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THE MAINE EVENT: SUMMER 2002 Predation by Gelatinous Zooplankton in the Gulf of Maine Dispatch 3 Saturday, July 01 2002 Latitude: 40°10.5950"N • Longitude: 68°11.9760"W Dispatch by Heather Holberger, HARBOR BRANCH Oceanographic Institution 
The morning began with a MOCNESS tow around 9am. The MOCNESS system consists of nine plankton nets connected to a giant frame. At the end of each net is a plastic canister called a cod end, where the animals are retained. The particular model that we are using is called a MOC 1, which indicates the nets have a mouth area of 1 meter by 1 meter. The MOCNESS is raised off the deck into the water with a crane, while marine operations technicians LaVern Taylor and Chris Pate from the University of Miami direct winching the net over the starboard side of the ship. As the MOCNESS is towed, it descends to a depth of 1000 meters. Once in the water, everything is regulated from a control room. The technicians 
are able to open and close eight of the nine nets in sequence in order to
collect animals from different depth intervals. Such controlled sampling
allows us to determine the abundance of prey (copepods) in relation to the
abundance of gelatinous predators (primarily the siphonophore
Nanomia cara).
Once the MOCNESS is hauled back onboard, zooplankton in cod ends are emptied
into buckets and the catch is preserved for future reference. However, the
catch is not always pickled immediately. Usually Heather Holberger, Dr.
Marsh Youngbluth's summer intern from Florida Institute of Technology,
siphons as many live copepods as possible for her Nanomia cara feeding
behavior experiments. Midwater fishes are also removed and will be sent to
Austrian colleagues for ongoing comparisons of taxonomic affinities.
A rosette of water bottles (pictured below) was deployed to collect
seawater from deep, cold, and dark environments. This water is used to
maintain the animals we collect and keeps them comfortable for their stay on
board. Rare and unusual animals are placed in the plankton kreisel for
observation and photography.
The plankton kreisel (not pictured) is a circular tank that is connected to a chiller/pump. We filled the kreisel with water from the rosette then activated the chiller so that the water would stay at 8°C. The water flows out of the chiller through a tube and into a diverter that fits in the top corner of the tank, which ultimately circulates the water around the perimeter of the tank. This movement of water prevents the animals from sinking to the bottom.  |  |
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