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Vernal Pools

PEI forests provide a critical but temporary habitat this time of year: vernal pools. Although you might think of them as just wet spots to avoid, their ecological role makes them among the most important habitats we have. 


Photo 1: A vernal pool in a PEI forest.

Vernal pools are seasonal wetlands flooded by snowmelt and spring rain, but dry by summer. They are common in forests growing on land that has never been farmed, where depressions in the forest floor allow water to collect (Photo 1).  It may seem strange that a temporary habitat has value to wildlife, but there are several reasons that vernal pools are essential for frogs, toads, newts, and salamanders.

 

First, because vernal pools are temporary, they are safe places for amphibians to reproduce. Permanent ponds and streams have fish that would eat the eggs and young.  

 

Second, amphibians don’t travel huge distances and so having breeding areas scattered across the landscape expands the territory they can use for the rest of the year. If they only used our permanent ponds, amphibians would be restricted to habitat within a few kilometres of those areas rather than being found across the Island. 

 

Finally, vernal pools are the ecological equivalent of not putting all your eggs in one basket (literally!). If predators such as insects, snakes, or birds eat all the eggs or young in a pool – or even all the pools in one area – there are still thousands of others in the landscape.


Photo 2: Spotted Salamander egg masses in a vernal pool on PEI.

In spring, you’ll find vernal pools full of amphibian eggs (Photo 2). These eggs are from the Spotted Salamander (Ambystoma maculatum), one of three salamander species on PEI (the others being Blue-spotted and Eastern Red-backed). Unlike Wood Frog eggs – also common in vernal pools in spring – salamander egg masses are covered in a gelatinous layer that gives the entire mass a smooth appearance (Photo 3). If those were frog eggs, the mass would be lumpy. Think tapioca for frogs, jello for salamanders. 


Photo 3: A Spotted Salamander egg mass. You can see the outer gelatinous covering that gives the mass a smooth appearance. Frog egg masses lack that covering and look lumpy.

That outer jelly-like layer around Spotted Salamander eggs may be clear or cloudy depending on the genetics of the mother; you can see examples of each in Photo 2.  Spotted Salamanders generally lay up to three egg masses, so you can pick out some individual clusters in Photo 2 based on this clear versus cloudy distinction. Those three cloudy egg masses in the lower left are likely from one female. The clear masses around it are from at least three or four different females.

 

Older egg masses are greenish due to symbiotic algae that grow with the eggs. The algae give the eggs oxygen in exchange for the nitrogen-rich waste from developing embryos. (The scientific name for this alga is Oophila amblystomatis: literally, salamander egg lover).

 

Most vernal pool amphibians (about 85%) return to the same place they were born to reproduce, so protection of these sites is very important. This time of year, vernal pools will have eggs and young in them, so please don’t walk or drive through them!  Instead, take a moment to appreciate these important parts of PEI untamed.

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