Tuesday, March 6, 2012

Egg-eating predators

The glassine waters of a vernal pool reflect the trunks of overshadowing trees, and mask the explosion of life under the surface. I was part of a group that visited this Adams County pool last Thursday.

While we saw plenty of critters on our diurnal Thursday expedition, the action was unbelievable on a nocturnal foray the following evening. I was out from 8 pm until midnight, roving about various amphibian breeding pools with John Howard and Tricia West. We visited several pools that were absolutely packed with salamanders and their eggs, as well as frog eggs. The dark-spotted billowing clouds in the photo are masses of wood frog, Lithobates sylvaticus, eggs. Excepting the Jefferson salamander, the wood frogs beat everyone to the punch and are among the first wave of amphibians to colonize the vernal pools, mate, and drop eggs.

Looking rather lovely, this little wood frog. They're tough; no other amphibian breeds as far north as do wood frogs, and they can virtually freeze solid, and recover to hop again another day.

This is an adult red-spotted newt, Notophthalmus viridescens. It is no friend of the wood frog, as we shall see. Newts are the most aquatic of our salamanders, and the adults live much of their lives in the water. The larval stage is termed a "red eft" (SEE HERE), and efts are terrestrial and highly mobile. Because of the efts' overland mobility, it is no mystery why newts can quickly colonize vernal pools.

A red-spotted newt floats just under the water's surface. It is gliding over huge masses of wood frog eggs, and for a newt, this situation is probably comparable to a kid with a sweet tooth living in a giant bowl of M & M's. Ditto that for the tiny strange-looking sharklike beasts in the backdrop. Those are the larvae of the marbled salamander, Ambystoma opacum.

Both newts and larval marbled salamanders are voracious predators of frog and salamander eggs. The pools that we examined were full of both species, eating their way through the jellied masses of amphibian spawn.

Tiny but deadly - at least if you're an egg - a larval marbled salamander floats over its meals. Marbled salamanders have an interesting reproductive strategy. The females lay their eggs under logs in vernal pools IN THE FALL, when all is normally dry. When rains finally strike, the wettened eggs hatch. Thus, by the time early spring rolls around and the rest of the amphibian crowd migrates to the vernal pools to drop eggs, the marbled salamander larvae are already there. And ready to plunder freshly laid eggs.

Between the egg-eating newts and marbled salamander larvae, scads of wood frog and other species' eggs are consumed. These predators are probably a factor that has led to the carpet-bombing strategy of egg laying for other vernal pool amphibians. If they can just produce enough eggs, some will survive the ravages of the predators.

Don't begrudge the marbled salamanders their eggs too much - they grow into the utterly spectacular amphibian shown here. I took this photo in fall a few years ago, in the very vernal pool shown in this post's first photo. John Howard took me there, as I had at that time never seen a marbled salamander and dearly wanted to. I was not disappointed.

This may be the smartest salamander breeding in the vernal pool. It is a four-toed salamander, Hemidactylium scutatum, and it's also our smallest species of salamander. Four-toeds stay out of the water, and lay their eggs under loose carpets of moss that drape moist logs that lay about the vernal pool. Thus, its eggs are not vulnerable to the predations of newts, marbled salamander larvae, and whatever other predators lurk in the waters. For a more detailed account of four-toed salamanders, CLICK HERE.



Scott said...

I'm thoroughly enjoying these posts on the vernal pools. Makes me want to head out and go wading.

Jared said...

Awesome post! I hadn't known that newts were after wood frog and Ambystoma eggs. Cool stuff :)

Bob (Powell OH) said...

More great photos, Jim. Love the marbled salamander and wood frog shots especially. I'm almost 64 and have never seen either.