Thursday, March 25, 2010

Vernal ponds...

Every spring, hope comes back to the world. Change occurs at a frantic pace, color returns and life reappears from places that seemed lost forever. One of my favorite things about spring is the appearance of vernal ponds. (bigger versions)

Vernal ponds only exist temporarily. They can occur anywhere spring rains and thawing snow collect and drain slowly enough that water remains present for a few weeks. The water is usually shallow enough (a few inches to a few feet deep) that enough oxygen exchange occurs without a constant flow of fresh water.

Because they only exist for a short time before they dry out, they never develop a stable population of predators (like fish) and so they end up being very successful places for frogs and salamanders to lay eggs. Often there are many types of masses in the same pond and a nearly identical pond only a few yards away will have none.

Right now the frogs are just beginning to lay eggs and while there are many types of egg masses, I suspect these are salamander eggs. Here you can see the nearly mature developing embryos protected by the egg jelly. While I was out in the ponds, some began to escape and swim away.

The survival rate is very low (which is probably why there are so many eggs). Most years the ponds seem to dry up too soon. On wet years the birds and snakes tend to eat really well... This year I kept a small part of an egg mass to watch them develop in a safe place.