By: Courtney Davis,
Environmental Education Intern
There is never a dull moment in the program office at the
North Lakeland Discovery Center. The excitement this morning was over a green
animal found by Tim Dobbins while searching through a bucket of plants from
Rice Creek. It looked like algae at
first but when I picked it up it didn’t fall apart like most algae would. What
could it be? It was a freshwater sponge!
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Caption: Tim Dobbins searches through his bucket of plants.
Photo Credit: Courtney Davis
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Freshwater sponges are strong and remain intact when picked
up and handled. They will grow on hard
substrates like sticks, rocks or plant stems and can be lobed, irregularly
shaped or have fingered like projections. Freshwater sponges have very simple
bodies made up of many cells but no organs.
Each cell has a very specific role in order to help the organism
survive.
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Caption: Excited about freshwater sponges!
Photo Credit: Anne Kretschmann
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Freshwater sponges can easily be mistaken as a plant. The greenish color comes from the algae
living on the animal. The algae and the sponge have a symbiotic relationship,
meaning they both benefit. The algae get
a place to live while the sponge is provided with oxygen and food. Freshwater sponges are also filter feeders
and will obtain food by running water through their bodies.
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Caption: A freshwater sponge attached to a small stick.
Photo Credit: Courtney Davis
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This animal is important because they are only found in
clean bodies of water with high levels of oxygen. This makes freshwater sponges
bioindicators. By finding them we know the body of water is healthy. They also
are a vital part of the food web and are eaten by ducks, crayfish and many
macroinvertebrates including caddisflies, midges, and spongillaflies.
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Caption: A segment of a freshwater sponge.
Photo Credit: Courtney Davis
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Overall there are 219 freshwater sponges in the world with
only 30 found in North America. In Wisconsin 13 different species have been
found. Freshwater sponges are most
common in the summer and the fall. Keep your eye out for this amazing underwater
animal next time you’re out and about on a lake, river or stream. They are tons
of fun to find!
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