Pool Patrol

In a recent post, I mentioned that I sampled the woodland pool near the house earlier in the week. The Marbled Salamander larvae have grown considerably since my last visit. Almost every dip of the net brought up one or more of the large, squirming pool predators. When first caught, they were very dark, which is typical of these larvae. But, after being in a bucket overnight, the few I brought to the house turned a much lighter color than normal. I placed them in my small photo tank for a few shots the next morning before taking them back to the pool to set them free.

Marbled Salamander larva

Marbled Salamander larva (click photos to enlarge)

Marbled Salamander larvae are easily distinguished by being the largest salamander larvae in area woodland pools this time of year. This is because, unlike the rest of our pool-dwelling species, they hatch in the fall, rather than the spring. The row of light spots along their sides is another diagnostic feature. The ones I caught this week were all large, between 2 and 3 inches in length. In this area, they usually transform and leave the pools in April or May, so these guys are just about ready to become full-time land-dwellers.

Spotted Salamander larva just after hatching

Spotted Salamander larva just after hatching

When they hatch, Marbled larvae feed on zooplankton and small macroinvertebrates. By the time spring arrives, they are large enough to gulp down much larger prey, including the hatching larvae of a common pool neighbor, the Spotted Salamander. The photo above shows a newly hatched Spotted larva caught in the pool this week. It is less than an inch long and still has the balancers, the two fleshy appendages under the head that help them maintain an upright position in the water. These are present for only the first week or so after hatching. Look closely at the image and you can see one pointing downward between the eye and the gill of the larva.

Marbled Salamander larva 1

Marbled Salamander larva

With the number of Spotted egg masses that are just now hatching, there is a buffet of small prey available to the Marbled Salamander larvae. They patrol the pool and use a lunge and gulp feeding strategy to capture a variety of other organisms as well, including small tadpoles, aquatic insects, and even terrestrial insects that fall into the pool. If food is scarce they are also known to nibble on their cousins, so it is not uncommon to see Marbled larvae missing portions of their tail or limbs.

Marbled Salamander larva head close up

Close up of head showing external gills

I plan to visit the pool again over the next few weeks and look for transforming juveniles around the edges. They will lose the bushy external gills and crawl out of the water to begin a terrestrial life, returning to this, or another low-lying spot, only to mate and lay eggs in the fall. Marbled Salamanders are among the many interesting and beautiful creatures that require these fish-less woodland pools to survive. But I worry about the future of many of these pools. I worry that fewer and fewer people know about the beauty and wonder that lies just beneath the surface of such shallow water habitats, and see them, instead, as just a mosquito hole or a place to drain and tidy up. It doesn’t take much disturbance to the landscape to alter the hydrology of a wetland area and leave it high and dry, eliminating this critical habitat for so many of our fascinating neighbors. If you, or someone you know, has such a pool on your property, I encourage you to sit by it, dip a net in it, get to know it and the inhabitants, and protect it. Our world will be a better place if you do.

Marbled Salamander eggs

Marbled Salamander eggs

Marbled Salamander eggs under log

Two friends from the Museum, Megan and Melissa, invited me to tag along with them yesterday, as they did some fieldwork for a future workshop. Megan made a great find as she and Melissa were turning over logs at the edge of a vernal pool, looking for salamanders – some viable Marbled Salamander eggs. It seemed really late to us for this species to still have viable eggs (when she looked closely, she could see the well-developed embryo moving inside the eggs) so she grabbed a couple to photograph.

Marbled Salamanders have an unusual reproductive strategy compared to many other species in that the eggs are laid in the fall (usually October and November in this area). The female often scrapes out a little area near or at the edge of a vernal pool.  Vernal pools are fascinating and important habitats that may be dry much of the year and then fill with autumn and winter rains. The key is they have no fish, which makes them critical habitats for a number of species of amphibians, invertebrates and other animals. She then will stay with the eggs for some time (often a month or more) waiting for the water to rise so the eggs will hatch. If it remains dry for an extended length of time, she may abandon them and return to her underground burrows in the nearby woods until the next breeding season. Studies suggest that egg clutches where the female remains with them until they are covered by water have a higher offspring survival, perhaps because she helps protect them from predation or getting too dry.

Marbled Salamander eggs

Marbled Salamander eggs

The 50 or 60 eggs Megan found were under a log at the edge of a large vernal pool. It was very moist under the log but the standing water was still a few inches away from the eggs. Embryos develop to the hatching stage within a couple of weeks after being laid, but do not hatch until covered by rising water. So these eggs were very well developed. You can see the front legs and feet, the larval gills, some of the diagnostic lateral spots, and the eyes in the waiting “larvae”. My salamander reference (Salamanders of the United States and Canada by James W. Petranka) states, “when covered by water the embryos become oxygen stressed…this triggers the release (from hatching glands on the snout) of digestive enzymes that dissolve the egg capsule and allow the embryo to escape”. Amazing!

Marbled Salamander eggs

A closer look

We put a couple of eggs in some water in a bug box so I could photograph them. Megan called Jeff Beane, a herpetologist at the Museum, and told him about the find. He said he did not recall seeing any viable eggs this late in the spring so he wanted to document the location. We walked down into the woods to show him, photographed the eggs and then walked back to the car. In those 40 minutes or so, the two eggs had hatched. The reference said it usually takes a few hours to a couple of days after flooding for the eggs to hatch. Guess these guys had waited long enough. The last picture is one of a larva from last year that I pulled from another pool. It was much older and larger than the ones from yesterday.

Marbled salamander larva

Large Marbled Salamander larva