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MISSION DISPATCH 7 • 09/01/01 Today's Weather - images courtesy of NOAA & RSMAS Dispatch by Rebecca Johnson - HARBOR BRANCH Oceanographic Institution 
Latitude: 42°25'57"N • Longitude: 69°45'40"W Early this morning the R/V SEWARD JOHNSON glided past the spit of land that marks the tip of Cape Cod and into the harbor waters of Providence, Rhode Island. A small skiff was lowered over the side, and two members of our research team, Juanita Urban-Rich and Jennifer Whiteis, climbed aboard to be whisked away into the mist. Alas, they had to become landlubbers again. They'll be missed. The boat returned with Jaimes McCarty, Juanita's graduate student at U Mass, who'll be gathering data for his Master's degree project. A major focus of this cruise is to investigate the feeding behavior and dietary preferences of Nanomia cara. For the past 24 hours, we've been conducting feeding experiments with Nanomia colonies that were brought up alive with the JOHNSON-SEA-LINK submersible in special acrylic canisters and maintained at about 45° F (7° C) in one of the cold rooms on board. This laboratory space simulates the dark, cold deep-midwater environment in which these animals live. 
Preparing dinner for Nanomia is quite a tedious process. First we collect copepods by hauling a 1-m diameter plankton net through the upper 50 meters of the water. Then we sort the capture into groups of single species by peering through dissecting microscopes and carefully siphoning off individual animals one by one. Next, samples of two species of copepods, Calanus finmarchicus and Centropages hamatus, are stained with a crimson vital dye to make these minute and nearly transparent creatures easier to see. Then it's feeding time! Into each canister that holds a famished Nanomia colony, we release about 50 stained copepods of a given species. Within moments, most have blundered into the siphonophore's deadly tentacles, and are held fast. As the tentacles contract, they reel the catch in toward the restless mouths of the gastrozooids, which eagerly engulf the red-stained prey. Digestion begins almost immediately. 
And it's remarkably fast. After just 1.5 hours, most of the copepods inside the gastrozooids are well on their way to being turned into nutrient soup. Over the coming days, we'll be repeating these feeding experiments, with variations, many times. Knowing how much a siphonophore eats, and how quickly it digests its meals, is information that's critical to determining the impact of Nanomia on the copepod populations in these waters. Do you have a question for the researchers on this ocean expedition? Just ask a scientist @Sea in our MISSION FORUM!  | |
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