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Limnol. Oceanogr., 49(1), 2004, 233238 2004, by the American Society of Limnology and Oceanography, Inc.
 

Summary: 233
Limnol. Oceanogr., 49(1), 2004, 233­238
2004, by the American Society of Limnology and Oceanography, Inc.
Optical control of fish and zooplankton populations
Dag L. Aksnes,1
Jens Nejstgaard, Eivind Sædberg, and Tom Sørnes
Department of Fisheries and Marine Biology, University of Bergen, N-5020 Bergen, Norway
Abstract
Aquatic food webs are affected from the bottom up by light through its effect on photosynthesis and productivity.
But light also has a top-down effect, because it is crucial for the visual foraging efficiency in many fish. Here we
present data suggesting that marine pelagic food webs are primarily structured top-down by light through its effect
on vision in fish. For light-limited fjord ecosystems, we show that the abundance of zooplanktivorous fish is
proportional to the vertical extension of a visual feeding habitat, represented by the inverse of the light absorbance
coefficient of the water column. We also show that both zooplankton abundance and body size are proportional to
the size of a vision-protected habitat that can be defined as the dimensionless product of the light absorbance
coefficient and the depth of the water column. Natural and human-driven environmental change may involve alter-
ations in the amount of surface radiation as well as in the optical properties of the water column. Our results imply
that such changes are likely to affect aquatic food webs top-down through vision as well as bottom-up through
photosynthesis.
Primary production is driven by light through photosyn-

  

Source: Aksnes, Dag L. - Institutt for biologi, Universitetet i Bergen

 

Collections: Environmental Sciences and Ecology; Biology and Medicine