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MISSION FEATURE The ecological impact of midwater gelatinous predators is virtually unknown, principally because reliable assessments of their distribution, abundance, and trophic interactions are difficult to obtain. Typically, these fragile animals are easily destroyed by plankton nets and water bottles, while data obtained from acoustic surveys is usually ambiguous. 
"The mixture of body parts that are found in the cod end catches of nets is usually an unidentifiable jelly mess," according to HARBOR BRANCH research scientist Marsh Youngbluth. That is basically what happens to the nets of commercial fishermen in the Gulf of Maine. A few years back, Dr. Youngbluth and co-investigator Dr. Bruce Robison from the Monterey Bay Aquarium Research Institute (MBARI) determined that the net-fouling slime represented the remains of the gelatinous colonial siphonophore Nanomia cara. The scientists also made the initial discovery that Nanomia appeared to be feeding almost entirely on the diapause (over-wintering) stage of a planktonic copepod, Calanus finmarchicus. These copepods form an important part of the diet of young cod and other commercially important fishes in the Gulf of Maine region. 
Although Nanomia appeared to be directly competing with young fishes and other planktonic
populations for this important dietary resource, the degree to which this species actually
impacts and shapes the planktonic food web in the Gulf of Maine could not be quantitatively
assessed at the time. Detailed information concerning the seasonal abundance, distribution
patterns, and foraging behaviors of Nanomia are required in order to predict its ecological role.
Mission Goals Colonies of the siphonophopre Nanomia cara constitute a persistent group of carnivores that inhabit mesopelagic (midwater) depth along the Atlantic Coast from Cape Hatteras to the Gulf of Maine. Previous SCUBA and submersible-based observations in the Gulf of Maine have indicated that relatively high densities of large colonies can be found distributed throughout the upper 200 m. Although year-to-year variations in abundance occur, no rigorous assessments of factors underlying the thousand-fold interannual fluctuation in population density have ever been published. This project will document spatial and temporal variability in foraging by Nanomia cara. Sampling will occur in late summer seasons during three consecutive years, and in late spring in years 2 and 3. The important questions researchers hope to answer include: Are these siphonophores selective or opportunistic predators? Does N. cara vertically migrate to feed in shallow water, or does it concentrate its feeding activities in the deepwater sectors of the Gulf of Maine? Does N. cara alter its prey selection and prey consumption in response to seasonal or inter-annual shifts in prey density and prey distribution?  |  |
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