October 1, 2012
Day four is all sunshine. A morning blue-water dive was cancelled due to wind, but today’s remotely operated vehicle (ROV) dive made up for it. When the ROV was brought up from the ocean floor at 7:00 p.m., we retrieved our collections for the day. They included several species of radiolarians, deep ctenophores, luminous polychaetes, bright yellow Aegina medusae, and a variety of siphonophores, including a very large “pine tree”-shaped species that glowed with a royal blue light.
Shortly thereafter the night activities began. The Haddock lab took advantage of their nocturnal nature. Meghan Powers and Warren Francis deployed the trawl (also called net tow, or tucker trawl). As a grants and accounting specialist, I only hear about trawls when say, the net or cable breaks and funds have to be rebudgeted to replace it and then people go back and forth about who actually pays the bill, so it was great to actually see how they use it—and nothing broke!
Before ROVs, trawling is how animals were collected (in little bits and pieces). Hoorah for ROVs. Apparently, if you collect larger creatures like squid, you use a larger three-by-three-meter net with thicker mesh and trawl at a faster rate. One such net was developed by Jim Childress and Bruce Robison.
Most trawling is done at night because we have a better chance at enticing into the net those animals known as vertical migrators: animals that surface at night to feed and hunt, then hide down deeper during the day. A large, fine-mesh net with a 1.5-by-1.5-meter opening is dragged behind the ship as it steams at about one knot (1.15 mph). The tucker trawl catches the slow swimmers, or creatures that can’t jump far enough out of the way. The water flows through the net and creatures are collected at the “cod-end” (a big jar), which is closed with a tripping mechanism. Meghan and Warren have a long-awaited shiny new instrument that measures depth and temperature, giving a detailed record of the trawl’s journey below the surface. We found that although we put out 1,000 meters (3,280 feet) of wire, targeting a depth of 600 meters (2,000 feet), the net actually only got down to 500 meters (1,641 feet).
Who were the slow swimmers of the evening? We caught a pyrosome (“fire body”)—one of the classic bioluminescent creatures reported centuries ago. We also got many interesting luminous crustaceans (shrimps, krill, and amphipods) that are usually too squirrely to catch with the ROV. The jelly bits, as usual, were a bit too chewed up by the net to be useful for bioluminescence studies.
One of the creatures that we are collecting with the ROV and scuba dives is Nanomia bijuga. Freya Goetz—a former student of MBARI collaborator Erik Thuesen at Evergreen College and former intern of Steve Haddock—now works in Casey Dunn’s lab at Brown University. She is in charge of relaxingNanomia bijuga. Yoga and dark chocolate aren’t going to do it. Nanomia is a multi-part animal called a siphonophore, which contracts its long stem at the slightest provocation. A magnesium chloride bath causes it to relax to a more undisturbed configuration. She preserves them this way for use in in situ hybridization, which is a way to map where various stem-cell genes are being “switched on,” or expressed in each individual polyp.
So why come all the way out to Moss Landing for this? Freya says Monterey Bay has numerousNanomia, and it’s the only place we know that you can reliably collect them via blue-water dives and ROV dives, otherwise their forms are crushed in the nets.
We leave you with one of Freya’s illustrations of one of her study animals.