THE MAINE EVENT: SUMMER 2002 Predation by Gelatinous Zooplankton in the Gulf of Maine Dispatch 5 Wednesday, July 04 2002 Latitude: 40°17.408"N • Longitude: 68°06.792"W Dispatch by Brandy Ninesling, HARBOR BRANCH Oceanographic Institution Today began with a cool, crisp morning and a sea surface that resembled polished glass. Like clockwork, at 6AM MOCNESS nets were once again sent to 1000 m and returned four hours later with hundreds of zooplankters and fishes. Each day the nets capture an array of amazing creatures to identify and this morning was no exception. We carefully sifted through the collections to remove midwater fishes. These animals and the remaining zooplankton were preserved in formalin. A CTD-water bottle cast was next in line to be deployed. This gear serves to profile temperature, salinity, fluorescence, and transmittance in the water column and collect water from the depths where siphonophore colonies were sampled by the submersible. After wrapping up the sampling duties we were drawn to the galley by the aroma of fresh baked bread. Meals, beautifully prepared as well as delicious, are served three times a day. In between, snacks of fresh fruits and sweet treats, most importantly chocolate, are in constant supply. At 1 pm the JOHNSON-SEA-LINK (JSL) manned submersible was lowered into the water for another three and one half hour adventure. As the sub descends we look for physonect siphonophores. Colonies that pass directly in front of the sub are counted and the depth and time are recorded. These data indicate where the siphonophores are concentrated in the water column. Once the vertical distribution is established the sub ascends to the depths where colonies were most frequently observed. Horizontal transects are then conducted at these levels for five to ten minutes. This procedure serves to quantify the relative abundance of siphonophores in a given volume. Occasionally a rare or spectacular animal that drifts into the illuminated water ahead of the sub is just too tempting to pass by. In these instances, the transect is temporarily halted to videotape the behavior and to capture the unusual creature for further study. During a dive, the upper critter gitter buckets are the first to be filled with Nanomia cara to ensure enough colonies for gastrozooid analysis. These animals are immediately immobilized with a low dose of preservative that is pumped into a sampler. By preserving the colony quickly the digestion process is halted and allows us to determine the number of stomachs filed with prey when we return to the ship. Additional colonies are collected in the other samplers and are used for feeding and digestion experiments on the ship. A few samplers are always available for other fascinating pelagic animals that are too irresistible to pass by. These creatures are brought to the surface to be observed and photographed and sometimes are returned to the depths where they were collected. When the Johnson-Sea-Link submersible returned from the afternoon dive the canisters were brimming with gelatinous life forms, i.e., siphonophores, ctenophores, medusae and appendicularians. Smiles were contagious as we removed the detritus samplers from the sub and carried them to the cold room. The contents of the critter gitter samplers were filtered with a sieve, which concentrated the preserved colonies and ensured that all of the gastrozooids were present. Then, we were off to the dry lab where we sorted and separated gastrozooids from the rest of the colony. Finally the abundance and type of prey in the gastrozooids were recorded. At 630 pm we begin preparations for the next submersible dive that will begin in two hours. All the equipment is checked and rechecked to make certain that latches are tightened, lids are sealed, and the JSL is ready to dive. At three thousand feet you canÕt just crawl out of the sub to readjust a sampler! Do you have a question for the researchers on this ocean expedition? Why not ask a scientist @Sea?

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