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Levai., Gyongyver ,W. Wakefield, T. M. Shank, P. Chevaldonne, and R. A. Lutz
1Institute of Marine and Coastal Sciences, Rutgers University, New Brunswick, NJ 08903 USA
Few trophic studies have been conducted on the mobile megafauna inhabiting deep-sea hydrothermal vents. The vent-endemic eelpout Thermarces cerberus (Zoarcidae) has been observed at numerous sites along the East Pacific Rise (EPR) and on the Galapagos Rift. We present preliminary investigations of gut content analysis and extensive video image analysis in an effort to define the ecological role of a primary predator, T. cerberus, in the dynamic hydrothermal vent community. The capture of three specimens, one from 20( 49.8ÕN (1990) and two from 9( 49.8ÕN (1994) on the EPR, provided an opportunity to assess questions regarding the feeding and general behavior of this vent-endemic fish. Gut content analysis was conducted via the removal of the stomach and the complete intestine, the identification and enumeration of prey items, and construction of indices of relative importance (I.R.I.) to characterize the diet of T. cerberus. The results of the gut content analysis indicate a predominance of the lysianassid amphipod Ventiella sulfuris, as well as the leptostracan Dahlella caldariensis. Other prey items included lysianassid amphipods, lepidodrilid limpets, brachyuran crabs, and siphonostomatoid copepods. Acanthocephalan parasites (Hypoechinorhyncus thermarceri) were discovered among the prey items of the 9(N specimens (predominantly in the middle and posterior thirds of the intestines). To our knowledge this represents only the third record of an acanthocephalan parasite in an abyssal fish, and the first documentation of a parasite in the 9(N hydrothermal vent area.
Video analysis using a high resolution 3-chip color CCD camera mounted on the arm of the submersible Alvin was conducted to observe the feeding behavior of T. cerberus. Feeding was observed in several microhabitats: in dense swarms of the amphipod, Halice hesmonectes (23 observations); around the base of the vestimentiferan tubeworms, Riftia pachyptila (3 observations); and amongst dense aggregates of mussels (10 observations). The video footage illustrates few instances of aggressive behavior between zoarcids and no aggressive behavior toward any other fauna within the vent community. Eighteen separate sightings of a juvenile T. cerberus were noted on the video. Further analysis, as well as the aid of more specimens, is needed to attain a better understanding of the role of T. cerberus within the hydrothermal vent community.
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