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THE MAINE EVENT: FALL 2003 Predation by Gelatinous Zooplankton in the Gulf of Maine MISSION DISPATCH 10 • Sunday, September 21, 2003 Location: Georges Basin (42° 18'N, 67° 30'W) Dispatch by Harry Breidahl - Marine Education Society of Australasia [MESA] Our second day at Georges Basin and the weather is thankfully on the improve but we are still surrounded by marine fog. The working day began before breakfast a with MOCNESS net tow, then followed a CTD cast and our first sub dive since Hurricane Isabel interrupted our at-sea activities. JOHNSON SEA-LINK II (JSL II) dive 3449 plunged below the waves at 1.00 pm (1300 hours). Colonies of Nanomia cara were numerous and aggregated in a 100 ft thick layer from about 650 to 750 ft. Only one colony was seen in the upper 150 ft. These observations contrast with those from the ROV last night when colonies were abundant throughout the upper 100 ft. Such results suggest that colonies migrate upward at night, perhaps to feed, and then return to deep water during the day. Such diurnal migrations were noted a few years ago in Wilkinson Basin when Nanomia cara was abundant there. 
By the time evening rolled around, the marine fog had evaporated and the seas were flat. Conditions were ideal for a night
dive. On this dive (#3450) we confirmed that a substantial segment of the siphonophore population moved into the upper
100 ft. Unfortunately, the suction pump on the rotary sampler failed to operate properly near the surface and so we were
unable to collect any of these colonies. Consequently, we were unable to confirm that these colonies migrated to feed in
shallow water. We did sample the deeper-living colonies of Nanomia cara and learned that less than 10% of the stomachs
(called gastrozooids) contained prey, and only calanoid copepods.
With only a few days remaining on this cruise and the weather on our side, we decided to steam to deep-water canyon sites in order to compare our studies of Nanomia cara from Georges Basin to a population of Nanomia cara living at 2000 ft. The canyons along the southern margin of Georges Bank, especially Oceanographer and Lydonia, harbor an abundance of colonies (see The Maine Event 2002) and a high diversity of other gelatinous zooplankton. Yesterday, graduate student Brian Ortman wrote about the Feature Creature Beroe cucumis. On this cruise Brian is collecting samples of gelatinous zooplankton for analysis of their genetic structure. In particular, he is concentrating on three midwater species - Nanomia cara, Bolinopsis infundibulum and, you guessed it, Beroe cucumis. He intends to compare the genetic make-up of the common species from site to site. Genetic information is basic to our understanding of how deep-sea communities are structured and how creatures interact in this little known, but supposedly homogeneous, habitat. Aino Hosia, another a graduate student, originally from Finland, is working on a doctoral degree at the University of Bergen in Norway. Her graduate studies will produce an ecological census of gelatinous zooplankton in Norwegian fjords. While aboard the R/V Seward Johnson Aino has been assisting Marsh Youngbluth with measurements of oxygen consumption using a novel optical approach. In her spare time, she also helps with the launch and recovery of diel MOCNESS tows to collect zooplankton, filters water from CTD casts for fatty acid analyses, picks out gastrozooids of Nanomia cara for predation studies, and photographs everything. 
New technology has always offered scientists alternate ways to conduct old tasks more efficiently or to pursue new avenues of
research. On this cruise, preliminary trials with a PC-controlled fiber optic oxygen meter have been successful. This
technology has allowed Aino to measure basal metabolic rates of the same three gelatinous zooplankton species, specifically
Nanomia cara, Bolinopsis infundibulum, and Beroe cucumis. Oxygen concentrations determined from separate analyses (the
traditional Winkler titration method) of water samples taken at the beginning and end of a given experiment have been consistent
with values recorded by a new micro optode system. The sensors are stable and respiration rates can be monitored continuously
for several hours. The images added to this dispatch show the components that accommodate two sensors. One end of an optical
fiber cable attaches to a detritus sampler held in a temperature-controlled laboratory. Pulsed light passes through the cable
and strikes a small (0.25 in by 0.25 in) piece of sensor foil glued to the inside of the sampler. Light emanating from the foil
passes back through the cable to the opposite end, which mates to the Fibox 3 meter. From here data passes through a transmission
cable that winds its way from the cold room to the dry lab in order to connect the meters to a computer. Data are logged at
1-second intervals. Results from a typical 16-h experiment with Nanomia cara are plotted, control (pink) and animal (blue).
Fun facts for the day • From yesterday you know that ROV = Remotely Operated Vehicle, so what about AUV and HOV. Simple, AUV = Autonomous Underwater Vehicle and HOV = Human Operated Vehicle. • In Dispatch 3, while talking about the bathyscaph Trieste I misquoted Jacques Piccard's nationality. In that dispatch I said Piccard was from Belgium but he was actually Swiss. The Belgium connection came in when Jacques's father Auguste Piccard built his first bathyscaph with the aid of funds from Belgium. In fact a range of European nations funded Auguste Piccard's initial work on bathyscaph construction. The bathyscaph in which Jacques Piccard and Don Walsh descended to the bottom of the Marianas Trench was named in honor of the Italian city of Trieste. • You should know that the deepest part of the ocean is around 11 km deep (6 1/2 miles). So here's another questions for you to think about, what is the average depth of the ocean?   |  |
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