No abstract

An 8-yr time-series study of the trophic coupling between a pelagic food supply and its utilization by the sediment community was conducted at 4,100-m depth in the eastern North Pacific between 1989 and 1998. Supply of sinking particulate organic carbon (POC) and particulate total nitrogen (PTN) was estimated from collections made with sediment traps moored at 3,500-and 4,050-m depth (600 and 50 m above bottom). Sediment community oxygen consumption (SCOC), an estimate of aerobic utilization of organic matter, was measured in situ. POC and PTN fluxes at both depths declined significantly from October 1989 through 1996 then increased in 1998. Organic carbon : total nitrogen (C : N) of the sinking particulate matter fluctuated ϳ10 throughout the study, except for a major peak (84.8) at 50 m above bottom in summer 1995, indicating lateral advection of organic material of terrestrial origin. POC : SCOC declined progressively over the first 7 yr, from a high of 0.99 in 1989-1990 to 0.22 in 1995-1996. In 1998, there was an increase in POC : SCOC to 0.43, suggesting that the food deficit was reduced by an increase in sinking flux. A continuing deficit in food supply cannot be sustained without ultimately affecting the structural and functional characteristics of the sediment community. The importance of undersampling by sediment traps, lateral advection of marine and terrestrial organic matter from the continental slope and shelf, and dissolved organic matter is evaluated. These other sources of nutrients for benthic organisms may be important in explaining some of the observed discrepancy between supply and demand in the abyssal Pacific. Decadal-scale climate variations that influence marine primary production and terrestrial discharges into the ocean may be extremely important in understanding biogeochemical processes in the deep sea.The food supply for deep-sea benthic communities originates almost entirely from primary producers in surface waters and is transferred to the sea floor either directly, in the case of phytoplankton blooms, or indirectly, through the pelagic food web. Sediment traps have been employed routinely to measure the passive flux of sinking particulate organic matter (POM) in the water column as an estimate of food supply. Long time-series measurements of POM fluxes AcknowledgmentsThis long time-series research would not have been possible without the help of countless participants on our 36 cruises to Sta. M and the expertise of the ships' crews on RV New Horizon, RV Wecoma, RV Atlantis II/DSRV Alvin, and RV Sproul. We specifically thank our colleagues, Rob Glatts, Fred Uhlman, and Bob Wilson, for their support throughout this study. Critical comments by Ellen Druffel, Jeff Drazen, Henry Ruhl, and Anders Tengberg improved the manuscript. We especially thank Fred Sayles and Tim Shaw for providing valuable insights into the evaluation of our data and making the presentation significantly clearer; their constructive and in-depth comments were very thought-provoking.

PRAMER. Evaluation of factors affecting survival of Escherichia coli in sea water. V. Studies with heatand filter-sterilized sea water. Appl. Microbiol. 9:400-404. 1961.-The bactericidal action of sea water was measured as the difference in survival of cells of Escherichia coli in untreated and autoclaved portions of water samples. The beneficial effect of sterilization by heat on the survival of E. coli in sea water varied with season and was most marked during summer months, however, the magnitude of the effect differed greatly from sample to sample. The more obvious and commonly suggested explanations for the bactericidal action of sea water were tested experimentally. The pH and salinity of sea water were changed by autoclaving, but the direction of the former was detrimental rather than beneficial and the significance of the latter was not clarified. The survival of cells of E. coli in filtered portions of some water samples was greater than that in untreated portions and equal to that in autoclaved portions, indicating that predators and competitors removed by filtration had contributed significantly to the rapid death of the bacterium in the untreated water. However, in the majority of samples tested, survival of E. coli in autoclaved water was considerably greater than survival in filtered water. The possibility that the beneficial effect of autoclaving over and above that of filtration resulted from inactivation or destruction by heat of bacteriophages and thermolabile toxic substances such as antibiotics was considered. Moreover, the suggestion was tested that the increased survival of E. coli in autoclaved sea water was due to the ability of heat to disrupt and degrade microbial cells and thermolabile compounds

Immunofluorescence assays for marine ammoniumand nitrite-oxidizing bacteria were used to assess the diversity of nitrifying bacteria isolated from marine environments. The antisera show relatively broad specificity, in that each reacts with several strains of the same physiological type as the strain to which the antiserum was prepared. The antisera do not, however, react with any strains of differing physiological type. Seventy percent of the 30 unidentified ammonium-oxidizing isolates tested reacted with one or both of the antisera produced to marine ammonium-oxidizing strains, and 8 of the 9 unidentified nitrite-oxidizing strains tested reacted with 1 or more of the 3 nitrite oxidizer antisera used. Ammonium-and nitrite-oxidizing bacteria were enumerated in samples taken in a depth profile (to 750 m) in the Southern California Bight by immunofluorescence assays for two ammonium oxidizers and two nitrite oxidizers. Average abundances of the two types of nitrifiers were 3.5 x 105 and 2.8 x 105 cells liter-', respectively. Nitrifiers constitute 0.1 to 0.8% of the total bacterial population in these samples.