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THE MAINE EVENT: FALL 2004 Predation by Gelatinous Zooplankton in the Gulf of Maine MISSION DISPATCH 11 • Friday, September 24, 2004 Dispatch by Ulf Bamstedt and Calle Stangenberg - University of Umea and Umea Marina Forskningscentrum, Norway The day began at midnight with a long transit, i.e., 13 hours of steaming in a NNE direction from Oceanographer Canyon to Georges Basin. During this period the temperature of the surface water became much colder, 24C to 15C. The slightly greener color of the water and a larger number of sea birds suggest that biological productivity is probably higher at this location. And, we have new guests on board. Two small song birds, who ventured far away from land and lost their orientation over the sea, have adopted R/V Seward Johnson II as a refuge. 
Like yesterday, we have calm seas and therefore stable working conditions. The mid-day dive with
the Johnson-Sea-Link submersible descended
to the bottom at ca 300 meters. Chief scientist,
Marsh Youngbluth
dove in the sphere. As expected, only a few kinds of animals were collected, reflecting the
difference in water masses from the previous location. The colonies of
Nanomia cara
observed from the sub were distinctly aggregated in a vertical layer around 175 to 225 meters and at
least twice as long as those observed in any of the canyons. Marsh and Tim (JSL pilot) estimated
the biggest ones to be three meters in length. Other morphological features (size, shape and color
of tentilla) differed from canyon specimens. Are there two different species of Nanomia? DNA
analyses being conducted by
Brian
may answer this question.
Collection bins on the JSL came up with a planktonic polychaete worm named Tomopteris helgolandica, several ctenophores (comb jellies) called Beroe cucumis and Bolinopsis infundibulum and euphausiids (= krill) named Meganyctiphanes norvegica. The euphausiids were collected for use in respiration and excretion measurements with the micro-optode instrument. It is worth noting that the specialized samplers on the JSL provide robust animals from deep water. Reliable quantitative studies of physiological activities are easily biased by other, less gentle collection methods, e.g., tows with plankton nets. However, nets are useful for estimating information on abundance and distribution. By combining estimates of metabolic rates and data from MOCNESS (a system with nine separate nets for vertically divided sampling) tows obtained on this and previous Maine Event cruises, Ulf and his group from Sweden will estimate the population carbon turnover rate of both Meganyctiphanes norvegica and the amphipod Themisto compressa. The respiration rates of small, but numerically dominant copepods, gently collected in the upper 10 m with a small plankton net, were also measured. In addition, tiny 
microzooplankton were sampled throughout the
water column in the Go-Flo bottles mounted on a traditional CTD-rosette frame. Respiration of these animals
will serve to indicate the extent to which different water masses vary in productivity.
A fact of oceanographic work, not always appreciated, is the limited amount of space available on a ship. The two main labs and two of the four temperature-regulated rooms on this cruise are always crowded with scientists and their equipment performing different experiments. It is amazing that conflicts can be held at an amusement level with all the ongoing activities. Scientists are obviously tolerant creatures. The night dive was a training exercise for the sub crew with Frank as pilot and Tim as co-pilot. This practice occurs on every tenth dive. Although no scientist participated, ctenophores and siphonophores were collected for shipboard projects. Horizontal transects were undertaken as well to estimate the vertical distribution and abundance these gelatinous zooplankton. We learned that a major portion of the siphonophore Nanomia cara population migrated upward from 225 to 40 meters. However, neither the kind nor the number stomachs filled with prey (=copepods) differed from those in colonies collected in deeper water during the day dive. The question "why do these animals migrate" remains unanswered for now. But we'll return to the undersea world tomorrow to continue investigations of the ways that zooplankton have adapted to survive in cold, dark, hyperbaric environments. 
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