[L&O Featured Article]Vol 47, Issue 4 (July 2002)

[lo-feature-admin@aslo.org]

Current Featured Article

The featured in the July 2002 issue of L&O is:

Hjerne, Olle, and Sture Hansson. 2002. The role of fish and fisheries in 
Baltic Sea nutrient dynamics. Limnol. Oceanogr. 47: 1023-1032. 

This paper is freely available at this Web address:

          http://aslo.org/lo/toc/vol_47/issue_4/1023.pdf

Instructions for reading PDF files are located on the ASLO web page: 

          http://aslo.org/help/loonline.html 

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Introductory comments by Mike Vanni, Associate Editor for the paper

The role played by heterorophs in the cycling of nutrients in aquatic 
ecosystems has been studied for decades. It is well established that 
bacteria, other microbes, and small animals such as zooplankton play a 
crucial role in nutrient cycling in both freshwater and marine ecosystems 
(Goldman et al. 1979; Schlesinger 1997; Elser and Urabe 1999). The 
importance of larger animals, such as fish, has been debated over the 
years (Vanni 2002). Some argue that fish are not likely to be important 
in nutrient cycling compared to microbes or metazoan zooplankton (Hudson 
et al. 1999), but recent studies show that in some lakes and streams fish 
can have large effects on nutrient flux (Schindler et al 1993; Vanni et 
al. 2002). Large, mobile animals have the capacity to mediate nutrient 
cycling not only by remineralizing nutrients into available forms, but 
also by translocating nutrients across habitats and ecosystems and by 
sequestering nutrients that would otherwise be available to primary 
producers and bacteria (Vanni 2002). 

The featured paper by Hjerne and Hansson in L&O 47(4) shows that fish and 
fisheries can have a large influence on nitrogen (N) and phosphorus (P) 
dynamics in the Baltic Sea. This appears to be the largest ecosystem (in 
terms of spatial scale) in which it has been demonstrated that fish can 
impact pelagic nutrient dynamics. In the Baltic, the impacts of fish and 
fisheries on nutrients derive mainly from their sequestration of 
nutrients, and the subsequent removal of nutrients via fish harvest. 
Hjerne and Hansson show that the increase in biomass of three common fish 
species (herring, sprat, and cod) in the upper 40 meters during summer 
can account for over 30% of the summer decline in “total phosphorus” 
(which by convention does not include P contained in fish!). In addition, 
commercial harvesting of fish represents a removal of nutrients equal to 
2.5 and 18% of the annual anthropogenic loads of N and P to the open 
waters of the Baltic. Because the Baltic has been culturally eutrophied, 
removal of nutrients via fisheries is of particular interest. Hjerne and 
Hansson use a simple model to show that the economic value of nutrient 
removal via fish harvest is substantial, compared to both the value of 
fish sold to market and to the economic costs of reducing anthropogenic 
nutrient inputs to the Baltic. 

This paper will stimulate research on the role of fish and other large 
animals in nutrient dynamics, as well as collaborations between 
oceanographers studying nutrient cycling and fisheries scientists.

References

Elser,J. J., J. Urabe. 1999. The stoichiometry of consumer-driven 
    nutrient recycling: Theory, observations, and consequences. Ecology 80: 
    735-751.
GoldmanJ. C., J. J. McCarthy, and D.G. Peavey. 1979. Growth rate 
    influence on the chemical composition of phytoplankton in oceanic waters. 
    Nature 279: 210-215
Hudson,J. J., W. D. Taylor, and D. W. Schindler. 1999. Planktonic 
    nutrient regeneration and cyclng efficiency in temperate lakes. Nature 
    400: 659-661
Schindler,D. E., J. F. Kitchel, X. He, J. R. Hodgson, and S. R. 
    Carpenter. 1993. Food web structure and phosphorus recycling in lakes. 
    Trans. Amer. Fish. Soc. 122: 756-772
Schlesinger,W. H. 1997. Biogeochemistry: An analysis of global change. 
    2nd ed. San Diego: Academic Press.
Vanni,M. J. 2002. The role of animals in nutrient cycling in freshwater 
    ecosystems. Annual Review of Ecology and Systematics. In press. 
Vanni,M. J., A. S. Flecker, J. M. Hood, and J. L. Headworth. 2002. 
    Stoichiometry of nutrient cycling by vertebrates in a tropical stream: 
    Linking species identity and ecosystem processes. Ecology Letters 5: 285-
    293.