The Comparative Ecology of a Subarctic and Tropical Estuarine Ecosystem as Measured with Carbon and Nitrogen Isotopes

Animals representing different trophic levels were collected from two estuarine environments; the subarctic Strait of Georgia (c. 50°N, 124°W) and the tropical coast of Kaohsiung (c. 22°N, 121°E). The animals were analysed for their heavy isotope composition of carbon and nitrogen in order to determine the trophic structure of the two environments. The tropical environment showed a greater enrichment in the13C isotope which could be attributed to previously reported latitudinal differences in the source of carbon for photosynthesis. In both environments there was a further enrichment of13C at higher trophic levels which was believed to be the result of significant grazing on benthic organisms in both systems. The much higher variation in the data encountered in the tropical environment was attributed to the sharp contrast between offshore oligotrophic waters from the South China Sea and the Kuroshio current that mix with estuarine waters, within a short distance of the coast.