biological diversity. The Big Three to look for are stonefly, mayfly, and caddisfly nymphs. If you have a variety of these guys, your stream has not yet died. Another important thing: these insects are a main food source for little salmon.

So, what did we find…?

Mayfly nymphs

Mayflies have a lovely name: Ephemeroptera. They are dust in the wind. The adults (air-dwellers unlike the larvae) live for a short time in an all-out mating frenzy. Mayfly nymphs have this charming habit of swimming frenetically, then freezing and floating on their back, legs rigid. It is a transition from frenzy to inertia that is almost too abrupt for the human eye to perceive.

The prong-gill. An old favorite. We found enough of these bugs, whose gills look like eyelashes with split ends, that we started to treat them like an underappreciated family member.

The flathead.

Caddisfly nymphs

Talk about tiny houses! I think bottleman should do a post on these bugs’ abodes. They use silk to construct little cases to live in. Beats the bower bird any day, in my opinion.

The northern case maker. I want to live in these houses! Imagine going to bed every night in a wee mosaic of pebbles. Or if you have hipper taste, a sleek, stream-lined pine needle chamber. We took samples at four different sites, and we kept hoping we would get one of these legendary beasts. They are measured in centimeters, not millimeters. At the last site, we finally got one!

The saddle case maker. I enjoy this motley, jewel-studded home, which looks like an amateur art project. That’s his rear end, not the face of an evil video game villain. Deprived of the case, they look like sweet baa baa black sheep.

The netspinner. This is a humble guy. He is green, always curled up, and seems unhappy. In personality he reminds me of a man who begins to go bald at twenty. But physically he is very furry. He has soft tufts all along his belly that I am sure are very dingleberry-prone. He spins a net to catch prey, but this diaphanous membrane is always lost in the process of capturing. Maybe this is why he is so sad.

The fingernet. This is the punk rocker of caddisflies. Electric yellow and translucent, he is a trip to look at under the microscope.

Stonefly nymphs

Stoneflies are the most sensitive, so their presence is an indicator of good stream health. They are burly-looking, and can be seen doing push-ups when deprived of oxygen (sounds counterintuitive, but it’s meant to pass more water over the gills). Among other kinds, there are the Little Yellow, the Little Green, and the Little Brown. Krzysztof Kieslowski should do a trilogy on these.

The little yellow. These are extra sensitive. We didn’t find any.

The little green. We found a few of these. They’re more slender and delicate-looking than their bodybuilding counterparts.

The little brown.

The roach-like. For some reason, reminds me of a vacuum cleaner.

Others

Aquatic earthworm. This thin annelid looks like red thread that is constantly tangling in itself. Apparently wayward, it doesn’t seem to know which needle eye it’s headed for. There is also the multicolored, candy necklace variety.

Riffle beetles. Yawn. We found a lot of these. Both the youth and the harlequin-patterned adult live in water.

Mosquito larvae. I was taken aback by how beautiful the larva of this pest is. Under a microscope, the feathered tail is very intricate. They have an almost regal appearance, as if wearing a puffy fur collar. Either that or as if a bubble was blown into their arse. They live in the water, but come to the surface to breathe air. Maybe that bulge is a big gulp of air?

Unidentified eel thing. (Sorry, no picture.) Something about the way this large thing moved gave us all the willies. It thrashed about like a kraken in our ice cube trays. It was much too large for the little compartments, reminding me of a fast-forwarded video of a teenage Hulk outgrowing his clothes.

The Verdict

The creek we monitored was moderately healthy. We have been monitoring water chemistry and flow here all year, and this result was consistent with what we’ve found. There is a lot of development upstream of the monitoring site, and this means few trees to provide shade, so the creek warms up (not what you want for fish or bug habitat) and suffers nonpoint source pollution.

For more information or if you want to get involved in macro sampling (and water quality monitoring in general) in the Portland/Vancouver area, email me or check out Michael Clapp’s great website. All these pictures are from him.


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Very cool page; thanks for assembling it. We just spent some time at a relatively clean Adirondacks “Kettle” lake, looking at the near-shore benthic invertebrates. We saw some very similar case-making nymphs.

Comment by jonesparg on 11.08.2011 um 10:44 am



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