March 23, 2003: Leg 3, Day #12

Pescadero Basin 

We are back at sea after a two-day port call in La Paz, where we cycled personnel, re-provisioned, stretched our legs, and bent our elbows. We left the dock at 0800 this morning, cleared the harbor, and headed to the southeast.  

Years ago, when I was just a pup, I visited the Gulf aboard Stanford's research vessel Proteus. We happened to be anchored in La Paz on the warm, star-filled night when Neil Armstrong and Buzz Aldrin first walked on the moon. That night we couldn't buy a beer. As we walked through the dark streets of the town, we could see TV sets glowing through the doorway of each little bar. "Hola gringos, que bueno!" was the greeting wherever we went, and wherever we went, the beers were on the house. We gringos were proud of what "we" had accomplished. We humans, Mexican and American alike, were proud that "we" had reached out and touched the sky that seemed much closer that night. 

This week, Americans were all over the TV in La Paz again. This week, the Mexicans we talked with were just as warm, friendly and considerate as they were last week, but it seemed clear that this time there was no shared adventure. 

On today's dive, we spent more than an hour watching a ctenophore eat a krill. That probably sounds like a good time to go out to the galley for a cup of coffee, but to some of us it was pure fascination. The ctenophore was Thalassocalyce, a transparent lobate with a delicate, diaphanous body. They are so fragile that it is virtually impossible to bring them back from a dive and study them in the lab. We have observed them in Monterey Bay and are familiar with the basic elements of their structure, but we had never seen them in action. Today we learned a great deal about how 
everything works. Thanks to some exceptional flying by Buck Reynolds and Paul Tucker, we have it all on video. 

Like most lobates, Thalassocalyce has lobes, like big soft catcher's mitts extending (out, down, up—it doesn't matter much in midwater) from the center of the body. When we came upon this one, it had already trapped a krill inside one lobe (see above and left). The krill was trying to escape but was carefully avoiding the sticky insides of the lobe. Slowly the lobe contracted—too fast and the krill might be expelled, too slow and it might find the way out. Eventually the krill became stuck on the lobe and was slowly transported toward the mouth. As the ctenophore continued to compress around the krill,  the shape of the transport pathway became apparent, something we had not seen before. Likewise,  the shape and position of the "stomach," and its relationship  to a pair of reticulated structures, became clear as the food passed through it (see below). 

Natural history observations like this are still extremely rare. It is one thing to observe, count, or even capture an animal in passing, but to be able to patiently observe a deep-sea predator while it is feeding is a wonderful thing. 

This was a good dive for fishes as well, and we saw further evidence that our expectation of latitude-specific distribution patterns is holding true. We regard the lanternfish Triphoturus mexicanus as the quintessential Gulf midwater species. Its 
abundance was highest in mid-Gulf, in the Guaymas and Farallon Basins. Here in the south, where the influence of Equatorial Water is strong, the relative numbers of  T-mex have declined and more tropical species like Vinceguerria lucetia have become prominent. This study is helping us to define
the niches in midwater communities by revealing patterns of ecological structure that repeat. While the species that fill the niches may differ from place to place,  if we find animals making a living the same way, then that's an indication that the niche is common to both communities. 

The gremlin showed up again and shut us down for a while. Dan Chamberlain has now chased him back to wherever he comes from, and we seem to be up and running again. But I think I'll fire this off while I still can... 

Bruce Robison