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MISSION DISPATCH 2 • 08/27/01 Today's Weather - images courtesy of NOAA & RSMAS Dispatch by Rebecca Johnson - HARBOR BRANCH Oceanographic Institution Latitude: 42°23'52.3" N • Longitude: 69°44'30.0"W After a night of steaming northwest, we arrive in the Wilkinson Basin area just after 8 am. Hopes are high that today the weather gods will smile on us and calm the white-capped ocean, at least enough to launch the submersible. 
Despite the bright sun glinting off the wet decks, the sea is anything but calm. The swells are still with us, occasionally breaking over the side to set the aft deck awash. So we channel our energies into MOCNESS tows. The MOCNESS is an array of plankton nets (pictured left) that can be lowered into the water as a unit and then opened and closed in sequence at various depths. This setup allows us to sample zooplankton throughout the water column, and, depending on what is captured in each net, get an idea as to where certain kinds of fauna are distributed in the vast depths below. No one really knows where Nanomia cara tends to be in these waters in late summer. A MOCNESS tow may help us find out, although the delicate nature of gelatinous animals makes any form of net-based sampling less preferable than submersible-based collection. 
The MOCNESS lurks on the starboard side of the aft deck, its nine nets neatly folded one atop
the other. Some of us have dubbed it "LOCHNESS" after the long-necked sea monster. The MOCNESS
is a bit of a beast, with its coils of fine-meshed net clamped within a framework of metal and
electronic gear. Each net terminates in a small plastic chamber called the cod end. When the net opens underwater,
planktonic animals are engulfed at the mouth, and tumble helter-skelter along the net's length
until they reach the cod end.
Marine operations technicians Allison Heater and Keith Martin from the University of Miami handle the launch and retrieval of the MOCNESS. Dressed for the part, they carefully winch the cumbersome gear over the starboard side into the water (pictured right). Moments later the unfurled nets sink toward the sea floor some 260 or so meters below. 
On computer screens in the control room, the techs monitor MOCNESS's actions underwater, triggering
the nets to open and close at appropriate depths. Those animals that are in its path and too
slow to make a dash for freedom are quickly swallowed.
There's an element of suspense in the wet lab, where Jennifer Bossart, Sarah Peters, and Jennifer Whiteis are busy filtering seawater and labeling containers to hold the treasures the nets capture. An hour later the uncertainty ends as the MOCNESS is hauled back aboard. Everyone crowds around, eager to catch a glimpse of "the catch." It's obvious to Norwegian scientist Per Flood (pictured below at right) that we've dragged the nets through a copepod heaven. The chambers are literally packed with thousands of tiny pinkish bodies that are actually the copepod 
(Calanus finmarchicus). Each is about the size of a grain of rice. Careful washing and sorting
also reveals several dozen thimble-size jellyfish (Aglantha sp.), amphipods
(Themisto compressa), euphausiid shrimp (Meganyctiphanes norvegica), chaetognaths (Sagitta spp.),
and a few luckless polychaete larvae. But, alas, there is no evidence of Nanomia or any other
siphonophore.
A second tow is equally rich in copepods. And again, Nanomia is absent. But that doesn't mean the colonies aren't out there. Sampling with plankton nets is always a grab in the dark, a blind reach into a watery environment that is constantly changing. The chance to hunt for Nanomia and other fragile plankton with a submersible often reveals what a net tow cannot. Perhaps tomorrow we will fare better.  | |
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