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March 13, 2003: Leg 3, Day #2

Pescadero Basin 

Today's dive took us more than 3,100 meters down into the deepest part of the Gulf of California. We saw some wonderful animals and made some important collections. Tonight we will head northward to the next basin in the chain of deeps that form the floor of the Gulf. 

This morning we launched again into calm seas and nearly ideal surface conditions. We quickly entered a layer of flashing blue lights that surprised us with their intensity and abundance. The source could not be bioluminescence because we were still near the surface, and the water was well illuminated by the sun and by ROV Tiburon's lights. Instead it was the iridescent bodies of tiny copepods, aptly named Sapphirina. Under a microscope the bodies of the males do indeed resemble sapphires, and the shining colors they reflect rival the plumage of the brightest tropical birds. Bill Hamner explained to us that groups of male Sapphirina arrange themselves into specific spatial patterns and use their bright reflections to signal females. 

When we entered the oxygen minimum layer today, we found many more fishes than we saw yesterday. Their numbers grew with increasing depth until we were between 400 and 500 meters, where their abundance was the greatest. Here we saw myctophid lanternfishes Triphoturus mexicanus and Diogenichthys laternatus and the bristlemouth Vinceguerria lucetia


Back in the Pleistocene, when I was a student, I studied these very fishes by collecting them with midwater trawl nets. In those days, I had to imagine what they were like in their natural habitat—today I could see them. What they were doing was waiting for the sun to go down so that they could safely return to the surface layers and resume feeding. In order to avoid visually cued predators, these fishes remain always in the dark. At night they are near the surface, feeding on copepods and shrimp but protected by the darkness. When morning comes they descend into deeper, darker
water to wait out the daylight hours. Here in the Gulf, the pronounced oxygen minimum layer means that activity levels at daytime depths are lower than in Monterey Bay, but this applies to the predators as well, so things even out.   

And speaking of nets, ours is still lost, somewhere between Guadalajara and La Paz. This means that we have to change the entire cruise plan and a couple of the projects, but then little challenges like this are what make expeditionary science so much fun.   

Mar13_ctd.jpg (49453 bytes)

 


This is a CTD image that shows the oxygen minimum layer. Oxygen is in green, temperature in yellow, salinity  in blue, and transmissometer in red.

Mar13_spider.jpg (87615 bytes) Karen Osborn looks pretty happy tonight. Today we observed and collected five different kinds of munnopsid isopods, or "spiders" as we call them. Karen studies these deep-sea spiders using classical morphology-based systematics, woven together with state-of-the-art genetic techniques, to establish the relatedness of the different munnopsid types. She is using this as an organizational background for studies of their biology, ecology, and biomechanics. 

Another endearing aspect of expeditionary science is that glitch gremlin I referred to a couple of days ago. Today we had to dive without the system that links all of our data together so that it makes a coherent database. The system also affects our ability to annotate our videotapes, make video frame grabs, log data, know where we are... little things like that. Throughout the day, the ROV team, and in particular Dave French, worked hard to repair and reconfigure the system. Finally, after many hours of effort, including phone calls back home to Doug Au, Dave fired it up, and we are back in business. 

The Tiburon is back at the surface 15 hours after we launched her this morning. But the day is far from over because our animals have just arrived, and many of us will be up the rest of the night working with them. They are the rarest of commodities, living deep-sea critters. While we work, the R/V Western Flyer will be carrying us to the Farallon Basin. More to come... 

Bruce Robison

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