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A Little Bit More

There was a time in the 1950’s when almost everyone knew about parasitic Sea Lampreys in the Great Lakes area of North America. Sea Lampreys are snake-like fish that accidentally got into the Great Lakes from the Atlantic and dramatically reduced fish populations there. Today that problem has been pretty well corrected after enormous eradication efforts were made; some still in-place. Although there has been considerable focus on this alien lamprey over the years, most people don’t realize that North America has its own native species of non-parasitic lampreys too. North American lampreys are a natural part of our environment and don’t cause any problems with the fisheries and therefore shouldn’t be associated with the alien Sea Lamprey.

Northern Brook Lamprey © Solon Morse

American brook lampreys are not a problem since they’re a non-parasitic species. Instead of feeding on fish, these lampreys are basically filter feeders feeding on floating plants, animals and organic material, and live for 7 years before maturing and spawning. Unlike the Sea Lamprey, they never feed on fish but on reaching adulthood, simply spawn and die. Adults spawn (make a nest in gravel, then lay and fertilize eggs) in late March or early April. The eggs hatch into larvae, called ammocoetes. The lamprey may exist as an ammocoete for up to seven years, living in the bottom mud and filter feeding, before undergoing metamorphosis into its adult form and breeding.

Lampreys are a modern remnant of a larger group of jawless fishes that flourished in the early Paleozoic Era. Lampreys have no bones; their skeleton is formed entirely of cartilage like sharks. They also lack scales and paired fins. Lampreys live in both freshwater and marine habitats with some species, such as the Sea Lamprey, quite comfortable in either habitat.

Activities

Science – Filter Feeders

This is one of those activities that is self-evident but is also one that is much more effective to experience. We can all imagine what a filter-feeder does and maybe even what the filtered material looks like but seeing it with one’s own eyes really cements this information.

1. Obtain a regular, paper coffee filter and one of those plastic coffee filter holders that holds the filter and allows water to run through.
2. Depending on your area, look for a pond or slow-moving stream that has a fair amount of material floating in the water column (ie. the water isn’t crystal clear). If you know of a place where you can get “green” water, you’ll certainly have plenty of material to filter. In fact, if you have green aquarium water, this will work well too. Get at least 4-6 liter(full household bucket) of water to do this activity.
3. When you’re ready, place the filter in the filter holder and pour the sample water into a water pitcher. Using the pitcher will make it much easier to direct water carefully into the filter. Now slowly pour your sample water into the filter until all has gone through the paper filter. The more material that is floating in the water, the greater amount of material will be filtered out but don’t be alarmed if there doesn’t seem to be much accumulating.
4. Once the entire 4-6L (use more if you wish) is filtered, you should be able to remove the paper filter to examine for what is left behind. You will find, however, that it is easier to see the filtered contents if you allow the filter to dry completely.
5. With your paper filter completely dry, you can now view its contents with naked eye, use a hand-lens or even place under a micro/dissecting scope. What you’ve filtered is exactly what a clam or other filter-feeder filters from that body of water.

Some questions for discussion

1. Can you think of some filter feeders besides the lampreys? Clams, barnacles, rotifers, sponges, krill, herring, Basking Sharks, even baleen whales .
2. What kinds of food do you think a filter feeder gets? They screen out a whole range of tiny plants and animals from the water in which they live.
3. Based on the amount of material you screened in your filter, do you think an animal needs to filter a little or a lot of water to get enough food? In most cases, they’d have to filter out lots and lots of water to get enough to eat
4. Do you think a filter feeder would get things other than food as it filters the water? Absolutely. If there is a lot of sediment (soil) in the water column, a filter feeder will get this too.
5. If you looked at a pond with very, very clear waters as opposed to a different pond with rather green waters would you expect that the filter feeders living there would be any different? Either the kinds of filter feeders would be different or the amount of filtering would be quite different. The filter feeders living in the clearer waters would have to filter much more water to get enough food.
6. Zebra Mussels are an alien invader in some lakes and rivers of eastern North America. When these filter feeders reproduce in large numbers, the clarity (clearness) of the water dramatically increases. Do you think this would have an impact on other filter feeders in those same waters? Yes, it would. The Zebra Mussels remove so much material from the water that other filter feeders often don’t have enough food for themselves.

Inquiry Activity you may want to pursue

If you can obtain a clam for observation, is there some way you can set up an arrangement so you can see just how a clam actually filters the water it’s in? Could you use food dye to check out this activity?

Key Concepts

Adaptations and Diversity, Behavior and Regulation, Environmental Issues, Identification, Life Cycles, Predator/Prey Relationships, Structures and Functions

Questions

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