Organisms at the benthic-pelagic interface 



Dives 1424 to 1428 were made south of Bermuda over a bottom 

 900 to 950 meters deep. Here, we found the "red fauna," 

 including medusae, siphonophores, ctenophores, crustaceans and 

 chaetognaths below 700 to 800 meters. Just above the bottom 

 there was often a distinct concentration of zooplankton and fish. 

 Some of these animals may have been driven down by the descent of 

 the sub, but the gelatinous forms showed no such behavior. The 

 red-brown narcomedusa Aeginura was seen only at this depth, 

 drifting just over the bottom with its tentacles hanging down. 

 An undescribed physonect siphonophore, also pigmented red, 

 behaved similarly. 



The most dramatic of the benthopelagic animals was a 

 specimen of Deepstaria, about 60 cm in diameter and colored a 

 deep red-brown. This scyphomedusa, a new species in the genus, 

 was seen drifting less than 1 meter above the bottom with its 

 large bell opened downward. We recorded its swimming behavior on 

 videotape, and accidentally triggered its prey capture mechanism 

 while attempting to collect it in the detritus sampler. On 

 contacting a protruding knob of the sampler with the edge of its 

 bell, the medusa contracted around it, enclosing the knob so 

 tightly we could only remove it with the suction collector. We 

 inferred that the medusa captures its prey, perhaps including 

 benthic organisms which swim up off the bottom, by engulfing them 

 in the bell and then ingesting them with the oral arms. A 

 description of the species and its behavior is given by Larson et 

 al. (1988b). 



DISCUSSION 



The data presented here are limited by the reduced number of 

 dives we were able to make, and the lack of an opportunity since 

 July 1987 for all observers to participate in analysis of the 

 videotapes. Although these results are only preliminary, some 

 patterns in distribution of macrozooplankton are evident in the 

 summary given previously. 



Little restriction in vertical distribution is apparent at 

 high taxonomic levels, like siphonophores or crustaceans as a 

 whole (Table 2), but lower taxa were often limited in range. The 

 vertical distribution of these groups will be refined further 

 when species and genus identifications from the videotapes have 

 been completed. 



The distribution of radiolaria appears to reflect their 

 trophic niches, with the photosynthetic colonial radiolaria 

 almost entirely in the top 200 m, and the detritivorous 

 phaeodarians mainly below 800 m. 



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