The Heron Files: Vernal Pool Training

This weekend I did my first serious Master Naturalist training. A large group from my local chapter went to learn about vernal pools in preparation for a research project we are starting. Vernal pools are temporary pools that usually form during winter and spring rains and then mostly, or totally, dry out during the summer and fall. This cycle prevents fish from taking hold; thereby, reducing the number of predators on the amphibians that use the pools to breed. This makes vernal pools key habitat for a number of species. Locally, the common amphibians in vernal pools are the spotted and marbled salamanders. These pools also hold frog eggs and tadpoles, and the larvae of many insects.

Training started with an introduction to the ecology of vernal pools and the main species we would expect to find in them. We then headed out into the field to explore two pools. It was a beautiful day to be out. Probably the warmest day so far this year and most of us soon lost our jackets.

At the first pool, Anne, our instructor, showed us several specimens in bottles of what we might encounter. All but one, the fairy shrimp, had been collected in the pools we were visiting.

Fairy Shrimp, not so common in the pools we will be monitoring

There was a wide range of weird creatures, mainly insects, that Anne showed us. There were crustaceans, a tiny freshwater clam, dragonfly larvae, midge larvae, and water beetles that live in the leaf litter at the bottom of the pools. After the showing us the bottles, Anne waded out into the pool and quickly found egg masses of the spotted salamander.

Anne, our instructor, collecting a salamander egg mass

As the eggs mature, a symbiotic algae appears. The algae photosynthesizes and produces oxygen which the embryo uses and expels carbon dioxide that the algae needs for photosynthesis. This helps the growing embryos grow faster. Then in 2010, scientist discovered that the algae is actually in the embryonic cells where they photosynthesize and provide energy directly to the salamander cells. Making the spotted salamander the first vertebrate species known to have a photosynthesis symbiotic relationship. In the picture below the upper egg mass is several weeks old and has the algae already growing. The lower egg mass was probably laid in the last two weeks and the algae isn't apparent yet.

Spotted salamander egg masses; with and without symbiotic algae

The spotted salamanders come to the pool during late winter on a cold, rainy night to mate and lay eggs. The males generally arrive first and set out little mounds of sperm on leaves or other debris. The female then follows and captures the sperm to fertilize her eggs which she then attaches to vegetation in the pool.

The egg masses are held in a very gelatinous mass. The one below probably has about 70-100 embryos.

In one of those ways that species vie for resources, the marbled salamanders come to the dried pools in late fall to lay their eggs so that their larvae emerge in the spring when the spotted salamanders are just coming to lay their eggs. In both species, the larger larvae will eat the smaller ones as they emerge. Below is a larval marbled salamander that we caught.

At the second pool we came across frog eggs. They look like the salamander eggs but a bit smaller and the egg mass is much looser. As seen above, the salamander eggs stayed in a tight clump when picked up, the frog eggs almost "run" through your fingers.

At this pool we also picked up a leech. The first I've ever seen.

A leech in the net is worth none on the leg

The leech really changed its body shape as it moved around. As shown in the net above, when still, it would pull itself tight together, sometimes almost becoming a ball. But when it would swim, it would stretch out to several inches long. The movie below shows it swimming around in a bag.

Also in this pool we find a newt, below, and several more insect larvae.