Q.
From Steve in Sunnyvale, CA: What are the small globs found on stones;
the globs are slimy and contain white, egg-type material? They are about
1/2" to 3/4" in size and stick tightly to the rocks that I lift from my
favorite streams. They could be insect eggs, but I'm curious as to what the
material is that contains them.
I read something about these someplace, but can't remember where. My
wife, 9-yr old son, and I are amateur entomologists and like to spend time in
the water researching and bring home samples of all types of aquatic life
forms for study under a microscope. Entomological techniques I have learned
over the past five years or so are quite fascinating. If nothing else, my
boy will get a short education and, hopefully, develop more interest down the
road.
A.
Without actually seeing what you have means I'll have to stick my neck
out a bit, but there are a couple of things you might have.
The most likely identification is just what you suspect – aquatic insect
egg masses that are found in various shapes and forms attached to rocks. The
slimy matrix can be clear, red, brown, yellow, or white and serve
to hold the eggs in place until they hatch into nymphs or larvae. The matrix
that you asked about is a gelatinous polysaccharide, one of a group of
complex carbohydrates.
Now, there is one other type of small, mucilaginous nodule found on
stones in some streams. These are usually dark green in color and are
colonies of the cyanobacterium (formerly called blue-green algae) genus
Nostoc. These clumps can be from pin-head size up to the size of a
walnut. One form is somewhat "ear-shaped" and contains a midge larvae.
One interesting aspect of these organisms is that they can "extract"
atmospheric nitrogen (N2), whereas green algae and diatoms can only
use nitrogen after it has been transformed into nitrates or ammonium.
Good luck to you and your family in your stream studies.
~ Stream Doctor
The 'Stream Doctor' is a retired professional stream ecologist and
author, now living in the West and spending way too much time
fly-fishing. You are invited to submit questions relating to
stream-ecology directly to him for use in this Q & A Feature
at streamdoctor@aol.com.
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