Sunday, November 30, 2014

Back to Entry Run -- and one more time on the Acroneuria carolinensis/lycorias issue

Safely back from Entry Run: apparently no one thought I looked like a deer (!)

I found a fair number of Perlids -- common stoneflies -- this morning, and most looked like the one in the photo at the top of the page, which I think is Acroneuria carolinensis.  But you'll recall that this ID is an issue (see the entries from 10/23/14 and 10/28/14).  Acroneuria lycorias nymphs look exactly the same.  And while Frison says they can be distinguished by the presence (lycorias) or absence (carolinensis) of anal gills, Beaty argues the distinction isn't that clear.   According to Beaty (in one of the e-mails he sent me), they have found both types of nymph (with and without the gills) in the very same water, so they're not sure that the gills are a real point of distinction.  However, in that same e-mail he told me that if every nymph that I find in the same section of the same stream has them or lacks them (anal gills) then I can probably feel certain about the ID.

The nymphs that I found this morning did not have anal gills.  The nymphs that I found in the upper Doyles River -- similar water to Entry Run -- on 10/23 did not have anal gills.  Every nymph in my reference vial -- and I think they're all from the Doyles -- lacks gills.  I have only found one of these nymphs with the gills -- the one I found on 10/28 at Buck Mt. Creek.  This one.

And these are the gills.

Acroneuria carolinensis has a tolerance value of 1.2; Acroneuria lycorias has a tolerance value of 2.1.  Entry Run and the upper Doyles River are both very clean mountain streams, both of them in or near the Blue Ridge: Buck Mt. Creek, while being a very good stream, runs through farm land away from the mountains.   Pretty clear where I'm going: I think we've got A. lycorias in Buck Mt. Creek but A. carolinensis in Entry Run and the Doyles.   That's my working hypothesis at the moment.

More photos from Entry Run.

1. More pix of two of the A. carolinensis nymphs that I found this morning.

2. A "weighted-case maker" (Goeridae): Goera fuscula.  They're still around.

Note the sternal plates -- one of the features that helps us with the species ID.

3. A spiny crawler mayfly -- first of the season: Ephemerella invaria (the one with tubercles on the rear edges of the terga).

4. Giant stonefly: Pteronarcys proteus.

5. And another "first of the season," a Uenoid case-maker: Neophylax consimilis.

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