For more than a century, one of the fundamental challenges in marine sciences has been to understand the structure and function of pelagic food webs. During the past two decades, with the
recognition of the importance of microorganisms, much of this resea rch has been directed towards understanding the linkage between microbial food webs and classical grazing food webs that lead to the production of fish and other large organisms. Recently, members of this consortium made an important
new observation (publ ished in SCIENCE) describing a possible new pathway by which nutrients may be transferred from microorganisms directly to copepods. In the published study (Eastern Mediterranean), we observed that following
the addition of phosphorous, the supposed limiti ng nutrient, chlorophyll decreased while copepod egg production increased after a short delay. To explain this unexpected result, two new hypotheses for the transport of the added P through
the microbial food to secondary consumers without resulting in ne w algae biomass; "Nutrient Tunneling" and "Nutrient Bypass". Focussing on the "Nutrient tunnelling" we propose to follow-up on these initial observations in a series of controlled laboratory based studies, and also a mesocosm study in the Eastern Mediterr anean where the waters are ultra oligotrophic and P-tunneling/bypass is likely to occur under natural conditions. The results of these studies, regardless of whether we verify or disprove the Nutrient Tunneling and Bypass hypotheses, will contribute signi ficantly to our understanding of the organization and function of marine food webs.