Ice is Magic

published Feb 5, 2020 in the York Weekly, Portsmouth Herald and Foster’s Daily and online at seacoastonline.com

I spent almost the entire first semester last year having my freshmen STEM class run experiments about ice. Every morning, when I walk my dog, we follow a path along the river and observe the ice, marvel at the huge slabs of ice that are carried downstream and stacked like pancakes in some places, crunch our way over the paper-thin ice that coated the hummocks of the floodplain after the last brief thaw, watch dangling orbs of ice form in the waterfall that spills down to feed the river. I, like so many others, am obsessed with ice.

If you think about it, ice formation on a pond or lake is fairly straightforward. As the water gets colder, it gets denser and starts to sink. Liquid water reaches its maximum density at 4 °C (39.2 °F), after that it continues to get colder and freeze solid, but as it freezes, it becomes less dense and floats to the surface and we end up with ice-covered lakes.

Ice slabs pile up in Little River

At first, the ice is paper-thin, fragile sheets that crumble in your hand. As winter’s cold progresses, the ice gets thicker and thicker as more ice is added from the bottom. As long as the pond or lake is deep enough, there should always be at least some liquid water underneath the ice. This is very helpful to the animals that live in the pond or lake. They can survive in the liquid water near the bottom until the spring thaw.

Now, think about a river or stream in which the water is constantly moving. All of that turbulence makes it difficult for a nice sheet of ice to form. On cold winter nights, the surface water of a river cools, crystals of ice form and start to grow. The constant water movement keeps the crystals from growing together into a solid sheet, instead you get a slushy mixture of water and ice called frazil ice. You can see this floating on the top of a river in early winter, or instead of floating on top, because the crystals are so small, they can easily be carried by the turbulence down to the bottom of the river.

Ice slab close-up with river behind it

As temperatures continue to drop, the frazil ice can start to join together at the surface and form round plates of ice with upturned edges (from the plates bumping together). This is called pancake ice. Or, what was more common on my river, ice will start to form along the edges of the river. Ice forms more easily along the edges because there is typically less water movement and the temperature of the shallow water on the edge cools faster. This is called border or shore ice. Border ice will generally enlarge toward the middle of the river until the ice from both sides meet.

Border ice forms along a small stream

Another interesting way a river can freeze is when the frazil ice that is transported to the bottom of the river attaches to the streambed and builds from the bottom up. This is called anchor ice. Anchor ice can grow very rapidly and block the flow of a river or stream causing local flooding. If there is particularly low flow of water along the bottom, an enormous amount of anchor ice can build up. This can be extremely harmful to aquatic life because the anchor ice can physically lift up parts of the streambed and move it downstream, movement akin to the action of a bulldozer, killing small fish and aquatic invertebrates (like dragonfly or caddisfly larvae) that live in the streambed, or freezing fish eggs that were waiting for spring to hatch.

I thought I first fell in love with ice in some dramatic location, perhaps when I crossed Lake Champlain on the ferry one cold winter’s night and watched the prow cut through the ice and listened to it grind against the hull of the boat, or when I was travelling as a National Geographic Grosvenor Teacher Fellow in the Arctic Ocean and witnessed firsthand the ethereal beauty of icebergs and the vast expanses of pack ice in the polar sea. But watching the beautiful, ever-mutable ice along my little river this winter has made me realize that I’ve loved ice since I was a kid watching icicles dangle from the gutters of my house, that no matter where you find it, ice is magic.

Join the soft-shell clam recruitment network

published January 29, 2020 in The York Weekly, Portsmouth Herald and Foster’s Daily and online at seacoastonline.com titled ‘Nature News’

Clam recruitment boxes will be placed on clam flats in Wells Maine this spring Brian Beal photo

Dr. Brian Beal, Director of Research for the University of Maine at Machais Downeast Institute (DEI)-the easternmost marine research laboratory in the entire United States – gave a talk a week or so ago up in Wells about a research project that will start this spring all along the coast of Maine. The main focuses of the DEI all have to do with shellfish, primarily clams.

Brian was down in Wells explaining why large wooden boxes would be appearing on some clam flats in Maine, from Wells north to Sipayik, this spring and summer. The boxes are part of a study aimed at understanding how best to protect young soft-shell clams at a critical time in their development-when they are transiting from a water-born planktonic life to settling into the mud and sand flats and growing into delicious steamers. 

The clam recruitment boxes appear to provide a safe place for juvenile planktonic clams to settle Brian Beal Photo

Protecting soft shell clams from what? Primarily the invasive European green crab (Carcinus maenas).  Green crabs were introduced to New England back in the early 1800s by travelling in the ballast of ships carrying cargo from Europe to the United States.  Since then they have travelled up the East Coast, decimating the soft shell clam industry and have more recently (the late 1980s) reached the West Coast where they are wreaking similar havoc from San Francisco up to Seattle.  One reason green crabs are such a problem is that, unlike our native crabs, green crabs can swim out onto the mudflats to hunt. Our native rock and Jonah crabs don’t do this-they can’t swim and can’t get out and back to the mud flats as the tides ebb and flow..  Adult green crabs swim out to the mud flats at high tide, grab the soft-shell clam siphons (the fleshy clam ‘necks’), pull them out and eat them. Our soft-shell clams have adapted to this by digging deeper into the mud so that they can escape. However, a probably bigger problem is that young green crabs  (-perhaps a couple millimeters in size) also settle on the mudflats and prey upon anything smaller than themselves-juicy morsels like young soft-shell clams. 

