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MISSION DISPATCH 7 June 8, 2005 | Jon Cohen | San Clemente Basin (off the coast of S. California) All is well aboard the New Horizon. The trawl net still has a few recurring issues, but in general is working well. Folks are making good use of the deep daytime samples (approx 800 m) and the shallower nighttime samples (approx 200 m). 
One animal that is common in the deep daytime trawls is of particular interest to me - the copepod Gaussia princeps. Copepods are tiny crustaceans (usually approx 1 to 2 mm in length), and are likely the most abundant animals on the planet. Gaussia is truly a giant in the world of copepods, measuring over a centimeter in length. This striking creature has black pigment on its back, a bright red gut, and produces a brilliant blue bioluminescent display when disturbed. Like many crustacean zooplankton, Gaussia is a nocturnal vertical migrator. Its daytime depth is approx 600 m, with a rise at night to a depth of approx 300 m. My goal for the cruise is to look at the visual system of Gaussia. I had never seen this copepod species prior to this cruise, so I wasn't sure what its eye would look like - or if it would even have an eye at all. Over the past few days I have found that Gaussia does indeed have an eye, and an interesting one at that! The eye of Gaussia is a two-part cluster of 6 to 8 orange-colored cells. This type of simple eye is common in copepods. A unique feature in Gaussia is a reflective pigment layer that covers much of the eye, with the exception of a small area towards the front of the animal. This reflective layer could serve to redirect light that was not initially absorbed by visual pigments in eye cells back toward these cells for a second chance at triggering a visual response. Another intriguing possibility is that this reflective layer protects Gaussia from being blinded by its own luminescent flashes. There are numerous cells that secrete luminescent material in close proximity to the eye, and the position of the reflective layer would seem to shield the eye from the glow of these cells. I am preparing several animals to look more closely at the eye structure once we return to shore. 
I have been able to record the neural activity of the Gaussia eye using a technique called an electroretinogram. This involves carefully inserting an electrode into the eye, presenting flashes to the animal, and using a computer to record the neural response. All of this is quite challenging on animals of this size to begin with, but the constant rolling of the ship adds another layer of complexity. These experiments are working however, and I have found that the Gaussia eye is maximally sensitive to blue light. This makes good sense as this is the color of its luminescent flashes, as well as the most available light in its mid-water habitat. The rest of the cruise should bring more insight into the visual system of Gaussia. Having the opportunity to work on these animals at sea is a great experience!! 
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