Variations in nutrient ratios and aquatic food webs
1R. E. Turner
2Nancy N. Rabalais
2Quay Dortch
1Dubravko Justic
1Coastal Ecology Institute
Louisiana State University
Baton Rouge, Louisiana
USA 70803
2Louisiana Universities Marine Consortium
8124 Highway 56
Chauvin, Louisiana
USA 70344
The dissolved Si:dissolved inorganic nitrogen (DSi:DIN) atomic ratios of riverine and coastal waters have been declining in many areas of the world to near a DSi:DIN ratio of 1:1, primarily because of land use practices affecting nitrate concentrations. These changes will profoundly affect coastal food webs. Diatoms, for example, begin the algae-zooplankton-fish food web and have an intracellular DSi:DIN ratio of 1:1. Also, the regeneration of DSi and DIN in the worlds ocean is approximately 1:1. This led Redfield and others (e.g., Redfield 1934, 1958) to postulate the existence of stoichiometric and physiological limits to phytoplankton growth. Results from field and laboratory studies have suggested that the lack of silica relative to nitrogen can control phytoplankton community composition, and Elser et al. (1996) have shown how nutrient ratios (commonly discussed in terms of nitrogen:phosphorus ratios) constrain organism organisation at the cellular, organismal and community level.
If the minimal DSi:DIN proportion of 1:1 for diatoms is not met, then an alternative phytoplankton community composed of non-diat October 31, 2005 yther (1980) argued that as the DSi:DIN ratio fell below 1:1, the fisheries web would re-form and be composed of less desirable species. It turns out to be a October 31, 2005 ippi River delta. Thus important fisheries could be affected by the relative quantities of nutrients being loaded into the receiving waters.