To understand how the recruitment boxes work you have to know a little bit about a clam’s life cycle.  Before I joined the Wells Clam Conservation Commission almost a decade ago, I hadn’t understood how complex that life cycle is and how threatened it is by the invasive green crab. 

The life of a soft-shell clam (Mya arenaria) begins on a warm spring day when both male and female clams release their sperm and eggs into the water, if the two should meet-fertilization occurs.  This is called broadcast spawning and time is everything. The young that develop from this union are planktonic, they don’t look much like adult clams, instead they look like tiny blobs with tufts of fine cilia that they use to swim through the water.  These larval forms are called trocophore larvae that then mature into veliger larvae. The veligers look like a shell-less swimming clam. These baby clams come to intertidal flats via the water column. They swim for 2-3 weeks depending on seawater temperature and location along the coast, and then settle to the flats.  They are about the size of a grain of sand. This is when they are most vulnerable to predation. Here is where the recruitment boxes come in.  

Recently settled clams are at most danger from juvenile green crabs Brian Beal photos

Recruitment boxes are large wooden boxes with mesh on both the top and bottom.  Planktonic clams that settle into these boxes appear able to have much higher survival rates than those settling on the unprotected mud or sand flat.  

Mesh on both top and bottom of the boxes protects young clams from many predators Brian Beal photo

Why put out recruitment boxes? Soft-shell clam landings across Maine have declined by 45% since 2001, and few seem to be aware of this. An interesting tie-in with climate change appears to be that warmer sea surface temperatures (as we have been seeing in the Gulf of Maine) encourage explosive growth of green crabs.  Brian’s project aims to increase public awareness of what is occurring within this iconic fishery and create a statewide data set for fisheries managers in the Department of Marine Resources, and for other fisheries scientists, to better understand factors that affect the health and well-being of the soft-shell clam fishery.  

Whether you live in Maine or New Hampshire, if you want to get involved in this ‘recruitment network’ contact Brian at the Downeast Institute.  Dr Beal is looking forward to working with clammers, clam conservation committees, elected officials, schools and students in each community to learn about the early life-history of clams and what may be regulating or controlling their numbers.  Ultimately, he would like to create a network where the coastal communities that are part of this first trial are a subset of a larger group of communities all doing similar work that may play an important role in how soft-shell clams are managed.

In winter’s cold, the subnivean zone is abuzz

Published January 21 2020 The York Weekly, Portsmouth Herald and Foster’s Daily and at seacoastonline.com Titled ‘Nature News’

The subnivean zone lies between the snow and the earth.

This winter has been troublesome; a few weeks ago it was so cold my pipes froze, then it we climbed to unseasonably warm temperatures, then some more snow, and now, very cold again-my pipes continue to freeze. One thing that makes me happy is that we have a nice layer of snow on the ground, insulation that is is vital to the survival of many of the plants and small mammals, even microscopic life forms, that are essential parts of our Northern ecosystem. So, for many, the recent snow was welcome relief from the cold.

While the surface seems empty, underneath, at the interface between ground and snow, a veritable city is rising. Old leaves and branches hold the snow up, creating an open space. The ground also radiates heat, warming the overlying snow, which instead of melting sublimates (when a solid turns into a gas without first becoming a liquid) directly into water vapor. Both of these processes leave a space between the snow and the ground, called the subnivean zone.

The word “subnivean” comes from the Latin for under (sub) the snow (nivean) and is a scientific term referring to the open passageways that form under deep snow.

Six or more inches of snow are all that are needed to trap the earth’s heat and allow a subnivean zone to form. This zone remains humid because of the transformation of snow into moist water vapor and is capped by a layer of ice that acts as an insulating roof. The temperature of the subnivean zone is generally a constant 32 degrees, protecting species that would otherwise freeze.

The most common inhabitants of the subnivean are mice and voles — they make tunnels under the snow connecting sleeping areas and sources of food. Red squirrels also burrow into the subnivean to stash food. Entrance holes to these networks allow carbon dioxide to escape. Carbon dioxide is released when these animals breathe and by the ground itself. Without the entrance holes to serve as ventilation shafts, carbon dioxide could build up to lethal levels.

While the subnivean zone provides protection for mice and voles, it is also the hunting ground for the short-tailed weasel (or ermine), a weasel that, except for its black-tipped tail, turns snowy white in the winter. This small weasel, just the right size to live and hunt in the tunnels under the snow, is a major predator upon small rodents.

All you need is about 6 inches of snow to allow the subnivean space to form

Recent research has unearthed a whole new category of inhabitants of the subnivean zone — microbes that are proving to be important players in the cycling of both nitrogen and carbon dioxide between the earth and the atmosphere. A deep snowpack with an active subnivean zone appears to encourage a healthy microbial population that, through respiration, releases significant amounts of carbon dioxide into the atmosphere. Studies suggest that as much as half of the carbon taken up by plants in the summer is released back into the atmosphere by microbes in winter (Paul Brooks, University of Colorado Boulder). At the same time these microbes, by processing and storing nitrogen, fertilize the soil as the snow melts.

Without a healthy snowpack, without these snowpack microbes, plants don’t do as well come spring. While these microbes may be releasing a lot of carbon into the atmosphere during the winter, they are also necessary for healthy plant growth — plants that will absorb carbon dioxide throughout the growing season.

For all these reasons, it seems to me, a nice deep snow, serving as an insulating blanket on the earth, is a welcome part of our northern winter.