What’s in your lake? Lake Ecology 101: Periphyton

Next time you visit a lake, find a submerged rock or dock support or even a submerged aquatic plant stem. Reach into the water and touch the submerged material. It likely feels fuzzy or even mucous-like. You might be inclined to call it gunk. Aquarium aficionados know it as the material that slowly grows on aquarium walls, if not removed.

Lake researchers call it periphyton, where peri means around and phyton refers to plant. Though relatively unobtrusive, periphyton plays a major role in lake ecology.

The material consists of an amalgamation of algae, bacteria, fungi, single-celled creatures, bits of silt, tiny particles of decomposing plant material, and various kinds of tiny animal life.

Its importance? Though it may look unappetizing to us, myriad aquatic life from insects to snails, from minnows to sac fry of game fish, find it a delicious source of food. That walleye you ate on the shore of Mille Lacs almost certainly fed on periphyton  for days.

Submerged plants benefit from having grazers nibble away at their periphyton coating. Here’s why. Periphyton, left un-nibbled, drains important nutrients from plants, reducing their growth. The food value of periphyton per unit is notably greater than that of many aquatic plants. Snails are notably effective at grazing periphyton, keeping it in check.

Periphyton also blocks sunlight penetration and has been reported to screen up to 80 percent of the incoming solar radiation that would otherwise support plant growth.

Large numbers of sunfish in an area can drastically reduce the number of snails, leaving periphyton free to thicken.

It has been said that in ecological systems one quickly discovers that everything is connected to everything else. That relationship certainly holds true for lakes.

I am off to the Wisconsin Lakes Association to deliver a keynote talk in the next few days. Wisconsinites are very concerned about their lakes, and have an extremely active lake citizenry. I will share what I learn when I return.

Darby Nelson

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