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.

A Mirror in the Woods

Spring comes earliest to the bottoms of stagnant pools – there no cool winds blow – no hoar frosts penetrate – but they grow protected as under a glass. There are fewer disturbing influences to rob them of the full advantage of the sun’s increased altitude.

~Henry David Thoreau

Conservation groups, in partnership with Partners in Amphibian and Reptile Conservation, are designating 2014 as the Year of the Salamander (http://www.parcplace.org/news-a-events/2014-year-of-the-salamander.html). So, naturally, one of my naturalist friends has decided this is the year to see as many of North Carolina’s salamanders as possible. With that in mind, a few of us went to Pilot Mountain State Park this weekend in search of whatever amphibians we could find.

Pilot Mountain Big Pinnacle

Big Pinnacle at Pilot Mountain State Park (click photos to enlarge)

While many visitors simply drive to the summit and gaze out across the valley, or enjoy the view of Big Pinnacle, we were looking for things in the low country, in the Yadkin River section of the park. I had been to this section only once, years ago, when working for the state park system as a naturalist, so it was a great chance to do some exploring.

oxbow epheneral pool

Oxbow pool along Horne Creek

Walking along Horne Creek we came upon an oxbow that isĀ now an isolated woodland pool, perfect for amphibians. An Upland Chorus Frog slowly called but soon fell silentĀ as we approached…a good sign.

vernal pool reflection

Pool reflection

These woodland pools, especially those devoid of fish, are incredible habitats for a wide variety of organisms from macro-invertebrates to frogs and salamanders, They are also beautiful woodland mirrors that reveal a multidimensional world as I stare into the surface, at first seeing only the trees above, and then the dark bottom, covered in leaves. As I walked along the pool edge, I could see a few Water Striders, but little else, until I got to an area where a cluster of sticks protruded from the pool’s surface – amphibian egg masses! At first glance I thought they were Spotted Salamander egg masses, but my friend, Megan, pointed out they were Wood Frog eggs.

wood frog eggs

Wood Frog egg mass

Compared to the egg masses of Spotted Salamanders, the Wood Frog egg masses tend to be more globular, somewhat larger, and lack the stiff outer gelatinous matrix of the salamander eggs. There were several blobs of eggs attached to the twigs, with some appearing recently laid, and others more developed. As they age, the eggs are colonized by a symbiotic algae, Oophila amblystomatis, which imparts a greenish color to the cluster. This same algae colonizes Spotted Salamander eggs and is believed to utilize some of the waste from the developing eggs while providing some oxygen for them.

wood frog eggs after spreading out

Wood Frog egg mass colonized by algae

The Wood Frog egg masses also tend to flatten out at the surface of the pool as they age. While staring at one I noticed some movement – there were Marbled Salamander larvae resting on them. Marbled Salamanders lay their eggs in the fall as these pools fill with rainwater, and their larvae are well-developed predators by the time many of the other amphibian species start to hatch. Looking down I saw one of these tiny pool tigers swim up to an egg mass and position itself, just in case there was an early hatching by a tasty Wood Frog tadpole. The more mature green egg masses had many more Marbled Salamander larvae in attendance (look for the dark elongate shapes in the photo above).

Marbled salamander larvca on wood frog egg mass

Marbled Salamander larva on Wood Frog egg mass

Since the Wood Frog tadpoles tend to cling to their egg mass for a few days after hatching (to feed on the algae), it is a perfect place for the Marbled larvae to hang out. The hatching frog tadpoles are weak swimmers and easy prey.

Wood Frog tadpole at hatching

Wood Frog tadpole at hatching

I gently scooped up one recent hatchling for a quick photo. Luckily for the frogs, each egg mass contains a few hundred eggs, which should be enough to ensure survival of at least some of the tadpoles.

surface reflection

Woodland ephemeral pools are critical habitats

I love spending time near these pools, waiting, watching, listening – there is so much life to be found. Yet these are often some of the first habitats destroyed when we alter the landscape. I have witnessed once thriving amphibians pools destroyed by nearby earth moving which forever alters the drainage pattern or by intentional draining due to concerns about mosquitoes. In fact, the thriving community of predators in a typical woodland ephemeral pool usually means few or no mosquito larvae can survive. And without the woodland mirrors, both our forests and our natural heritage are diminished.

I encourage you to get out in the next few weeks and sit by the edge of a woodland pool and marvel at the life it contains. But, beware, anyone seeing you at such a pool may start to wonder, as did a neighbor of Thoreau’s back in 1858…

I learn that one farmer, seeing me standing a long time still in the midst of a pool (I was watching for frogs), said that it was his father, who had been drinking some of Pat Haggerty’s rum, and had lost his way home. So, setting out to lead him home, he discovered that it was I.