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THE MAINE EVENT: FALL 2004 Predation by Gelatinous Zooplankton in the Gulf of Maine MISSION DISPATCH 8 • Tuesday, September 21, 2004 Dispatch by Franz Uiblein - Institute of Marine Resources, Norway Today started at 0400 with the retrieval of the vertically-hauled plankton net from 600 m. A sample of fishes has become a rather rare event on this cruise since the failure of the MOCNESS winch last week. Consequently, the notice that Francesc left on my computer saying "fish sample for you in the cold room" was a wonderful surprise. A dragonfish of the genus Eustomias, a lanternfish (family Myctophidae, genus Benthosema), two larvae, and several bristlemouths belonging to the common vertebrate genus Cyclothone were in the sample. The name of the latter group is derived from the numerous tiny teeth that slightly protrude from their mouths. These teeth are an important diagnostic character for some species. Another common name that has been given to this genus is "deep-sea minnow" referring to their small size, about 2-3 in (5-8 cm) long. What makes the appearance of Cyclothone in a cruise featuring zooplankton studies particularly significant is the fact that ecologically this group is often regarded as plankton because they are drifters rather than members of nekton, which actively move independent of water masses. Another reason why Cyclothone has been a study object during our cruises is its possible role as food for large zooplankton including siphonophores like Nanomia cara. 
The bristlemouth fishes are fragile and individuals collected with nets are often badly damaged
making identification to the level of species rather difficult. However, a collaboration with a
world top expert in Cyclothone taxonomy, Maskai Miya of the Natural History Museum, Chiba, Japan,
has allowed us to overcome this problem to some extent. On this cruise, one rare species C.
microdon arrived in good condition as a "by-catch" of a medusa at 2,768 ft (844 m) from
JSL dive 4782
in Oceanographer Canyon.
During my seven dives so far, in situ species identification of small mid-water fishes has been difficult because video resolution is rather low and animals directly observed are somewhat size-diminished when viewed through the 4-in (10 cm) thick acrylic sphere of the JSL submersibles. However, many larger nekton and zooplankton can be identified to lower systematic groups. On our dive last week we recorded 574 individuals comprising at least 24 different taxa. 
Today's onboard activities included the continuation of respiration experiments with deep-sea
octopuses, various gelatinous zooplankton, and crustaceans.
During the afternoon dive in the Atlantis Canyon, Ulf observed and collected a variety of large zooplankton for further taxonomic, trophic, and experimental studies. A single specimen of the rare scyphomedusae Atolla gigantea (165 mm in diameter fully extended) was collected at 831 m (see image photographed by David Shale). Less than 10 specimens have ever been recorded, mostly from the Southern Ocean, and none from Atlantic waters. Per's evening dive in Veatch Canyon was equally successful. Two specimens of an undescribed species of the scyphomedusa Poralia were sampled at 762 and 774 m. Both types of medusa are dark red, a typical color of bathypelagic species. Calm weather is forecast for the next few days. We'll be diving in Oceanographer Canyon again tomorrow. 
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