Monday, April 6, 2009

Life in a Vernal Pool

I previously posted about the Spotted Salamanders and Wood Frogs breeding in one of the vernal pools on the Wood Thrush trail. While the Spotted Salamanders have come and gone, and the Wood Frogs are soon to follow, there is still a lot of life in this temporary pond. Here are some of the other creatures we've discovered in the pond last Wednesday, April 1.

Egg masses are the only evidence of the Spotted Salamander's visit to the vernal pool. There were nearly a dozen of the oblong masses, each filled with a few dozen individual eggs that are rapidly developing into salamander larva. The majority of the egg masses are like the one pictured below, but a couple of them are opaque. The opaque masses contain an anti-freeze component that protects the eggs from being destroyed should the temperature drop sharply and freeze the shallow pool. As the pool's temperature increases through the course of spring, these eggs will hatch, the larvae rapidly grow, and the adult salamanders will emerge from the water to live life underground until next spring. Very few of the eggs will actually complete their journey to adulthood due to predation and other influences.
Spotted Salamander egg mass

Wood frogs have laid a number eggs the pool thus far as well. At first glance these eggs look exactly like the salamander eggs. However, these eggs are laid in a very loose cluster as opposed to the tightly packed mass of salamander eggs. Wood Frogs also tend to lay their eggs together, making one gigantic blob of eggs floating near the water's surface. The handfull of eggs below were just a tiny fraction of the entire blob that was nearly 3 feet across and 18 inches wide. That's a lot of eggs! Like the salamander eggs, they will soon turn to tadpoles, grow rapidly and turn into adults with only a small percentage actually surviving to adulthood.

Wood Frog eggs

While most of amphibians are in the process of, or soon will be, laying eggs, one local species completed that job last fall. The Marbled Salamander lays its eggs in fall in anticipation of the winter snow and spring rain filling the vernal pool with water. After the eggs hatch, the larvae grow rapidly. The larva pictured below likely hatched a few weeks ago, well in advance of the other amphibians laying their eggs. This is to the advantage of the Marbled Salamander who will grow rapidly by eating the smaller larvae of other amphibian species. Look closely at the photo and you will see the feathery gills of the larva and its two front legs that have already sprouted.

Marbled Salamander larva

While we were searching around the pool, we ran into an American Toad who was quite intent on reaching the water. He wasn't at all interested in modeling for the camera, so we decided to pick him up for a photo op. This also allowed us to figure out if it was a male or female toad. Generally males of amphibian species are the first to congregate in the pools, ponds, and lakes to initiate the breeding season. I assumed this particular toad was a male, but there's one good way to make sure: Hold the toad by his armpits. When males are held this way, they illicit a squeaky, vocal response. Why? Breeding males hang onto females with their front arms tucked into the female's armpits (known as amplexus). When males are jockeying for a mate, sometimes they make a mistake and latch onto another male. When this happens, the male being latched onto makes the squeaky vocalization in protest.

American Toad - Have you ever seen a more handsome specimen?

One more amphibian in the vernal pool that night. Upon returning all of the other specimens back into the water I happened across this Red-spotted Newt. This is an adult. Newts have a complex lifecycle unlike most other amphibians. These critters develop from aquatic larvae to emerge as an eft, which lives on land for 2-3 years. The red eft returns to the water to transform into a permanently aquatic adult capable of breeding. While handling this creature, it seems as though the newt has not a care in world as it casually walks from hand to hand. These guys can be particularly toxic thanks to poison glands in the skin. If another animal puts one of these dudes in their mouth, they'll likely remember no to do that again. The red coloration is a visual warning of the newt's toxicity and care should be taken while (and after) handling these guys.

Adult Red-spotted Newt

While the amphibians are the more attractive members of the vernal pool community, there are a number of other creatures calling this place home. Listed amoung them are a host of insect species: Mosquito larvae, various diving beetles, Backswimmers, Water Striders, Water Boatmen, etc. One of the more interesting to me are the caddisfly larvae. Two different species are pictured below. I'm not sure of their species names, but caddisfly larvae can be identified by the their size and the type of "shell" or case they construct and carry with them. The first caddisfly larva has constructed it's case of leaf fragments tiled together to form a long cylinder. The second larva's case is a spiraled conglomerate of leaf stems and fragments. The adult caddisfly looks a lot like a moth and can be seen around outdoor spot lights and lamps during the warmer months of the year.
Caddisfly larva with case of leaf "tiles"


Caddisfly larva with spiral case of leaf stems and pieces

Interested in seeing more of these amazing creatures in living in our vernal pool? Please join us on April 17 or April 18 for one of our amphibian hikes. Herpetologist Peter Warny will be joining the Westmoreland Sanctuary staff for these events and brings a lifetime of knowledge and experience with both reptiles and amphibians. Please visit http://www.westmorelandsanctuary.org/ for more information about the amphibian hikes.
-Adam Zorn, Naturalist

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