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FUTURE DIRECTIONS IN OCEAN SCIENCES 99 



Benthos 



Deep-sea benthic organisms receive a slow nonseasonal rain 

 of fecal pellets and dead organisms. Recent studies in the North 

 Atlantic show that additional large pulses of organic particles ar- 

 rive at the bottom within weeks to months following the spring 

 phytoplankton bloom, probably accelerated by formation of ma- 

 rine snow particles. A complementary study in the same general 

 area indicated that benthic organisms grow faster than previously 

 believed, with maximum growth rates following the annual depo- 

 sition of phytoplankton detritus from the spring bloom (Lampitt, 

 1990). An open question is the extent to which benthic organ- 

 isms rely on these episodes of rich input. Certain large animals 

 may metabolically cache food resources. 



Ocean Margins ' 



The role of coastal areas in global ocean carbon and nutrient 

 cycles is controversial. Several issues remain, such as the per- 

 centage of seasonal and annual coastal production that is exported 

 to the deep sea, the percentage of global productivity that takes 

 place in the coastal ocean, and the extent to which the coastal 

 ocean functions as a net carbon sink because of the massive in- 

 puts of nutrients. Interdisciplinary studies will be required to 

 resolve the controversies regarding lateral exchanges between es- 

 tuaries and the coastal ocean, and between coastal and deeper 

 waters. This point is developed further in "Directions for Coastal 

 Ocean Processes." 



Biology of Hydrothermal Vent and Hydrocarbon Seep Habitats 



Most oceanic food webs are based on photosynthetic produc- 

 tivity occurring in the upper regions of the ocean. A little more 

 than a decade ago, it was discovered that dense bacterial and ani- 

 mal communities, which rely largely on in situ chemosynthetic 

 activity, thrive at deep-sea hydrothermal vents and at hydrocar- 

 bon seep zones. Carbon fixation in these habitats is driven by 

 highly reduced substances, such as hydrogen sulfide, that are ex- 

 ploited by both free-living bacteria and bacteria living within ani- 

 mal tissues. 



The role of deep-sea hydrothermal vent systems in generating 

 and dispersing fixed carbon is an area of active study. Although it 

 is unlikely that carbon fixation at the hydrothermal vents is a 



