MEPS 313:13-26 (2006)  -  doi:10.3354/meps313013

Size-dependent carbon flow in the epipelagic food web of the Western Equatorial Pacific

Momoko Ichinokawa1,*, Masayuki Mac Takahashi2

1National Research Institute of Far Seas Fisheries, Fisheries Research Agency, 5-7-1 Shimizu-Orido, Shizuoka 424-8633, Japan
2Graduate School of Kuroshio Science, Kochi University, 200B Monobe, Nankoku, Kochi 783-8502, Japan

ABSTRACT: The present study examines the complexity of plankton food-web structure related to size diversity in lower trophic levels of the Equatorial Pacific and its possible effects on community stability and food availability of mesozooplankton. Food-web interactions and carbon flows in the plankton community were estimated from size-dependent predation, carbon transfer between trophic levels and size–biomass measurements determined in 5 independent field investigations. The community was separated into 10 different functional groups, which consisted mainly of pico-, nano- and micro-phytoplankton, bacteria, heterotrophic nanoflagellates, heterotrophic dinoflagellates, ciliates, nauplii, copepods and chaetognaths. The major carbon flow on all 5 occasions was consistent with a general conceptual food-web model, even though the study region was subjected to different oceanographic conditions—warm pool in 1990 to 1993, equatorial divergence in 1994. The 5 food webs showed distinct differences in structure, dependent on the size composition within each functional group, suggesting potential inherent non-steady-state dynamics at the intra-functional group level. The apparent stability of food-web dynamics in the equatorial plankton community may be a consequence of complex food-web interaction and resulting fluctuations, the effects of which neutralize each other over time.

KEY WORDS: Pelagic food web · Equatorial Pacific · Size-dependent predation · Food-web complexity · Community stability · Functional group

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