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THE MAINE EVENT: FALL 2003 Predation by Gelatinous Zooplankton in the Gulf of Maine MISSION DISPATCH 12 • Tuesday, September 23, 2003 Location: Oceanographer Canyon (40° 17'N, 68° 07'W) Dispatch by Harry Breidahl - Marine Education Society of Australasia [MESA] Yesterday we dove in Lydonia Canyon, today we have explored Oceanographer Canyon to a depth of 985 meters (close to 3000 feet). The feeling out here is that we are into the seriously deep blue ocean but, in truth, we are only on the edge. The canyons in which we are working only mark the boundary of the relatively shallow continental shelf. If we were to travel a little further east there would be as much as 3000 meters (approaching 10,000 feet) of water below us. Even more staggering is the fact that the average depth of the abyssal plains that make up most of the ocean's floor is around 4000 meters (over 13,000 feet). 
Last night's sub dive at Lydonia Canyon was
JOHNSON SEA-LINK II (JSL II) dive number 3451. Although there
were plenty of Nanomia cara
colonies, the dive was marred by equipment problems. Both the upper and lower critter gitter racks broke down
part way through the dive and one of JSL's nine electric motors conked-out. As soon as the sub landed on the aft
deck around midnight the sub crew began stripping off the broken bits and pieces, adding spare parts, and replacing
the dodgy thruster motor. By morning JSL II was ready to dive.
All JSL launches are witnessed by several deck-bound onlookers but dive 3452 drew a larger than usual crowd because Aino Hosia was making her first dive in the forward acrylic sphere. For those of us who still play at being contortionists to see out of the small viewing ports in the aft chamber, the thought of a seat and an uninterrupted view of the ocean's interior is like heaven. According to Aino "one of the best parts of the dive was watching the bioluminescence when the sub was ascending, it was awesome." Once the submersible was placed in its cradle on the aft deck, live colonies collected in the detritus samplers were quickly moved to the cold room to continue measurements of their oxygen consumption rates. Preserved siphonophores were taken to the dry lab to look for prey in their gastrozooids (stomachs). Other live fauna like medusae and siphonophores were placed in aquaria and photographed. 
Despite some recurrent problems with a sampler on the sub, we plan to continue exploring Oceanographer Canyon with
JSL II, MOCNESS
net tows and CTD casts. The wind speed has been increasing steadily this afternoon as a cold front
moves closer. Wave height is building and so it's likely that the night dive will be cancelled.
Today's Feature Creatures - Siphonophores by Francesc Pages Since the first time I saw a siphonophore in a plankton sample (it was Chelophyes appediculata, a species common in temperate waters), I was captivated by the unique architecture of their transparent nectophores (swimming bells) and the variable inner canal system. Like other planktonic cnidarians, siphonophores combine a very fragile, gelatinous main body with a network of stinging cells, the cnidocysts or nematocysts. These stinging cells are used to catch and paralyze their prey - ( view animated Nanomia cara feeding sequence). Siphonophores have a complex morphology with specific types of nectophores (swimming bells) forming the nectosome and with several kinds of polyps along the siphosome (stem). Whenever I see a siphonophore I want to know what species it is and how it is built. But what makes siphonophores unique to my eyes is the spreading of their tentacles and tentilla (cnidocyst batteries, the stinging sectors) to catch prey in the water column. Dozens or hundreds of highly contractile )
tentacles may stretch several meters in length to form a dense, curtain-shaped trap in the water column. These are such
delicate creatures that their natural beauty can only really be appreciated from a submersible, such as the JSL II. An
in situ view of a long-stemed siphonophore displaying highly synchronized movements of thousands of small pieces is most
impressive. Apart from the target species for our current project, the physonect Nanomia cara, my favorite siphonophore
on this cruise is a 20 cm (8 inch) long physonect. At a depth of 675 meters (2216 feet).we collected an unknown colony
of Apolemia , a poorly known genus that comprises at least 12 more undescribed species.
Fun facts for the day • Going back to a question in Dispatch 10, you now know that the average depth of the ocean is around 4000 meters (that's over 13,000 feet). • The average depth of different ocean basins varies from 4,200 meters for the Pacific, 3,300 meters for the Atlantic, and 1,300 meters for the Arctic Ocean. • There are some seriously big siphonophores around. Apolemia sp can grow to 30 meters (100 feet) in length, while Praya sp holds the record at around 40 meters (130 feet). By way of comparison, the largest blue whale ever measured tipped the tape at 33 meters (110 feet). The longest bony fish in the world measured 15 meters (50 feet) but what kind of fish was it?   |  |
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