June 16, 2009

6-16-09--Post written by Eli

Studying a biologically productive ecosystem can be incredibly fascinating. Nevertheless, such productivity can present challenges when it manifests itself in the form of numerous jellyfish that cover your instruments and fill your sample nets. When we reached Slime Bay it was clear how it got its name (not loved by fisherman). While at each sampling station the ship lowers its CTD (Conductivity-Temperature-Depth) recorder into the water to make measurements such as salinity, temperature, pressure, depth, and density down the water column. When the CTD returned to the surface I thought the brown stringy material hanging from the recorder was some type of algae. But, after surveying the surrounding water I could see many translucent jellyfish bells (Chrysaeora spp.) ranging from 6 to 12 inches across. In the picture you can see the tenticles wrapped around the top of the CTD.

In the galley several of us discussed the issues with jellyfish covering the CTD. Some expressed their displeasure with jellyfish clogging up their sampling equipment and leaving an unpleasant smell on anything they touch that is difficult to get rid of. I had been aware of large lion's mane jellyfish (up to two meters across) becoming a problem clogging up Japanese fishing nets. Tracy informed me that jellyfish of this size had always been present in the ocean, but they are occurring closer Japan because of changing ocean currents and more favorable conditions for jellyfish larvae (warmer, calmer, higher salinity waters). It has been hypothesized that these changing currents are due to climate change. A crew member noted that others have speculated that jellyfish will become the dominant predators in the ocean with favorable conditions (mentioned above) and overfishing.

On a lighter side, the same crew member described a prank that he and his friends used to set up at the beach by digging a hole in the sand, filling it with jellyfish, and covering it with a thin layer of sand at the top so that an unsuspecting person would step into a pit of jellies. They never waited long enough to see someone fall victim to the trap. One would hope, if they were not involved in the plan, that such a burrow would cave in and fill with sand after a short amount of time in order to avoid the slimy surprise.

During our nightly krill tow we experienced the same fate as the CTD operators. As the net was lowered into the water we tried to will each passing jelly from entering the net like an opposing fan watching a basketball approach the rim from a buzzer beating shot. When the nets were pulled up, after being submerged down to 80 meters, we definitely bagged some unwanted gelatinous guests. There were seven in all, but given the quantity we observed in the water it could have been much worse. Only three of the seven made it to the cod ends. When it was all said and done we had enough krill for a few measurements, but not quite enough for any eye dissections yet.

Picking up more than one jellyfish at a time is definitely a challenge. Another scientist sampling plankton from a separate series of nets filled up a pitcher with jellyfish in order to measure the volume they displaced from his nets. When he tossed the jellyfish from the pitcher into the water, Rachel described the site as jellyfish fireworks. While I was certainly anxious to dissect some krill, and a little disappointed that we did not have enough from the second tow, Rachel reassured me. "Don't worry," she said. "There will be so many krill later on that you won?t know what to do with them all."

-Eli