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THE MAINE EVENT: FALL 2002 Predation by Gelatinous Zooplankton in the Gulf of Maine MISSION DISPATCH 7 • 09/16/02 Today's Weather - images courtesy of NOAA & RSMAS Dispatch by Harry Breidahl - Marine Education Society of Australasia [MESA] 
The second week of the Fall 2002 Maine Event ended with unsettled weather still limiting the use of
Johnson-Sea-Link I (JSL) at Atlantis Canyon (rough seas make launching and recovery of JSL unsafe).
A brief period of relative calm conditions did allow for a JSL dive on Saturday night. All sub launches are dramatic but night deployments create an unworldly setting. Powerful arc lights mounted on the vessel's superstructure bathe everything on the aft deck in an eerie artificial glow. In this light the whole scene takes on a science fiction mood with the space vehicle-like JSL occupying center stage. In essence it is a space vehicle, one designed to explore inner space (the ocean) rather that outer space. While opportunities to launch JSL have been limited, other elements of the research program continued. The MOCNESS multi-net system and the French underwater video profiler (UVP) were hoisted over the starboard side on a number of occasions. 
This dispatch is the last in the series of three messages dealing with research techniques aboard the
R/V Seward Johnson II in the Gulf of Maine. This time the focus is on the French UVP, a unique deep-sea
research tool that has been developed over a 10-year period (go to
www.obs-vlfr.fr/~pvm/indeng.html for
details). We are using the fourth generation profiler to investigate the vertical distribution of particles
and plankton.
The UVP consists of a rectangular metal frame upon which a number of instruments are mounted. The primary components are two video cameras and two strobe lights. The second main instrument, called a CTD ( = conductivity, temperature and depth), senses and records physical and chemical parameters. These data are stored in a special computer mounted on the UVP and then downloaded to a shipboard computer when the profiler is back on deck. Once in the water, the UVP is lowered on a steel cable at a rate of 1 meter per second (2 knots) to a pre-selected depth. The video cameras are designed to take multiple images (snapshots) of whatever passes through their fields of view (7 and 40 cm2) as the UVP descends - as deep as 1,000 meters (3,000 feet) on this cruise. Each camera creates a continuous profile by taking 12 video frames per second for the duration of the descent. On a trip down to 1,000 meters that makes for a great many images to be analyzed. Over 12,000 frames are obtained with each camera and each frame may contain up to 1,000 images! Most of the objects detected in the UVP's light fields appear as ghostly white images on a jet-black background. The vast majority of these small dots are produced by marine snow (fine particles that are temporarily suspended or constantly raining downward from the productive sunlit waters). The UVP computer 
recognizes and analyses these images automatically. The remainder of the frames, usually 100 or more, show
several kinds of zooplankton. These frames are highlighted on the computer for later analysis by Marc Picheral
and one or more of the scientists on board. The ethereal white silhouettes contain enough detail for the
trained eye to identify larger animals such as ctenophores (comb jellies), euphausids (krill), medusae (jellyfish)
and appendicularians (larvaceans). One highlight of the UVP work occurred on Sunday night when an incredible
image of the siphonophore
Nanomia cara was displayed.
Although a single video profile represents only a very narrow cross-section of the water column, repeated profiles can be combined to present a picture of the complex layering of oceanic waters at a particular research site. The vertical distribution of animals can also be imaged in this way. To date we have profiled the water column in Atlantis, Hydrographer and Oceanographer canyons.  |  |
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