Sunday, January 25, 2009

Ostra-blog 7 - Trapping ostracods

Some ostracods are attracted to traps, namely bait traps and light traps. My first experience with ostracod trapping came in 1998, during my trip to Japan (see ostrablog-5) as a graduate student intern.

My Japanese host, Katsumi Abe took me, along with members of his lab to his "mountain home", near Tateyama. Abe's mountain home was a geodesic dome, mostly without walls on the inside, except for the bathroom (complete with remote-controlled toilet), which thankfully had walls. This mountain home seemed to be designed as a well spring for creativity: puzzles, games, and books littered the structure. I remember signing the guest book, and writing a Haiku, inspired by the well spring, and by the beautifully wooded and mountainous surroundings. My lab mates and Abe's son constructed flutes from bamboo growing outside.

In nearby Tateyama, there is a pier, and this is a very famous place to catch "umihotaru", which translates to "sea fireflies" - the scientific name is Vargula hilgendorfii, an ostracod. This animal is a scavenger. At sunset and later, they rise from the bottom, where they rest all day, and follow the scent of dead flesh to find and feast on fresh carcasses. We can take advantage of this behavior and design traps to attract umihotaru. In Tateyama at this pier, the animals come to the traps by the thousands.

We arrived at the pier just before sunset. Professor Abe was a celebrity there. Meeting us were a class of high school students and several members of a biochemistry lab, who study the light producing chemistry of umihotaru. Abe walked the pier proudly. Many people came up to him asking him questions, bowing deeply. The show was about to begin.

We placed traps in the water; glass jars with holes drilled through the lids. Inside, we placed pig liver, which attracted the umihotaru nicely. After leaving the traps in the water for 20 or so minutes, we pulled up the ropes, and dumped the contents into an aquarium net to separate ostracod from liver and from water. When the ostracods hit the net, they were disturbed, and when they are disturbed, the produce their intense blue light. The light producing chemicals mixed with the sea water, and cascaded down on to the pier, through the planks, and back into the ocean. The biochemistry lab was thinking big. They came from far away in Japan, and needed a large haul of umihotaru to support their studies for a while. They had many traps, and one after the other, they emptied animals into a square container, perhaps 2feet wide by 3 feet long by 2 feet deep. By the end of the night, this container was half full with ostracods; thousands upon thousands of them.

The night felt festive. Enthusiastic students were asking questions, and marveling at the light show. I felt a part of this community. Despite my knowing very little Japanese, I felt I understood a lot from context, from body language. By that time I had also built a language with my lab mates - I'd learned which English words they knew, and which phrases and verb tenses to avoid because they caused confusion. I remember naturally answering someone excitedly in the affirmative with "so so so so", as I'd often heard the Japanese do, and this came naturally to me. Caught up in the festiveness, I decided it would be fun to eat some umihotaru. The ostracods tasted like .... seawater. My mouth glowed with the bright blue light we'd watched cascading down the pier all night. I'm quite certain the students thought me a crazy "gaijin", and they were happy to laugh and talk excitedly among themselves, and my mouth continued to glow.

I have some video of trapping umihotaru, taken at this very pier. This video is from a Japanese science documentary that featured Abe's lab. I copied the VHS tape while there, and I moved some parts to computer a while back (I also sped up the video a little, so I could show it in seminars and not take too much time):

Since my first introduction to trapping ostracods, I've designed my own traps. These are cheaper, lighter, and safer to transport than glass jars. Since I'm working on an invited book chapter on how to collect ostracods, I've made a figure describing my design. Perhaps you want to try to trap ostracods where you live:

Figure 1 - a. Inexpensive 50 ml conical tubes are available from many vendors, and are nearly ubiquitous in labs conducting molecular biology. b. The first step is to saw the end off of the tube, above the conical portion c. a hole is drilled in the bottom of the cone. The size of the hole can be varied; only animals that fit through this hole will be trapped. d. The cap is removed, and the cone-end is placed in the opening. Friction holds the cone tightly in place. e. Bait (such as imitation crab meat made of pollack) is placed in the tube, and the open, sawed end is covered with material (such as that cut from an old t-shirt), and secured with a rubber band. Numerous traps can be secured to nylon rope with plastic zip ties.


Ceuthophilus said...

I like your trap design, but doesn't if float? Do you weight it down somehow?

Todd Oakley said...

Ceuthophilus - I attach dive weights to the rope using zip ties to keep the traps down. I put several of the traps on one rope.

Ava said...

Hi Todd,

This is Ava. I'm a blog newbie, but really enjoy your thought provoking posts. I had a question about the blog and was wondering if you could e-mail me at so I can explain what I mean.

Thank you!

Frank Anderson said...

Very cool. There are lots of bioluminescent cephalopods, but I've seen only one species alive. The bioluminescent members of the squid group I focus on are all in SE Asia.

I guess I should've worked on ostracods, or studied sepiolid squid (some of whom are bioluminescent and conveniently live in shallow water in Hawaii).

Eric Heupel said...

Brilliantly simple!
It's sometimes amazing how many contraptions we can find already in the lab with some creative thinking.