Tuesday, July 16, 2013

How to Corner a Copepod? - Aaron

Sometimes even the most simple research design doesn't yield simple results. My first experience in biological research is being quick to teach me this.

As I mentioned before, I've been working with Dr. Kelly Sutherland to observe how small-scale turbulence affects the feeding rates of Mitrocoma cellularia (a water jelly). The method we are using is perhaps as simple as it gets: put jellies in a tank along with prey for a certain amount of time and count how many prey are missing at the end of the trial; run trials with turbulence and with no turbulence (control). Presumably, any missing prey were eaten by jellies. If there is a consistent difference between turbulent and still experiments then there is support for the hypothesis that turbulence affects feeding rates. Done and done!

The data so far has hinted at a trend showing that the jellies eat more in still water than they do in a high level of turbulence. (I'm just working with the high-level turbulence generator, while Kelly is running other experiments to test affects of medium and low levels of turbulence).

However, we decided it would be necessary to test the dependability of our prey recovery and counting techniques. To do this we ran the still-water and turbulence experiments in the tanks in the absence of jellyfish. The experiments all start with 200 prey, and since no jellies were present to eat the prey, we should have recovered 200 prey at the end of each trial as well. The results were all over the place! At times, we received the desired results and recovered 97-101% of the prey. Other times, we recovered just over 50% of the prey. With no jellies around to snack on them, where did all of the prey (copepods and artemia larvae) go? Did we miscount? Did they get stuck somewhere in the tank, filters, or siphons? No one on the "jelly predation team" thinks that 40 percent of prey could be lost to any of these sources.

One of my main projects for the rest of summer will be to plug this inexplicable leak of plankton prey. For this new round of test trials I'll be working by myself to rebuild the turbulence generator and count out the prey under a dissecting scope before and after each experiment. I'm excited by the prospect of honing a precise experimental method and halting the loss of prey. On the other hand I have a tiny fear that the leak will never be discovered or fixed. It's a tiny one though!

Does anyone have any ideas on how to recover and count 200 prey from 10 gallons of water without any loss?
Spiders... keeping it simple and capturing prey.

1 comment:

  1. Aaron,
    Welcome to OIMB. This sounds like a tricky problem. You might want to go talk with Dr. Alan Shanks (he is in the downstairs lab of the Terwilliger building). He is very good at equipment type ideas and solving problems.