Hostname: page-component-7c8c6479df-hgkh8 Total loading time: 0 Render date: 2024-03-27T11:27:29.356Z Has data issue: false hasContentIssue false

The role of grazing in structuring Southern Ocean pelagic ecosystems and biogeochemical cycles

Published online by Cambridge University Press:  30 November 2004

VICTOR SMETACEK
Affiliation:
Alfred Wegener Institute for Polar and Marine Research, D-27570 Bremerhaven, Germany
PHILIPP ASSMY
Affiliation:
Alfred Wegener Institute for Polar and Marine Research, D-27570 Bremerhaven, Germany
JOACHIM HENJES
Affiliation:
Alfred Wegener Institute for Polar and Marine Research, D-27570 Bremerhaven, Germany

Abstract

This review examines the links between pelagic ecology and ocean biogeochemistry with an emphasis on the role of the Southern Ocean in global cycling of carbon and silica. The structure and functioning of pelagic ecosystems is determined by the relationship between growth and mortality of its species populations. Whereas the key role of iron supply in conditioning the growth environment of land-remote oceans is now emerging, the factors shaping the mortality environment are still poorly understood. This paper addresses the role of grazing as a selective force operating on the structure and functioning of pelagic ecosystems within the larger conceptual framework of evolutionary ecology. That mortality due to grazing decreases with increasing cell size is widely taken for granted. We examine the impact of this principle across the range of size classes occupied by Southern Ocean plankton and show that relatively few species play crucial roles in the trophic structure and biogeochemical cycles of the Southern Ocean. Under iron-sufficient conditions, high growth rates of weakly silicified diatoms and Phaeocystis result in build-up of blooms that fuel “the food chain of the giants” (diatoms-krill-whales) and drive the carbon pump. In contrast, high grazing pressure of small copepods and salps on the regenerating microbial communities characteristic of the iron-limited Southern Ocean results in accumulation of large, heavily silicified diatoms that drive the silicon pump. The hypotheses we derive from field observations can be tested with in situ iron fertilization experiments.

Type
Research Article
Copyright
© Antarctic Science Ltd 2004

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)