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MISSION SYNOPSIS HARBOR BRANCH research scientist Dr. Marsh Youngbluth and a team of international experts will conduct a week-long series of novel experiments aimed at clarifying the importance of appendicularians and their feeding houses in cycling organic material through ocean food webs. 
The R/V SEWARD JOHNSON will leave home port on Monday, 16 April 2001, for a week of submersible-based research focusing on appendicularian (pelagic tunicate) populations within the western edge of the Gulf Stream. The planned cruise route will cover waters from Fort Pierce, Florida, northward to Jacksonville, Florida. Dr. Youngbluth and his colleagues are planning to field-test an array of unique in situ techniques from the JOHNSON SEA-LINK 1 (JSL1) research submersible. The research findings from this initial study will form the basis for more detailed, longer-term investigations of the ecological roles that relatively large appendicularians and their associated feeding houses play in pelagic regimes. Although poorly studied thus far in the natural environment, these animals are ubiquitous in the water column on a global scale. 
Among the goals of the research mission are the documentation of in situ rates of appendicularian feeding, house production, and house flux. The sinking of abandoned houses to deeper waters represents a potentially major net export of energy to those waters.
"The scant but compelling field information from previous appendicularian studies," notes Youngbluth, "suggests the animals must have a central role in the flux of material throughout the water column, especially in particle-rich layers. These animals are capable of very rapid generation times. Most species are capable of high grazing rates on a wide spectrum of particles, including microbial phytoplankton, bacteria and detritus." To maximize the amount of data collected, a rigorous schedule of sampling and experimentation is planned. Dives will span day and night periods to account for any diel variation in feeding rates. One of the research activities will be the use of a new broadcast quality, high-resolution digital video recording system aboard the JSL1 to estimate rates of water flow through the houses of larger appendicularians, rates of food passage through the gut, and fecal pellet release rates. Evenly illuminating the video field and staining the houses using a special squid ink suspension will allow investigators to map the chamber volumes in situ with precision. 
Passive sinking rates for abandoned feeding houses (and possibly fecal pellets) will also
be examined in situ. To accomplish this, a neutrally buoyant fluorescent dye will be squirted into the water column a known distance below a house. The time required for the house to sink to the dye cloud will be recorded, and sinking rates calculated. The effects of house size, age, degree of deflation/deformation, water temperature, and density will all be considered in this initial investigation.
Appendicularians will also be collected during the dives and transported to the surface for shipboard laboratory studies. Since a primary target species, Bathochordaeus stygius, lives at depths of less than 100 meters, up to three shallow submersible dives per day will be made. On each shallow dive, up to 10 animals and their houses will be collected using the JSL1's static samplers. On alternate days, two deeper (ca. 500 m) dives will be made to sample other, smaller appendicularian species that are concentrated in the benthic boundary zone. Shipboard investigations of static sampler collections will involve microscopy to examine house structure and particles associated with houses, clearance/defecation rate studies, chemical analysis of gut contents, fecal pellets, and houses, and house production rates. 
A carousel sampler on the JSL1 will also be used to obtain a dozen additional appendicularians for taxonomic determinations and more extensive gut content analyses. "I think we have a high chance for success because we just may have the right tools for the job," speculates Dr. Youngbluth. "The proposed research projects are exploratory, but they will carefully address in situ and laboratory approaches that can quantify various processes." "Such data, when combined with documentation of the vertical distribution, relative abundance, chemical composition, and particle loads of appendicularians and the multiple houses these animals produce each day, are likely to substantively broaden the understanding of how pelagic food webs really work."  | |
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