Horseshoe Crab Density
I chose to study Horseshoe Crabs in May of 2001 after listening to a scientist from DNR talk about the subject of raising Horseshoe Crabs. Then I talked to my science teacher and he said he would allow me to set up a few tanks in his classroom. From there, I was privileged enough to go on a spawning survey. My science teacher, my mother, and I went with a young DNR employee to count the number of Horseshoe Crabs spawning on a beach. After that, I was ready to start cultivating. I set-up seven tanks that would hold my Horseshoe Crabs. I received at least a thousand Horseshoe Crabs from the DNR scientist. I was ready to begin!
In the beginning, this project concerned only one problem. That was, what population density would maximize the growth of juvenile Horseshoe Crabs. I set up seven tanks with different amounts of Horseshoe Crabs in each one; two had 50, two had 100, and two had 200. Then I had another tank that was the nursery, all the extra Horseshoe Crabs went in there. Once a week I took water quality tests on all seven tanks and twice a week I fed them.
I planned on measuring them for two weeks in November. The way I would do this is to blow up the sand with a turkey baster. Then suck up the Horseshoe Crab with the baster and put it in a petri dish. Using a millimeter caliber, measure the length and width of the Horseshoe Crab. Unfortunately, when I went to measure the Horseshoe Crabs, I found them all to be dead! The only crabs left were the ones in the nursery. Now I had three problems, the original problem that I couldn’t answer, why they died, and how much a Horseshoe Crab can grow in 5 months.
The first problem I tried to answer was, how much Horseshoe Crabs can grow in 5 months. I used the turkey baster method and found 34 live Horseshoe Crabs in the nursery. Each one I measured with the caliber then put in a tank that was empty because all its occupants had died. I found out that a Horseshoe Crab grows about 8.35 millimeters in length. So my hypothesis was very close to being correct, only about 1 millimeter off. The next problem was why did the Horseshoe Crabs in my experimental tanks die? I e-mailed a scientist from DNR and asked him for his opinion. I also asked my science teacher about it. I have concluded that the Horseshoe Crabs died a natural death. In the wild, 1 out of 100 Horseshoe Crabs live, and I only put 700 Horseshoe Crabs in my tanks. So, only about 7 would have lived but numbers don’t match up exactly. In my whole experiment there is always the factor of Human error. Most likely, when I went to make sure all my Horseshoe Crabs were dead, I missed one or two in a tank being alive. I could use all this data for next year’s experiment to better understand Horseshoe Crab life cycle.
- What population density maximizes the growth of juvenile limulus polyphemus?
- Why did the limulus polyphemus die?
- How much do limulus polyphemus grow in a five month period of time?