The Critters of Watkins Creek

On October 19, our Stream Team sampled for macroinvertebrates at one of the sites that we monitor, at the east end of Coal Bank Road. We kicked up the creek bottom in order to trap the macroinvertebrates (invertebrates such as insect larva, snails, and worms that are large enough to see without magnifying equipment), herein after referred to as critters, in a net. We also rubbed the larger rocks in the sampled area in order to dislodge and collect the critters that make rocks their home. Then we sorted them out and counted how many of different kinds of macroinvertebrates we found in the portion of creek bottom that we stirred up. After counting, and photographing a few of the critters, we returned them back to the creek so they could continue to live their lives.

One of the good things about counting critters is that it’s easy to do. We only need to be able to stir up the bottom and rub on rocks, hold the net in place, see the critters on the net, and move them into the collection container (ice cube trays) with tweezers. Children can do it as well as adults. Another good thing is that many of the critters we study spend several weeks to months living in the creek bed. Some of them, like mayfly and stonefly larva, are very sensitive to harmful changes in water chemistry during the time they are larva. Some others, like aquatic worms, can live even in water so polluted that nothing else survives. By counting the different kinds of critters, then using a scale that Missouri Stream Team developed that rates each kind of critter for how sensitive it is, we can determine if Watkins Creek has excellent, good, fair, or poor water quality. If the sensitive critters are there, it means the water quality has been good for the last several months. You can learn more about water quality monitoring and the Missouri Stream Team programs from their website. Besides all that, it’s fun to play in the creek! How often do we adults get to do something fun that also does good?

How does Watkins Creek rate? Unfortunately, not as well as we’d like. At best it has fair to good water quality at the lower end of the stream. And the water quality may be on a downward trend; 2010 and 2011 data show fewer kinds of critters than does the 2008 and 2009 data, rating only fair both years. If this is so, we don’t know why.

Here’s a photo of three of the mayfly nymphs we found.

You can see the gills on the abdomen (between the legs and the tails) of the nymph on the upper left. Mayfly nymphs breathe with their gills like fish do. Most kinds need good water quality in order to live and thus are considered a marker of good water quality; some kinds can live in lower-quality water. I don’t know what kind of mayfly nymphs these are, however. Mayfly adults are delicate-looking flies that live only a very short time, hours to a few days. The nymph stage can live for several weeks to months.

Here’s a photo of a damselfly nymph.

In this case its gills (more properly, lamellae) are the three tail-appearing structures on its back end. Damselfly nymphs are considered somewhat sensitive to pollution but less so than mayfly nymphs. Adult damselflies look similar to dragonflies, but hold their wings more toward the vertical when at rest than dragonflies do.

And here is a picture of the area that we monitor, looking upstream. This is one of the nicest locations that Watkins Creek has to offer, and it’s easily accessible off of Coal Bank Road.