Sloppy semantics on my part are the source of some of the questions posted
here. Here's some clarification:

First, by "escaped" i used a euphemism that generally means purposely
introduced or gone feral from some ill-advised introduction -- aquatic
snails rarely "escape" like the family parakeet does. Both are the case with
Marisa. It is certainly a common aquarium species, and undoubtedly was
dumped at some time or another into these river systems, along with
Melanoides and Tarebia, for which we have no other viable explanation for
their presence, and several "Tropical Fish" species which also inhabit these
springs and headwaters (putting even more things at risk). Marisa was also
introduced as an aggressive herbivore in hopes that it would control the
also purposely introduced and now invasive Water Hyacinth, which it has
failed to do of course. The greater threat from these snails in this system
is that they may be a direct threat to Texas Wild-rice, an endangered
endemic known only from the springs. If they are a threat to the endemic
Elimia, it is indeed from "crowding out" so to speak, from the consumption
of native plants, resulting in out/overcompetition. The trumpet snail
Melanoides is even more threatening in this regard, as it may be so abundant
as to seem to hardly leave space for other invertebrates. In my original
post i said "may be" a threat and that was purposeful wording, as we haven't
proof yet, though it is widely hypothesized. Just a few months ago i did a
sample sweep in the Comal and came up with 596 Melanoides, 2 Tarebia, 2
Marisa and 3 Elimia. Elimia has certainly declined but it is still holding
on, and thought to be stable -- it probably also benefits somewhat from
management designed to protect the other endemics there (for which i also
failed to mention Salamanders as endangered). Marisa is more localized in
its abundance that Melanoides in my experience -- while Melanoides is common
throughout the upper springs area, Marisa may be abundant in a 25 foot
stretch and then almost absent 50 feet away. All the invasive snails are
apparently limited by a low tolerance for cold, and are not found
systemwide.

Secondly, on the extinction list, i was probably sloppily bold in saying
"this" was a list of 387 recently "extinct" species. I was merely passing on
a website i found while trying to look for answers to questions posted here
about Lottia. This list, by the way, is repeated in various forms across the
net -- the one i posted here i believe is the original compilation (and my
"trust" in it certainly had something to do with the imprimatur of the
AMNH). I too have problems with individual species on the list. I suspect
that certain minimal criteria were used for adding forms to the list, they
were done by "committee", and not much follow up research to determine
actual status was done. There are likewise some problematical listings at
USFWS and in CITES that probably are of the same ilk. The list IS advertised
as a beginning and fairly begs for corrective input. Putting the word out on
forums like this may be one of the better ways to begin correcting
inappropriate listings as workers more familiar with local situations become
aware and post their own findings and impressions, so that we all can bring
attention to problems as they occur.

blue
austin, texas

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