Marine ecosystems nitrogen isotopes

Minor element contents and isotopic ratios are used for physiological purposes. Sr/Ca ratios in bone and teeth are said to reflect the diet of the animal (herbivores versus carnivores). Stable isotope analysis of teeth and bones provides direct information on the lifetime diets the nitrogen isotopes reflect the trophic level of the protein that has been consumed. Within an ecosystem, they can identify herbivores and carnivores, while the carbon isotopes tell mainly about the amount of protein in the diets from terrestrial versus marine ecosystems. 

Horrigan, S. G., Montoya, J. P., Nevins, J. L., and McCarthy, J. J. (1990). Natural isotopic composition of dissolved inorganic nitrogen in the Chesapeake Bay. Estuar. Coast. Shelf Sci. 30, 393—410. Horrocks, J. L., Stewart, G. R., and Dennison, W. C. (1995). Tissue nutrient content of Gracilaria spp. (Rhodophyta) and water quality along an estuarine gradient. Mar. Freshw. Res. 46, 975—983. Howarth, R. W. (1988). Nutrient limitation of net primary production in marine ecosystems. Annu. Rev. Ecol. Syst. 19, 89-110. 

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