Meaanvctiphanes norvegica . 



Settling velocities of pellets, measured under shipboard 

 laboratory conditions and integrated to account for physical/ 

 chemical differences throughout the water column, averaged 8.3 m 

 • h -1 + 1.2 SE which indicated that pellets produced near the 

 sea surface could settle to the deep basins in the Gulf of Maine 

 at 240 m in about one day (29-h) . If all of the pellets 

 collected near the pycnocline were to reach the sea floor, the 

 accumulated abundance would be 5000 pellets ■ m~ 2 ■ d" 1 . 



Fluorescence microscopy indicated that the fecal material 

 contained a variety of microbial populations. The major live 

 microbes, their abundance (cells • pellets -1 ) and enrichment 

 above background seawater concentrations were <10 u m eucaryotic 

 autotrophs (1.3 x 10~ 3 , 9200X) , coccoid cyanobacteria (7.5 x 

 10" 4 , 20,000X) and heterotrophic bacteria (1.2 x 10~ 5 , 1200X) . 

 Living microbial carbon, however, accounted for only 0.1% of the 

 average fecal carbon content (2.6 + 0.6 SE ug C • pellet 1 ) . 

 Scanning electron microscopy of the pellets showed only a few 

 recognizable phytoplankton tests and zooplankton exoskeletons 

 interspersed among masses of unidentifiable amorphous, granular 

 matter. These data were consistent with proximate chemical 

 analysis which revealed the feces to be high in ash content (76% 

 dry weight, DW) and low in organic components (protein=4 . 5% DW, 

 lipid=0.4% DW, carbohydrate=2 . 1% DW) . Carbon and nitrogen 

 values (C=5.1% DW, N=0.9% DW) produced a high C:N ratio of 5.7. 



DISCUSSION 



In spite of the low organic content, this single source of 

 fecal material could supply 35 mg C • m -2 , • d -1 to the benthic 

 community. This biomass represented 2 0% of the daily primary 

 production in the mixed layer (Townsend and Cammen, 1985) . If 

 oxidized completely, the fecal material would yield an oxygen 

 consumption rate of 10 ml 2 * m~2,- d -1 , i.e., at least 8% of 

 the total benthic community respiration (Smith and Hinga, 1983) . 



Assuming a gut evacuation rate of 1 - 2 h and a daily 

 grazing cycle of 8 h in the mixed layer (Willason and Cox, 1986; 

 Heyraud, 1979) , about 7-68 euphausiids ■ m -3 could have 

 produced the number of pellets observed near the pycnocline. 

 This conservative estimate of population abundance supported our 

 visual observations that in most cases only a small portion of 

 the euphausiids, which aggregated near the bottom, actually 

 migrated upward at night into the mixed layer. Furthermore, the 

 deep-living cohorts in the benthic boundary region usually had 

 full stomaches and appeared to be foraging when observed, i.e., 

 feeding on particulate material in the epibenthic nepheloid layer 

 and possibly on the flocculent "fluff" layer at the sediment- 

 water interface. 



These direct observations of Meqanyctiphanes norvea/ica 

 support previous trawl-based investigations of the distribution 



210 



