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March 12, 2003: Leg 3, Day #1

Leaving La Paz

We let go our lines and cleared the dock at 0800 this cool morning with only Steve Etchemendy and one of the dock dogs to send us off. The sky was clear and blue and so was the sea, just different shades. Our destination was Cerralvo Bank, a nearby seamount of sorts, with a peak that rises to within a couple of hundred meters of the surface and a steep western face that drops quickly to 1600 meters.

Should be a good spot to get started. Perspective shifts are common at times like this. When the R/V Western Flyer was tied up at the dock, she was next to a modest freighter that just towered over her. Compared with the Mazatlan ferry or most of the other vessels we passed between Cerralvo Island and the tip of Baja, she still seemed small. But breaking clear of the land changes everything, and with only the sea and sky for scale, all ships are tiny. Now that it's just us and the deep ocean, the Flyer seems just right.

Our plan is to drop the ROV Tiburon in, right over the peak of the bank, then slide down the sheer wall and into the deep trough. We will be looking for changes in the pelagic fauna and also among the adjacent benthic animals as we pass through the broad depth zone of reduced oxygen. Tiburon's instruments will give us a real-time readout of oxygen 

concentration as we descend, so that we can correlate this parameter with the patterns of animal distribution we see with the video cameras.

Shortly after the ROV launches, we will also send out a team of blue-water scuba divers to work in the upper part of the water column. They will make direct observations and gently hand-collect animals to bring back to the ship's lab for studies of behavior, physiology, and bioluminescence.

We'll be pretty busy for the next 16 hours or so, and we will let you know tomorrow how things went today. Stay tuned... 

En route to Pescadero Basin

Tonight we're steaming eastward for tomorrow's dive site in a complex of deep basins near the mouth of the Gulf of California. We are staying within range of La Paz because there's hope that our lost trawl net will arrive there tomorrow (and there are some dot-com IPOs we're going to look at as well).  

Today's dive into the Cerralvo Trough was filled with surprises. As soon as the ROV Tiburon got wet, we encountered a thick layer of larvaceans that look very much like the Bathochordaeus we see at greater depths back home. Below this was another distinct layer of their discarded feeding filters, or "sinkers," similar to the ones we have been working on as carbon transport vectors in Monterey Bay. Then came a large layer of salps that reached down to more than 200 meters. The stratification was quite pronounced, and the layers were well defined. We believe that the layers form because the animals are being squeezed into the upper levels of the water column by the near absence of oxygen in the depths below.  

As we worked our way down the face of the bank, we found great expanses of nearly empty space both in the water column and on the steep sea floor. Once again, this is probably due to the paucity of oxygen. What we did not expect to find were the patches of animals that apparently crop up simply because that's where the other animals are. We also realized that the sinkers seemed to be almost everywhere. 

These observations support our measurements back home about their importance as a major food source for the deep benthos. There were virtually none of the benthic scavenging animals we usually see along the sea floor. Instead, carcasses, sinkers,  and other food falls everywhere were covered with ghostly patches of white, filamentous bacteria.  

Mar13_stomias.jpg (60160 bytes)During our ascent back toward the surface we observed and collected some animals that occupy niches similar to counterpart species in Monterey Bay, yet they remain distinctly different and are clearly adapted to this southern habitat. Among these was the blackbelly dragonfish Stomias atriventer (see left). In more northern waters, Stomias is replaced by the viperfish, Chauliodus macouni. Both species feed on shrimp and other fishes and both make a living in roughly the same way. The only place that they co-occur is where the cool waters of the California Current meet subtropical waters in the southern California borderland. Tonight, Edie Widder recorded Stomias' spectacular bioluminescent display.

Kim Reisenbichler, Steve Haddock, Brad Seibel, and George Matsuomoto made a blue-water plankton dive while Tiburon was working deep. They brought back pteropods, heteropods, siphonophores, and a strange planktonic nudibranch named Phylliroe.  

We're beatómore tomorrow... 

Bruce Robison 

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