A Little Bit More
When we think of non-native plants and animals (animals and plants introduced into areas where they don’t normally live), we think of European, Asian, even African intruders. But, animals and plants living in one area of North America can and do get moved into other North American areas they don’t belong and become intruders too. This is the case of the Rusty Crayfish, Orconectes rusticus, whose natural range is in the Ohio, Kentucky and Tennessee region of North America. It is believed that these crayfish have gained access to other regions of the country when fishermen have dumped them into waters beyond their normal range.
But what’s the problem, anyway? In any “natural” area, the animals and plants live in a kind of harmony or balance. No, this isn’t a perfect balance but for the most part, these animals and plants are able to coexist together over long, long periods of time. However, if an introduced animal or plant is able to establish itself in an area (most introduced organisms simply fade away), this causes a change in the balance and usually this adversely affects other organisms living there.
In the case of the Rusty Crayfish, this animal is more aggressive than many other crayfish species and this has contributed to its success in new waters. On the one hand, Rusty Crayfish force native crayfish from the best daytime hiding places, which makes native species more vulnerable to predators. Also, Rusty Crayfish are most likely to assume a claws-up defensive posture when threatened while other species are more likely to attempt to swim away and be eaten, thus leaving more Rusty Crayfish to reproduce. Furthermore, Rusty Crayfish have a higher metabolic rate than most other species and eat more plant material, which in turn reduces hiding and feeding sites for young fish. So, as you can see, what would appear to be simply a new and different species of crayfish living in new waters, becomes a problem that tips the balance that had been established. With the balance tipped, other species become adversely affected and their numbers may be reduced or even eliminated from these waters. Of course, the answer to this environmental problem is not to introduce ANY animals or plants into any new areas – one never knows where it will lead!
Activities
Pincers Galore
Objectives: See how some tools are similar to crayfish pincers
Materials: none necessary but could use a tool catalogue or actual tools
This will take some thinking on the part of your students and their ages will determine just how much they can add to this list. If you have a catalogue of tools available, you might want to use this to help students discover which ones would be similar tools to that of crayfish pincers. Another approach would be to bring in a whole assortment of tools and ask the students to choose those that are similar in function to a crayfish’s claws.
Here are some tools that accomplish tasks similar to those of a crayfish’s claw.
1. Pliers (holding on to items)
2. 2 Chopsticks (manipulating objects)
3. Tweezers (picking up objects)
4. Scissors (cutting or tearing objects)
5. Clippers (hair or yard clippers that cut objects)
6. Artificial hands ( pick up objects)
7. Shovel (some crayfish use pincers as a digging tool)
“Pet” Crayfish in your room
Depending on the area where you live, crayfish are often quite easy to acquire from a local stream. If you have an aquarium in your room, you may want to include a crayfish. Be sure to have some areas in which the crayfish can hide, it should be in reasonably cool, well-oxygenated water and you can feed it goldfish pellets that sink (not the floating ones).
Pet stores also have crayfish for sale but be aware that these will be exotic species so especially important that they NOT be released in local waters. Crayfish can be interesting animals to observe and should be fun and informative for students to watch as they manipulate their food with their pincers as they eat.
Key Concepts
Structures and Functions, Environmental Issues
Questions
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Posted by alicia mackinaw on May 25, 2006 at 09:45 AM
Q: what plants and animals are threatened by the rusty crayfish?
A: Be sure to look at our unit on the Rusty Crayfish www.enaturalist.org to get an overview of this species and the problems it can cause.
The exact plants and animals that are affected by this intruder will vary, depending on where this introduced species is located. Of course, in your case it's in Massachusetts' waters. But in general, a variety of water plants and the young of larger fishes are most affected. When these crayfish eat lots of plants in an area, they not only reduce plant material for others but also reduce the shelter this plant material provides - less shelter means smaller fish are easier prey to larger fish. Hope this helps you out. Thanks for asking.