[vernalpool] An interesting observation from Michigan

Hi Folks,

VPA received the question below this week. With permission, I am
throwing it out to the community. I have already visited one long
hydroperiod pool this spring with a substantial population of green frog
tadpoles. The water level was lower than usual but still over 4 ft in
the deepest area. The tadpoles were grazing at the wood frog egg rafts
but didn't seem to be any more predaceous than in other years. Has
anyone else seen green frog tadpoles completely remove wood frog eggs.
Or is something else going on here? Is this observation an answer to an
earlier observation about "missing frog eggs"?

Leo

Quote begins:

Hello. I'm hoping you are willing to to take the time to read my account
below and lend some expert insight into what I'm finding to be
unsettling developments on our vernal pool.
We've lived on property in lower Michigan for 23 years with a one-acre
vernal pool and use it annually for education purposes. This past hot
stretch in March provided water temperatures that were comfortable
enough to swim in, where in every other March, a wade through it is a
numbing experience. This year, we've noticed, for the first time ever,
that there were absolutely no fairy shrimp in the water. Could the
unusually warm water have killed the larval shrimp immediately upon
hatching?
On another unsettling note, due to warming... Every year, in addition to
6 other species of frogs breeding on the pond, green frogs attempt to
breed there. Since greens do not begin breeding until May, peeper,
chorus, wood, leopard and Am toads are well into their breeding cycle
with tadpoles growing in the pool. Green tadpoles appear to take about 3
months to grow and metamorphose. Tadpoles that hatch from eggs laid
later in the summer do not make it. Either the vernal pool dries out and
kills them, or, if there is shallow water remaining in the pool at the
onset of winter, the green frog tadpoles are winter-killed.
Through the wimpy winter of 2011-12, the shallow water on the pond went
through several periods of freezing and thawing instead of the permanent
freeze of any past normal winter. The green frog tadpoles did not
winter-kill. Then the wood frogs laid their eggs 3 weeks ahead of
schedule. I made a youtube video of their breeding action on March 16. A
few nights later, I waded to the location where hundreds of eggs masses
could be found. I shined the flashlight on them to reveal large green
frog tadpoles engulfing them. The light scared them and they darted into
the grassy depths below. A few days later, I waded to the same spot. It
was as if the eggs were never laid. I believe the green frog tadpoles
ate the entire season's breeding effort of the wood frogs. In any other
year, wood frog tadpoles are abundant. This year, we have not seen a
single one, and only a couple of tiny peeper tadpoles, which are
also always abundant.
It appears starkly obvious that green frog tadpoles overwintering
successfully in a vernal pond is very detrimental to the breeding
success of wood frogs. By extension, the early spring presence of green
tadpoles is most certainly detrimental to the breeding success of other
frog species and of the mole salamanders, too. On your site you list
some obligate vernal pool species of amphibians. They cannot breed
successfully in waters occupied by fish. It appears to us that the green
frog tadpoles are playing the role of "fish" in a warming vernal pond.
With the apparent inevitability of climate change, it is easy to imagine
more such warm winters ahead and the associated mass declines and local
extinctions of all amphibians that rely on vernal pools for reproduction.
Can you point to any research or past findings that corroborate what
we've noticed here, or offer any other comments? Thanks a lot for your time.
Jim McGrath,
Nature Discovery
Williamston, MI
www.naturediscovery.net <http://www.naturediscovery.net>
naturedisc@cablespeed.com

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